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Community and Q&A

Ducting in slabs & passive solar

GBA Editor | Posted in Green Building Techniques on

I’m looking for research that examines the effects of using ducting in concrete slabs to circulate heat. Specifically, I’m interested if there is any added efficiency in passive solar applications where air is circulated through the slab. My impression is that this technique opens you up to a lot of potential moisture/mould scenarios. Does anyone know of any research that looks at the implications of this technique?

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  1. mike | | #1

    a number of articles by ASHRAE and others on the use of radiant loops in slabs for heating or cooling (TABS, thermally activated building systems). for real world applications, the works of meierhans and transsolar is pretty phenomenal.

    ducting would seem an extremely inefficient method of collecting and distributing the heat in the slab.

  2. homedesign | | #2

    you may find this Contrarian article interesting
    Don't Forget about the "Gerbil Factor"

  3. Chris R | | #3

    There are a large number of passive solar homes in Nova Scotia, Canada using a system of 5" air ducts in an 8" slab. (designed by Don Roscoe). I don't know of any formal research on these houses, but you could contact him through

  4. Doug McEvers | | #4

    There is a concern about ductwork in or below the slab allowing radon into the system.

  5. Daniel Ernst | | #5

    Jay - I would encourage you to step back a minute. The slab only gets heat through south facing glass / windows. So before you look at the slab, you should look at the window issue.

    I would also encourage you to read more about saving heat (superinsulation techniques) vs. gaining and storing heat (passive solar). Martin gave a great review of this topic here:

    You don't give your climate, but if you're interested in passive solar, then you must be in a heating dominated climate . . .

    Remember that most south facing windows lose more heat then they gain. Based on my research, there are only a few triple-glazed, high R-value, high solar heat gain coefficient (SHGC) windows built in North America that have a net positive effect (gain more heat than they lose).

    Canada has put together an excellent rating system for windows. Basically, the Canadian ER rating measures the window's "overall performance, based on three factors: 1) solar heat gains; 2) heat loss through frames, spacers and glass; and 3) air leakage heat loss."

    Few windows pass onto the positive side of the ledger. Of course, so much of this depends on your site and the installation. I hope that reading this information will help you make the right decision.

    For passive solar, the slab or walls directly coupled to the south facing windows absorb the sun's energy, thus helping to prevent large temperature swings. That's the benefit. If you strip away the heat from the slab via these air ducts, how does this improve your efficiency? It might allow you to move the heat to the northern / colder portions of your house, but this doesn't improve your efficiency. In fact, it's not passive any longer. And you have to add the electricity used to run the fan(s) to the heat gain / loss calculation . . . making the situation worse.

    I think there are better options than ducted slabs.

    Anyway, that's my two cents. Good luck!

  6. Anonymous | | #6

    350 homes built over decades.

  7. wjrobinson | | #7

    Daniel, Bruce Brownell has spent a lifetime designing, refining and building (via contractors) homes with slabs enclosing active air ducts that to him even out the temperatures in a home from top to bottom, from night to day, from day to day. I have been in two of them and they are very livable enviroments. The owners almost heat alone with very small heat sources, hot water tanks, woodstoves or just the sun at many times.

    Adirondack Alternate Energy - Low-Energy Passive Solar Homes

    Adirondack Alternate Energy
    98 Northville Road
    Edinburg, NY 12134 Phone: (518) 863-4338
    Fax: (518) 863-4192
    E-Mail: [email protected]

    I think ducted slabs are a great choice among many.

    Anyway, that's a bit of my sense.

  8. Daniel Ernst | | #8


    Jay asked if anyone knew of studies concerning passive solar ducted slabs. Unfortunately, there's not much out there. Fact is that it's hard to find research on even well promoted building systems, much less fringe techniques (like ducted slabs).

    So without being able to reference studies - we're left with a few things: the larger library of building science and building history, our understanding of heat transfer, and our personal experience.

    Anyone studying the history of passive solar will learn a lot from the groovy experiments conducted in the '70s and early '80s. But only certain elements stood the test of time. Many ideas and methods simply didn't work. There's a reason that ducted slabs didn't become mainstream. There's a reason that ducted slabs aren't currently promoted by building science experts. They passed by the wayside along with a number of techniques.

    Remember that we don't install windows for their thermal performance (they are the weakest link in the chain). Good designers try to minimize that weakness.

