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Musings of an Energy Nerd

‘Walls Need to Breathe’ and 9 Other Green Building Myths

The Energy Nerd plays Whack-a-Mole with some common misunderstandings in home building

Some myths just won't stay down
Image Credit: Daniel Morrison

Just for fun, I’ve rounded up ten oft-repeated statements that are either half-truths or outright falsehoods. I’m sure some readers will disagree with my conclusions; if you’re one of them, don’t hesitate to post a comment.

Green building myth #1. New York City is an environmental nightmare

This myth has been debunked many times, most recently by author David Owen, in his New Yorker article titled “Green Manhattan.” In fact, the average resident of Manhattan uses much less energy, and has a much smaller carbon footprint, than the average American. Compared to a resident of New York City, the average suburban American is wearing carbon clown shoes.

Owen wrote, “Most Americans, including most New Yorkers, think of New York City as an ecological nightmare, a wasteland of concrete and garbage and diesel fumes and traffic jams, but in comparison with the rest of America it’s a model of environmental responsibility. By the most significant measures, New York is the greenest community in the United States, and one of the greenest cities in the world. … The average Manhattanite consumes gasoline at a rate that the country as a whole hasn’t matched since the mid-nineteen-twenties, when the most widely owned car in the United States was the Ford Model T. Eighty-two per cent of Manhattan residents travel to work by public transit, by bicycle, or on foot. That’s ten times the rate for Americans in general, and eight times the rate for residents of Los Angeles County.”

In a separate article, Owen explains why the residents of Manhattan are so much greener than Vermonters.

Green building myth #2. Walls have to breathe

Bored readers may move on to the next item; I know that this is a tired old argument. But the “walls have to breathe” statement…

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  1. jeff williams | | #1

    Tons of good info
    I'm pretty new to the site so I wasn't aware of all of the myths. I especially enjoyed the in-floor heating one. Do you have the link for the temp comparison study for the in-floor vs forced air? I'd love to see how the 75 homes break down. If they had similar outdoor temps, from the same region, etc.

  2. GBA Editor
    Martin Holladay | | #2

    Response to Jeff Williams
    Jeff Williams,
    Here's a link to the Canadian study: Thermostat Settings in Houses with In-Floor Heating.

    I'll add the link to the body of the article as well.

  3. homedesign | | #3

    Diminishing "Value" of R-Value ....Myth?
    How about this caption from A FHB article:

    "As the thickness of the insulation increases for both open-cell and closed-cell foam, the insulating value of each diminishes drastically."

    Many of my friends buy into this "Myth".

  4. GBA Editor
    Martin Holladay | | #5

    Response to John Brooks
    That's a good one. I could have included it in this list. There's no doubt that the FHB article muddied the waters instead of clarifying the truth on that issue.

    As I have often pointed out, the R-value per inch of spray polyurethane foam, like the R-value per inch of all insulation types, does not appreciably change with thickness. If an insulation has an R-value of R-3.5 per inch, then 2 inches of insulation has an R-value of R-7.0, and 10 inches of insulation has an R-value of R-35.

    The FHB article should have noted, "As the thickness of the insulation increases for both open-cell and closed-cell foam, the insulating value also increases."

  5. greenophilic | | #6

    radiant heat systems
    Martin, I think you've written off some of the potential savings from radiant heating systems with hot water distribution. I agree with most of your points, but I think that when you say that distribution is not important, we have a point of disagreement. The differences between hot water distribution and forced air distribution are interesting and meaningful. Heat transfer/loss is a function of surface area, thermal conductivity and the temperature rise across the surface (in this case either a duct or a water pipe). Water stores heat much more efficiently than air, meaning that a smaller volume of water can deliver the same Btu's as a much larger volume of air. As a result, you need a much smaller distribution system, usually with MUCH smaller surface areas (think of 3/4" pipe vs 10" air duct). This minimization of distribution surface area certainly increases the overall efficiency of a hyrdronic heating system in comparison to a forced air system of the same combustion efficiency. Of course, the delta temp may be higher, which could offset some of this benefit...When you say: "the distribution equipment plays only a minor role in system efficiency", I believe you are incorrect...unless you're saying that in-floor radiant is equally efficient as baseboard radiators, and you are ignoring the system that brings heat to these devices? I would say that it is clear that distribution equipment (ie. hot water piping, forced air ducts, etc) has a MAJOR impact on overall heating/cooling system efficiency. Of course, all your other points are valid and entertaining, good post.

  6. GBA Editor
    Martin Holladay | | #7

    Response to Brennan
    In most homes in the Northeast, whether heated with a furnace or a boiler, the distribution system is entirely within the home's thermal envelope. (We don't put ducts or pipes in attics here in New England.) Any heat loss from distribution pipes or ducts just heats the interior of the home.

    There are exceptions, of course. If ductwork is located between the joists separating the first floor from the second floor in a two-story home, and if the supply ducts are leaky, they can pressurize the joist bays. This pressurization can force heated air outdoors through the rim joist, decreasing the efficiency of the distribution system.

    Obviously, to take an extreme example, a hydronic distribution system that is located entirely within a home's thermal envelope will certainly be more efficient than ductwork located in an unconditioned attic. But that's an apples to oranges comparison, and an example of gross stupidity.

    The standard heat distribution system in northern New England is hydronic baseboard. I don't see any evidence that in-floor radiant heat distribution is more efficient than hydronic baseboard heat -- and if the hydronic system requires high slab temperatures in a slab-on-grade home, the in-floor system may be less efficient.

    If we are comparing in-floor radiant to forced hot air, you are quite right that the in-floor radiant distribution system should be much more efficient than ductwork installed in an unconditioned attic.

    You wrote, "This minimization of distribution surface area certainly increases the overall efficiency of a hydronic heating system in comparison to a forced air system of the same combustion efficiency." Why would that be? Again, for apples to apples, let's assume both distribution systems are inside of the home's thermal envelope. Heat is heat. Where is the heat going -- the distribution losses in the forced air system that you allege contribute to forced-air inefficiency?

  7. greenophilic | | #8

    Heat is heat, but it is also not where you need it
    You are right that the location of the distribution system is important, but to say that heat loss/gain in conditioned/semi-conditioned spaces has no impact on system efficiency, I believe is false. At the very least, if a system is dumping large amounts of heat into a basement in the NE, then the delivery temperatures will be lower and the unit will need to run longer in order to change the sensible temperature at the thermostat. Or, the home will become uncomfortable. Heat that is dumped into the basement is not necessarily "lost", but it also is not delivered in the necessary way to a region that requires heat. To say that heat lost along the way within the thermal envelope is the same as heat delivered is untrue. For example, in a basement, the accumulated heat from distribution losses will tend to follow the strongest temperature gradient, which almost certainly is through the foundation walls and basement slab. That heat does not necessarily travel into the useful space upstairs, and if it does, it does so with a time lag, thermal losses along the way, and with uneven mixing. In situations where the heat is lost into interior partition walls or framing chases, then that heat creates thermal drive, turning that cavity into a chimney. Once again, the heat lost along the way, even when in the thermal boundary, more likely escapes directly to the outside, rather than transferring to the conditioned space. Cheers.

  8. GBA Editor
    Martin Holladay | | #9

    Response to Brennan
    As you can imagine, GBA provides advice to builders of green homes. In general, green builders strive for low levels of air leakage through their thermal envelopes, and high levels of insulation.

    In such buildings, it's extremely unlikely that radiant-floor heating systems will have distribution systems that are more efficient than other heating systems.

    As you probably know, with the trend toward Passivhaus buildings, designers are realizing that it is less and less important where heat is delivered. The better the envelope, the less it matters. Some Passivhaus buildings are heated from a single point source.

    You are certainly correct that if a boiler or furnace is located in the basement, some heat will be lost from the ducts of a forced air system, just as some heat will be lost from distribution tubing of a hydronic system. You still haven't demonstrated why the fact that some tubing is stapled up to the subfloor, while other tubing runs through hydronic baseboards, affects efficiency.

    If you're losing too much heat through your basement walls, then for heaven's sake, insulate your basement walls!

    Obviously, good heat distribution system design requires loads to be calculated for each room, and for distribution systems to deliver the right amount of heat to each room. Distribution ducts or tubing should be insulated to minimized heat loss, unless it is desirable to heat the basement. Bad distribution system design results in a bad outcome -- no matter whether you have an in-floor radiant system or a forced-air system.

  9. w5mRKW6vhr | | #10


    I'm not sure if I understand #3. Are you trying to say that feature for feature, renovation is more expensive than new construction? Because it seems like even the most rigorous deep energy retrofit is still cheaper than building a whole new house. I understand that you may be saying, "tearing off all of your siding, insulating, sealing and residing an existing house is more expensive than just building an exterior wall on a new house," but it doesn't read that way.

    #10 could also have wording to soften #3. Perhaps a renovation would cost more in some ways than new construction, but the environmental impact is radically smaller.

  10. Bryce | | #11

    In-floor heating
    In our neck of the woods, in-floor heating tends to INCREASE energy use as 99.99% don't understand the second law of thermo-dynamics. They use "double-bubble" insulation and think they've done a good job until they get their first electric bills. The issue comes from the delta-t....the higher slab temperatures have increased the heat transfer through the slab to the soil below. As they can't increase the r-value of the slab, I recommend they install a forced air system and abandon their slab heating. Amazingly, their energy use goes down.

  11. CanAmSteve | | #12

    Best thing I've read in the last five years
    Great column!

    I'm always amazed by how many people ignore the laws of physics or attempt to bend them to their will.

    Energy can neither be created or destroyed, folks.

    The higher the differential/potential, the greater the transfer.

    Simply put, you put energy (let's call it heat in this case) into a house. It wants to get out.

    The higher the differential between in and out, the quicker it leaves. There are ways to mitigate this. You can seal the house. You can insulate it. And you can turn the thermostat down.

    But it doesn't matter if it is hot-water, hot-air, electric baseboard, radiant electric, hydronic or infra-red from the planet Zon - you are going to use X amount of energy to get Y effect.

    The biggest benefit in energy savings (after decent building standards) is probably zoned heating with setbacks so that heat is only used where it is needed.

    Can we also address the myth (IMHO) that incandescent light bulbs "waste" energy? Where I live (in Maine) we have short days in the winter heating season and long days in the summer. If I turn on a 100 watt light bulb to read on a winter's night, where does that "waste" heat go to?

  12. greenophilic | | #13

    Back to Martin
    I agree that in-floor vs. baseboard systems should be similar, except that most baseboard systems deliver heat at a point on an exterior wall with some thermal drive to the outside. I am approaching this issue more from an existing homes perspective, rather than from a passive house sort of mindset. So, I do agree that with more efficient envelopes, all these issues become less important. BUT the fact of the matter is that, on its face, hydronic heat distribution, in an apples-to-apples comparison, will have less heat loss along the way, likely making it more efficient. The impact of this efficiency gain will be less in an efficient home (both in terms of energy and comfort), but it still seems to me that it will be there. I totally agree that a poorly designed hydronic system will perform badly, but equally well-designed hydronic and forced air systems will not perform the seems to me to be a matter simply of surface area and leakage losses, both of which will be less in hydronic systems. Same length, same insulation level, same location, same fluid temperature; hydronic will lose less heat long the way. Thanks for the banter.

  13. wjrobinson | | #14

    Do you want to go green? Stop reproducing.
    There is only one way to personally truly impact sustainability
    1) Do not have offspring
    2) Convince others to not have offspring
    3) Vote for those that advocate reducing world populatiion
    4) If you have offspring, convince them not to have offspring

    Building and renovating homes to any present known way... is not doing what one less birth can do.

    Earthly sustainability is directy related to population and little else by several orders of magnitude.

    Play with your neighbor's kids and build any home you want. That is living as green as one can.

    Or just get off the planet yourself. If you choose this last choice, thank you.

    Don't take me wrong.... as I do enjoy redesigning homes to use less energy.... I just know that it has very little impact compared to overpopulation.

  14. Ray T. | | #15

    Walls need to breathe
    You sort of have it correct. Healthy walls need to be able to allow water VAPOR, not water, to pass easily. When walls get wet, they dry out by evaporation. Hence the need for water vapor permeable membranes or coatings. Walls can be insulated AND vapor permeable. They are not mutually exclusive. No need for non-biodegradable polyiso this or polyiso that.

  15. GBA Editor
    Martin Holladay | | #16

    Response to Ray T.
    Ray T.,
    I'm afraid I still don't agree with you. As my example (a wall with polyiso sheathing) demonstrated, walls don't have to be vapor permeable. They just need to be able to dry on either side of their least permeable layer.

    You are correct that walls CAN be vapor permeable. (A straw bale wall performs extremely well, as long as it is protected from rain and has a dry footing.) But they don't HAVE to be vapor permeable. Nor do they have to "breathe," whatever that means.

  16. GBA Editor
    Martin Holladay | | #17

    Response to Paul Brazelton
    You asked, "Are you trying to say that feature for feature, renovation is more expensive than new construction?"

    Yes, that's what I'm saying. If you want a new kitchen with an island sink, oak cabinets, granite counterops, Viking range, and Sub Zero refrigerator, the kitchen will be cheaper to install a new home than it will to retrofit into your current home.

    You wrote, "It seems like even the most rigorous deep energy retrofit is still cheaper than building a whole new house." Ah, but it isn't -- especially if you mean "the most rigorous deep energy retrofit." Here's the story of one such retrofit:
    A Leaky Old House Becomes a Net-Zero Showcase

    The owner of a simple ranch house had a simple dream -- and her dream came true, $1,190,000 later.

