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Musings of an Energy Nerd

Net-Zero-Energy versus Passivhaus

Each approach to building a superinsulated house has its strengths

The least-cost approach to designing a superinsulated house. Savvy designers evaluate the cost of energy-efficiency measures by comparing the cost and energy savings achieved by each measure with a similar investment in PV. However, installing a PV array on a residential roof rarely makes economic sense.
Image Credit: Ben Southworth

In Europe, builders interested in energy efficiency are gravitating to the Passivhaus standard. Meanwhile, American researchers — and a few American builders — have developed a fascination with the idea of the net-zero-energy house. The U.S. Department of Energy has established as a goal that new buildings in the U.S. will be built to a net-zero-energy standard by 2030.

Passivhaus buildings and net-zero-energy buildings have a lot in common. Both types of buildings aim to reduce the amount of energy used for space heating or cooling by designing envelopes with a low rate of air leakage, thick insulation, and high-performance windows.

While Passivhaus designers are content with achieving a very low energy budget, net-zero-energy home designers add frosting on the cake by including a rooftop photovoltaic (PV) array sized to produce enough site-generated electricity to balance the home’s annual energy use.

While both approaches have merit, both approaches are also open to criticism.

Advantages of the net-zero-energy approach

The best aspect of the net-zero-energy approach is the fact that, in order to balance energy loads with energy production, designers are forced to evaluate the cost-effectiveness of each energy-efficiency measure and compare it to the cost of a PV array. The aim is to find the least-cost path to building optimization.

Here’s the way such analysis works. Say you are building in Syracuse, N.Y. Designers know that a 1-kW PV array — that is, an array that now costs about $7,000 to install — will generate 1,123 kWh per year in Syracuse. In other words, each $1,000 you invest in PV will reduce your energy expenditures by 160 kWh per year. [Update: in September 2012, the cost of a 1-kW PV system has dropped to $3,500. That means that a $1,000 investment in PV will generate twice as many kWh per year — about 320 kWh — as the calculations shown in this article.]

Using that investment in PV as a benchmark, it’s possible to evaluate other $1,000 investments. For example, what will be the effect of adding $1,000 worth of extra cellulose insulation to your attic floor? With a good energy modeling program, it’s easy to do the math; if the cellulose saves more than 160 kWh per year, it’s a good investment compared to PV.

Once you’ve designed a good shell, each incremental improvement adds to the cost of construction, but saves less and less energy. As thicker insulation or additional layers of glazing begin to cost more than PV, it’s time to question the logic of the investment. If you’re building a zero-energy house — that is, a home with a PV array on the roof — it doesn’t make much sense to invest in insulation upgrades unless the investment yields more kWh savings than a PV array.

In 2004, engineers at the National Renewable Energy Laboratory in Golden, Colorado developed a software program, Building Energy Optimization (BEopt), that performs the calculations necessary to determine the least-cost path to building a zero-energy home. For more information on BEopt, see BEopt Software Has Been Released to the Public.

Apples to oranges

Most Passivhaus builders defend investments in envelope improvements that cost considerably more than PV. Their main argument: comparing insulation to PV modules is an apples-to-oranges comparison. While PV modules may wear out in 30 or 40 years — and may require maintenance or repairs along the way — insulation is likely to last far longer and is virtually maintenance-free.

The argument has merit. Nevertheless, when large amounts of insulation are used to save only a handful of kWh per year — the classic example being a very deep layer of rigid foam insulation, in some cases up to 14 inches deep, under a slab foundation — it’s worth stepping back and considering the situation from a neighborhood perspective.

Far more energy will be saved when two houses are each equipped with 7 inches of sub-slab foam than when one house has 14 inches of foam and the other has none. This example raises the question of whether installing very thick layers of insulation in a handful of houses is a good use of the world’s limited resources.

Advantages of the Passivhaus approach

The best aspect of the Passivhaus approach is that it doesn’t fall into the trap of assuming that electricity production is best performed on a residential roof.

It’s hard to understand why so many researchers in the U.S. have concluded that homeowners need rooftop PV. In fact, generating electricity on residential roofs rarely makes sense, for the following reasons:

  • Residential roofs are often shaded by trees or neighboring buildings.
  • Many residential roofs don’t have the optimal slope or orientation for a PV array.
  • A rooftop PV array greatly complicates re-roofing.
  • Most homeowners don’t want to be responsible for maintaining and repairing energy-generation equipment.
  • It’s far cheaper to generate electricity from utility-scale wind turbines — or even from a solar thermal plant in the desert — than from small PV arrays.
  • The cost of tax credits and subsidies doled out to homeowners who install PV arrays increases the tax burden and the cost of electricity for the general population.
  • Programs that encourage the installation of residential PV arrays draw investment dollars away from more logical investments (like improved air-sealing measures) which yield more energy savings per dollar invested.
  • There are far cheaper ways to reduce carbon emissions — for example, upgrading old coal-fired power plants with cleaner technology — than the installation of PV arrays.

Combining the best of both approaches

Although I’m well aware that the expected service life of insulation is longer than that of a PV array, I think that it’s sensible to use the cost of PV as an upper limit or “reality check” when considering the cost of any envelope improvement. It’s a useful way of reining in an out-of-control designer who’s about to go over the cliff.

That doesn’t mean, however, that a superinsulated house will necessarily benefit from a rooftop PV array. If you do the math, you’ll discover that homeowners who invest in PV pay more for their electricity than homeowners who buy their power from the grid. If we go back to the example of the house in Syracuse, NY, we discover that a $1,000 PV array saves only $19 per year, assuming that grid electricity costs 12¢ per kWh.

In other words, these homeowners are deliberately choosing an expensive source of electricity. (There is an exception to this rule: in areas of the country with generous PV subsidies, tax credits, or feed-in tariffs, the installation of a PV array can sometimes save a homeowner money. That’s only possible, however, when the homeowners pass along some of the cost of their PV array to utility ratepayers or taxpayers — in other words, their neighbors.)

The fact that PV-generated electricity is very expensive is a further reason to be wary of any investment in insulation or windows that yields fewer annual kWh savings per dollar invested than PV.

A designer who advocates installing insulation that costs more than PV is anticipating a future with fuel costs that exceed the current cost of PV-generated electricity. That’s an unlikely scenario, considering the fact that the cost of electricity generated by utility-scale wind turbines is now much lower than PV-generated power, and considering the fact that PV prices are still dropping.

If a homeowner borrows money to pay for insulation that costs more than PV, the mortgage amounts to an investment that only pays off if future fuel prices exceed the price of today’s PV-generated power. To me, that’s a risky stock to invest in.

So here’s my recommendation: design your house using the net-zero-energy approach to cost optimization — but don’t buy or install the PV array.

Are some elements of the Passivhaus standard arbitrary?

Passivhaus proponents have been known to bristle when energy experts suggest that a few elements of the Passivhaus standard — for example, the airtightness limit of 0.6 ach50 or the annual space heat limit of 15 kWh/m²/year — are arbitrary.

Passivhaus proponents have proposed the following explanations for the 0.6 ach50 limit and the 15 kWh/m²/year limit:

  • The purpose of the 0.6 ach50 limit is to avoid structural damage to the building.
  • The purpose of the 15 kWh/m²/year limit is to make it possible to deliver space heat through a home’s ventilation ductwork.

For example, on the first point, here is what Dr. Wolfgang Feist had to say: “The airtightness is one of the things that we really have to stick on in almost all climates. There are only a few climates where this might not be a [requirement], but very few — like in San Francisco. In San Francisco you might not need to have it airtight, but in almost all other climates you need that. A major part of the airtightness requirement is to avoid structural damage. You have bad indoor air with humidity, and if there is an exfiltration through the construction you get really big problems of condensation in the structure. This is the major reason to make it completely airtight, and even in subtropical climates and of course in tropical climates, it has to be airtight because you get structural damage without airtightness.”

Feist’s statement doesn’t bear up well to close scrutiny, however. Plenty of wall systems are robust enough to be fairly immune to structural damage related to air leakage — for example, ICF walls. Moreover, there have been examples of extreme structural damage without air leakage — the most famous being SIP homes in Juneau, Alaska, that suffered catastrophic roof damage due to convective loops through the SIP seams. These convective loops led to condensation and rot, even when no exfiltration occurred.

Finally, almost all wood-framed homes with air leakage rates of 2 or 3 ach50 are doing fine, with no evidence whatsoever of structural damage.

Why does heating energy use need to be so low?

When it comes to the 15 kWh/m²/year limit, there is a good deal of evidence that the limit was chosen to allow space heat to be delivered through ventilation ductwork — at least in central Europe.