    James Kachadorian's book "The Passive Solar House" provides a lot of information on ducted slabs. And if you want to build a house that uses concrete block as ductwork, then you can follow his instruction (of course he claims there is no mold in the "ductwork"). Or you can buy one of Bruce Brownell's houses. There are only a handful of builders in North America that have used this technique (and apparently none of them visit this site). Or you could even buy one of these kit houses (that use a similar concept):

    But do you know of any controlled studies that compare House A (with ducted slab) to House B (without ducted slab)? Where are the Btu measurements? The hygothermal models? The documentation? The kWh equivalent energy use for these houses? How many are net-zero (or net zero ready)?

    You say that Mr. Brownell's houses are very livable, but that doesn't mean his ducted slab adds anything to the thermal performance of the house.

    I'm not in a position to judge Mr. Brownell's houses. They are probably fine homes. But I can question the science behind the claims made on his website. Windows only provide a certain quantity of heat. Given a particular location, we can use the site's solar insolation value and the window's SHGC to determine that gain. But no matter what climate or window or house, you can't create a system that uses passive solar gain to heat air, and then use that air to heat 70 - 100 tons of masonry to any meaningful extent. The physics and calculations don't support the concept. There is no evidence that it works. If it does, then perhaps you can encourage Mr. Brownell to measure and monitor and post the actual energy data for some of the houses he built . . . like this one:

    He could start with graphing the thermal mass temperature for a six month period, along with the diurnal fluctuation in room temperature (or duct air temperature).

    BTW - I don't think the Passivhaus folks would swoon over a $900 - $1200 annual heating bill.

    My point to Jay is that passive solar doesn't have to be complicated. The groovy experiments of the '70s taught us to keep it simple:

    • Good site orientation
    • Climate appropriate shading
    • A fairly normal percentage of high R-value, high SHGC south-facing windows
    • Some internal mass to help moderate the temperature swings (not 100 tons)

    All the rest is fluff. When you've applied these basic principles of passive solar, you're done. Your focus should then be on creating an airtight and well insulated building envelope . . . and a lot of other things that go into creating a durable and beautiful house.

  9. GBA Editor
    Martin Holladay | | #9

    Daniel Ernst,
    Excellent post! I agree with you completely.

  10. wjrobinson | | #10

    Daniel Ernst,
    I too agree with most of your posts and yes excellent to the point.

    As to Bruce, I may have to see if he will join here and post a bit.

    He I believe is an engineer, and did very much study, test, gauge etc before and after numbers to do with his designs.

    As to my livability comment, the homes I toured definitely had a feel of even comfort; I know... not too scientific a point.

    Now... his home design has been improved and tweaked for years and years. He is not designing still in the 70's,

    Seems like everytime I mention Bruce there are "attitudes" here at GBA. What's with that? is this a little clickish group of greenies or something? Bruce started down the road of green before I bet many many here and for sure before most of us in this country. He should be applauded for all his efforts over all these decades. He didn't stop when the price of energy came back down. He didn't do like Reagan our president did and rip all the solar off the White House.

    I think you should give Bruce a call Daniel. This debating his work without his presence is just leading to conjecture, and negative at that.

    I like the guy. He has been at this idea of lower energy use homes for a long time. The homes are very nice. Maybe not Passive House, but neither is my own home and I bet yours isn't either.

    phew... had to get that off my plate..... still yes... Daniel very good post.

    Since I don't know more about you am thinking you are a builder or architect?

  11. Jay | | #11

    Hi folks,
    Thanks for all the great responses. Perhaps I should have been more clear when I posted originally. I'm not building a passive solar house but rather am interested, like Daniel suggested, in getting my hands on some research that compares non-ducted slabs to ducted slabs. My instincts are that ducted slabs don't offer sufficient benefit to outweigh what I see as their potential to introduce moisture and mould problems down the road.
    That said, I realize "passive solar builders" in many climates still use ducted slabs. I'm wondering why and science they're basing this decision on. I thought there might be a paper or study out there that shows a quantifiable benefit to ducted slabs.
    Thanks for the great discussion,

    Thanks for the great discussion. I appreciate it.

  12. Daniel Ernst | | #12

    I hope that no one would take my comments about Mr. Brownell as slanderous. As I said, he probably builds fine homes. I'm simply skeptical of the benefit provided by a ducted slab. That was the entire point of my post: keep passive solar simple.

    I would be more than happy to see any data available on the topic. If I'm wrong, then I deserve correction. Furthermore, I believe we learn more from our mistakes than our successes.

    Previously (in an earlier post) you attempted to have Mr. Brownell join this forum. Unfortunately, he declined. So until we have actual data to review, we are left with a more conceptual discussion.