  17. Dan Kolbert | | #18

    Agreed - as someone who does both new construction and renovations, the latter is far more expensive, illogical though it may sound. May be less material-intensive, though.

  18. Dan Perunko | | #19

    distribution efficiency

    Great article I enjoyed it. I am, however, dissapointed to hear you say that distribution efficiency is not very important. We think we are seeing 50% or greater distibution losses in forced air systems in CA. I don't have a handy number to throw around for hydronic floors, but I have seen some really well heated rim joists out here. One of the primary improvements we focus on for occupant comfort and energy consumption is the distribution system, be it forced air or hot water. Maybe the building stock is just much worse in my market? In any case improving the distribution system in the typical CA home can reduce the building load by 30%. That is, with out improving the building itself we can reduce the required capacity of the conditioning equipment by as much as a third when we correct the delivery system.

  19. GBA Editor
    Martin Holladay | | #20

    Response to Dan Perunko
    Dan Perunko,
    I am a strong believer in the proper design of heating distribution systems. As you point out, hydronic systems are often very effective at heating rim joists, and forced-air duct systems are often very effective at heating and cooling the great outdoors.

    I have little patience, however, for hucksters and salespeople who exaggerate and mix issues to suit their economic purposes. All residential heating systems, whether hydronic or forced air, need good distribution system design. Bad thermal envelopes leak heat -- whether at the rim joist, basement walls, or second-floor ceilings. The solution to bad thermal envelope design is better thermal envelopes. The solution to poorly insulated hydronic tubing or ductwork in unconditioned spaces is to move the tubing or ductwork inside of the conditioned space.

    I remain unconvinced that in-floor radiant heating systems save energy compared to other types of heating systems -- which was the point I was trying to make.

  20. Kevin Dickson, MSME | | #21

    The Greenest Building is... One Already Built
    This myth is similar to #3 above. Unfortunately, it is being spread as absolute fact by nearly all preservationists.

    Preservation is very important and often for the greater good, but the adoption of an unscientific slogan is a classic case of myth-spreading.

  21. tim Rowledge | | #22

    Re: Diminishing "Value" of R-Value ....Myth?
    Original problem paragraph - "As the thickness of the insulation increases for both open-cell and closed-cell foam, the insulating value of each diminishes drastically."

    I suspect that what might have been intended would be
    "As the thickness of the insulation increases the marginal insulation value of each inch diminishes"
    Add qualifiers about open and closed cell as needed. If you add 1" to a 2" layer you get a 50% improvement. Add 1" to a 6" layer and you get a 15% improvement. Adding 1" to a 12" layer gains you 8% etc. In general the cost of adding each 1" is about the same (I guess - there are probably places where it cost more when you get to using odd size lumber and stuff) so it is reasonable to consider each increment having 'less value'.

    It's all part of the discussion about how valuable it is to achieve actual Passiv-Haus or Net-Zero status. Does it make sense to spend $20,000 to reduce the annual energy bill by $300? How about $50,000 to save the last $300? Can anyone invent a practical way to reduce the payback time? And so on.

  22. user-659915 | | #23

    Response to Kevin Dickson
    "The greenest building is the one already built" may be an oversimplification but is perhaps a necessary counter-perspective to the new-construction bias of much of the green building dialectic. Your linked article carefully points out the significant financial considerations in the historic preservation calculus. Many historic preservation battles are fought over locations where the land value has come to greatly exceed that of the building which sits upon it. For many of us laboring in the vineyard of more modest structures the reverse is true and it is simply not an option for our clients to demolish a home with poor energy performance because its bricks, shingles and lumber represent the bulk of their financial investment in the property. If any of them consider building new it will be on a new lot with new infrastructure to assemble and most likely further out of town: meanwhile the old 'gas-guzzler' continues to consume more energy than it should, just as before only with a new owner. No matter how 'green' the new home is it represents a net addition to overall energy and material consumption, just as buying a new Energy Star refrigerator while moving the old one to the garage to keep a few beers chilled results in a net energy-use increase. For that reason alone I will continue to encourage my clients to rehab and upgrade wherever it makes sense for them and the overall condition and arrangement of the home justifies it: I do not even need to mention the cultural and community value of maintaining and improving neighborhoods through upcycling of existing housing stock.

  23. Greg Duncan | | #24

    Great post.

    Tim, the value of each additional inch of insulation can be calculated on a case by case basis. I did a very quick rough estimate based on a townhouse in Germany. Increasing the insulation from 25 mm to 275 mm would cost about $10,000 but save about $3000 per year. Increasing the insulation from 275 mm to 525 mm would also cost about $10,000 -- probably more due to additional installation costs -- and only save about $200 per year. Passive House status was achieved for this building with 275 mm of insulation. It seems to me that as a general rule, additional insulation is worth the investment up until the point where the thickness interferes with constructibility and other practical concerns. No, it does not make sense to spend $20,000 to reduce annual energy costs by $300. But spending $10,000 to save $3000 per year does.

  24. Interested Onlooker | | #25

    Offsetting of Environmental Penalty
    "...meanwhile the old 'gas-guzzler' continues to consume more energy than it should, just as before only with a new owner. No matter how 'green' the new home is it represents a net addition to overall energy and material consumption..."

    Is the environmental cost of the green new-build not offset by the fact that the people who moved into the 'gas guzzler' did not incur the environmental penalty of the house that they didn't build?

  25. GBA Editor
    Martin Holladay | | #26

    On remodeling costs, new construction ethics, and tear-downs
    Retrofit an existing house or build a new superinsulated house? What to do?

    1. The U.S. today has too many homes -- more than the market can absorb. This situation will probably last for a decade or more. This is Fact #1: America doesn't need any new homes.

    2. Developing undeveloped land is an environmental sin. In some cases it is a small sin, but it is a sin nevertheless.

    3. As our country struggles to meet future carbon-reduction goals, we'll need to find cost-effective ways to slash our energy consumption. Eventually, carbon taxes will completely change the economic equation, and many homeowners, unable to afford space heating or cooling, will need to make a choice between a deep-energy retrofit or new construction.

    4. For the majority of American homes, a deep-energy retrofit costs more than new construction. For those who are desperate to come up with a solution to this dilemma, the solution will usually involve a bulldozer. So -- in the future, we probably won't be developing much undeveloped land, but we will be doing a lot of tear-downs.

  26. DoctorJJ | | #27

    Radiant in-floor
    Overall great article. Lots of good info.
    In regards to comments numbered 8 and 9, it seems that an in-floor radiant system would save money due to the energy penalty of distribution with a forced air system. In number 8 you discuss the sometimes quite significant energy usage of a fan blower on a furnace which surely is more significant than the energy usage of a small pump associated with a hydronic system. Even considering that a BTU is a BTU and that both are within the envelope so that no heat in either type of system is lost to the outdoors, it still seems that a radiant in floor system would save energy through the above proposed mechanism. Or also consider the efficiency of an electric floor heating system such as the STEP Warmfloor where there are really zero losses fr having to move warmed air or fluids throughout a home. Again, mentioning the "hidden" energy usage of a furnace because it's fan isn't listed and may not be an energy efficient type in comment number 8 but then failing to account for this in comment number 9 doesn't make a lot of sense. I still loved the article though. Thanks again.

  27. GBA Editor
    Martin Holladay | | #28

    Response to DoctorJJ
    Remember, all of the electricity used for forced-air blowers or circulators during the heating season helps heat the house. Although using electricity to heat a house is expensive, at least the extra thermal energy is useful during the winter. (By the way, using electric resistance coils for a radiant floor is the worst of all possible worlds -- since all of the heat is derived from electric resistance, a very expensive form of heat.)

    I wish you were correct that circulators on hydronic systems were not a significant energy load; unfortunately, you're wrong.

    In an article I wrote for the June 2007 issue of Energy Design Update ("Near-Zero-Energy in New England"), I reported on the high electrical energy use of circulators in a carefully designed in-floor radiant system installed in a superinsulated house:

    "Aldrich [Robb Aldrich, an engineer at Steven Winter Associates, one of the designers of the space heating system] is still not convinced that the in-floor distribution system was a wise choice. “Because of the radiant slab, storing direct solar gain is out of the picture,” he noted. “Having invested so much in the envelope, they could have gone with a really simple, cheaper, lower-cost heating system. In their next project, RDI does not plan to do a radiant floor because it is just too expensive.”

    " ... Before deciding on in-floor radiant heat, the system’s “parasitic” energy load -- electricity required for pumping -- must be calculated. “We looked at pumping energy a lot,” said Aldrich. “It’s a big concern of mine. I was fairly rigorous on all the friction and pressure calcs. On the solar thermal
    system, we decided to use a PV-powered DC pump. We chose the smallest possible circulators for the radiant ... We ended up with a constant circulation system -- basically, the pumps operate continuously for the entire heating season.” The Colrain heating system has two circulators that together draw 173 watts. Since the circulators will operate for 4,000 to 5,000 hours per year, they are likely to consume between 19% and 23% of the annual output of the home’s PV array. “The radiant pumping energy will really be a significant load, which definitely bothers me,” Aldrich wrote ... One of the little battles I picked (and won) was sizing the circulators as small as they are. Takagi recommends a circulator twice as large for moving water through their water heaters. I did some fairly careful pressure-drop calcs and insisted we could use a smaller pump.” "

  28. Art | | #29

    Myth #7
    This is hardly a "green" solution and I think your missing basic problem - the original AC system was oversized so that it is cooling the house too quickly to lower interior humidity. Dehumidifier are basically AC units themselves. Have you actually added up the energy consumpution of (1) running a compressor that is larger than it should be (2) running another compressor inside the building to remove moisture and (3) running the main compressor yet again to remove the heat created by the dehumidifier?

  29. GBA Editor
    Martin Holladay | | #30

    Response to Art
    Of course the green solution is to open the windows and live without air conditioning. However, most people in Houston aren't doing that.

    The solution came from Armin Rudd of the Building Science Corp., one of the smartest engineers in the country. No residential AC units are yet available that provide adequate latent cooling for a small, very well insulated house. The best available residential AC equipment still leaves these homes humid; the use of a small stand-alone dehumidifier is a relatively inexpensive solution to the problem.

  30. Armando Cobo | | #31

    1560 sf house
    No kidding, Martin.... I just designed a 1560 sf house that requires .9 tons of cooling and 18K btuh, but have to install a 1.5 ton and 40K btuh as minimum units by the manufacturer. It's a model home and the production builder wants to keep prices low on his end. Manufacturers of residential equipment are not doing favors to the industry!!!

  31. Jim | | #32

    In-floor radiant heating systems
    A home in the south east US will need cooling more than heating so the air system is there anyway. I suspect that in the not to distant future we will be way more concerned about our carbon output than cost. Would it be reasonable then, to add an in-floor hot water system to take advantage of a solar water heater?

  32. GBA Editor
    Martin Holladay | | #33

    Response to Jim
    There's no simple answer to your question. You wonder whether rising energy prices will make an expensive investment in a solar thermal spacing heating system cost-effective. I don't know. I certainly know that such a space heating system is not now cost-effective.

    If I understand correctly, you live in the Southeast corner of the U.S., in home that is already equipped with ductwork. The easiest way to retrofit an active solar thermal space heating system in such a house would probably be to install a hydronic coil in your air handler.

  33. user-659915 | | #34

    On remodeling costs, new construction ethics, and tear-downs

    1. - agreed. There are already too many homes and greenies need to consider other strategies than just adding to the inventory.

    2. - ditto

    3. and 4. - false dichotomy. If my experience is anything to go by most Americans will not choose between deep-energy retrofits and new construction, they will go for the third option of a more modest energy retrofit which will nevertheless result in substantial energy savings.

    Financial reality check: in our area a typical older home in a pleasant mature neighborhood goes for about $300,000. The lot value of such a home is about 25% of the total or about 75K. Demolish the home to build new and you have just spent $330,000 (house value + demo and landfill fees) for a $75K lot. While I agree that a super-insulated home is easier and cheaper to build new than to retrofit it's not THAT much cheaper. In nearly twenty years of practice here with many hundreds of clients I have encountered exactly one to whom that seemed like a reasonable option - and as it happened the replacement home this client chose to build (without my help, I'll add) was very far below Passivhaus or zero-energy standards.
    Energy savings. It would not be unusual for our typical $300K house to consume about 30-40,000KWh per year. A 'shallow' energy retrofit (sealed crawl, attic insulation upgrade, general air-sealing, new high-performance mechanicals, new Energy Star appliances) can easily reduce that energy use by half, at a cost of perhaps a tenth of the 255K write-down represented by the tear-down option. If we regard the total resource available across the country for residential energy upgrade as a zero-sum game the total aggregate energy and carbon savings represented by millions of low-cost upgrades will far exceed that of a few thousand zero-energy flagships. I'm not fond of the phrase 'the perfect is the enemy of the good' but in this situation I think it describes well the dismissive attitude of many green builders and designers to the rank and file of existing low-performimg homes.

  34. GBA Editor
    Martin Holladay | | #35

    James, we're in agreement
    I agree with most of what you wrote. Of course there won't be a single response to sharply rising energy costs -- there will be a variety of responses. In most cases people will respond as you suggest.

    All I'm saying is -- there will be a lot more tear-downs in the future, because many American homes can't be affordably prepared for a future in which energy costs are very high. You look at some homes and you say, "Wow -- fixing all of this home's problems won't be easy." That's when you invite in the bulldozer.