According to the Passipedia Web page, “A Passive House is a building for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling of the fresh air mass [ventilation air] which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air. … All airtight buildings (any low-energy building needs to be airtight) require the use of an efficient ventilation system. In Passive Houses this system is also used for heating purposes, without the need for additional ducts, major technical interfaces, auxiliary fans etc. … The way to go therefore involves cutting back on one of the two systems: either on the ventilation system, e.g. by installing an exhaust system only; in this case the building will become a low-energy house with conventional heating; or on the heating system by using the ventilation system for heating as well – in this case the building will become a Passive House. This heating concept automatically implies extremely low energy consumption. After all, using the fresh ventilation air for heating without an additional heating system can only work in buildings with minimal net losses.”

In the colder regions of Scandanavia and North America, it’s extremely difficult to deliver enough space heat through ventilation ducts to keep a Passivhaus building warm in cold weather. This needn’t be a problem, however, since Dr. Feist says that it’s perfectly acceptable for a Passivhaus building to deliver space heat through other mechanisms. Feists’s concession is certainly useful. However, once it becomes permissible to use any type of heat delivery system, the justification for the 15 kWh/m²/year limit loses its original importance.

Thousands of dollars of insulation to save just a few BTUs

Ultimately, it really doesn’t matter whether Passivhaus limits are arbitrary or firmly based in a consistent philosophy of conservation. What does matter is whether the extremely thick (and expensive) layers of insulation needed to meet the standard in a cold climate can be justified by anticipated energy savings.

In northern areas, meeting the 15 kWh/m²/year limit requires insulation levels that are hard to justify. For example, Phil Kaplan, an architect in Maine (and one of the Podcasters in GBA’s “Green Architects Lounge” series), is designing a superinsulation retrofit project for Claudia King, a homeowner in Falmouth. Working with energy consultant Marc Rosenbaum, Kaplan proposed a series of retrofit insulation measures (including 4 inches of polyisocyanurate foam on the exterior of the walls) to lower the home’s energy use. After running the numbers, the team found that they were still short of the Passivhaus goal.

By adding more insulation — including 2 additional inches of polyiso on the walls, for a total of 6 inches — the house could meet the Passivhaus standard. But these heroic measures would add at least $2,880 to the cost of construction, while only saving 950 BTU/sf/year. Assuming that heat is supplied by a ductless minisplit heater with a COP of 2.0, the extra insulation would have a simple payback period of about 58 years.

“We wanted to know if we could meet the Passivhaus standard,” Claudia King told me. “We thought it would be really cool if we could get certified. We did all the figuring, and we found that we needed to do a little more upgrading — to add more insulation in the cellar and more foam to the outside walls. We calculated that the cost of doing wasn’t worth it for the gain we would get — the savings were not worth the extra investment. We could get the same gain for less investment by putting up some more PV panels, so the expense could not be justified.”

For more on this topic, see “Are Passivhaus Requirements Logical or Arbitrary?”

This article has been translated into Serbian: Dva Pristupa Energetski Efikasnim Zgradama

86 Comments

  1. Kristen Simmons | | #1

    Interesting comparison! One
    Interesting comparison! One correction and a couple of comment.

    To achieve Passive House Certification, specific heating demand needs to be ≤ 15kWh/(m2/yr) and for refurbishments seeking the Passive House EnerPHit Certificate ≤ 15kWh/(m2/yr).

    Getting Passive House Certification does not preclude using site generated energy, be it pv, wind, etc. In the case of one project that I am working on, building to the passive house standard will allow the pv's (with net metering) to meet all the annual primary energy demand. If the client chooses, the project could even be net positive.

  2. Kristen Simmons | | #2

    Hit send too soon...
    My other

    Hit send too soon...

    My other comment is that cost benefit analysis depends very heavily on the assumptions that one is making about the cost of fuel and inflation over time, which really depends on the mindset of the person (the owner) who's doing the evaluation. Incentives can further skew this calculation.

  3. Marc Rosenbaum | | #3

    Get the facts straight please
    The Passivehouse standard doesn't have a heating limit of 10W/m2. It does have an annual heating energy criterion of 15 kWh/m2/year maximum.
    People invest their resources ultimately where it makes them feel good. It's hard for me to invest my resources in making a coal plant infinitesimally cleaner, but fairly easy to invest in PVs. I choose to do that rather than to invest in a more expensive kitchen or car, just because it feels to me that it's the right thing to do, and it's within my personal sphere of influence.
    It's true that a few boutique houses, either ZNE or PH, don't make a difference really. However, we can look at isolated cases, like parts of Austria, where the PH standard has made significant inroads into the new building stock. Whether it is the right target for a country with such diverse climates as the US is still an open question, but it represents an actual target, which has been sorely lacking in this country. My observation about people that I've trained in PH Consultant trainings is that taking the course forever changes their idea of what a building can be, and that ripple effect is more powerful than the one I've seen teaching people to do ZNE buildings.

  4. User avater
    Carl Seville | | #4

    Nice Analysis
    Thanks for the solid overview, Martin. I particularly liked this comment about PV: "Programs that encourage the installation of residential PV arrays draw investment dollars away from more logical investments (like improved air-sealing measures) which yield more energy savings per dollar invested." There has clearly been too much emphasis put on incentives for "things" like PV, geothermal, solar thermal, etc, while improving process and behavior have been all but ignored. This is mostly due to the fact that businesses can make more money by selling things than process, so they put their money into lobbying for thing incentives. The best evidence of this is the fact that the Home Star program, a good, although imperfect, set of incentives for high performance homes has languished while other incentives have succeeded.

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to Kristen Simmons and Marc Rosenbaum
    Kristen Simmons and Marc Rosenbaum,
    Thanks to both of you for catching my error on the Passivhaus limit for space heating energy; I have corrected the text.

    To clarify: 15 kWh/m²/year is the space heating energy limit; 10 W/m² is the recommended (but not required) power limit for the space heating system at the design temperature.

    The correction of the typo, however, does not affect my basic argument, which remains as originally presented.

  6. Mark Attard | | #6

    Comment
    I would agree that Passive house does not preclude the use of PV or other renewable energy sources. Though the bottom line is, why make up for energy loss that is unnecessary? ROI must also include an analysis of the embodied energy of the products used. We know that there is a fair amount of embodied energy used in the production of PV panels not to mention the energy it takes to ship them. This embodied energy is an offset to the energy production of the panels. Depending upon the type of insulation used, the embodied energy in these products can be zero. There should also be life cycle considerations when choosing between building systems and materials. I feel much more confident that Passive house standards can obtain a 100 year plus building scenario with a greater carbon neutrality than net-zero housing.

  7. User avater GBA Editor
    Martin Holladay | | #7

    Response to Mark Attard
    Mark,
    Although the embodied energy of insulation materials can be very low -- when it comes to purchased materials, cellulose insulation usually shines as the insulation material with the lowest embodied energy -- I've never seen an analysis that shows that an insulation material has zero embodied energy.

    In an article in Home Power magazine, Justine Sanchez cited a 2006 study conducted by CrystalClear that calculated the estimated energy payback time (EPBT) for grid-connected roof-mounted PV systems. According to Sanchez, the study looked at the EPBT for PV systems, including balance of system (BOS) components (racks, inverters, wires, etc.) and assumed a system efficiency of 75%. “The study shows the EPBT for standard, single-crystalline module PV systems to be two years,” Sanchez writes. Systems using polycrystalline modules (produced with a casting method) had an even shorter EPBT at 1.7 years; modules produced with a ribbon method had EPBTs of 1.5 years.

    The study used average solar data for southern Europe, estimated at 1,700 kWh/m2 [158 kWh/ft2] per year; average solar production in the U.S. is higher (1,800 kWh/m2 [167 kWh/ft2] per year), meaning the EPBT for U.S. installations shorter.

  8. markobmf | | #8

    It's clear
    that the approach we follow that ultimately works best for our home and climate may be a hybrid or a custom approach and that a certification may be counterproductive. In CA solar PV keeps us out of higher rate tiers and has a marked effect on payback. It works well when our utilities have incentives to save rather than sell more power. Using Katrina as an example, solar PV could also help CA victims of a major earthquake weather a few weeks or months of no grid power if they have PV on their roofs.

  9. User avater GBA Editor
    Martin Holladay | | #9

    Using grid-connected PV during weather emergencies
    Mark Obmf,
    I doubt if the average California homeowner has the wiring skills necessary to make use of their rooftop PV arrays in the event of a major earthquake or extended power outage.

    First of all, their grid-tie inverters will be useless, because grid-tie inverters require power from the grid to operate. So their rooftop PV arrays will only produce DC, not AC.