    I'm an owner / builder, and a geek when it comes to building topics. My work history is very eclectic. I still don't know what I want to do when I grow up ;-) I live in a "passive solar" home that I designed and built. It works, and it's comfortable, but you're right - it's not to PH standards (built before Katrin Klingenberg started waving the PH flag over here in North America). You live and learn . . .

  13. kevin_in_denver | | #13

    Just another designer/builder/resident/engineer of a direct gain passive solar house chiming in - Daniel has nailed it.

    The work of Douglas Balcomb, going back to the 60's has corroborated all of this. Although Kachadorian and others may have built very successful homes, simplicity is key. In my opinion, if a blower, or even passive ducts, are needed, you've left the realm of a simple passive solar house.

    Ducted slabs also give me the willies because I know they will crack at all those discontinuities (changes in concrete thickness).

  14. wjrobinson | | #14

    I hear you all... good posts... as to cracks... Bruce is pouring 12" thick slabs to get what he thinks is the proper amount of mass and most likely he is not getting cracks at this thickness that bother. The homes are not theoretical. They exist. Customers are happy. Mold is not an issue from what I know which is not enough for sure having only been in two.

    My angle is... I think Bruce is able to build these ducted slabs successfully.

  15. user-659915 | | #15

    12" slab? Producing a single cubic yard of concrete releases about 400 pounds of CO2. Worldwide, cement manufacturing accounts for approximately 5% of CO2 emissions. If you're planning to triple your slab thickness it'd be smart to have the data to show it's worth it.

  16. wjrobinson | | #16

    James... talk to the hand! You get in touch with Brownell and jump down his throat. His slab is much less concrete than a whole cellar which is the norm around here.

    You produce a totally green home and post the specs here. I can't wait.

  17. Rhaud | | #17

    I have been designing residential and commercial structures since early 1976 and honestly question your positionally. I would suggest that scientific analysis is not the 'definitive' in HUMAN COMFORT. Please simply take the time to look at the history of 'scientific design/data' and 'scientific analysis' within our most relatively recent 'recorded' history and the decisions that were made based upon these 'scientific inputs ', factors such as - (please include the negative repercussions that have resulted both in terms of habitable structures and the environment); local, regional and global; forests, oceans, agriculture,energy production and consumption.
    Question?: Is not mold simply an issue indicative of a high/low humidity factor directly correlated to the internal or external environment and directly incumbent upon the ability/inability of a single or combination of materials to mitigate that humidity by transference to the lesser humid? Or simply sometimes called drying?
    Impervious membranes of all types have been continuously promoted by both scientific data/thought and manufacturers, unfortunately that has resulted in a misdirection much to the demise of the investor and the health of the occupants of far too many buildings throughout the world.
    I also would like to understand why there appears to be NO OFFICIAL/PROFESSIONAL acknowledgment and very limited incorporation of the knowledge of indigenous builders that have occupied similar if not identical climates to NORTE AMERICA for thousands of years, nor the recognition of the profound successes that they have/had/and do realize within their environmental regions. Sadly, there has only been a further drive for the greedy to patent anything, simply anything, from the learned past and then only to add some high-tech scientific twist to it ensuring that a extremely high cost replacement of the high-tech control parts well before the life of that so-called "new" innovation is complete. So, now we are stuck with experts who are re-inventing a wheel that has been used for millennium, and we are also stuck with these experts once again revisiting the obvious and justifying only that which suits their needs or mandate. Innovations must be somehow justified, impericcaly not empirically, and worth a bundle of cash - and so goes the "GREEN REVOLUTION". I would suggest that the time is growing short to justify positions and still have a majority of this planet really and simply habitable for humans.
    I was once told by a very wise man that what we know we know only incorporates a small portion of our knowledge some 90 to 110 degrees of our perspective and what we are unaware that we know fills the rest the other 250 to 270 degrees of the whole issue (360 degrees).
    Consider this tubes in a slab (properly proportioned) whether H2o or air ( in fact any fluid capable of carry calories) can and do prove to be beneficial to any occupants 'comfort', when incorporated clearly and correctly into a solar gain design.
    You have totally avoided any conversation about insulated window design (automatic or manual), and have clearly stated that a fan assisted system is required. I am hopeful that you rare aware that air is a fluid and operates on the basis of convection, the very same way as any of the fluids on this planet.
    I would suggest you give this issue a just a bit more thought beyond the 110 to 120 degrees you declare as your stance (scientific or otherwise) and acknowledge and work on the other 240 degrees available to you in terms of perspective. I would humbly suggest that it be especially about wet-bulb & dry-bulb, respiration, transpiration, thermal retention and transmission, and fluid dynamics. FIY - the majority of these factors were worked out empirically many decades if not eons before now. Look forward to your thoughts on this!