  35. Michael Blasnik | | #36

    PV powered minisplits + wood

    I'd like to hear details of your scenario where tearing down homes to build super efficient new ones will make sense compared to the alternatives that already exist. The effective cost of energy to heat a home should not rise above the current cost of PV powered ductless minisplits used to heat conventionally retrofitted homes. The actual cost should be much less than that. Add in the potential for supplemental wood heat and it's really hard to imagine that scenario you envision. I'm not even including the likelihood that people will build lots of nukes if we somehow (unlikely) have a huge carbon tax to make fossil fuels 10x their current cost. .

  36. GBA Editor
    Martin Holladay | | #37

    Response to Michael
    First of all, none of us can predict Americans' responses to steeply rising energy prices, if indeed prices rise steeply. I'll be the first to admit that my crystal ball is cloudy, and your predictive powers may be better than mine.

    Heating a home with ductless minisplits balanced by the production of a grid-tied PV array isn't cheap -- especially in an old leaky house. Many New England families are now paying $2,000 a year to heat their houses. If that cost rises to $10,000 or $12,000, what's going to happen?

    Poor people will have few choices, and will depend on programs like the WAP for low-income families. Those higher up the income ladder will long for a zero-energy house that is very tight and very well insulated. They may call up a contractor and ask whether retrofit work will convert their leaky old house to a net-zero-energy house, and be appalled at the high cost of the retrofit work. In some communities, old hard-to-retrofit houses will be undesirable and will languish on the market. Those who can afford to will want to buy a new zero-energy home.

    If an older home is in bad shape and is hard to retrofit, the bulldozers may be called in. If the lot is in a desirable location close to public transit, it would make sense to build a new home on the lot.

  37. w5mRKW6vhr | | #38

    On remodeling costs, new construction ethics, and tear-downs
    James, thanks for the back-of-the-napkin math you just presented. Only the wealthy can afford to simply destroy an existing house so they can start with a blank slate. Much of the 'wealth' people own is tied directly to their home, and most of it is in reality the balance owed on a mortgage.

    Martin, I know you're not an advocate of tear downs, but are attempting to present a realistic view of costs - especially in an energy poor future. But I'm still troubled by the notion that getting to the goal of a low energy home requires the massive use of virgin materials and energy. It sounds like a contradiction of sorts - to survive a low energy future, we must expend an enormous amount of energy. Not to mention the market dynamics of attempting to replace a significant portion of the nation's housing stocks in a short period of time...

  38. GBA Editor
    Martin Holladay | | #39

    Response to Paul
    We're entering uncharted territory as our species releases enough greenhouse gases to change the climate of the entire planet. Predictions are very difficult.

    You may well be right. I certainly think that we will not be as materially wealthy in the future as we are now. Clearly, most American families will not be able to afford to move into a new net-zero-energy house. Instead, we may all be living in much smaller quarters -- perhaps heating a single room with a small space heater.

    As I've often said, I have a long history of making bad predictions about our energy future. During the late 1970s, I was sure that energy prices would continue to rise steadily. I was certainly wrong on that one.

  39. Kevin Dickson | | #40


    The scenario you describe is happening right now in my neighborhood. I can hardly believe it, but in the last two weeks, eight brick bungalows were demolished. These homes were quite serviceable and decent sized, at 900-1200 sq.ft.

    Energy costs aren't the reason, however.

    The replacement homes will be at least 2600 sq.ft. The reason the old homes were scraped and not remodeled was economic. The ROI of the completely new home is always a bit higher than a complicated retrofit and expansion of the old home.

    Unfortunately, energy costs are important to only a small percentage of people. No one is paying significantly more for a low energy house. And why should they care? The mortgage payment will be $54,000/yr, and energy costs will be $4000. There are at least six things more important to these buyers than saving that $3-4000/yr.

    The desirable location is the key driving force. Future energy costs, if higher, will just add to the ROI of the new house, and guys like us will be scratching our heads trying to tighten up homes built to 2010 minimum code specs.

  40. Michael Blasnik | | #41

    $10,000 heating bill?

    I really don't see $10,000 heating bills (in today's dollars) happening anytime soon (ever?) except for people who are rich and living in huge homes and can afford it. If oil becomes unaffordable, electric will provide a backstop cost and wood use will skyrocket and people will lower thermostat settings and zone heat. What sort of consumption of what type of energy will lead to this cost you envision?

    Even if there are $10,000 heating bills, few people will abandon or tear down their homes -- which they are often paying several times that each year for mortgages and taxes and maintenance. The tear down or deep energy retrofit will still have to compete with other options that are almost always more affordable.

  41. GBA Editor
    Martin Holladay | | #42

    Michael, let's have a beer in 2025
    Let's get together in 15 years or so and see where the planet is at -- and how much we're all paying for energy. You live in Boston; I live in northeast Vermont. If we both get on our bicycles, we can meet in Laconia, New Hampshire. I'll buy the beer.

  42. Sea Wolf | | #43

    tear downs
    I agree with Martin, there will be more teardowns in the future. Right now, some people are still doing late-20th-century teardowns. You know, buy an expensive 1500-sq.-ft. Bungalow on a city lot, tear it down, build a 2500-sq.-ft. modern home. Eventually, more and more people will do Martin's version of this -- tear down a leaky, uninspired, 1200-sq.-ft. house from 1920 and replace it with a super-efficient new house of the EXACT SAME SIZE. This almost makes economic sense in parts of Seattle, where a $400K buys you a $250K lot and $150K of beat-up-old house; triple the price of energy, and it will make perfect sense. I suspect we'll also see the opposite of the late-20th-century teardown -- tearing down a ridiculous (and poorly built) new 3500-sq.-ft. beast on a nice urban lot and building a smart 1500-sq.-ft. house in its place. I certainly hope so. Maybe we'll call this new trend house halving.

  43. Steve Satow | | #44

    Walls that breathe.
    This email (and all the corresponding posts) have arrived in my mailbox five days late which means that I have not waded through them all, so I apologise if I am repeating something that has been said before, but... when people talk about walls that 'breathe' what they really mean is walls that transpire. As has been noted by Martin, walls do need to transpire (aka breathe) since it is virtually impossible to ensure that no moisture will ever penetrate them. But, my purpose in writing is to point out that, historically, walls that breathe (and therefore transpire) have outlasted building that are highly vapour-impermeable by a factor of four or five (and possibly a lot more). Virtually all the building stock in the UK and Europe built before the war has walls that transpire and many of them are 500 years old. I question whether modern sealed building are likely to last that long? Yes, they are not as energy efficient, but rebuilding every fifty years isn't very 'green' either.

  44. David Whte | | #45

    sensible heat fractions
    Hi Martin,

    In the Texas study, what sensible heat fractions were encountered in the homes? Conventional air conditioners may be inadequate, but I've been impressed recently looking at capacity tables for mini splits. The lowest SHF I've come across is for the Mitsubishi Halcyon - I found 0.63 in the capacity table for the 9,000 btu model, at 95 outdoor 75DB/63WB indoor (around 50% RH).

  45. David Whte | | #46

    radiant floor heating
    if you are generating heating hot water with non-combustion sources such as solar or a heat pump, then a lower supply temperature can make a big difference. best example i've seen is the Balanced Office Building in Aachen, Germany. With very low loads, the heating supply temperature is seventy nine (79) F. they achieved a measured COP of 4.2 (including all plant loads) on their geothermal system because of this. an air system for the same building would need a much higher temp on the water or refrigerant side.

  46. GBA Editor
    Martin Holladay | | #47

    Response to Steve Satow
    So, a wall has to traspire; presumably you mean that a wall must be vapor-permeable.

    You note that for many years, humans have been building walls that are vapor-permeable. Well, that's true. We've built walls with stone and timber and plaster, because these materials are available and they work well.

    We now have many materials that were unavailable in 1510 or 1610, however. You propose a rule: walls have to breathe (or perhaps, walls have to transpire, or walls have to be vapor-permeable). Whenever a rule is proposed that limits designers' ability to specify materials, I want to know if the rule has a purpose.

    So, I ask simply, Why? It isn't good enough to answer, "Because that's the way walls have been built for 500 years."

    Here are examples of wall components that aren't vapor-permeable: window glass, structural insulated panels (SIPs), and insulated concrete forms (ICFs). Sure, you could impose a rule to make these components forbidden (although you'd get a lot of resistance if you insisted on building walls without any windows). But I'd ask, Why?

    SIPs and ICFs are useful because they insulate very well. Older building materials that are vapor-permeable (solid masonry, timber frames with wattle-and-daub infill) don't insulate as well. If you are going to propose a ban on useful building systems that insulate very well, you are going to have to come up with a reason why we can't build that way.

  47. Interested Onlooker | | #48

    500 years old
    Do I sense a deliberate mis-understanding? The point about 500 year-old walls that are vapor-permeable is most definitely not "Because that's the way walls have been built for 500 years", rather it is that walls built that way are 500 years old. Of course, anyone who has read "How Buildings Learn" (which eveyone in this field should read IMO) will know that the building may be 500 years old but many of its constituents may not be. The point is that the building has survived rather than being torn-down and replaced. If we are serious about limiting the environmental impact of our building then this is an important consideration.

    BTW If the greenest building advice is "Don't build" do we need a GBA? ;o)
    Of course we do - since building will not stop just because it isn't needed it must be guided on ways to limit its deleterious impacts.

  48. GBA Editor
    Martin Holladay | | #49

    Response to Interested Onlooker
    Interested Onlooker,
    I don't think there is any controversy concerning your point. I certainly agree that most (perhaps all) 500-year-old walls are vapor-permeable. So what?

    I'm still waiting for an answer to the question I asked Steve Satow: Is there any reason to establish a rule that forbids designers from specifying wall components that aren't vapor permeable -- in other words, walls that include window glass, SIPs, or ICFs ?

  49. Interested Onlooker | | #50

    Walls or Components
    The argument that walls have to be vapor-permeable does not preclude components in those walls which are not vapor-permeable. The questions are :

    Should walls, as a whole, be vapor-permeable and why?

    If so - how permeable ?

    If so - how much of the wall can be non-permeable?

    Are there arrangements of non-permeable components which constitute poor practice?

    Is vapor-permeability to be measured for every building or assured by building to agreed standards?

    BTW on re-reading Steve Satow's posting I was unable to find a suggestion that designers would be banned from using wall components which were not vapor-permeable.

  50. Bob "Hardie Siding Houston" Green | | #51

    Caulking issue
    We speak with a lot of clients on the issues of over-caulking the exterior of their home. Never caulk the overlaps of lap siding! Never caulk the edge of the frieze board on brick! We had one client recently that insisted we caulk the weep holes at the bottom of their brick exterior walls at the plate - No!

    This is not a "walls have to breathe issue" -- this is a moisture-control issue.

  51. GBA Editor
    Martin Holladay | | #52

    Response to Interested Onlooker's second post
    Interested Onlooker,
    This is what I wrote: "It’s possible to build a high-performance wall that is, for all intents and purposes, vapor-impermeable and airtight. Consider a well-sealed wall that is sheathed with foil-faced polyisocyanurate insulation. Almost no water vapor or air can get through the wall, so most people would agree that the wall doesn’t 'breathe.' But it can perform quite well, as long as it can dry on both sides of the polyiso."

    Steve Satow wrote that "Walls do need to transpire (a.k.a. breathe)," in a context that appeared to challenge what I wrote. Perhaps I misunderstood Steve; perhaps he does NOT mean that walls need to be vapor-permeable. If Steve is saying the same thing I am -- that a wall assembly must be able to dry in both directions from its least permeable layer -- then we are in agreement. But that's not what Steve wrote.

    Interested Onlooker, I'll try to answer your questions:

    Q. Should walls, as a whole, be vapor-permeable and why?

    A. No, they don't need to be vapor-permeable. They just need to be able to dry out in both directions from their least permeable layer.

    Q. If so - how permeable ?

    A. See answer to Question #1.

    Q. How much of the wall can be non-permeable?

    A. Almost all of it (for example, a SIP wall).

    Q.Are there arrangements of non-permeable components which constitute poor practice?

    A. Yes, of course. For example, consider a cold-climate wall that includes a layer of exterior polyethyelene over OSB over 2x6 framing filled with fiberglass batts. (No one builds walls this way, thank goodness.) Such a wall will fail quickly.

    Q. Is vapor-permeability to be measured for every building or assured by building to agreed standards?

    A. The overall permeance of the whole wall assembly tells you very little. An impermeable wall assembly can work very well or fail very quickly, depending on its design. Good wall assembly design can be achieved by prescriptive building codes or hygrothermal analysis -- take your pick.

  52. Interested Onlooker | | #53

    Many Thanks
    Many thanks for answering these questions so promptly and lucidly.

    "Q. Should walls, as a whole, be vapor-permeable and why?
    A. No, they don't need to be vapor-permeable. They just need to be able to dry out in both directions from their least permeable layer."

    Would I be right then to think that the forces driving the vapor always act away from the least permeable layer?

  53. GBA Editor
    Martin Holladay | | #54

    Response to Interested Onlooker's third post
    Interested Onlooker,
    You asked, "Would I be right then to think that the forces driving the vapor always act away from the least permeable layer?"

    No, you wouldn't be right. Imagine a SIP wall in winter. The vapor drive is from the warm, moist interior toward the cold, dry exterior. From the interior of the house, the vapor drive is TOWARD the least permeable layer -- toward the foam in the center of the wall. From the exterior surface of the foam, the vapor drive is AWAY FROM the least permeable layer -- toward the exterior.

    However, the wall assembly works well. Although the vapor drive during the winter is from the interior toward the foam, there are no cold surfaces where condensation can occur.

  54. Roger M. Woodbury | | #55

    Eliminating absolutes in response to changing circumstances
    Interesting article and the responding comments.