    Most grid-tied arrays now produce higher voltages than the old 12-V DC systems of the 1980s, so these California homeowners won't be able to use their rooftop arrays to power any appliances from their recreational vehicles (most of which run on 12 V DC).

    So, in order for these homeowners to be prepared for the Big One, they need to buy and install:
    1. A transfer switch that disconnects their rooftop array from their grid-tie inverter.
    2. An off-grid inverter that matches the voltage of their rooftop array.
    3. A large battery bank so that they can have some electricity at night.

    Those items will cost at least $5,000. But if they buy and install all that stuff, they'll have lights on when the Big One hits. Unless, of course, their home is seriously damaged by the earthquake.

  10. J Chesnut | | #10

    scrutiny is good and . .
    Martin,
    Your scrutiny in this comparison leads to better informed professionals. This contributes to better decisions and combining the strengths of both approaches.

    As a designer I obviously gravitate towards Passivhaus. The reason being that designers see value in a well developed concept and energy modeling tool that allows the leveraging of free AND DIRECT passive solar gains to radically reduce energy required for heating. This is not just a matter of adding insulation; it is the coordination thru design of the thermal envelope, orientation of the building, and fenestration.

    Many designers have the luxury to work on custom homes where cost-effectiveness does not necessarily dictate the design of the home. I imagine builders tend towards net-zero energy because the bottom line is the driving factor.

    Say we were to argue which is the best approach for a "more sustainable" future. In this context maybe cost-effectiveness needs to be understood as a reflection of CURRENT conditions and as a requirement may tend to uphold the status quo.

    The Passivhaus limits should be scrutinized and understood and changed if beneficial. Although there is a cache to a fixed and branded concept. There is a niche market for Passivhaus design because, like LEED, for the consumer it is 'well-packaged'.

  11. J Chesnut | | #11

    Passivhaus retrofits vs new construction
    When you end with an example of retrofit work trying to meet Passivhaus this is not the best way to argue that Passivhaus is not cost effective.

    Passivhaus represents holistic design of an orientated thermal envelope. Retrofitting a building not designed to these principles is a completely different exercise than new construction.

  12. User avater GBA Editor
    Martin Holladay | | #12

    PHPP is good
    J,
    Concerning your statement, "As a designer I obviously gravitate towards Passivhaus. The reason being that designers see value in a well developed concept and energy modeling tool that allows the leveraging of free AND DIRECT passive solar gains to radically reduce energy required for heating."

    You're right -- PHPP (the Passivhaus spreadsheet) is an extremely useful tool.

    Of course, most designers of superinsulated houses and net-zero-energy houses also consider (and take advantage of) passive solar gains, even when these designers don't use PHPP.

  13. J Chesnut | | #13

    fair point, how can we do it?

    I think that it’s sensible to use the cost of PV as an upper limit or “reality check” when considering the cost of any envelope improvement. It’s a useful way of reining in an out-of-control designer who’s about to go over the cliff.

    This is a sensible exercise and in the interests of the client. Don't know if I would go as far as to set it as the upper limit but it does offer the reality check context.

    When I think how this can properly be accomplished the designer will need to know the performance of the thermal envelope at different insulation levels to compare prices with solar installation bids.
    I can imagine how to accomplish this using the PHPP energy modeling software. Are you aware of other methods of measuring the performance of proposed thermal envelopes at different insulation levels accounting for passive solar gains?

  14. User avater GBA Editor
    Martin Holladay | | #14

    Energy modeling software
    J,
    The field of energy modeling software is a huge one, and hard to get a handle on or keep up to date with.

    The U.S. Dept. of Energy lists 345 energy modeling programs on its Web site:
    http://apps1.eere.energy.gov/buildings/tools_directory/subjects.cfm/pagename=subjects/pagename_menu=whole_building_analysis/pagename_submenu=energy_simulation

    Just considering the software programs with "Solar" in the title, I notice SolaCalc, Solar-5, SolArch, and SolarShoeBox. But a great many residential energy modeling programs -- the majority, I think -- make an attempt to account for solar gains. Obviously, that includes the hundreds of programs that don't happen to have "solar" in their title.

  15. Andrew Henry | | #15

    Reduce the demand
    Martin,

    To keep things 'pleasant' we need to reduce carbon emissions as close to zero by 2050, which means we are going to undergo (hopefully) a profound transformation in our energy supply. This challenge, to me at least seems best met by doing all we can to reduce our energy demand.

    Net Zero doesn't do enough to reduce the demand, it makes up for the buildings energy demand with on site renewables, whereas Passive House focuses on the demand.

    More importantly there is a temporal disconnect with NZE between the buildings peak demand and it's renewable electric generating capabilities peak supply. A disconnect you have pointed out with PV for those wanting to live off-grid. Buildings', in heating climates, peak demand is in the winter when there is very little electricity produced from PV. So with NZE you can end up with buildings with higher energy demands (assuming the NZE didn't meet Passive House) and no way to make up for that higher demand because it's winter.

    Hypothetically, say a northern jurisdiction mandates that all new buildings be NZE. That jurisdiction could well end up with a much higher winter energy demand compared to a jurisdiction that mandated Passive House. It would have to import supply from other jurisdictions to make up for that demand in winter. The flip side is that the NZE jurisdiction may also have to 'give away' energy in the summertime as it produces far more than the jurisdiction needs.

    As for retrofit's, J Chestnut was right in pointing out the use of a Passive House retrofit as an example of costs. I didn't think it was a valid example for comparison.
    As well, (this is off topic) I question whether retrofits are worth the bother financially. I recall reading one article pointing out that economically it made more sense to tear down the existing building and start again. Then the design constraints for achieving Passive House, or whatever the goal is are greatly reduced.

    Finally, with respect to Passive House ACH targets being overly ambitious, whether or not the ACH target can be met in new construction seems to be an issue that is best resolved by good design practices rather than heroic implementation efforts. From the Passive House examples that GBA has showcased, good design seems to have dealt with the goal of meeting the ACH targets.

    Respectfully,

    Andrew

  16. Lucas Durand - 7A | | #16

    Apples and oranges
    Martin,
    From the point of view of conservation of resources, I think your argument makes a lot of sense. A "reality check" should be part of any project.

    I have noticed that ROI (ie: a comparison of monetary investment vs energy return) is often the only approach used to make the required comparisons.
    While certainly useful in many cases, it is not clear to me that ROI is the best way to understand where certain thresholds lie. Comparisons seem to become very complicated due to cost variations which are not universally applicable across the land.
    In an earlier comment, Mark Attard said:

    ROI must also include an analysis of the embodied energy of the products used.

    I agree with Mark in the sense that I think a better understanding of embodied energy could provide a more accurate "picture" while also possibly being a less complicated shortcut to understanding conservation in building.

    There is a sort of "ROI" that compares energy inputs to energy return and is known as EROEI (Energy Return On Energy Invested).
    EROEI has the advantage of balancing comparisons between dissimilar components (like PV panels and insulation) by eliminating the variable monetary aspects and focusing strictly on the net energy return.
    By focusing on EROEI, "reality checks" by comparing the cost of insulation to the cost of PV might be side-stepped all together by direct analysis of (for example) the net energy return of increased foam thickness or the net energy return of a PV installation.
    Obviously, an EROEI analysis requires accurate data on life-cycle energy use of all components considered in the analysis. Obtaining a comprehensive dataset could be a challenge.
    A software program similar to PHPP could be used to run such analyses.
    What do you think?

  17. User avater GBA Editor
    Martin Holladay | | #17

    Response to Andrew Henry
    Andrew,
    All good points; thanks for your thoughtful post.

    Anyone contemplating a new-home construction project has several goals to juggle. Often the best house for the planet is not the same as the best house for the homeowner's budget.

    Weighing these competing goals can be tricky. (Moreover, many homeowners can't afford to choose a best-for-the-planet design if that option is significantly more expensive than the best-for-my-budget design.)

  18. User avater GBA Editor
    Martin Holladay | | #18

    Response to Lucas Durand
    Lucas,
    I'm not sure whether it will ever be possible to develop a software program that can accurately and usefully integrate "energy return on energy invested" data into residential design.

    For example, mud and straw homes, if their walls are sufficiently thick, will probably have excellent "energy return on energy invested" numbers. Does that mean that all homes should have walls built of mud and straw?

    Perhaps -- but there are so many variables in the equation that it's hard to see how your proposed metric would be integrated with other requirements.

  19. Lucas Durand - 7A | | #19

    I see your point.
    I suppose my proposal was more aimed at making certain specific choices within a specific project...
    For instance: "am I really saving anything by going to 12 inches of XPS instead of staying at 6 inches?"
    Maybe 12 inches is what would be required for PH certification, but that doesn't necessarily mean there is going to be a net energy advantage to getting that certification which was a point I think you were trying to make in your blog.
    I think EROEI has a lot to offer in these types of comparisons although when its application is most appropriate may be a bit fuzzy.