    Disregarding your roots, disrespects your growth.
    With regards and respect,

  18. GBA Editor
    Martin Holladay | | #18

    1. Passive solar builders are very familiar with the importance of window specifications and window orientation.

    2. The use of movable window insulation has been tried by hundreds of builders and homeowners. Some people enjoy the twice-a-day chore; most don't. Automated movable window insulation systems have not proved dependable.

    3. Most of your post is rambling and never clearly states a point. You wrote, "I would humbly suggest that it be especially about wet-bulb & dry-bulb, respiration, transpiration, thermal retention and transmission, and fluid dynamics." Okay -- lots of big words. That said -- we still need to know what type of construction you recommend; the incremental cost; the indoor temperature ranges in your building; and whether or not your proposed measures save any energy compared to simple superinsulated buildings with proper passive solar orientation and fenestration.

  19. user-659915 | | #19

    AJ - defensive much? It's always been my assumption that the fundamental premise of green building is mindful and appropriate use of the materials and processes we employ for our shelter. Whatever the norm may be in your area, suggesting there might be data to justify a triple-thickness slab is jumping down no one's throat. Environmental benefit returned for environmental cost invested is not a difficult concept.

  20. adkjac | | #20

    James, meet Bruce then we'll talk.

    Post for us the last 350 homes you built and how much concrete was involved.

  21. mike | | #21

    the number of homes built is hardly an indicator of how 'green' someone is... just ask centex, toll brothers, etc.

  22. wjrobinson | | #22

    Mike, same for you Mike... you build 350 low energy use homes and get back to me. Then you can judge Bruce's work possibly. Armchair analysis is worth lots less than actual experience to me.

    Better yet, go to Edinburg, NY to see for yourself. I very much respect Bruce.

    I think all that visit this site should too.

  23. wjrobinson | | #23

    Check out this thread... Peter Powell builds very similarly to Bruce Brownell.

    A Contrarian View of Passive Solar Design By Peter Powell, AIA

    As to concrete... there is a movement working on formulas of concrete that have less embodied energy. The other point raised by some is that if the home lasts long enough the embodied energy point is less important.

    Going green is a direction many of us are headed. We don't have to get there today.

  24. user-659915 | | #24

    Response to AJ:
    So let me get this straight: no one can may be allowed to comment on ducted slab construction unless and until they travel from wherever they happen to be based (I'm in North Carolina) to upstate New York to experience at first hand the work of one particular builder for whom you have a particular enthusiasm, without the benefit of any documentation? Hmmm. Kind of misses the point of an online discussion forum, don't you think?

    And as to track record: I've been in practice as a residential designer in North Carolina for nearly twenty years and have many more than 350 energy-efficient projects under my belt, including not only new homes but also remodels and renovations, which are generally far more challenging and not susceptible to one-note solutions. The vast majority of these projects are not only energy-efficient but also highly materials-efficient too, especially with regards to the high-embodied-energy products like concrete (tip: this is much easier to achieve if you eschew the 'you can never be too rich, too thin, or have too much thermal mass' school of design.

    Talking of which, I would be intrigued to know why so many architects, designers and builders in the green building movement do seem to worship at the altar of generic high thermal mass. The theory seems to make sense only for a few very specific climates (hot dry days, cool dry nights, most days of the year). This would seem to be born out by the thermal high-mass building traditions (adobe, mud brick, tile) found in in such climates and nowhere else. I think we can assume that our ancestors actually knew something about low-energy-input buildings as they had very little alternative. Certainly in the mixed-humid climate where I live and work you'll find no examples of high-mass vernacular buildings before the modern period, though we have plentiful supplies of both stone and brick-clay. And I have yet to see a single properly conducted comparative empirical study which demonstrates the energy performance benefit in mixed-humid climates of high-mass floors, other than in marginal building elements such as over-insolated sunspaces. If anyone can point me to such a study I'll gladly eat my words.

  25. wjrobinson | | #25

    James... now... I have an idea what you have done. Thank you! Helps with posting back a forth.

    With all the time you have to post here, I would think you could place a simple call to Bruce. If you reach him he may be able to give you reams of info. I know he is an engineer, not sure about registered... blah blah. He sure is intense about it all if I am remembering my meeting with him correctly.

    So, point me to your site James, and to posts here where you share what you think is a top notch James Morgan design. Post the costs, materials, construction details, etc along with calculated and actual performance. I would love to look it over.