    We are in the process of planning a new home here on the downeast coast of Maine. We have an outstanding solar site just inland of the water, about 120 feet above sea level. Our intent is to build completely off grid and our goal is to achieve Passive House standards. We are a year away from construction start at best, but it appears to us that there are several issues that are part of the bank of "conventional wisdom" in building that may not properly reflect the current and future state of American life.

    One major concept that seems to always be a part of every discussion is that housing in the future will be exactly as it has become in the past two or three decades. The current economic downturn must radically reverse itself before the housing industry can return to the same-old, same-old philosophy of building bigger houses in response to a massive demand to "upgrade" to a new, bigger house can happen. It seems likely that more and more people will be able to afford any house on any basis until and unless people begin again to save rather than consume and as a people, Americans in particular, begin again to produce products of value. I believe that big houses full of cheap junk made in huge Chinese or other "developing" nations' factories are ikons of a previous era. We need to get over the idea that we can continually get more stuff. We as a people now no longer can do that.

    I disagree with the concept that trees "must" be cut, and that foundations "must" be dug. In the future a successful home will be one that truely melds with the site, and takes advantage of the features of the site. In our case we have completed a therapeutic forest harvest that the forester described as necessary for the overall health of the forest on the 18 acres we own. At the same time we were able to create a road to the building site, itself on an exposed granite outcropping. We will not "dig a basement" for several reasons, one of which is that a basement for most housing is wasted space, difficult to get to, to store in, to use effectively, and often is poorly insulated, heated and dehumidified. It may be that our house will end up being smaller than we might like, and that will mean that we may have to have a bit less "stuff". Perhaps we will merely concertrate on the stuff that we really need.

    Perhaps the idea advanced already that we will be tearing down big houses to replace them with smaller ones of greater efficiency is spot on. But it seems likely to me that over the next twenty plus years, in this country, fewer new houses will be built, and the tendancy toward irrevocable sprawl will go into reverse, driven not by any desire of a population to be more "green" but because they will simply not have the money or credit to do otherwise.

    The idea of "payback" from more efficient design and construction is a foolish concept. There is very little if any "payback" from the installation of solar thermal water heaters, solar panels, or the extra few inches of insulation. Reducing the amount of energy that each living module and each human being consumes should be a goal in itself. It is politically and economically necessary for us as a nation to become more independent of foreign controls, and reduction of combustion of fossil fuels for merely keeping body and soul together must end. To date no elected leadership has emerged that has been able to effectively sell the concept, but sooner rather than later it will become a part of daily life that whatever we have will need to be much more efficient in energy use than has been before the case.

    My wife and I have decided that the best way for us to proceed is to aspire to Passive House certification in our new home. Quite frankly, we don't really care if we actually get to that level provided the house functions at the highest rate of efficiency that we can get it with as little imprint on the environment as we now now it, and can project it to be over the last thirty years of our lives.

  55. GBA Editor
    Martin Holladay | | #56

    Response to Roger M. Woodbury
    Thanks for sharing your story. It sounds like you will be building a wonderful house.

    You're right that it's possible to develop undeveloped land without cutting any trees or building a concrete basement. But you're still developing the site and putting in a house. You're removing a patch of habitat from the squirrels, deer, and moose.

    If it must be done, it should be done with a light touch, as you are doing. But eventually, all of the people living on this planet will have to decide whether we can continue to develop undeveloped land for new homes.

  56. Roy E. McAfee | | #57

    Breathing wall and moisture
    Martin Holladay's argument about walls not needing to dry works well on paper. That is where it should stay. While a "high performance" wall can be built to not need to dry out (because it never gets moist), the reality in human building is that very little is ever perfect. The position is also dependent on zero change. That is, no settling, no shifting, no deterioration and no damage. Nice thoughts and pretty pictures.

  57. GBA Editor
    Martin Holladay | | #58

    Response to Roy E. McAfee
    I don't mind being challenged, but I mind being misquoted. I never said walls don't need to dry out.

    In fact, I wrote:

    -- "Although walls don’t need to breathe, they do need to be able to dry out when they get wet."

    -- A wall sheathed with vapor-impermeable polyisocyanurate "can perform quite well, as long as it can dry on both sides of the polyiso."

    -- "A wall assembly must be able to dry in both directions from its least permeable layer."

  58. Hallie Bowie | | #59

    New construction vs. renovation
    It is important that we all learn how to build super-efficient houses so we know where the ultimate goal is. At the same time, I agree with James Morgan that many, many more home owners are in a position to make small improvements to their existing homes vs. building new homes on existing lots. And those in the U.S. who do build new, super efficient homes are still using today's ideas of appropriate square footage and location. As the actual costs of energy rise, our ideas of what makes a livable floor plan are apt to change dramatically. Moving too quickly to replace our existing housing stock could result in having lots of houses that are new, but already out of date in 50 years.

    Please make sure GBA continues to support and educate those of us doing renovations for the not-so-wealthy. Especially since we do already have plenty of housing already built. We need support in deciding which energy efficiency upgrades make the most sense to add to projects where the homeowners' main goal is a slightly bigger kitchen.

  59. GBA Editor
    Martin Holladay | | #60

    Response to Hallie Bowie
    I can assure you, GBA will do its best to continue to support and educate those who are doing renovations for the not-so-wealthy. That's the kind of work I did when I was a builder.

  60. Pam | | #61

    Hi Martin, great article as usual. I still don't believe the Green NY thesis, or at least the philosophy of it. Seems to me: Money is the proxy for carbon footprint. The key is how much one CONSUMES (i.e., spends) in total. If a given New Yorker has a second house and/or flies to Europe four times a year and/or eats out 5 times a week and/or buys a lot of Manolo Blahniks (sp?) --- and ends up spending lots more money than a given suburbanite -- their carbon footprint will be higher, won't it? Also, I'd like to see a complete Life Cycle Assessment of what is going on in NYC, rather than use of selective data. Also, if energy costs go up, won't groceries and the like get lots more expensive to cart into the city? Sorry, then things get tough, I want my backyard to grow my own potatoes -- oh, and my entire extended family - who live in the city - will come live with me. That'll bring our s.f./pp up and carbon output pp for housing down. Hmmm, maybe this pitting cities vs. suburbs is not totally productive - I don't know it gets at the nut of the issue -- maybe better would be: Wealthy (who consume) vs. not so wealthy (who have a lower footprint because they simply don't consume as much.)

  61. Keith | | #62

    Breathing/transpiring walls.
    I have been looking at moldy commercial and residential houses for the the last 30 years. The original article is correct. If you have a vapor barrier in the internal wall cavity, the spaces on both sides must have the capability to dry out.

    What I see is the condition where the vapor barriers are on the outside of the wall envelope (EIFS on the outside and 6 mil plastic and/or vinyl wallpaper on the inside). I have not seen a wall that can be truly "sealed". Vapor will infiltrate. Just think 95 degrees outside with 85% RH, and your house is air conditioned. Where do you think the dew point is? Somewhere in you walls.

  62. GBA Editor
    Martin Holladay | | #63

    Response to Pam
    You're right: one's carbon footprint tends to be directly proportional to one's income. Many years ago, Stewart Brand pointed out that the best thing any of us could do to protect the environment is to strive every year to earn less money than the year before.

    I think you're pigeon-holing New Yorkers, however. New York is full of low-income people, not just upper income people -- just like the suburbs and rural areas.

    The desire for a big enough yard to grow a few vegetables is understandable. The luckiest people can find such a yard in a city with a good public transportation system -- somewhere where they can get around by bicycle, bus, or subway. When it comes to our carbon footprints, transportation tends to be one of the two big elephants in the room. (The other, of course, is residential energy use.)

  63. GBA Editor
    Martin Holladay | | #64

    Response to Keith
    You wrote, "I have not seen a wall that can be truly 'sealed.' " I'm not sure whether you are talking about a wall that is sealed against air infiltration or a wall that is sealed against vapor diffusion.

    If you want, it's a fairly trivial task to design and build a wall that is sealed against air infiltration. Green builders do it every day.

    It's also possible to build a wall that doesn't permit vapor transmission, if that's what you want. Two good ways to build such a wall: install exterior rigid polyisocyanurate foam with taped seams, or use closed-cell spray polyurethane foam on the exterior side of your wall sheathing.

    Concerning your comment -- "Where do you think the dew point is? Somewhere in your walls" -- I think the comment is misleading. Condensation can't happen in the center of a foam panel. Condensation happens on a cold surface. If you analyze a proposed wall to determine the likely temperatures of any surface subject to condensation, you can easily determine whether there is any risk of condensation. Often all it takes is to thicken a layer of foam to turn a risky wall into a very safe wall.

  64. Pam | | #65

    Thanks, Martin. I didn't mean to pigeonhole - I was really calling out the example to make a point. Yes, there are affluent consumers in cities, suburbs and rural areas -- just as there are middle-class and lower-income in all areas. I wonder what the breakdown is, actually -- if cities have a greater proportion of low income, that also dovetails with my suspicion that it's all about the money. If you did a carbon footprint analysis, would it also dovetail with that old law: The top 20% of earners account for 80% of carbon emissions?

  65. Interested Onlooker | | #66

    Alternatives to Foam
    If I am understanding correctly, the desired effect in the wall designs you seem to be recommending is that the dew point (or at least the point where the RH rises to harmful levels) always occurs within a thickness of vapor-impermeable insulation.

    Are there such insulations which do not use hydrocarbons as a raw material?

  66. GBA Editor
    Martin Holladay | | #67

    Response to Interested Onlooker's latest post
    Interested Onlooker,
    Stay tuned for an upcoming blog on dew-point calculations and condensation.

    Contrary to common understanding, condensation in walls does not occur within fibrous insulation like cellulose or fiberglass. Condensation (or moisture accumulation) occurs on hard surfaces that are below the dew point. What actually happens is that, in winter, it's possible to get frost or moisture accumulation on the interior face of the exterior sheathing (boards, plywood, or OSB); during the summer, it's possible to get condensation on the exterior surface of polyethyelene installed behind drywall.

    It is certainly possible to design a wall insulated with dense-packed cellulose that performs very well. For years, many New England builders have been building double 2x4 walls with a total thickness of 12 inches.

    Recently, building scientist John Straube has raised concerns about the use of OSB sheathing for such walls, since OSB is notoriously quick to rot, and since the sheathing in such walls is cold.

    The best advice for building such walls is to use plywood or diagonal board sheathing, followed by a ventilated rainscreen gap between the sheathing and the siding. Such a wall should perform very well.

  67. Interested Onlooker | | #68

    Thanks for another lucid and helpful reply. I look forward to the upcoming blog that you trail.

  68. GBA Editor
    Martin Holladay | | #69

    Response to David White
    You asked, "In the Texas study, what sensible heat fractions were encountered in the homes? Conventional air conditioners may be inadequate, but I've been impressed recently looking at capacity tables for mini splits. The lowest SHF I've come across is for the Mitsubishi Halcyon - I found 0.63 in the capacity table for the 9,000 btu model, at 95 outdoor 75DB/63WB indoor (around 50% RH)."

    I sent an e-mail to researcher Armin Rudd, and this is how he answered: "I prefer not to talk too much publicly about the dehumidification performance of mini-splits or multi-splits while we are still executing the ASHRAE research project on residential dehumidification (RP-1449). I can say, though, that when an SHR of 0.0 is needed (no sensible capacity, but only latent capacity), even the relatively low 0.63 SHR stated is nowhere near low enough to dehumidify without over-cooling."

  69. ja9PtwChNE | | #70

    It seems the way Taunton often attracts attention these days is to cherry pick, and provide provocative readings that stir debate and discussion and sheds a little light. Take #1 for example, the author shares

    1-New York City...: Absolutely true in some ways, but not in others and what do you mean by environment? The pollution is so concentrated that people get very sick from it (at much higher rates than elsewhere); virtually all of the street runoff goes directly to the ocean. The anonymity fosters crazy and criminal behavior (eg Wall Street); many of the 18% that drive also are some of the worst polluters on the planet, when you count the whole footprint; which has to take into account the fact that the whole city relies on the "outside" for essentially every thing it really needs to survive (food, water, even sewerage and trash disposal) so include the "costs" of that in the footprint too, and the numbers won't be as dramatic. Their trash that has to be dumped someplace else: "...carted off to landfills—located in various surrounding states—which are now nearly all at capacity." New transfer stations located in each borough, "will allow us to transport nearly all of the city’s residential garbage, and more of our commercial garbage, by barge or rail. As a result, sanitation and tractor-trailer trucks will travel nearly six million fewer miles every year." I wonder how many miles are left? Yes, I know our collective totals may be more. Trash is a problem everywhere, but in NYC it's not considered a NIMBY problem because it isn't dumped in their back yard (though maybe the back alley, where it can run down the street drains and directly into the river). Notice that the authors (of this and the referenced article) don't live anywhere close to resembling NYC.

    2-Walls have to breathe: Most walls do need to breath, from one side, to allow any moisture from dew point condensate to dissipate. You say so your self in your foil-faced polyisocyanurate example. Most folks who say walls need to "breath" mean moisture needs to be able to dissipate sufficiently to avoid mold and rotting issues in the wall cavity. Deceptive exclusion in your point is not useful. In fact all walls do breath to some extent; even the best SIPs "breathe" to some extent, though I know your intent. To suggest sheathing a wall with foil-faced polyisocyanurate insulation is a poor example to leave out there for some folks to consider or to use in debating your point, as there is far more involved in such a decision (eg climate, other wall details).