  20. 5C8rvfuWev | | #20

    situational
    @ Andrew Henry

    I'm not at all equipped to debate the subject, but if checks and balances is the focus of this blog and great discussion, I cringed when you made your comment (which I recall you said was Off topic):

    > I question whether retrofits are worth the bother financially. I recall reading one article pointing out that economically it made more sense to tear down the existing building and start again. Then the design constraints for achieving Passive House, or whatever the goal is are greatly reduced.

    If we are going to speak of "durability" and "sustainability" and "recycling" I can't see that a blanket statement on "tear it down" works very well. I don't mean to be as obvious as this becomes -- but doesn't the renovation or rebuild or remodel of a structure depend on a wide range of variables?

    Indeed, there are some that the neighbors would probably help destroy. I however was the "looney tunes" in my neighborhood once upon a time and took down two decaying NE barns to use in a house.

    I doubt you meant the statement the way I took it, but again decisions on what to do need to be decided through 'checks and balances.' Or so I'd think.

    Respectfully,
    Joe Wilson

  21. User avater GBA Editor
    Martin Holladay | | #21

    Further response to J Chesnut and Andrew Henry
    To J Chesnut and Andrew Henry,
    J Chesnut wrote: "When you end with an example of retrofit work trying to meet Passivhaus this is not the best way to argue that Passivhaus is not cost-effective."

    Andrew wrote: "As for retrofits, J Chestnut was right in pointing out the use of a Passive House retrofit as an example of costs. I didn't think it was a valid example for comparison."

    Actually, I'm going to disagree with you here. I think that any honest designer of a cold-climate Passivhaus building will admit that, even for a new construction house, you end up using insulation levels that cost more than PV.

    That's why Katrin Klingenberg ended up with 14 inches of sub-slab foam at her Illinois house.

    That's why Rachel Wagner ended up with R-60 sub-slab foam and R-40 foundation walls on her not-quite Passivhaus building in Duluth, Minn.

    That's why the Waldsee Biohaus in Minnesota ended up with 16 inches of sub-slab insulation and R-55 basement walls.

  22. Edgar Lopez | | #22

    I really Enjoyed This Post
    It is certainly a topic that requires further study and discussion but I do favor the Passivhaus standard for the following reason:

    - Resilience: passive systems such as insulation are simple, long lasting and the article mentioned, virtually maintenance free.

    Each additional inch of insulation saves less energy the the previous one but each inch still bears the same cost. This diminishing-returns view is a little narrow. Depending on the type of insulation and location of installation, each additional inch can contribute towards improving air-sealing and reducing thermal bridging.

    Other than lasting longer than a PV system, Passivhaus-amounts of insulation reduce the size requirement for the heating system... there's more savings there.

    In my opinion Passivhaus just makes achieving Net Zero really easy. Is it possible to lump the cost of a Passivhaus certified home and some renewable energy into the mortgage?

  23. User avater GBA Editor
    Martin Holladay | | #23

    Response to Edgar Lopez
    Edgar,
    If three builders get together -- one who follows the tradition of superinsulation, one who builds net-zero-energy homes, and one who builds Passivhaus buildings -- all three will agree that lots of insulation is good.

    The question is simply, "When do I stop?" It's not an easy question to answer.

    In general, I believe that it is true that insulation lasts longer than PV modules. But that isn't always true. The Claudia King project (mentioned in the blog) is a renovation of a 1975 house. When the walls were opened up, it was discovered that the 35-year-old insulation (admittedly, fiberglass batts -- we all know what they are worth) was deteriorated and rodent-infested. All of the wall insulation had to go into the Dumpster.

    Meanwhile, my oldest PV module (from 1980) is working fine -- I'm sure it will last longer than the fiberglass batts in the King home. The PV module hasn't required any maintenance, other than snow removal (which is optional).

  24. mike eliason | | #24

    PH v ZEB
    i don't see them as mutually exclusive or competing - PH makes achieving zero-energy buildings w/ significantly reduced cost and area of PV arrays possible.

    add in the comfort factor of a Passivhaus, and i think that only makes it more favorable approach towards ZEBs.

    the other nice thing about PHPP is that you can calculate the amount of PVs needed to be plus energy and even carbon negative building.

    there are a few projects that come to mind combining both, specifically rolf disch's solarsiedlung/sonnenschiff in the freiburg (DE's) vauban district.

  25. User avater GBA Editor
    Martin Holladay | | #25

    Response to Mike Eliason
    Mike,
    Here in colder regions of the U.S., Passivhaus designers are NOT finding that "PH [the Passivhaus standard] makes achieving zero-energy buildings with significantly reduced cost and area of PV arrays possible."

    The least-cost path to building optimization -- basically the net-zero-energy or BeOPT path -- results in thinner insulation (in cold climates) than the Passivhaus approach. As I showed in my earlier blog on this topic, Can Foam Insulation Be Too Thick?, Passivhaus levels of insulation often exceed the cost of PV.

  26. J Chesnut | | #26

    PH in cold climates

    Here in colder regions of the U.S., Passivhaus designers are NOT finding that "PH makes achieving zero-energy buildings with significantly reduced cost and area of PV arrays possible."

    Passivhaus built in cold climates are still in a prototype phase. There is still some room to bring down costs within the PH approach. Of course solar rebates are a variable subject to change also.

    I'm on a third PH design, the current design for a ~2800 sf home. We were surprised in our initial calculations that we could move from an ~R70 (for a carbon neutral operations home @ 1940sf) wall to a ~R45 wall and meet the standard. I wonder if there is a tipping point in the size of home where PH overtakes net-zero in cost effectiveness even in cold climates.

  27. mike eliason | | #27

    colder regions
    that might be true, i haven't taken a stab at anything colder than zone 5 ON PHPP - though that might be an interesting undertaking.

    also, in terms of net zero, are we talking source or site?

  28. User avater GBA Editor
    Martin Holladay | | #28

    Site or source energy?
    Mike,
    In the U.S., most definitions of net-zero-energy homes refer to site energy, not source energy.

    Needless to say, you can use any definition you want.

  29. J Chesnut | | #29

    PH retrofit vs new construction

    Actually, I'm going to disagree with you here. I think that any honest designer of a cold-climate Passivhaus building will admit that, even for a new construction house, you end up using insulation levels that cost more than PV.

    I don't doubt this Martin and I wasn't disagreeing with you here.
    My point is there is a big distinction between the financing of a new construction to meet PH versus trying to convert an old home.
    Deep energy retrofits in general cannot be reasonable financed but someone who can afford to hire an architect for a custom home can with adequate solar exposure attain a design that meets the PH standard within a custom home budget.

  30. Zane Selvans | | #30

    It depnds on your purpose
    Which approach makes sense depends on what your driving goal is. Most builders are just trying to minimize up-front costs and create a superficially attractive building that conforms to current lending requirements and won't result in their being sued down the road. A custom home builder with a client taking a long-term financial view will do some upgrades -- much better insulation than code requires, heavier copper in the wiring, a tighter envelope than most buildings, and good windows, but almost never any on-site generation (depending on available subsidies). The financial sweet spot seems not to be code, nor net-zero, nor PH. Net-zero is a nice simple aesthetic goal, but it doesn't necessarily require a particularly efficient building if you've got money (or subsides) to burn on PV, and it doesn't take into account the embodied energies of your materials, and if what you care about is climate, then low-energy materials and the lowest possible grid-tied load really matter. Afternoon solar power can effectively offset natural gas peaker plants, but if you're on a coal-based grid, all the electricity you draw at night (or throughout the winter) puts emissions up, and they don't come down no matter how much solar power you generate. My understanding of the PH standard was that it grew out of the same conversations that generated the Swiss 2000W society initiative. If we want to run our civilization on renewable energy, then with 7-9 billion people, we each get at most about 2000W to work with, which means our buildings need to pretty much take care of their own energy demands.

    Saul Griffith does a great job of laying this view of energy out in his talk Climate Change Re-calculated.

  31. User avater GBA Editor
    Martin Holladay | | #31

    Response to Zane Selvans
    Zame,
    I don't know why you have concluded, "Net-zero is a nice simple aesthetic goal, but it doesn't necessarily require a particularly efficient building if you've got money (or subsides) to burn on PV."

    I have never yet seen a net-zero-energy building that didn't have a very low level of air leakage, very high levels of insulation, and high performance windows.