    By the way, I am not saying a Brownell home is the ultimate, but to me it is a great choice amongst many. Sure beats fiberglass batts 16" OC thrown up as fast as some subs can fly so as to get to there evening beer fests.

  26. mike | | #26

    maybe in 36 years (when i'm bruce's age), i'll have 350 semi-energy reducing houses. my goal is to have 350 CO2 sucking, energy positive homes.

  27. adkjac | | #27

    Read much of this thread again. What I found with my visit to a Brownell home is that the temperature swing is much less than a home without the ducted slab. And yes... a superinsulated Passive house would do so with no mass added. So I agree with Maritin and the idea of low mass high insulation. But I still like Brownell and he does design a worthy home. And the point made that keeping the passive gain temps lower by moving the air through the slab is a gain via lowering the delta T makes sense to me too.

    Anyway.... I know these homes are quite nice. I would recommend them to anyone anywhere.

    Show me your work and I will recommend you too. Nice lively topic, enjoyed everyone's thoughts. Mike, what to yaa build... are you a builder or architect?

  28. adkjac | | #28

    This site is trying to be part of the leading bleeding edge of sustainable green building and saving the planet from human extinction etc....

    When will Taunton invest in updating site to editing capabilities for the users that are not GBA advisors?

    LOL... Ok... Maritin=Martin to=do

  29. Kevin Dickson | | #29

    I should have mentioned above that slab cracking isn't a very big deal unless you plan to use it as the finished floor (which I do).

  30. wjrobinson | | #30

    Do hockey players like my favorite trail in Vermont, The Goat?

    How bout you Jay... ski... Jay... Jay ski... errr... somthin liiiike thart?

    Phish fan here Mad River Glen... phish it if yaa can

    all good ski country up your all's way. And nice views on top of my lakes and awesome Adirondacks at Sugar.... bush.

  31. user-659915 | | #31

    to AJ, again (sigh):

    "What I found with my visit to a Brownell home is that the temperature swing is much less than a home without the ducted slab." You found this out how, exactly? And which 'home without a ducted slab'? A production house form Toll Brothers? This thread began with a request for documentation on such otherwise meaningless claims. You believe that Mr. Brownell nonstandard floor system has something special to offer in energy performance and you wish to proselytise it to the world: good for you, but you should expect to supply some data before the world will be prepared beat a path to his, or your, door. Reflected glory may be very gratifying, but you will need to make some effort to earn it. It's very presumptuous of you, by the way, to tell me how I should be spending my time. For my own part I have no reason to publish data on the homes I design: I claim nothing special for the systems I employ, they are mostly time-tested best practices as I understand them. I have nothing to sell.

  32. Riversong | | #32

    Below is an expanded version of the comment I posted on this site (, which describes a Brownell-inspired house.

    Most passive solar designers would consider Brownell's ideas with skepticism, not least because his approach is no longer passive solar but requires active redistribution of heat.

    Given the poor passive solar design of this house (excessive overhang on the second floor and no solar shading on the larger first floor windows), this house requires active heat redistribution in order to remain livable. This is typical of the early mistakes that many passive solar designers made in in the 1970s.

    Some of the early experimentation, including air ducting in the floor and between double walls and roofs (the envelope house) or excessive or inadequate thermal mass, has been rendered obsolete by better design and a more comprehensive understanding of thermodymanics and building science.

    The claim that this envelope is far superior to conventional houses is absurd, given that the R-26 walls are little better than code minimum today. And such a tight house requires fresh air exchange, such as with an HRV or ERV, which is not mentioned in the description. Living in a "picnic cooler" is fine for a soda but not for living people. Such a non-breathable house also likely violates hygro-thermal engineering principles that are essential to incorporate into a healthy and durable home, including a breatheable envelope and hygric buffering.

  33. wjrobinson | | #33

    Cooler times prevail I hope now. At least today was wonderfully cooler and less humid. Yeah!

    Robert the best home is one not built. The worst, I don't know. A Brownell home is much more worthy than your continued ranting against such. My opinion.

    And yes... I too believe a Larson Truss... or Riversong home may indeed be a more green home.

    love you big guy

    How well do you get along with Joe L... when you rant on about only your views are valid and all else is nonsense?

    The universe is a bigger petri dish than maybe you realize... enough room for some variants in the amoebae and all that are within RR. And I know... we are all one... connected as you say... so... consider me appropriately such part as you desire.

    more love....