    3-Renovation is less expensive...: Of course it all depends, but your point isn't a green one, it is a financial one. The two are not the same. Many of us decide to spend more (time and money) to be green. And what of the disposal costs (environmental and financial) to throw away all of those existing materials. If I can stretch the use a little further by making improvements, perhaps by the time it does get disposed of the overall footprint will be less, perhaps regulations, social standards, disposal technology and replacement choices will be improved (asphalt shingles converted to pavement; lead paint removal regulations, roofing made of recycled or recyclable and longer lasting materials, etc...).

    4-Spray polyurethane foam creates an air barrier: Of course most installers and most people for that matter, know that it is only a barrier where is is used. You left out the whole floor (of most old houses), the upper ceiling, and the crack between the subfloor and the rim joist, the cracks around windows, doors, vents and the numerous other penetrations.

    5-Caulking the exterior...: What? "...newspaper advice columnists have been telling homeowners...? What about home building magazines? In nearly every issue (I don't always pay attention) I can find "bad advice" allowed to sit out there for everyone to assume is true. And "It’s not unusual to see caulk installed by [professional contractors and painters,] where it doesn’t belong — for example, blocking drainage at the horizontal crack between courses of lap siding, or blocking weep holes in [storm and other] windows." In truth, properly installed exterior caulking does help to reduce unwanted air leakage, as do house wraps, and it certainly helps to prevent water damage.

    It is easy to sit and pick a myth to debunk, and easy to debunk the debunker, but far broader thinking has to enter the picture. Taunton needs to help builders and homeowners find the best solutions, not simply offering provocative articles. They could start by stopping their appeals to base desires of people...that is by stopping the appeal to conflict in their provocative articles and instead offering independently proven advice, and by stopping the appeal to greed in their far too often showcasing of outrageously expensive homes.

    But I guess what sells is what sells...whether it good or not.

  70. ja9PtwChNE | | #71

    Perhaps a better approach
    Perhaps a better approach would be a comprehensive review of each issue as a separate but adequate article.

  71. GBA Editor
    Martin Holladay | | #72

    Response to Peter Martel
    Pater Martel,
    I welcome your comments, and I agree with most of them. It is in the nature of a myth-debunking article to be somewhat provocative, to be sure.

    1. The essential point of the "Is New York City green?" debate is an important one. The issues you raise -- trash hauling, ocean pollution, and so on -- are also important, but many of them also apply to suburbs and small towns.

    Here's the point: environmentalists who live in the suburbs or rural areas often underestimate the effect of their transportation energy use and underestimate the energy advantages of multi-unit housing. Implemented on a large scale, the energy savings achievable by implementing these strategies are impressive.

    2. When it comes to my "walls have to breathe" discussion, I made two main points: The word "breathe" should not be applied to walls, and walls don't have to be vapor-permeable. It appears that you disagree with the first point, but we agree on the second. Not bad. Of course you can continue to use the word "breathe" if you prefer it.

    We certainly agree that walls need to be able to dry in both directions from their least permeable layer.

    For all intents and purposes, most SIP walls are vapor-impermeable. As to your point that "climate matters," even a cursory reading of the GBA Web site should confirm that we hammer home that point all the time.

    3. In your reaction to my discussion of the myth, "renovation is less expensive than new construction": you wrote, "your point isn't a green one, it is a financial one." Well, that should have been obvious; isn't that the point of a discussion of which option is "less expensive"? In another blog, I wrote, "It’s better to renovate an existing building than to build new."

    Better, but usually more expensive. So I'm glad you agree with me on that.

    4. I'm glad you also agree with my on air leakage in spray-foam-insulated houses, and I'm glad you decided to add to my list.

    5. I'm also delighted that you are part of a cohort of energy nerds eager to counter bad advice. (You wrote, "In nearly every issue [of home building magazines] (I don't always pay attention) I can find 'bad advice.' " You're right! Sounds like you're a myth-debunker like me.

    Although caulk is useful to prevent air leaks -- for example, between the bottom plate of an exterior wall and the subfloor -- it's rare to find anywhere on an exterior wall that will benefit from caulking.

    6. "It is easy to sit and pick a myth to debunk, and easy to debunk the debunker, but far broader thinking has to enter the picture." I agree. I'm all for broad thinking. "Taunton needs to help builders and homeowners find the best solutions, not simply offering provocative articles." We're trying to do just that.

    Spend some time on the GBA Web site and you might see that "helping builders and homeowners find the best solutions" is exactly what we're trying to do.

    7. Three cheers for your statement that all of us should "stop the appeal to greed in the far too often showcasing of outrageously expensive homes." I couldn't agree more.

  72. Barry E. LaDuke | | #73

    Another variable in favor of radiant FLOOR heat
    I've enjoyed the lively debate regarding radiant vs. forced-air heating. As has been noted in many posts, there are many variables that have not yet been measured well to determine the true differences between air vs. water BTU distribution.

    One variable, however, has been overlooked in this discussion: Convection of air taking BTUs to the ceiling vs. radiant floor heating keeping the BTUs closer to the flor and thus closer to the occupants of the home.

    Forced-air, meaning forced convection, uses air as the primary medium to transfer heat. As we all know, heat does NOT rise, but hot AIR does. Most conventional furnaces deliver heat to the duct at somewhere around 112 - 115 degrees F. Those BTUs get quickly concentrated at the ceiling even with the mixing that the "forced" air fan provides. Does anyone need to measure and confirm this or can we stipulate that it's true?

    We've all experienced cold feet and warm foreheads in a forced air house. Yes, all the BTUs are within the envelop, but they aren't doing us much good when we actually live on the floor.

    Radiant heating travels in a straight line from the source to the nearest surface and is either absorbed as heat or is reflected back to the source (is your skin or ceiling shiny?). It also diffuses as it travels, giving off BTUs to the air mass it travels through. It won't be as warm at the ceiling as at the floor.

    With radiant floor systems, the temperature at the floor will always be greater than the temperature at the ceiling, usually with surface temps hovering just above the thermostat set point by a few degrees. The temperature at the ceiling will likely be just below the set point of the T-stat. Some who have never been in a radiant floor-heated home will need proof, so those of you with radiant floor heating can measure and confirm this since it isn't as common an experience as the stratified air example.

    Given equal insulation values at the ceiling for either method, even the best insulated homes will experience heat loss through the envelop (else why would we even need heat appliances?). Heat always goes to cold. The rate at which it travels will be greater as the temperature difference is greater.

    Assume a 30 degree outside temp: A ceiling at 100 degrees creates a 70 degree difference. A ceiling at 70 degrees creates a 40 degree difference. Which one creates a faster rate of heat travel? Even if heat has to go through R-38 ceiling assemblies, it will still eventually leave the building; in a forced-air home at twice the rate of the radiant floor home.

    This is math based on the laws of thermodynamics. Change the numbers to reflect a more scientific approach than mine, but the math equation still applies.

  73. GBA Editor
    Martin Holladay | | #74

    Response to Barry LaDuke
    Barry LaDuke,
    You wrote, "Radiant heating travels in a straight line from the source to the nearest surface and is either absorbed as heat or is reflected back to the source."

    That's true. But in most homes with in-floor hydronic heating systems, radiant heat rarely plays much of a role. Convection is an important part of how these floors work. In a well insulated house, the floor is usually at room temperature (or even cooler), because the heat isn't on. Only on the coldest days of the year will the floor be warm for a significant number of hours.

    You wrote, "The temperature at the floor will always be greater than the temperature at the ceiling." Nope. During most hours of the day, the floor will not be heated. The floor will be at room temperature (or cooler), while warm air will concentrate near the ceiling (due to the stack effect).

    The most important factor determining issues of comfort and temperature stratification is how airtight the envelope is. If you have a fairly airtight envelope (and a well-insulated slab), you'll be comfortable, regardless of your heating system. If you have a leaky envelope, you'll have temperature stratification, regardless of your heating system.

  74. Interested Onlooker | | #75

    If condensation does not occur in porous materials when their temperature is below the dew point, does the water stay as a super-cooled vapor?
    Surely the surface of even porous materials is smooth and impermeable at the scale of a water molecule?
    Does the water condense and wick away immediately giving the appearance of not condensing?

    This may seem an academic point but I'm simply trying to get my head round what is actually happening.

    Thanks in advance.

  75. Rhaud | | #76

    Breathing walls
    Is it possible that in all your full-blown desire to enjoin the debate of the "breathing" wall, it may well have resulted in you having in your own unique way missing the possibility of the very real and earthly prevalent 'transpiration factor' which is in fact the natural way of dealing with ridding oneself of humidity and controlling both heat and of coolling? Why is it so-called 'experts' (you an exclusion of course to this definition) always operate within a set of parameters or a possible box; and why is it of more often than not a set of values determined by the retrospectively questionable and OOPS- IFU discourse of so-called experts? Experimentation beyond the known, accepted, preferred and dictated is the one and only way that determined how and when we arrived at where we are now in any area of endeavor, consistently challenging the "CODE" or else we would inevitability still be knapping flint and other pieces of stone. Let's face it, Newton was not reflecting on nor operating within limitations, nor was Watts nor Galileo.
    How about a little bit outside of the box from you and yours, our environmental awareness that could be and should be, was fundamentally realized so many millennium ago by the simple experiential practicality of survival amongst and within so many diverse and unique environments. by so many peoples living within so many and countless and diverse cultures surviving and thriving to this day., Why do you and others choose to ignore them or impose high tech solutions (read as high environmental deficit with regards to production, shipping, life-efficiency, repair and replacement to ensure maximum efficiency), while disregarding thousands of years of energy/climatically efficient innovation? How and why has the building/design industry become such a "one size fits all" doctrine. Each and every climatic zone requires a unique and specific design, even down to a given valley, (ask our myriad of ancestors). Then again maybe I'm way off base!!!
    Your argument of radiant slab versus heated forced air or radiant baseboard is only justifiable given very specific climatic zones and defined by informed or unique design omissions/stupidity, .As you are an 'expert' and a 'prognosticator' of building standards willing to determine that the specific application of an approach in terms of building envelopes, heating and cooling systems, etc.,etc. Are you also willing to advocate/and ensure that the 'one approach system', is a then a viable and will embody the least environmental impact? If in fact this is the case, I have a great number of concerns too great to ask here on this forum. However, given the aire of your statements, I have a number of questions!
    1) how are you differentiating specific climatic zones- those climates within climates? OOPS! Bio-regional climates!
    2)how are you interpreting the environmental impact of the various systems you espouse, does that include: manufacturing, shipping and the distributing impacts?
    3) In your analysis of retrofitting an existing home have you considered the locale of the home or the relative regional access to new construction materials or retro-fitted components
    4).Do you ultimately perceive that the insulation/isolation of an structure from its real environment rather that the thermal/participation of that structure is the ideal way to build?
    5) Do you advocate the utilization of electronic controls to determine the comfort of our environment ( which I prefer to call disconnect)? Or do you rather that we actively participate with our structural environment ---- which could instill a conscious awareness of our real environment (beyond our interior environment) and possibly provide the opportunity/ability for us to interact with a conscious concern of the consequences of our actions?
    Just a few of many questions I have about your and your organizations focus;

    With regards.

  76. GBA Editor
    Martin Holladay | | #77

    Response to Small d / Rhaud
    Small d / Rhaud,
    Q. "How are you differentiating specific climatic zones- those climates within climates?"

    A. The GBA Web site hammers home the idea that different climates require different solutions. (If you spend any time on our Q&A page, you'll see this response offered as a mantra to almost any question from a newbie: "What's your climate?") We can't answer a question without knowing your climate.

    Here's an example of a climate-specific article: Hot-Climate Design.

    Q. "How are you interpreting the environmental impact of the various systems you espouse, does that include: manufacturing, shipping and the distributing impacts?"

    A, The GBA Web site covers these topics all the time. For example, here are two articles on the topic:

    Life-Cycle Assessment

    “Transportation Energy Intensity” of Buildings

    Q. "In your analysis of retrofitting an existing home have you considered the locale of the home or the relative regional access to new construction materials or retro-fitted components?"

    A. See the article I just referenced (“Transportation Energy Intensity” of Buildings). Also see this blog, in which I wrote, "It’s better to renovate an existing building than to build new."

    Q. "Do you ultimately perceive that the insulation/isolation of an structure from its real environment rather that the thermal/participation of that structure is the ideal way to build?"

    A. I wouldn't use the term "ideal." However, I've done a lot of camping, and slept under the stars for many nights. When the black flies are swarming, or the wind is blowing across the Himalayas, or a tropical storm is dropping two inches of rain an hour, any normal human being appreciates shelter.

    Every winter I see temperatures of -20 degrees F, and some winters it has dropped to -38 degrees F. A little bit of space heating is a good thing in my climate.

    Q. "Do you advocate the utilization of electronic controls to determine the comfort of our environment (which I prefer to call disconnect)? Or do you rather that we actively participate with our structural environment ---- which could instill a conscious awareness of our real environment (beyond our interior environment) and possibly provide the opportunity/ability for us to interact with a conscious concern of the consequences of our actions?"

    A. I have no electronic controls in my own home. I have a wood stove. In most cases, I believe that simplicity trumps complexity. When I'm cold, I adjust the damper on my wood stove or add another log to the fire.

  77. GBA Editor
    Martin Holladay | | #78

    Response to Interested Onlooker's latest question
    Interested Onlooker,
    You asked, "If condensation does not occur in porous materials when their temperature is below the dew point, does the water stay as a super-cooled vapor? Surely the surface of even porous materials is smooth and impermeable at the scale of a water molecule? Does the water condense and wick away immediately giving the appearance of not condensing?"