    It just wouldn't make financial sense to build a building that was "not particularly efficient" and then buy a PV array 3 times larger than necessary -- simply because the designer was too lazy to build a good shell. It just doesn't happen, because your hypothetical approach is much more expensive than the normal way (a very efficient building with the smallest possible PV array).

  32. Aj Builder, Upstate NY Zone 6a | | #32

    My list of what I like that works today
    http://www.passivehouse.us/passiveHouse/PassiveHouseInfo.html

    http://www.aaepassivesolar.com/low-energy.html

    http://www.minnesotagreenhomebuilder.com/docs/Amaris%20Wall%20Section.pdf

    Google Natural Building http://en.wikipedia.org/wiki/Natural_building

    I am leaning toward what I have done, which is get the solar details as right and as passive as the site allows. Get the ACH down low, which I do now. Use continuous insulation as much as possible no matter what insulation chosen. I am OK with all kinds of insulation, it just depends on the design, budget and the desired level of going natural and truly sustainable.

  33. markobmf | | #33

    PV in an earthquake - from Outback
    Martin,

    This seems cost effective and user friendly and by no means an obscure brand or technology. I understand your objections but an analysis for my circumstances in the bay area really make PV on my roof a great solution.

    "SmartRE is the revolutionary Smart Renewable Energy solution from OutBack Power, bringing you simplified grid-tie solar with back-up power for residential and small commercial applications. Designed with an emphasis on ease of installation, a SmartRE solution installs and operates similarly to basic grid-tie solar inverters but with the unique additional benefit of providing UPS quality battery back-up during utility outages. An integrated ultra-fast AC transfer switch guarantees that even sensitive back-up loads, like computers, never know when a utility outage occurs. Recommended AGM batteries are maintained and charged by an innovative OutBack multi-stage charging process. This valuable feature assists in providing reliable back-up power and will help extend your battery life up to 10 years."

  34. Steve Landau | | #34

    Payback
    In all this discussion, the quote from the article comes back to me as most disingenuous.

    "By adding more insulation — ....... Assuming that heat is supplied by a ductless minisplit heater with a COP of 2.0, the extra insulation would have a simple payback period of about 58 years."

    Insulation and the shell easily would last 58 years. I can't see the compressor in a Minisplit lasting more than 15. So you would need to buy 3 minisplit systems, and 2 PV systems to last that 58 years.

    Passive, is passive, no compressors, no PV panels or wires outside to rot n the UV and weather of the sun. PH only needs a small fan inside, protected for ventilation.

  35. Aj Builder, Upstate NY Zone 6a | | #35

    Less is more
    KISS, keep it simple rules... Less is more..... Hard to argue with what Steve posted. Things like replacing the inverter 10 times in 58 years, and a well build superinsulated home may be just getting broken in. We can build homes that last for centuries if we want to. We can chose where to live so that less is needed to live at the chosen location.

    One thing is for sure, the planet will not have trillions of humans some day. There has to be a limit to human population on Earth at least. No one really knows how many of us this planet can handle. But there is a limit and we need to stop adding humans by enacting a one child per law worldwide. This law is way more important than this blog's "which is better" debate.

    No human to house and the debate.. is moot. Save the planet, get your tubes cut.

  36. Garth Sproule | | #36

    airtightness
    Martin
    Another great blog.
    You said "Finally, almost all wood-framed homes with air leakage rates of 2 or 3 ach50 are doing fine, with no evidence whatsoever of structural damage."
    I have no doubt that this is true. But the reason that they are "doing fine" is quite likely because of the excessive heat flux through the structure which drying the assembly. Is it not true that as the insulation level goes up, the potential for moisture problems increases because there is much less heat flux? So the requirement for extreme airtightness varies with the amount of heat flow??

    Dr Joe writes about this here
    http://www.buildingscience.com/documents/insights/bsi-028-energy-flow-across-enclosures?topic=doctypes/insights

  37. User avater GBA Editor
    Martin Holladay | | #37

    Response to Steve Landau
    Steve Landau,
    You wrote, "Insulation and the shell easily would last 58 years. I can't see the compressor in a Minisplit lasting more than 15. So you would need to buy 3 minisplit systems..."

    So? All Passivhaus buildings have heating systems. Here in the U.S., the most common heating system for the Passivhaus buildings I've seen is a ductless minisplit system. But it's possible to use other heating systems.

    I used the example of the most common heating system used here because it's the most realistic. Choose another heating system if you want, and my basic argument doesn't change. Every Passivhaus building has a heating system! And you're right -- that equipment will eventually need to be replaced, just as it must in any building.

    Concerning the fact that insulation generally (but not always) lasts longer than PV, I already conceded that point several times in my article.

  38. User avater GBA Editor
    Martin Holladay | | #38

    Response to Garth Sproule
    Garth,
    You wrote, "Is it not true that as the insulation level goes up, the potential for moisture problems increases because there is much less heat flux?"

    Yes. I wrote about that phenomenon here: How Risky Is Cold OSB Wall Sheathing?

    You wrote, "So the requirement for extreme airtightness varies with the amount of heat flow?"

    Actually, the likelihood of moisture accumulation varies with a great number of factors. In addition to the heat flow, these factors include:
    - the outdoor temperature
    - the indoor temperature
    - the indoor relative humidity
    - the pressure difference between the indoors and outdoors
    - the size of the hole and the rate of air flow
    - the type of materials exposed to these conditions.

    Most experts would NOT agree with you that well-insulated homes with 2 ach50 experience "excessive heat flux." (Of course, the R-value of the building assemblies as well as the airtightness are important factors in determining whether heat flux is "excessive.")

  39. User avater GBA Editor
    Martin Holladay | | #39

    More on off-grid inverters
    Mark Obmf,
    Your suggested solution is the same as mine. If a homeowner wants to buy a transfer switch, and an inverter designed to work off-grid, and to buy and maintain a large battery bank, then it's possible to have a PV system that works when the grid is down.

    I still maintain that my estimate for the extra cost for this system -- at least $5,000 more than a system without battery backup -- is about right.

    So we both agree. However, it's important to point out that very few California homeowners who have installed PV have forked over the $5,000 or more for such a system.

  40. Shane C | | #40

    Bang for Your Buck
    It seems to me that both the PH design and Net-zero design are attempting to achieve the same goal, albiet different paths of getting there. I think they compliment each other. I think the comparison between PV arrays or more insulation is apples to oranges. Insulation conserves Heat or cool air in the home. PV generates electricity. Heat savings are measured in BTUs, Electrical savings are measured in KWHs.
    All I know is Electric costs way more to heat a house than Hydronic, air, or wood.
    I think the net-enrgy input into a material produced is a valid consideration. Its like Ethanol. It takes 95k BTUs to produce to get a fuel that produces 65k BTUs. Its a negative return.
    Martin, you say "With a good energy modeling program, it’s easy to do the math; if the cellulose saves more than 160 kWh per year, it’s a good investment compared to PV."
    It would be safe to say that it costs more to produce electricity than it does to heat your home.
    When looking at dollars, I see people drivin around in cars that they bought for 40k-80k dollars. The value of new car drops as soon as you leave the lot. Is this a good investment? no.
    PV arrays and lots of insulation complement each other, the trick is finding the sweet spot for both.

    Also, Martin in your article you say a 1kwh system

  41. User avater GBA Editor
    Martin Holladay | | #41

    Response to Shane C
    Shane,
    You wrote, "All I know is electric costs way more to heat a house than hydronic, air, or wood."

    Actually, it depends. If you heat with electricity using an air-source heat pump (a ductless minisplit unit), the cost can be comparable to other fuels. That's why most U.S. Passivhaus buildings are being heated with electricity (usually using a ductless minisplit).

  42. Garth Sproule Zone 7B | | #42

    Heat Flux
    Martin
    You wrote "Most experts would NOT agree with you that well-insulated homes with 2 ach50 experience "excessive heat flux."
    Do you think that "most experts" believe that homes that are insulated to today's building code levels are considered "well-insulated"? I live in Zone B where a nominal R20 wall will meet code. This wall probably has a whole wall R value of less than R12 in our climate. I am no expert, but I think that R12 is waaay to little.

  43. Garth Sproule Zone 7B | | #43

    More
    I want to add that the nominal R20 walls that I referred to in my previous post, are probably very durable walls and will easily tolerate 2 or even higher ACH rates and probably higher indoor RH levels as well. But they are durable mainly due to the amount of energy flowing out through the walls. Am I wrong here?

  44. User avater GBA Editor
    Martin Holladay | | #44

    R-12 and R-20 walls
    Garth Sproule,
    I'm sorry if my previous posts weren't clear.