  34. Jim | | #34

    Jay, we're currently building with 2 feet of gravel beneath the slab. We've constructed a plenum using CMU and we're taking air off the ceiling and blowing it thru the plenum where it circulates thru the gravel and comes out of registers in the concrete floor on N&S walls. Our architect used this design on his home (1985) and has not had a problem. Mould requires both moisture and something to eat (cellulose). If you can things dry you should have no problem. I know this is not the research you're looking for but I thought I'd weigh in anyway.

  35. Riversong | | #35


    Mold requires moisture and warmth as well as almost any organic food, including dust, smoke particles or pollen. Every forced air duct that is not protected by HEPA filters is a potential breeding ground for mold.

    Subslab warm air ducting through CMUs, rock and other media that allow capillary action or moisture diffusion is a problem waiting to happen. If everything can be guaranteed to remain perfectly dry, such a system may work. But that's pretty difficult in a sub-grade environment.

  36. Riversong | | #36


    The best home is one that serves the needs of its occupants and its environment as effectively and efficiently as possible and at an affordable cost to occupants, society and environment. Perhaps you meant to say that the most sustainable house (the structure, not the living place) is the one not built. A home can be a cave or a clearing in the woods or a piece of pavement under a highway overpass.

    I do not "rant". I offer experience-based, science-based, environmentally-sound and appropriate solutions and critiques of inappropriate "solutions" such as what is presented of the Brownell system (which you seem to worship like a fools-gold calf). I have also routinely critiqued Joe L's ideas, such as his absurdly "perfect" wall. Yet he and I have considerable respect for each other since, unlike some how lurk here and offer nothing of value, we both have contributed greatly to building technology and science.

    Perhaps if you open your horizons beyond that "petri dish" you claim to live in and realize that there are greater things than amoebas, flagella and parasites, you would understand the legitimacy of my critique.

  37. Peter Powell | | #37

    I have designed, built and, for over 30 years lived in a number passive solar homes with ducted slab storage. As outlined in my "Contrarian" post I've learned a few important lessons from doing this approach: 1. It works- we've monitored slab and air temperatures for years and the heat transfer provides better storage temperatures than simple direct gain. 2. It improves interior comfort on a year around basis. 3. The in-slab ducts MUST be accesible for cleaning and arranged to eliminate access by dust (and gerbils) and the interior surface of the ducts must be smooth. 4. It allows higher than rule-of-thumb glass area and thus additional storage duration. 5. Mold and condensation in the ducts is a non-issue if designed as I suggest. 6. Yes, it requires a fan and simple controls, but this is preferable to running a furnace or burning more wood.
    To those who say this is not truly a passive approach, I say humbug. Given all the other mechanical systems in houses now, no current designs are truly passive, nor should they be for optimal performance.

  38. Riversong | | #38


    Of course a properly-designed and properly-constructed active solar storage system will be more effective than a purely passive system.

    You can say "humbug" all you want, but an active system is a completely different beast than a passive system, which requires no mechanical equipment nor purchased energy to operate. And, from my perspective, based on more than 30 years of designing and building, a truly passive approach is one that also doesn't require daily occupant intervention. This, too, requires careful design, but requires no maintenance effort or replacement costs or operating energy.

    It is disingenuous to call an active system passive (as some proponents do). They are two entirely different approaches to design. Which one is "optimal" depends entirely on how you choose to measure inputs and outcomes. In sustainable design, costs are measured not only in dollars and cents or in BTUs of purchased energy, but in the entire spectrum of environmental, social, and personal impacts and in the health, safety and comfort of the home.

    By those broader measures, a simple passive system is always preferable to an active one.

  39. Rick Miller | | #39

    Thanks for posting the good information.
    It reminds me that this GBA Q&A site is very funny. A reader may often get what he or she paid for, but sometimes can get infinitely more than they have paid for.