    I decided that the best person to answer your question is Professor William Rose, who graciously provided the answer by e-mail. He wrote:

    "At the scale of a water molecule, non-crystalline surfaces such as cellulose and lignin (wood) are anything but smooth. They are physically jagged, and they are loaded with unbalanced electric charges. The water molecule, too, is unbalanced, so it forms hydrogen bonds readily with any available molecules and parts of molecules. With pure water at atmospheric pressure, there is essentially one energy of attachment from solid to liquid and another from liquid to vapor (condensation and evaporation). The bonds that attach water to surfaces may fill a whole range of energies. Immerse a sponge in water then lift it out. Some water drains out—the water with attachment bonds weaker than gravity. Wring out the sponge and the capillary water (matric bonds) comes out. Set the sponge on a counter and additional water comes until it comes into equilibrium with the air in the sorption range. Getting the rest of the bound water out requires oven drying.

    "We’re familiar with the rules governing phase change for pure materials. We think of solids as composed of molecules with fixed bonds allowing no translation. Liquid has cohesion but the bonds reconfigure and allow translation. Gas molecules are not bound to one another. The rules change considerably with mixtures of materials, especially porous materials. Porous materials have holes and the holes contain vapor. Capillary water allows some translation with cohesion—liquid. And some molecules are rather tightly bound in place to parts of fixed molecules—solid. There is a rather smooth gradient from the most attached to the least attached water molecules.

    "There was a conscious effort in the 1930s to sell the idea that “condensation” happens with porous materials under the same conditions that condensation appears on a window pane. That sales pitch has really set back the public’s understanding of what really happens in building envelopes. The current version of the ASHRAE Handbook chapters on building envelopes discourages the use of the term “condensation” in reference to porous and hygroscopic materials such as wood and masonry."

  78. Interested Onlooker | | #79

    Reply on Condensation
    Thank you for a comprehensive answer.

  79. Interested Onlooker | | #80

    All Consumption is not Created Equal
    "I don't know it gets at the nut of the issue -- maybe better would be: Wealthy (who consume) vs. not so wealthy (who have a lower footprint because they simply don't consume as much.)"

    One pair of hand-made shoes or ten pairs of Third World sneakers

    Locally-crafted wooden cabinet or a dozen MDF chests of drawers

    Surely part of being green is not buying loads of cheap transient goods but rather supporting local craft workers even if you can only do it once a decade...

    Only the really poor don't consume much relative to their peers.

  80. Geekeldr | | #81

    Radiant Floor vs Forced Air HEating Systems
    We have just gone through an extensive analysis of a new home to be built in Northern California. While the owners wanted radiant heat they also wanted to get the most bang for their buck when it came to heating the house. Due to lifestyle issues and the variability of the weather it was decided that the ability to have a zoned heating system that responded rapidly to occupancy and significant differences in day to day weather temperature variations would be of high value.
    Investigation revealed that do to latency issues gypcrete radiant systems could take 3-4 hours to heat the house. On the other hand systems such as Warm Board have a 45 minute to 2 hour latency but are roughly 2x the cost. Further investigation of local residents revealed that to combat the latency issue, most homeowners never turned their radiant systems off. Moreover, radiant systems cannot take any major advantage of setback thermostats except through the use of expensive complicated weather based predictive controllers that can be programmed to compensate for latency.
    On the other hand forced air systems can heat an entire house within 15 minutes or so. Coupled with zone heating and set back thermostats they intuitively seem more responsive to the variables of occupancy and weather conditions.
    When the zoned radiant and forced air systems were compared the radiant heat systems was over 2x more expensive to purchase. As to operating costs it seemed that the rapid response to occupancy and temperature conditions gave forced air systems a distinct advantage over radiant systems.
    The final issue was perception or comfort of radiant heat versus forced air systems. Radiant does have a “coziness” feel to it and supposedly heats the air more uniformly than forced air systems which can stagnate air in the higher areas of the ceiling. There are technologies that can deal with the stagnant air. Given the acquisition and operating costs of forced air and the promise of a whisper quite forced air system that will eliminate hot air trapped on the ceiling It was decided to go with the forced air system.
    This analysis was based on the unique microclimate weather conditions of Northern California and the lifestyles of the occupants. IT might not apply in other conditions.

  81. Mike Legge | | #82

    Higher thermostat settings with radiant heat
    If you have two houses with the same envelop it is reasonable that they would have somewhat similar energy use irrespective of the heat distribution method allowing for different life styles. Energy is energy whatever system one uses. The efficiency of the heat source is more significant. Just using one parameter, i.e thermostat setting, to make a solid decision seems moot. For example radiant folk may be older (with more money)and typically they like more heat as they are not rushing around after kids. Fifty houses is not a powerful statistical number. Were there any outliers in the figures? Do people at weekends like to wander about bare foot in floor radiant heated homes ? The thermostat reading was from only one thermostat, what about the average of all the thermostat ? I don't think the survey is statistically robust. It does however point out that floor radiant heat is not magical, except as far as purveyors of radiant floors are concerned.

  82. Geekeldr | | #83

    Radiant Floor vs Forced Air HEating Systems
    I appreciate your comments. When we did the survey we tried to factor in similar lifestyles and ages. IT was by no means scientific. I guess the point I was trying to make was that Forced air systems Heat the house very quickly and therefore can be better controlled by a low cost set back thermostat. The biggist deficiency of radiant heat systems is their latency. Assuming both syutems are shut doiwn at 11:00 PM nightly and the owner wants a comfortable heated environment at 6:00 am, Forced air system can be kicked on at 5:45 where the radiant heat system would have to come on somewhere between 2:00 AM to 4:00 PM to make up for the thermal discharge.

  83. Paul Risberg | | #84

    As a professional solar designer/builder who frequently has solar thermal systems that produce viable BTU's for space heat applications, in addition to the much more viable domestic hot water applications, we have utilized many ways to get the heat into the home, which we insist be the most efficient HVAC structure it can be. (well insulated)

    Radiant floor systems are not intrinsically more energy efficient, if you surveyed owners about the cost of heating a well insulated structure. This is a practical statement, based on both engineered system predicted and actual performance. The author of this article is correct about most of his assumptions. They like them, though, and so do I.

    One exception we have found, and it may seem almost too simplistic. Setback schemes can work pretty well, but the simply need to be time adjusted. In your example above just quit loading 2 hours earlier, and start loading two hours earlier. This will not work well for high mass (slab on grade) or thick (3" plus) slabs.

    In 2005, I believe, I built the floor described below in my home, straight out of a Fine Homebuilding Mag article. A high strength 1.5" polished concrete slab, with 1/2" radiant tubing anchored 1/4" from the subfloor, constructed of 5000 PSI concrete, isolated from the 3/4" T and G sub floor with poly sheet, with Glass fiber additive and 2" metal reinforcement , sitting on 2x12's on 12" centers, is a great finish floor. We built this system 42" wide, around the perimeter of a large living room and kitchen. The insets are bamboo flooring. (they do not contain any radiant tube). It works beautifully, and has no cracks. Fired by a gas boiler and solar thermal array, I do not believe it has saved us money. But it doesn't use much energy to get those Btu's into the space, and because it is an envelope that is very well insulated (4" foam), we don't purchase a lot of fuel.

  84. Paul Risberg | | #85

    Forgot to add, setbacks and environmental controls work much more effectively with radiant floor sensors in the mass, instead of air thermostats. No, they do not bring a house up to temp in 15 minutes. I don't think I have ever wanted to heat a whole house in 15 minutes

  85. smalld | | #86

    radiant floors
    Maybe you ought to research which area of the body, meaning portion/s of, extremities of the human body sense and determine bodily COMFORT then get back to us all about radiant floor heat. You may or not be surprised as to its location! I would suggest that thermal mass and radiant floor heat may well be at least part of the answer? Just check it out and research/think outside the' box' and into the physiology and psychology of the human being.
    ps. - Transpiration is a recognized form of 'BREATHING' in the world of physiology, at least on this planet!!!

  86. GBA Editor
    Martin Holladay | | #87

    Response to Small D
    Small D,
    In a well insulated house with a low rate of air leakage, interior temperatures tend to be uniform. Even if the house has in-floor hydronic heating, the heating system is usually off. It's not as if occupants have warm feet and cold heads, in spite of what many radiant floor advocates imply.

    Moreover, plenty of people who live in radiant floor homes have told me they don't like warm floors. It's a matter of taste.

    When I lived in South Korea, I stayed in many inns with heated floors. Of course Koreans sleep on futons on the floor, and so did I. I often woke up in the middle of the night, sweating. It's a matter of taste, I guess -- but it that case I wasn't comfortable.

    In short, to create a comfortable interior, you need good design. An excellent thermal envelope gets you most of the way to good design. Once you've got that, the type of heating system isn't very important.

  87. Vigilant1 | | #88

    Animate Objects
    Hmm. First we have "Walls don’t have any blood that needs to be oxygenated, so they don’t need to breathe." True enough. But then we read "Heat wants to flow from the hot side of the fiberglass batt to the cold side." Really? Heat has a thought process and a voluntary desire to move in a particular direction? This opens up possibilities. Maybe it would be more efficient to reason with it and offer it inducements to remain in the house rather than go outside to play with its friends, wind and rain.

  88. Anonymous | | #89

    After reading your "Green Building Myths" It occurred to me that you don't site any real research yourself. I would assume that any studies you mention are probably funded by your imagination.
    That's not to say you are wrong about some of what you say, but opinion isn't research.
    Mostly, you seem to be trying to find something to write about.
    None of your "myths" were myths to me. There are too many variables in building technique, site location, materials used etc. to make the gross generalizations that you have made. New Yorkers may use less energy getting around, but they make for it by all of the hot air that the emit. You say walls don't have to breath, and then say you need to keep the moisture out and provide a permeable membrane on the inside. Renovation is much cheaper in some parts of the country because of high permitting cost for new construction. Radiant heating can be far more efficient because of where the heat is placed. Also a good heat exchanger can transfer heat to a liquid far more efficiently than to air. I grow tired of the effort...

  89. Frank Lee | | #90

    Vapor barriers = sick buildings ~ in mixed humidity regions
    The Army for a period of time "Value Engineered" interior paint and maintenance in barracks and choose to finish interior gyp board vertical surfaces with vinyl wall covering - higher durability saved repainting cost, lowering cost-of-ownership. ..
    The Corp of Engineers later determined that in regions with mixed humidity - humid summers, cold dry winters, the interior vinyl vapor barrier will trap moisture. Removing the vinyl from exterior walls revealed toxic molds feeding on moisture, gyp board paper and wall covering paste. Many sick Army barracks required total demo or deep rehab with mold remediation.

    If Summers are humid and Winters cold-dry, eliminate vapor barriers. But multiple air barriers are extremely valuable.

    Exterior caulking, I agree, is not for air tightness. It is for durability of the exterior finishes. The rain barrier is properly behind the siding, Brick veneer has a back cavity and weep holes at the bottom course. Even solid masonry walls have an internal cavity that allows moisture to fall out and exterior air to move through the interior to dry out moisture..

    Gee it sounds like walls DO BREATH. But more like fish, they breath moisture.

  90. Glenn | | #91

    Greater energy loss with radiant?
    Isn't the loss of energy greater with radiant heating? Heat loss is the temperature difference between two objects. R values are the same in this example, the building one story, no basement. If the building is at 68 degrees and the outside temperature is at 48, heat loss to the environment, through the insulation, would be the difference of 20 degrees. Forced air would fall into this category would it not? The "heat" is placed into the room space and the "wall" temps would remain 68 degrees. If radiant heating was on delivering say 78 degree "heat" to warm the room. The floor would see a difference of 30 degrees, the walls and ceiling 20 degrees. Wouldn't the floor be losing 50% more energy than the forced air?
    I have always felt that the back of the radiant emitter should have room air to drop the differential temperature to the outside environment and thus reduce heat loss. Is my logic wrong concerning the room heat loss?

  91. KatyDaly | | #92

    New construction vs. 120YO poorly insulated house
    Sorry, not much of a technical wizard here, just a homeowner in a new, well-designed (by architect and engineer) very tight house, and yes, it does have radiant floor heat.

    Husband and I (no kids) recently moved from an old house in NJ with forced-air (natural gas) heating. We both like our new warm floors, and with 4 zones we can pretty easily cut back on the thermostat. We are in upstate NY, and keep the 2 zones that need heat the most most set at 68°, and the others (upstairs bedroom and living room) set at 64°, or off, depending on the weather. The living room has a woodstove, which we use as often as possible.

    My first comment is that this radiant heat (propane-fired Baxi boiler) is ridiculously expensive! Granted it is colder up here than in NJ, but I never expected my heating bills here to be higher than my combined heat and electric in the old, barely insulated house. And that is with the frequent use of the supposedly high-efficiency new Harman woodstove.

    We tried to be as green as possible in building the new house, but were prevented mostly by the cost of things like solar panels and wind turbines. A wind turbine would work great on this very windy site, but I couldn't convince my husband, and the neighbors would have gone ballistic! Solar panels would not work well with how the house is situated.

    The other thing that surprised me was that my builder and even my plumber pretty much fought me from the get-go on all of the energy-saving features that the architect and engineer had worked out. Even though I spent hours staking the house site to make use of what I knew of passive-solar technology (with the help of my architect) the builder was more concerned about my views from the big windows in the living room, and he simply moved the stakes when it came time to dig the hole. Forget having a discussion about certified wood products and plywood that doesn't give off harmful gases.