    This discussion in this blog refers to net-zero-energy houses and Passivhaus buildings. In making comparisons between these two design approaches, I'm working with the basic assumptions I listed in the second paragraph of the blog: "Both types of buildings aim to reduce the amount of energy used for space heating or cooling by designing envelopes with a low rate of air leakage, thick insulation, and high-performance windows."

    In general, cold-climate net-zero energy homes usually have R-20 foundation insulation, R-40 wall insulation, and R-60 ceiling insulation, along with triple-glazed windows. There are exceptions, of course, but this is the type of building I'm talking about.

    I wasn't talking about R-12 or R-20 walls. That's a whole different kettle of fish.

    I think that a net-zero-energy building with these specs can perform well (without structural damage) with 2 ach50, as long as the design is intelligent. Of course, 0.6 ach50 is better, and I admire builders who attain that goal. But I don't think there is much evidence that 1 ach50 buildings or 2 ach50 buildings, if intelligently designed, are suffering structural failures due to the fact that their air leakage rates are higher than 0.6 ach50.

  45. Green Mountain Realty | | #45

    Passivhaus
    We are a green home builder and an eco green realtor here in Asheville NC. We sell green homes and build custom green homes for clients and will always argue that it is far wiser to spend more money on super insulating and sealing the envelope more vs. installing a ton on Pv on the home to offset energy costs. Just our opinion as degreed engineers, and certified green home builders here in Asheville.

  46. Kevin Dickson | | #46

    Neighborhood PV vs. Large Scale Renewables
    Thanks Martin for another blog post that shakes up the conventional wisdom.

    I think you overlooked a few minor advantages of neighborhood PV:

    1. Transmission losses - - Although grid-tied PV needs a functioning grid, most of the PV kilowatthours generated at a PV-equipped house stay in the neighborhood and aren't diminished by transmission losses which are usually quoted at 30%.

    2. Autonomy - - Let's say you are building a spec house that you want to have low net energy usage. If you install PV, you have added value, but if instead you donate money to the local wind farm, there isn't currently a way for you or your buyer to recoup that money.

    3. Utility power outage avoidance - - Once PV market share reaches a crucial point, the local utility will see the potential of outage avoidance that distributed PV inherently has. At that point they will start providing that $5k upgrade you describe, because they can do it much cheaper. Utilities receive big rewards for reducing outages.

    In Colorado, Xcel is required by law to reach 30% renewable energy by 2020. Neighborhood PV is one of the top 3 ways this will happen, partly because it's easy and incremental compared to larger, more cost effective but cost intensive measures.

    Is a Renewable Energy Standard an artificial incentive? Of course it is, but until a carbon tax is implemented, there is no other incentive to reduce the use of fossil fuel.

  47. mike eliason | | #47

    ZEB walls
    martin,

    i put together a 1400 sf, 3 BR project for indianapolis that was designed to meet Passivhaus, which utilizes less insulation than the above mentioned R-20 foundation, R-40 wall , and R-60 roof. here in Seattle - it's possible to get away with even less (I realize we're not 'cold').

    migrating the project's climate to toronto while upping envelope to R-20/R-40/R-60, and verification just misses PH standard at 5.20kBTU/ft2a. a slight bump to R-28 under slab, and verification shows 4.69kBTU/ft2a.

    so i think, given the proper design, it might be possible to achieve PH in colder climates without significantly more insulation than the net zero approach mentioned. also, a larger multi-family project should be able to achieve PH in colder climates with even less insulation than a single family (again, if properly designed).

  48. User avater GBA Editor
    Martin Holladay | | #48

    Response to Kevin Dickson
    Kevin,
    Thanks for pointing out some advantages of distributed generation, especially PV. These are real advantages (although transmission losses are far lower than 30%) -- usually advantages to the utility, not the homeowner, although advantages none the less.

    If the day ever comes when local utilities subsidize the installation of large battery banks in private homes, as you predict may happen, this will not be an unalloyed day of joy for homeowners. Battery banks contain lead and acid; they regularly lose water vapor and need to be topped up with distilled water on a routine basis; they get corroded terminals which need to be cleaned and tightened; and they have to be replaced every 6 to 10 years.

    In short, these battery banks are a pain in the butt. I know that because I live with one.

  49. User avater GBA Editor
    Martin Holladay | | #49

    Response to Mike Eliason
    Mike,
    Thanks for sharing encouraging specs from your projects. That's good news.

    It's always good to hear of Passivhaus projects that don't cost too much money or require outlandish amounts of insulation. Let's hope that such projects become more common.

  50. Greg Duncan | | #50

    Purpose of PV?
    What is the purpose of the grid-tied PV for most projects? Is it a financial investment or is it used as an offset for moral or marketing reasons?

  51. mike eliason | | #51

    martin,
    we're also interested

    martin,
    we're also interested in more affordable PH buildings, and our approach relies on better glazing and less insulation. we'd like to see more of those as well.

    i worked for an architecture firm in germany that did low-energy buildings without any insulation in walls, and sometimes roof (utilizing thermal storage, winter gardens, process energy and air collectors) so i know it can be done - it just takes the proper planning and accurate modeling.

    greg,
    is there anywhere in the US that PVs could be considered a financial investment, at least at the residential scale?

  52. User avater GBA Editor
    Martin Holladay | | #52

    Response to Greg Duncan
    Greg,
    You asked, "What is the purpose of the grid-tied PV for most projects?"

    Good question; to get an answer, you would have to interview owners of grid-tied PV systems. I imagine that you will get a range of answers, including:
    - A desire to lower the environmental impact of a home's electricity consumption;
    - A concern about global warming and carbon emissions;
    - A response to worries about future energy price increases;
    - In some cases, the desire to display a "green badge" that is visible to the neighbors.

  53. markobmf | | #53

    Response to Greg Duncan
    Greg,

    I agree with each of Martin's points and think it depends on the person using grid tie. I've had to talk a few clients out of PV because the resources were wasted and implemented, solar electric would have little impact. Others who do grid tie love the toy factor. Here in the Bay area, there's money and there's a reverence for whatever iteration of the green movements are currently circulating so people don't always make decisions based on the proper analysis.

    But I assure you, in many instances it makes sense to smart people, who make smart decisions in many aspects of their lives in addition to home energy. In most parts of the country, admittedly, solar electric is a waste versus more meaningful and value driven home energy improvements. However, here in the bay area, a fairly moderate insulation and air seal retrofit very often negates the need to add any BTU's during the heating season and we really don't have much of a need for AC either in our mild climate. However, I have a swimming pool. Yes, I should just fill the sucker in to be truly responsible. But I like my pool and with a 8 year payback for solar thermal and electric based on my particular circumstance, it makes sense to me, not to mention the domestic hot water I get in the process which truly is a necessity. The way it works here in CA, my pool minus solar puts me into tier 3 electricity rates in the summer, and when the PV is giving ooodles of watts during those months I now go back down to tier 1 baseline. This is the reason for the awesome payback. Not to mention, I live on the hayward fault, and appreciate a backup option for a loss of power.

    Should tax incentives continue for residential PV? Perhaps, if you own a pool since in evaluating numerous clients circumstances, this is the most common instance where PV makes sense only after a variable speed efficient pump upgrade. However, I'd much rather see someone upgrade a cooling system installed in 1977 with the money they'd be spending on PV and see them get incentives to do so. Here in California, we would all be better served if incentives were better tailored to more meaningful retrofits of residences and commercial buildings. Governments clouded by politics and self interest don't always pass legislation that makes sense but it's usually spun to make it seem so. As a result, solar electric is hot here and will be for the foreseeable future.

    -Mark Costa

  54. User avater GBA Editor
    Martin Holladay | | #54

    Response to Mark Costa
    Mark,
    I completely agree with your conclusion: "Here in California, we would all be better served if incentives were better tailored to more meaningful retrofits of residences and commercial buildings."

    In the meantime, utility ratepayers and taxpayers will continue to subsidize the installation of renewable-energy hardware in the homes of well-off California homeowners who are worried about the expense of running their swimming-pool pumps.

  55. User avater
    Jesse Thompson | | #55

    Passive Solar + PH
    Martin,

    What we've seen (mike please verify) is that the prime difference between Passivhaus projects that have "outlandish" amounts of insulation and those that don't is how well they are able to utilize passive solar.

    Remodels, urban single family homes and houses with special views in the "wrong" direction often have to make up for the lack of a good supply of free heat through the windows with extra insulation.

    GO Logic's passivhaus is a prime example in my mind of this, they really focused on the passive solar, and they were able to build a passivhaus affordably and with reasonable insulation levels in a 7,500 HDD climate: https://www.greenbuildingadvisor.com/blogs/dept/green-building-news/cohousing-community-readies-construction

    Jesse Thompson
    Kaplan Thompson Architects

  56. User avater GBA Editor
    Martin Holladay | | #56

    Thanks, Jesse
    Jesse,
    Yes, Go Logic's prototype is a great (and handsome) example of Passivhaus design.