  40. smalld | | #40

    Two Btu's acquired by natural means and resulting in only 1 Btu being transmitted into a living zone for humans beings will result in one less Btu acquired by some form of energy produced by an artificial means - ie; power production (coal ,nuclear, hydro-electric), and with one out of two retained we would be far beyond any or our immediate and present demands. .To produce a' thermal 'well' or mass is essential, in fact critical, as exemplified by the natural environment around us, be it flora or fauna, in alpine, savanna, oceanic, or temporal forests.
    Yes, many have been proven and dis-proven empirically by many cultures, over many millennium. Yet, I am concerned that much of what that you espouse (such as isolation from the real environment) is a repeat of our mistakes of the past, and although with a new and innovative scientific bent I believe will result in a further isolation of humans from the reality of the actual environment they live in and on.
    Interactive participation in the domestic and working environments of our lives is essential for our survival as a species and will require some significant changes. And in some cases capturing and retaining interacting with that acquired energy will require a significant amounts of initial cultural changes, along with significant changes in the production and transportation of energy. And they could prove to be some positive steps toward the acquiring of natural energies and diminishing our demand for artificially acquired ones.
    I sense that the question is; will any approach in the long term continue to supply an even more significant portion of the 'comfort level' of the occupants of a building with even less demand on the environment for many years beyond and exceed the initial demand by decades and more if properly applied? Retention is one answer, however' exclusion by isolation' as you espouse, is of great concern to me and others I converse with. What about interaction with our environment, 1) transpiration which is a predominant form of 'breathing' on this planet? 2) heat retention by absorption and retention which is another in terms of natural cycles, animal forms and plant forms on 'this' planet! There are many more examples that our one and only planet gives us.
    I recognize that there is no one single answer to any of the energy challenges of our dwellings, or our present way of life in the more privileged? world, however I believe that as long as we continue to tread the paths we have traveled in our more recent 'modern' scientific inquiries and continue to ignore the empirical evidence of the many civilizations, cultures of our ancient and collective past throughout the myriad of regions of our collective planet, then we may unfortunately - just continue to repeat the same mistakes.
    Then with a little more than a simple addition of some sophisticated and scientific justifications we will ensure our downward slide. That very science that has brought those of us in the more privileged world to the very brink of the environmental collapse of the world as we have grown to know it, and dragging those less privileged throughout the world with us. I would suggest a much more 'LATERAL' (as in lateral thinking) approach and actively utilizing what has been the collective experience of our species over many millennium of our habitation on this planet and a focusing far less on the obeisance of the more recent religion of scientific certainty. A certainty which has proven to be less certain with each passing day, and is revised at least once a week - pending the next scientific revelation - that more often than not confirms the collective and age-old empirical experience and wisdom of the human species. Is it not time for to designers or structures to emulate and incorporate the systems of the natural world around that we luckily inhabit rather than attempt to mitigate its reality?
    Solar absorption, retention and modification works for all the other species and exospheres on our planet why do you insist it doesn't for us or our buildings?

  41. GBA Editor
    Martin Holladay | | #41

    In the early 1980s, I spent a winter sleeping in an igloo. From Dec. 25 until March 23, when an early rain began to melt my igloo, I slept in my igloo every night. So I'm no stranger to the concept of living in contact with nature rather than separating myself from the natural world.

    The fact is, however, that when the wind is blowing and blizzards move in, most families are grateful for shelter. That means protection from the wind. That means keeping rain off your bed. And that usually means raising the temperature of your shelter during the winter, especially if you have infants and small children.

    If you acknowledge the need for shelter, it's a good idea to provide shelter in a way that minimizes energy consumption.

  42. Riversong | | #42


    I wish you would use your real name, since you are one of the very few here who "gets it".


    If shelter would once again mean "protection from the wind...keeping rain off your bed, and... raising the temperature...during the winter", rather than creating a super-sized designer habitat for all possible human desires and appetites, then we will have re-learned the true nature of green and responsible living.

  43. Steve El | | #43

    Hey Martin, I've done a bunch of nights in tents, snow caves, and quinzees too. It was almost all fun, except when the toilet paper ran out. What's a guy to do? Leaves are under the snow... pine cones are sticky and some are pointy.... in the end, it seemed an "easy" choice between the remaining options: frozen fresh caught trout or snowballs....

    I'm glad I have a permanent place to park the toiletries when being in the wind is no longer "fun". It is interesting though, those moments watching the sun go down in the backyard, and looking out across the neighborhood, occasionally realizing that everyone on the street is still living under the sky, in very rigid and rather non-portable tents without much fresh air and for the most part not thinking about the sunset or the sky overhead. Is there some specific number of square feet per person where a home becomes an evil instead of a good thing? I mean, when does white become black and vice versa?

    Anyway.... if Jay is still listening.....

    I owned a slab foundation house in a snow state in a very flat - and I mean flat - yard with clay soil. The house was built in 1954 and since the edge wasn't insulated, there were pillbugs and slugs alive and well in a solid mass huddled up against the always-melted 1/4" of mud next to the wall. The snow melting away formed ice dams on the ground, making a soupbowl around the slab. Further snow would melt, and the part that made it into the unfrozen ground next to the slab had only one place to go.... under the slab. I didn't know anything about buildings when I bought the house, and so when winter came and I hit the furnace I expected humidity to go down like normal. But I ended up running a dehumidifier all winter long to the RH down to 60%. It seems the ducts filled with water and gave a new meaning to the term "whole house humidifier". Anyway, if you're still listening and have not yet built take all the drainage, insulation and site prep suggestions to heart, and then study up a second time to make sure you didn't miss anything. You only get one more or less affordable chance to prevent in-slab design flaws.