    Finally, the damage is done, we have already built this new home. But I also think (like the man from Maine) that we chose our site responsibly. I really believe that we will make up for our destruction of this natural environment with what we plan to do to improve it. Although we will never live off-the-grid, we do hope to plant and harvest enough of our own fruit and veg, and possibly get into some other organic farming ventures like raising goats, pigs, chickens...feeding ourselves, but also finding out what's missing at the local Farmer's Market and filling in the gaps.

    Our site is old farmland that was pretty much already stripped of trees. In our first few years here we planted maybe 10 adult trees, and close to 100 seedlings that we get from local sources and the Arbor Day Foundation. We walked the 20-acre site with a State forester to discuss future improvements. As soon as we can afford it, we hope to remove/recycle the 1959 mobile home that was already here, and I hope that the legacy we leave is a piece of land that is improved, rather than neglected, or worse—broken up into smaller lots, or developed in some other destructive fashion. People love to buy up open land up here and build things like storage facilities, McMansions, and (God forbid) strip malls and WalMarts! We hope to leave our land to a Land Conservation group so that long after we are gone, most of these 20 acres will live on, naturally.

    We are not green heroes, by any stretch of the imagination, but we do what we can. I think that a lot of people these days do try to live responsibly, but often it is not as easy as just trying. I also think that the more people out there who ask for "green building", the more chance there is that up-and-coming builders will learn more about it.

    Thanks for putting all this good information out there...for both the homeowners and those builders who "already know how to build a house", and everyone in between.

  92. jesse | | #93

    Based on recent demographic trends, the house of the future will be two bedrooms, 1 1/2 baths, one car garage. Those homes will be constructed with maximum energy efficiency, more sensible space configurations and with smart systems to use energy wisely. Although do-it-yourselfers are not professionals, many are far more conscious of doing things right than fast, hence, heat leakage is at a minimum. Save me from the contractors and subs that measure success by the profit made by building fast and leaving a path of mistakes in their wake that will haunt the home owners for decades through high heating costs. Simple solutions are already here, but profit/costs will always rear it's ugly head.

  93. Anonymous | | #94

    Nothing like a good controversy to end the year. I think that anything that sparks discussion is good, as long as it is not offered up as expert advise, likely to be lapped up by newbies as fact and truth. IMHO, this article lacks credibility, starting with its title, especially the word myth. The best definition of this word I ever heard was that a myth is something that's not true on the outside, but true on the inside. The best examples of myths are teaching fables which, are factually untrue, but impart wisdom nontheless.
    To suggest, then that "Walls must breathe" is a myth would mean that although factually untrue, was in spirit, correct. But I disagree. I feel that the statement is actually true.
    Experienced tradesmen who use the phrase, in plain english that needs no dictionary to decide what words like permeable mean, are saying 'Moisture, no matter how it gets into a wall, must be able to quickly get out before it incites mildew and rot' is clearly, and patently true, and as such not a myth. Builders of my ilk refer to this as 'breathing'.
    A vapour barrier such as polyethelene on the warm side of an insulated exterior wall simply prevents moisture from inside a building from reaching the cold side of the insulation where it would condense, both in the in the colder portion of the insulation layer and on the inside of the exterior sheathing, creating an enviroment ripe for rot and mildew, especially if the wall system also includes an exterior layer that inhibits that moisture from evaporation (such as Vinyl siding)
    Due to this differnce of understanding, I feel that this portion of your article was not helpful nor credible.

  94. Audetat | | #95

    Myth #9 is a myth.
    Following a recent and inexplicable fad (perhaps generated by the HVAC industry that dominates the US market) the argument that radiant floor heating is not efficient is as absurd as suggesting it doesn't work.

    It is true that people living in homes with properly designed warm floors are comfortable and the vast majorities are more comfortable than those that suffer from forced air mediocrity. It is also undisputable that a person in are radiant heated room will be relatively more comfortable at the same ambient temperature than a person in the same room “heated” with forced air.

    Naturally both systems must be designed using best practices e.g. a forced air heated room with severe stratification has not been well designed and a radiated room that lags behind the thermostat has suffered from the same neglect.

    Lower ambient temperatures will reduce fuel consumption. Radiant panels lower stratification, (warm air accumulated near the ceiling) which increase temperature differential and heat loss. Whether people reduce the thermostat setting is beyond the designer’s control, but your anecdotal "study" is statistically insignificant.

    Properly designed radiant panels - be they floor, wall or more especially ceiling - will most certainly run at lower design water temperatures than the lowly, fin-tube baseboard, which was originally designed to save on installation cost by operating at 180°F average water temperature (AWT). Fin-tube is not a true radiator, rather a water driven convector. It is quiet, provides comfort and uses less electricity than a comparable furnace (one 60-90watt circulator) but is not the standard for modern hydronic heating. Any comparison to radiant floor heating systems in this context is specious at best.

    Radiant panels, by contrast, are true radiators (qualified by giving off more than 50% of their energy in radiative rather than convected energy). A radiant panel is designed to run at much lower AWT than fin-tube or fan coil. Many of my systems have never operated above 90°F. The vast majority of the systems I design are operating well below 140°F in retrofit applications and below 120°F in new construction. These are a significant numbers, since condensing boilers start condensing when return water temperatures reach 130°F or so. Energy savings with condensing boilers are significant ranging in the 10 to 50% range in retrofit applications. These savings can generally not be had with the equivalent dollar investment in weather stripping, replacement windows or added insulation.

    I know this from retrofitting 100s existing homes using existing cast iron radiators, cast iron baseboard, radiant ceilings and floors dating from the turn of century to this summer.
    Distribution matters. AWT matters. Control systems matter.

    If a condensing boiler with outdoor reset (ODR) is installed on an existing fin-tube baseboard system, a 15% fuel savings is nearly guaranteed. Lower AWT due to ODR resulting in lower differential wall temperatures (perimeter in and out), sealed combustion and condensing heat exchanger account for the savings.

    Radiant floors, walls and ceilings being true radiators emit the majority of their energy in the infrared range (little convection). This lowers fenestration, and heat loss. It also contributes to comfort. With lower water temperature you have lower heat loss. The recent mania for sealing ducts, since in-the-envelope is no longer good enough, the focus has been heating the space where people are. This is as it should be and can’t be done any more efficiently than with a radiant panel.

    Aside from these simple facts, water will carry approximately 3500 times more heat by volume than air. Which brings me to another radiant “related” myth. “Pumps use a lot of energy.” Only a person trying to go “off the grid” would care, since the average homes hot water circulator (most have just one) will burn about 90 watts/hour and here in Minnesota cost $72.00/year to operate.

    Whereas it is true that the average circulator is not particularly efficient in terms of work per kW it is more efficient at transferring energy than the average forced air blower. But times are changing and like the high efficiency furnace the well-designed hydronic system employs the smaller circulators possible and take advantage of new technology including ECM motors and modular flow rates. I have a 2200 sq.ft. house running on 4-14 kW.

    To make sense of it all, one has to distinguish between new construction and old. Windows are the source of much discomfort and infiltration in old homes and perhaps the main source of discomfort in new homes. Windows make cold floors by virtue of the waterfall effect of air cooled next to an exterior window. Radiant floors and to a lesser degree baseboard and wall-hung panel radiators can correct this common source of thermal discomfort.

  95. Richard | | #96

    Keeping a refrigerator cold
    Sigh. Although this is not wholly relevant to the topic, the discussion brought it to mind. My sister thinks it takes energy to keep things cold.

    We were talking about the 'fridge in her kitchen, and I told her that having a lot of occupied volume in the freezer works to your benefit if you are opening the freezer a lot. You're better off filling otherwise-unused space with empty, sealed, cardboard boxes, or solid frozen food, since you won't spill as much cold air when you open the door. Oh, no, she said, think of all the energy necessary to keep more food cold! Barring that your food is radioactive, or battery-powered, of course it does not take a flow of energy to "keep it cold" once it is at stable temperature.

    My education (physics, electrical engineering) is of little worth in arguing with a preconceived intuition.

    That reminds me of those who think intelligent design should be taught right alongside evolution in public school science class, but then we would be seriously off topic! I'll just stop now.

  96. Glen Eaton | | #97

    Radiant Floors
    My house, in NW Washington, is totally heated by marble over concrete radiant floors--four inch slab on grade. The hot water circulates continuously, 24 hours a day, so the floors are always warm. The water temperature controller senses the outside temperature and sets the water temperature according to an algorithm in the controller.

    The inside temperature is fairly constant. The thermal lag through the building insulation is matched, more or less, by the thermal lag in the floor. The system works well; we like our warm feet.

  97. Pilgrim | | #98

    Too tech.
    You lost e at polyisocyanurate.
    Do you want to live next to that?

  98. semar | | #99

    10,000 heating bill
    I don't quite get it. Most Americans have mortgages on their homes. Would the bank happily allow their assets being torn down and joyfully re-finance the project? Bank is owed (say) 100 000, now the property valued at 300 000 is reduced to 75 000 landvalue. The new home is costing about 300 000 to 400 000 to build. Now the debtload is increased to at least 400 000. How does the owner qualify ? Or are Americans so superrich that they could afford to undertake a project like that?

  99. Anonymous | | #100

    I read all of the way down to #90. I do appreciate the comments about climate. I also appreciate the comments about in and out of box thinking. I would appreciate some thoughts on the following, with regards to the statements made in the article and the first 90 posts.

    1. Set up a test with a square foot of R13 fiberglass, unfaced, between a cold dry (under 50%RH) and a warm moist area (over 90%RH), ensuring that the dew point is reached within the thickness of the fiberglass. Weigh it before and after exposure. In my experience, it is a lot heavier after exposure. I am certain Professor William Rose can set me straight, but water will drop out of air when the dew point is reached and collect upon pretty much any horizontal surface.

    2. Temperature stratification can be seen in closed containers. Why does perfect sealing of a home eliminate temperature stratification?

    3. A small window A/C, 3 Amp, run continuously will wring considerable moisture out of a house without introducing heat into the house. In practical experience here in Houston, It does not make the house too cool. I am running it today, Dec 31, 72 degrees outside and inside, and about a 35% humidity differential outside to inside--no other HVAC. It is far less expensive than a dehumidifier. It requires annual cleaning of about 30 minutes. It can be placed in an area of the house near the largest sources of humidity--exterior doors and kitchen. If proper humidity management is performed in bathrooms (squeegee after shower or bath, drying walls, removal of wet towels, closing toilet lids), it is relatively easy to hit 75 degrees and 45% humidity. It is also relatively easy to install one of these A/C units with a good air seal if you slightly modify the case and purpose build the surround.

  100. GBA Editor
    Martin Holladay | | #101

    Response to "Credibility by Anonymous"
    Dear "Credibility by Anonymous,"
    Sorry, I have to disagree.

    You wrote, "A vapour barrier such as polyethylene on the warm side of an insulated exterior wall simply prevents moisture from inside a building from reaching the cold side of the insulation where it would condense, both in the in the colder portion of the insulation layer and on the inside of the exterior sheathing, creating an environment ripe for rot and mildew, especially if the wall system also includes an exterior layer that inhibits that moisture from evaporation (such as Vinyl siding)."

    1. Polyethylene vapor barriers on the interior side of walls are a double-edged sword: while they may help keep a wall dry during the winter, they can keep a wall damp during the summer. To read more about this problem, see When Sunshine Drives Moisture Into Walls. See also the comment to this blog from Frank Lee, who correctly notes that vinyl wallpaper causes the same problems with mold and rot -- especially in warm, southern climates -- as polyethylene vapor barriers.

    2. Contrary to your statement, vinyl siding is a well-ventilated siding that helps walls dry quickly to the exterior.

  101. Dr. Dave | | #102

    Myth 9 Radiant vs. Hot water baseboard
    Radiant floor heat circulates water at a lower temperature, allowing the boiler to be set at a lower temperature. That can result in substantial fuel savings, because of recapture of the latent heat of vaporization in the flue gas (with countercurrent combustion gas-fresh air exchange) and condensation in the boiler heat exchanger. Condensing boilers are designed to capture the latent heat of vaporization of the water vapor created during the combustion of hydrocarbons (540 cal/g). The lower the water temperature on the other side of the heat exchanger, the more latent heat can be captured. The difference between condensing and non-condensing boilers can be as much as 11% for natural gas, which is:
    HHV = LHV + hv x (nH2O,out/nfuel,in), where HHV represents the heat value with water condensation and LHV represents all the water going up the chimney as vapor. hv is heat of vaporization of water and n refers to moles of water and fuel. For more information see:
    Air Quality Engineering, CE 218A, W. Nazaroff and R. Harley, University of California Berkeley, 2007 or the excellent article in Wikipedia: Heat of Combustion.
    Let's say you capture half of the heat of vaporization. That means 5.5% fuel savings. That is not trivial in my opinion. Circulation water at 118 va 150 degrees would probably save you at least that much. Further, using lower water temperatures provides greater efficiency gains with heat pumps and solar heating, where raising water temperatures greatly decreases efficiency. For more information, I suggest:

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    ^ Papers on Traditional Public Baths-Hammam-in the Mediterranean, Archnet-IJAR, International Journal of Architectural Research, Vol. 3, Issue 1:157-170, March, 2009
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    ^ High Commission for Erbil Citadel Revitalization, The Hammam,
    ^ Gallo, E., Jean Simon Bonnemain (1743-1830) and the Origins of Hot Water Central Heating, 2nd International Congress on Construction History, Queens' College, Cambridge, UK, edited by the Construction History Society, 2006,
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    ^ The Medical and Surgical History of The War Of The Rebellion Part III., Volume II., Surgical History, 1883.
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    ^ Panel Heating, Structural Paper No.19, Oscar Faber, O.B.E, D.C.L (Hon), D.Sc. (Eng.), The Institution of Civil Engineers, May, 1947, pp.16
    ^ PEX Association,The History and Influence of PEX Pipe on Indoor Environmental Quality, [1]
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    ^ The Canadian Encyclopedia, Industry - Petrochemical Industry ,
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    ^ Moe, K., 2010, Thermally Active Surfaces in Architecture, Princeton Architectural Press , ISBN 978-1-56898-880-1
    ^ Kolarik, J., Yang, L., Thermal mass activation (Chpt.5) with Expert Guide Part 2, IEA ECBSC Annex 44, Integrating environmentally responsive elements in buildings, 2009
    ^ Lehmann, B., Dorer, V., Koschenz, M., Application range of thermally activated building systems tabs, Energy and Buildings, 39:593–598, 2007
    ^ Low Temperature Heating Systems, Increased Energy Efficiency and Improved Comfort, Annex 37, International Energy Association
    ^ Boerstra A., Op ´t Veld P., Eijdems H. (2000), The health, safety and comfort advantages of low temperature heating systems: a literature review. Proceedings of the Healthy Buildings conference 2000, Espoo, Finland, 6–10 August 2000.
    ^ Eijdems, H.H., Boerrsta, A.C., Op ‘t Veld, P.J., Low temperature heating systems: Impact on IAQ, thermal comfort and energy consumption, the Netherlands Agency for Energy and the Environment (NOVEM) (c.1996)
    ^ Rea, M.D., William J, “Optimum Environments for Optimum Health & Creativity”, Environmental Health Center-Dallas, Texas.
    ^ Buying An Allergy-Friendly House: Q and A with Dr. Stephen Lockey,
    ^ Asada, H., Boelman, E.C., Exergy analysis of a low temperature radiant heating system, Building Service Engineering , 25:197-209, 2004
    ^ Babiak J., Olesen, B.W., Petráš, D., Low temperature heating and high temperature cooling – Embedded water based surface systems, REHVA Guidebook no. 7, Forssan Kirjapaino Oy- Forssan, Finland, 2007
    ^ Meierhans, R.A., Slab cooling and earth coupling, ASHRAE Transactions, vol. 99(2):511-518, 1993
    ^ Kilkis, B.I., Advantages of combining heat pumps with radiant panel and cooling systems, IEA Heat Pump Centre Newsletter 11 (4): 28-31, 1993
    ^ Chantrasrisalai, C., Ghatti, V. , Fisher, D.E., Scheatzle, D.G., Experimental validation of the EnergyPlus low-temperature radiant simulation, ASHRAE Transactions, vol. 109(2):614-623, 2003
    ^ Chapman, K.S., DeGreef, J.M., Watson, R.D., Thermal comfort analysis using BCAP for retrofitting a radiantly heated residence (RP-907), ASHRAE Transactions, vol. 103(1):959-965, 1997
    ^ De Carli, M., Zarrella, A., Zecchin, R., Comparison between a radiant floor and two radiant walls on heating and cooling energy demand, ASHRAE Transactions, vol. 115(2), Louisville 2009
    ^ Ghatti, V. S., Scheatzle, D. G., Bryan, H., Addison, M., Passive performance of a high-mass residence: actual data vs. simulation, ASHRAE Transactions, vol. 109(2):598-605, 2003
    ^ Cort, K.A., Dirks, J.A., Hostick, D.J., Elliott, D.B., Analyzing the life cycle energy savings of DOE-supported buildings technologies(PNNL-18658), Pacific Northwest National Laboratory (for U.S. Department of Energy), August 2009
    ^ Roth, K.W., Westphalen, D. , Dieckmann, J. , Hamilton, S.D. , Goetzler, W., Energy consumption characteristics of commercial building HVAC systems volume III: energy savings potential, TIAX, 2002
    ^ Analysis of renewable energy potential in the residential sector through high-resolution building-energy simulation, Canada Mortgage and Housing Corporation, Technical Series 08-106, November 2008
    ^ Herkel,S., Miara, M., Kagerer, F. (2010), Systemintegration Solar + Wärmepumpe, Fraunhofer-Institut für Solare Energiesysteme ISE
    ^ Baskin, E., Evaluation of hydronic forced-air and radiant slab heating and cooling systems, ASHRAE Transactions, vol. 111(1):525-534, 2005
    ^ Hoof, J.V., Kort, S.M., Supportive living environments: A first concept of a dwelling designed for older adults with dementia, Dementia, Vol. 8, No. 2, 293-316 (2009) DOI: 10.1177/1471301209103276
    ^ Hashiguchi, N., Tochihara, Y., Ohnaka, T., Tsuchida, C., Otsuki, T., Physiological and subjective responses in the elderly when using floor heating and air conditioning systems, Journal of Physiological Anthropology and Applied Human Science, 23: 205–213, 2004
    ^ Springer, W. E., Nevins, R.G., Feyerherm, A.M., Michaels, K.B., Effect of floor surface temperature on comfort: Part III, the elderly, ASHRAE Transactions 72: 292-300, 1966
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    ^ Galanti v. The Goodyear Tire & Rubber Company and Kelman v. The Goodyear Tire & Rubber Company et al.
    ^ Radiant ceiling panels, Ministry of Municipal Affairs, Electric Safety Branch, Province of British Columbia, 1994,
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    ^ E.g. Radiant Panel Association, Canadian Institute of Plumbing and Heating, Thermal Environmental Comfort Association of British Columbia, and ISO Standards.
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    ^ ISO 7730:2005, Ergonomics of the thermal environment -- Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria
    ^ Bean, R., Kilkis, B., 2010, Short Course on the Fundamentals of Panel Heating and Cooling, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.,
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    ^ Rishel, J.B., Wire-to-Water Efficiency of Pumping Systems, ASHRAE Journal, April, 2001
    ^ Fig. 5 Effect of Inlet Water Temperature on Efficiency of Condensing Boilers, Chapter 27, Boilers, 2000 ASHRAE Systems and Equipment Handbook
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    ^ Fitzgerald, D. Does warm air heating use less energy than radiant heating? A clear answer, Building Serv Eng Res Technol 1983; 4; 26, DOI: 10.1177/014362448300400106
    ^ Olesen, B.W., deCarli, M., Embedded Radiant Heating and Cooling Systems: Impact of New European Directive for Energy Performance of Buildings and Related CEN Standardization, Part 3 Calculated Energy Performance of Buildings with Embedded Systems (Draft), 2005,
    ^ Heat, Work and Energy
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    ^ International Energy Agency, Annex 37 Low Exergy Systems for Heating and Cooling in Buildings
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    ^ Pedersen, C.O., Fisher, D.E., Lindstrom, P.C. (March, 1997), Impact of Surface Characteristics on Radiant Panel Output, ASHRAE 876 TRP
    ^ Simmonds, P., Gaw, W., Holst, S., Reuss, S., Using radiant cooled floors to condition large spaces and maintain comfort conditions, ASHRAE Transactions, vol. 106(1):695-701, 2000

  102. Anonymous | | #103

    Re: Martin's Response to Credibility
    Thanks for your clarification Martin. I had my head in the sand when i failed to consider conditions of warm moist air outside, and an air conditioned interior, (a condition which seldom exists in my locale). Short sighted of me, to be sure, however after seing what happens to Vinyl sided houses with no rain screen here on Vancouver Island BC, I'd still have to disagree on your statement that Vinyl siding is well ventilated. And, I guess that I'd like to re-iterate my main point: I will still say "Walls have to breathe" for the forseeable future ;-)

  103. GBA Editor
    Martin Holladay | | #104

    Second response to Anonymous
    You wrote, "I'd still have to disagree on your statement that Vinyl siding is well ventilated."

    You can disagree all you want, but the research data all support my position.

    See, for example, a research report ( by John Straube and Jonathan Smegal, who wrote, "An experimental study of drainage in small gaps behind cladding was previously conducted together with Oak Ridge National Labs and Building Science Corporation (Straube et al 2000). This study was limited to vinyl siding and stucco on various sheathing membranes. The experiments determined the drainage capability by applying water to the face of the cladding as a spray or poured into the top edge of the wall behind the cladding. It was found that water that passed through joints and penetrations in the vinyl siding drained and was caught in the horizontal edges and directed laterally to the j-trim where it drained vertically. It was concluded that significant areas of the drainage plane were not wetted with either water application method. This conclusion was subsequently visually confirmed when 12’ wide x 6’ high samples of horizontal vinyl lap siding were tested when installed over a transparent plexiglass drainage plane."

    See this chart of siding permeance prepared by the Building Science Corporation:
    Vinyl siding is at the top of the chart -- the most permeable siding listed -- for this reason: "Approximately 40 perms due to the air leakage of the siding joints."

    See also this document from the Building Science Corporation:

    "The key difference between brick and vinyl is that brick is a moisture reservoir and vinyl is not. Brick absorbs rainwater and holds it within its internal pore structure. Vinyl siding is not porous and does not absorb rainwater. When a moisture reservoir is located on the exterior of a wall assembly it can act as a source of water that can migrate by a process called vapor diffusion. Water vapor will move by vapor diffusion from a high concentration of water vapor to a lower concentration of water vapor. ... If a reservoir is not present, this mechanism does not occur. Vinyl is not a moisture reservoir; therefore this moisture transport mechanism cannot occur with vinyl siding."

  104. Natur Haus | | #105

    Martin, sometimes experience trumps information!
    Martin, there may be gaps behind vinyl siding, but in the west we see tremendous damage from vinyl siding that is covering wood siding. Although obviously not airtight, the vinyl holds humid air behind it and when the condensation happens, which happens daily, it causes damage. The tests you mention were set up in created lab conditions that DO NOT resemble the situations we see. Resort to your breathing anomaly all you want, but the pre-vapor impermeable assemblies of old did not know the moldy situations that exist today, which is a function of vapor impermeability, pre-digested building materials, and lack of building science and understanding. EIFS, spray foam, polyethylene, and others have too great of chances for failure. These are not OLD problems, these are problems that come from our NEW logic. You may be wiiling to live in a plastic petri dish, sealed up nice and tight, but others such as me just don't see why we should go there. I believe the future will give us answers that the past have held for a long time, natural materials contain the best chemistry known in the world.

  105. GBA Editor
    Martin Holladay | | #106

    Response to Matthew Amann
    I've inspected lots of old houses, and I've seen plenty of mold. I agree with you that "sealing things up in a plastic petri dish" can lead to mold. The classic material causing these problems is polyethylene -- especially when installed on the interior side of stud walls filled with fiberglass batts at the perimeter of a basement.

    Vinyl siding is nothing like polyethylene. It hangs loosely on the exterior of a building, and wind goes right through it. It leaks water like a sieve and it leaks air like a sieve. It's hard to imagine a cladding that is more ventilated than vinyl siding. Really, if you wanted to air-seal a wall or make a wall waterproof, and you were depending on vinyl siding to accomplish these two tasks, you would fail miserably.

    When it comes to airtightness, water tightness, and vapor permeance, stucco -- which some green builders think of as a "natural" siding material -- is far "tighter" and less permeable than vinyl siding.

    I've never seen mold behind vinyl siding, so I have to disagree with you.

  106. Natur Haus | | #107

    Thanks, Martin
    I agree with most of what you are saying. I didn't mean to imply that the failure(behind vinyl siding) was related to mold, more that the wood siding (which has failed paint on it, hence the vinyl siding) isn't able to dry as easily, and rot accelerates. Also, different from the lab conditions against clear plastic viewing substrates, and perfectly new WRB behind the vinyl, most old wood siding (with the failed paint on it) absorbs the channeled water and doesn't release it as readily as it would without anything on top of it. I admit, it could be worse, I just don't believe these findings should act as a supportive argument for vinyl siding, especially considering the huge Dioxin levels in our environment attributed to vinyl production. Dioxin is a cumulative toxin, not good.

  107. user-1044661 | | #108

    distribution efficiency
    Great article, but I do have one quibble. you write: "Other radiant floor proponents have suggested that homes with radiant floors can have lower boiler temperatures compared to homes with baseboard units. This factor, however, would be responsible for only very minor energy savings, if any"

    I think this statement is demonstrably false. Especially with high efficiency condensing boilers, combustion efficiency is a strong function of boiler return water temperature, especially at part load. The attached graph shows, for example, that a while a boiler running with typical fintube baseboard return water temperature (170 deg) achieves only 88 % efficiency, while at typical radiant return temperatures (90 deg) that same boiler is achieving over 96% efficiency.

    I'd consider that improvement to be more than a 'minor' improvement, wouldn't you?

  108. GBA Editor
    Martin Holladay | | #109

    Response to Fortunat Mueller
    Fortunat Mueller,
    You are correct that boiler temperature affects efficiency. In most cases, the boiler temperature should not exceed the temperature necessary to keep the house comfortabe.

    However, the issue is complicated. Boiler temperatures can be lowered to improve efficiency -- but only up to a point. Moreover, the effect of lowering boiler temperatures differs depending on whether the boiler is a condensing or a non-condensing boiler.

    Other factors affecting boiler efficiency include the percentage of time that the boiler is operating at part load versus full load, and whether the boiler is short cycling. If boiler controls include an outdoor temperature sensor, it is often possible to operate baseboard radiators (as opposed to in-floor radiant tubing) at a low temperature (and therefore at a higher efficiency) for much of the winter, with high boiler temperatures only necessary on the coldest days of the year.

    In short, calculating efficiency differences due to high boiler temperatures is complicated, and varies widely by circumstances. I'll concede, however, that lower boiler temperatures can contribute to efficiency.

    Thanks for your comments.

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