    A quick Web search shows that the house has R-40 walls, an R-80 roof, and triple-glazed windows. I haven't yet been able to find information on the building's foundation insulation.

  57. User avater
    Jesse Thompson | | #57

    FPS foundation
    Martin,

    Alan Gibson from GO Logic wrote an article in April 2010 for JLC describing his foundation techniques, I think his photos and info were from this project: http://www.jlconline.com/cgi-bin/jlconline.storefront/4d2b35600bb6dea927170a32100a063e/Product/View/1004sup

  58. Greg Duncan | | #58

    thanks for the responses
    Mark and Martin, thanks for the responses. I don't know how California can afford to subsidize private swimming pools. The whole issue of subsidies should be its own blog post.

    Where I live, in Brooklyn, it is often impossible to install enough PV to achieve Net Zero. For example, the building I live in is a five-story brownstone with party walls. It is built to the maximum height allowed by zoning and PV panels are not allowed above the maximum height. Even if it were permitted, the size of the array would be impractical. However, a near Passive House retrofit -- or a similar new construction meeting Passive House standards -- would be easy to achieve. In Manhattan, of course, it is even more difficult to achieve Net Zero because of the taller buildings.

  59. User avater GBA Editor
    Martin Holladay | | #59

    Response to Greg Duncan
    Greg,
    Your example supports my point that many residential buildings aren't suitable for PV.

    Following the Passivhaus standard may, or may not, be the most cost-effective way to proceed in your case. In many parts of the country, a more cost-effective approach is to use the net-zero-energy design approach -- and then leave off the PV array.

  60. mike eliason | | #60

    passive solar + passivhaus
    jesse,

    this is in fact what we are noticing. those that really spend time dialing in the right glazing, as well as testing window sizing/orientation and really focus on strong passive solar strategies are utilizing about 35-60% the amount of insulation (depends on climate)

    also, we're also finding that with the right windows/glazing, you can get away with more windows on the north than you would in a typical passive solar (or even passivhaus).

    for me, this is the greatest benefit of PHPP - that we can quickly test how to best reduce insulation - especially the petroleum-based stuff.

    btw, what prevents the GO Logic from overheating in summer?

  61. User avater
    Jesse Thompson | | #61

    GO Logic
    Mike, that lines up with what I remember the folks from PHI saying at NESEA years ago, that all the sun we get in the northeast should make up for how much colder it is than Germany. You in the Pacific NW, however...

    About the overheating on the GO Logic prototype, I'll have to ask them, I can't figure it out either.

  62. Aj Builder, Upstate NY Zone 6a | | #62

    Sharing PV solar siting locations
    Great posts lately, more more more. I have had an idea lately that would solve a previous posters dilemma with siting his PV arrays. We should start to share quality siting locations. For instance, on my short dead end street we have one home that has a 5KW array. And we have darn few homes of about 20 that could duplicate his great exposure to the south. Why are we not sharing our roofs and yards I ask? We should be. We should in my town which has many huge school rooftops be allocating our public solar spaces to those that would use them.

  63. Aj Builder, Upstate NY Zone 6a | | #63

    The smarts of the Germans
    What are we doing here in the USA? France went almost all in nuclear after the 70s oil shock. Now Germany is going like all out Solar. Ten years from now they may be completely solar and wind. Where will we be? 5%?

    The Germans are smart go getters. When they put their minds to a task. fo get bout it. Done.

    Passive House, fully solar. I imagine gardens of self sufficient food sources is next on their list.

    Germans are not waiting for the disaster of shortages. They are going to be sitting pretty in 2020.

    Let's get in on the act here in the USA and show them how it is done, the USA way. Go solar and go Passive House and go natural built all in.

  64. mike eliason | | #64

    sunny NW!!
    jesse,

    i think i would rather have a lot more sun and be freezing, than 6 months of gray drizzle and milder temps. although that varies depending on how long it's been since i've seen the sun.

    but that better glazing/less insulation strategy works in toronto, indy and urbana - with significantly less under slab insulation than other PH projects we've seen. i don't really have any zone 6 or zone 7 climate to test that in PHPP.

    j
    that larger percentage is for here and similarly milder regions. though we noticed with the project in indy that we weren't far above code minimum and still able to hit PH space heating numbers.

    and yes, it definitely comes down to an 'integrated design' approach. i wonder on some level how many PH projects aren't sited/massed/designed well, and if this is one of the reasons for the 'outlandish' amounts of insulation. there is also tons of room for improvement in the NA glazing industry.

  65. J Chesnut | | #65

    response to post #60
    I haven't spend enough time with PHPP to speak authoritatively about how much more the glazing/ insulation proportions can be optimized (I have to think any PH designer engages this aspect to some extent) but based on the work I have done in MN (where we have great annual solar insolation amounts) a 35-60% reduction in the amount of insulation seems optimistic. This depends of course on how bad a baseline you start with.

    Some of the PH design work I have been involved with has had relatively ideal site/circumstances where we were able to eliminate or radically reduce windows on the north side and we've used/modelled with Optiwin's with 60+% SHGC and still come out with "relatively thick" insulation packages.

    Per my earlier post (#26) a change in square footage seems to make a significant difference in the insulation required to meet the standard speaking to the criticism that the standard doesn't adequately dissuade from building larger structures.

    - retracted comment -

  66. Greg Duncan | | #66

    Response to Martin
    "Following the Passivhaus standard may, or may not, be the most cost-effective way to proceed in your case. In many parts of the country, a more cost-effective approach is to use the net-zero-energy design approach -- and then leave off the PV array."

    What is a net-zero-energy design approach if you leave off the PV array? Do you mean using wind turbines or purchasing renewable energy from a utility?

    In my case, the dollar amount difference between a Passive House vs. a code-compliant building is trivial. If you have triple-glazed windows for acoustic performance, the difference is close to $0. For a building that will sell for $750/SF, I'm not concerned about the cost of a few inches of foam.

  67. User avater GBA Editor
    Martin Holladay | | #67

    Understanding the net-zero-energy approach to design
    Greg,
    Clearly, if you are talking about a building in the $750 per square foot range, your concept of cost-effectiveness is very different from that of most U.S. home builders. I'm glad that you can afford to achieve the Passivhaus standard. You are making the right decision.

    You asked, "What is a net-zero-energy design approach if you leave off the PV array?" The approach I am talking about was described in the section of the blog under the subhead, "Advantages of the net-zero-energy approach." The design approach requires the cost-effectiveness of each incremental building envelope measure to be compared to the cost-effectiveness of a PV array. Once the PV cost limit is reached, the designer refrains from further building envelope improvements.

    This design approach can be used even if the owner decides not to install a PV array or a wind turbine. The approach will result in the most cost-effective building envelope -- as long as the owner remembers NOT to buy a PV array. (PV electricity is expensive, so PV is not a good investment.)

    This approach is usually cheaper than adhering to the Passivhaus standard, because there is no reason to pay for measures that aren't cost-effective. Trying to achieve the 15 kWh/m²/year limit in a cold climate often results in measures that aren't cost-effective; the standard sometimes forces the building owner to pay for insulation that makes no sense.

  68. J Chesnut | | #68

    #66 continued
    I didn't consider the fact that Net Zero then did not necessarily mean making the investment in the PV and actually meeting a Net Zero Energy performance goal. I think naming it Net-Zero-Energy is a source of confusion.

    Martin have you seen a PHI graph that showed the cost optimization argument for PassivHaus (for the conditions in Germany I presume)? As I heard the argument PH requirements were in part based on the cost optimization achieved from the heat being delivered through the ventilation equipment and the boiler/furnace dropping out of the picture freeing up money for envelope improvements and better windows.

    I think the ideal solution is, maybe going back to the state of PH for the mid-European context, a set energy performance goal based on regional cost-effectiveness.

    The fact that Net Zero isn't tied to a required performance goal makes me wonder what the range of performance is within this approach.

  69. User avater GBA Editor
    Martin Holladay | | #69

    Response to J Chesnut
    J,
    In my blog, I explained how most net-zero-energy home designers go about optimizing investments in building envelope upgrades.

    When it came time to making recommendations to readers, I suggested that the net-zero-energy design approach is very logical. I recommend following it, with one variation: don't buy the rooftop PV.

    This is just my recommendation. Plenty of people seem willing to shell out thousands of dollars for rooftop PV systems, and these systems are generating electricity with almost no carbon footprint. That's good. But it's not particularly cost-effective.