  44. GBA Editor
    Martin Holladay | | #44

    I'm with you. Shelter is something must less complicated, much less expensive, and much less energy-intensive than a "super-sized designer habitat." We all need to learn how to simplify our lives.

  45. Steve El | | #45

    Sounds good to me too.

  46. Riversong | | #46
  47. Anonymous | | #47
  48. Riversong | | #48

    Speaking of living in a cardboard box...

    Daniel Quinn, author of the visionary and prize winning Ishmael books, who speaks of the necessity of restoring a tribal economy if we are to return to a sustainable way of living, suggests that the only authentic tribes in the US today are traveling circuses and the homeless who live in encampments (like the hobos of the first Great Depression).

    I was in Santa Barbara CA in the early 70's when one of the last of the hobo villages was bulldozed into oblivion. The public rationale was, of course, that their encampment was illegal and unsightly (Santa Barbara was fast becoming a nouveau-chic designer city). But I wonder whether a subconscious or unspoken reason was that it represented a living example of a cooperative, non-consumptive and non-materialist "outlaw" culture that, by its very existence, was a challenge and rebuke to the way we live.

  49. GBA Editor
    Martin Holladay | | #49

    No, my igloo was considerably more humble than that suburban model.

  50. smalld | | #50

    It may surprise you to know that I also learned a thing or two; with farmers, lumberman, prospectors, trappers, big game guides/hunters and indigenous peoples in the Selkirk and Rockie Mountains- as well as the many inhabitants of the deserts,coastal and mountain regions of North Africa, the Mediterranean, temperate and high altitude climates of Europe and Persia as well as the innumerable climatic regions of Southeast Asia, Oh! - & the central and northern regions of Canada - did I mention east/west coasts of several continents? Ooops, there also New Mexico, Colorado, and California in the late 60's and early & 70's----alternate communities some from as far away as MIT . I lived with the people, worked with the people on their ancient non 'scientific' [turf] or experimental lands and not just for a day or two!
    And without being dismissive- by the way, Dec.- March does not a winter or summer make.

    Please recognize, Mr. Holladay, that I do not write here to attack or belittle your observations, only to challenge your premise and supposition that new 'tech/science' is the only answer. I respect and honour the challenge(s) you take on each and every day in your blog, your job, your culture and in your life. I would humbly submit that you read my submissions with this in mind
    (tip of the hat to you Robert R) -Rhaud Macdonald = (smalld)
    "Divisiveness is not the tool for wonderment, inquiry or creativity. Nor is it a tool for excellence or survival. Only discourse, discovery and cooperative synthesis with a keen filter of reality provides any hope." -smalld

  51. GBA Editor
    Martin Holladay | | #51

    Rhaud Macdonald,
    Wow -- this is an old thread. It took some re-reading for me to remember when this thread was all about.

    Rhaud, it sounds like you have traveled widely and lived in many interesting places. That's great. I envy your experiences.

    Concerning the question of whether December to March is the same as a winter: you're right, it's not. That is just the igloo season here in Vermont. Before Christmas, it is often hard to get enough high-quality snow to build a good igloo. And the last week of March is when my igloos usually melt.

    Anyway, I'm not sure what your point is. If you mean that you have lived in places with a longer igloo season than we have in northern Vermont -- then I would say, that's great.

    I have no idea where you got the impression that I think that "technology is the only answer." In fact, an over-reliance on technological solutions is currently leading the planet over a cliff.

  52. GBA Editor
    Martin Holladay | | #52

    Rhaud Macdonald,
    After I posted my latest comment, I found a blatant example of the type of thinking -- a variation of "technology is the only answer" -- that will contribute to our civilization's doom.

    Time magazine has just reported on the invention of a $40,000 murder weapon -- a self-propelled pilotless drone that is small enough to be carried in a backpack. It can be launched by a single person and can be directed to its target with a remote control unit that includes "real-time video." It is described as a "kamikaze" weapon that "detonates on impact."

    It doesn't take much imagination to wonder what will happen when an assassin deploys such a weapon at an event at which, for example, the President of the U.S. is giving an outdoor speech.

    It's disheartening, of course, to realize that graduates of engineering programs at some of the best universities in the country are devoting their careers to developing weapons like these.

    The surprising part of the story, however, is this kicker: Time magazine hailed the invention as a boon, and included it in its list of "The 25 Best Inventions of the Year."

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