    Anyone who follows my recommendations will save money compared to a neighbor who builds a net-zero-energy house.

    THE PHI graph showing that homes designed to meet the Passivhaus standard are at the bottom of the cost-effectiveness curve has been widely reprinted and I am familiar with it. However, I believe that this graph does not accurately reflect the cost-effectiveness of measures used to meet the Passivhaus standard.

    There are a lot of climates in this world, and different measures will be cost-effective in different climates. I propose the following:
    - In many climates, ventilation systems other than HRVs are more cost effective than HRVs (which are mandated by the Passivhaus standard).
    - In many climates, the most cost-effective insulation results in space heating loads that are higher than 15 kWh/m²/year.

    Making heroic efforts to achieve 15 kWh/m²/year makes no sense if you are spending thousands of dollars just to save $20 or $40 a year. To call a spade a spade, 15 kWh/m²/year is arbitrary. It doesn't represent calculated cost-effectiveness.

    Finally, most Passivhaus homes in the U.S. have HVAC equipment that costs more than simple non-Passivhaus homes. So I don't believe that "eliminating the boiler" is saving HVAC installation dollars.

  70. J Chesnut | | #70

    I see, I misunderstood your
    I see, I misunderstood your recommendation as an aspect of the Net-Zero approach in practice.
    Thanks for your clarification.

    THE PHI graph showing that homes designed to meet the Passivhaus standard are at the bottom of the cost-effectiveness curve has been widely reprinted and I am familiar with it. However, I believe that this graph does not accurately reflect the cost-effectiveness of measures used to meet the Passivhaus standard.

    The graph I saw was in German. I assumed it was an early publication making the case for PH to the German building professionals before PH was introduced to the States. I have been assuming that PH is cost-effective for the German climate and market. In your response I assume you are talking about the American market or are you saying you don't think it is even cost effective in Germany?

    There are a lot of climates in this world, and different measures will be cost-effective in different climates. I propose the following:
    - In many climates, ventilation systems other than HRVs are more cost effective than HRVs (which are mandated by the Passivhaus standard).
    - In many climates, the most cost-effective insulation results in space heating loads that are higher than 15 kWh/m²/year.

    My context is on cold/ very cold climates. My understanding is that HRVs are cost effective for this climate because of the extreme low temperatures in winter. Would you agree?

  71. User avater GBA Editor
    Martin Holladay | | #71

    On cost-effectiveness in Germany and HRVs
    J,
    I don't know enough about German construction costs to know whether Passivhaus insulation levels are the most cost-effective way to build in Germany. But I suspect that it's possible (even in Germany) to build a cheaper, more cost-effective house by ignoring some Passivhaus requirements.

    Heat-recovery ventilation systems are expensive to install. There are a lot of variables in the calculations to determine when the investment in an HRV makes economic sense. In very cold climates, the investment can eventually pay off through energy savings.

    I am intrigued by the ventilation system experiments that Carter Scott is undertaking in Massachusetts. He has designed several houses using a single Panasonic WhisperGreen fan as a whole-house exhaust ventilation system or a whole-house supply ventilation system. The efficacy of such systems depends on good ductwork to introduce the fresh air where it does the most good, along with passive grilles to allow air to move in the house from pressurized rooms to adjacent rooms.

    There are two good aspects to these systems: low cost (the fan costs about $140) and very low energy use (13 watts).

  72. 5C8rvfuWev | | #72

    Carter Scott houses?
    Martin, are the houses you mention the ZNE homes w/mini-split heat pumps that have been discussed before? I've seen discussions of the mini-split application here, but not the Panasonic application. Do you have a link? I did a quick google and there are a lot of overviews for the awards, etc., but I saw nothing re ventilation.

    Thanks, Joe

  73. User avater GBA Editor
    Martin Holladay | | #73

    Response to Joe -- questions about Carter Scott homes
    Joe,
    Carter Scott is holding his cards close to his chest concerning the details of his ducting and grilles, because he wants to present his ventilation methods at an upcoming conference. I certainly respect his desire to release the information in the manner he has chosen, and I look forward to the day that he shares these details fully.

    Yes, Carter Scott has heated his homes with ductless minisplit units. Needless to say, these heating systems are not ventilating units.

    For anyone who is interested, here is Carter Scott's Web site: http://www.transformations-inc.us

  74. 5C8rvfuWev | | #74

    drum roll
    thanks, Martin. I'll wait. Patiently.

    Joe

  75. User avater
    Jesse Thompson | | #75

    NESEA Building Energy
    Martin,

    Is that what Carter is presenting at NESEA Building Energy this spring? Hope so, I've enjoyed their presentations greatly other years: http://www.nesea.org/be11/trackoverview/#t5959

    Best conference out there folks, don't miss it if you're close...

  76. User avater GBA Editor
    Martin Holladay | | #76

    Response to Jesse
    Jesse,
    I'm not sure which conference will feature Carter Scott.

  77. Paul Eldrenkamp | | #77

    Regardless of what you think of the Passive House standard
    ... its introduction into the US market has completely changed the conversation regarding what constitutes enough insulation in a home, how tight it should be, and how much energy it should use. Passive House may not, in the end, provide all the right answers, but it certainly asks the right questions. For this alone it deserves our serious consideration and respect.

  78. Roger Lin | | #78

    I love this discussion. I
    I love this discussion. I also can't help feeling that some of the arguments are like splitting hair. I believe the results of both building systems are air-tight and very well insulated and is either very close to net-zero or is actually net-zero. I meant you won't reasonably build a net zero energy home without a certain level of air-tightness and insulation. So like Martin said in the original article, they are not so different.

    I can think of perhaps the two approaches differ in different climate zones and house size. In some regions, building a passive house really does not require much more insulation than code and I think there are probably some warmer places where it doesn't make sense to insulate under the slab. In those regions, building a PH is basically building tighter and swap out the giant HVAC system for a Mr. Slim. I think that's where PH truely shines in a financial sense.

    Another thing that surprised me when working on PHPP was that as the size of a house increased, it was actually easier to get the numbers under PHPP requirements. Presumably, the house is more energy efficient. I don't know if that is true with a Net Zero approach.

    Finally, whether it is net zero or PH, people talk about numbers with the premise of "pay back". Payback is a tricky topic of discussion. I think this is mainly because these investments whether in PV or extra insulation actually have a payback. Why don't people ever ask the payback on their sub-zero refrigerator or giant screen TV?

  79. Mark I. | | #79

    Tear down and rebuild
    A few responses to this blog talk about tearing down an existing home and building new to avoid being constrained in the application of PH standards. No rebuttal was given by anyone about the embodied energy inherent to such a wasteful strategy of property abandonment. Unless someone can convince me with data that suggests otherwise, the greener perspective is to improve on the home you already have.

  80. User avater GBA Editor
    Martin Holladay | | #80

    Response to Paul Eldrenkamp
    Paul,
    I agree with you completely. The Passivhaus standard "has completely changed the conversation regarding what constitutes enough insulation in a home, how tight it should be, and how much energy it should use. Passive House may not, in the end, provide all the right answers, but it certainly asks the right questions."

    Interestingly, most of these "right questions" (and a high percentage of right answers) were also provided in 1985 by R. Ned Nisson and Gautam Dutt in their landmark book, The Superinsulated Home Book.

    For whatever reason, Nisson and Dutt's book didn't inspire many builders. The Passivhaus standard seems to be finally beginning to do the trick.

  81. User avater GBA Editor
    Martin Holladay | | #81

    The small-size penalty
    Roger Lin,
    You wrote, Another thing that surprised me when working on PHPP was that as the size of a house increased, it was actually easier to get the numbers under PHPP requirements."

    This small-size penalty is due to the fact that that the Passivhaus standard has a 15 kWh/m²/year heating energy limit. Whenever energy limits are expressed per unit of area, it's easier to meet the goal with a large house, which has less surface area per square foot than a small house.

    Many people have criticized the small-size penalty in the Passivhaus standard. Some observers, including me, note that it makes more sense for each person to have an energy budget (in kWh per year or BTU per year) -- rather than giving a higher energy budget to those who choose to build a big house and a smaller energy budget to those who choose to build a small house.

  82. User avater GBA Editor
    Martin Holladay | | #82

    Response to Mark I. - tearing down vs. retrofitting
    Mark I.,
    You are worried about demolishing existing houses because of "the embodied energy inherent to such a wasteful strategy of property abandonment."

    I've talked to builders involved in Passivhaus retrofit jobs, and I seriously doubt that there are any embodied energy savings in taking the retrofit path compared to starting with a bulldozer. On two different projects, builders have told me flat-out that the bulldozer option would have been cheaper.

    Of course, taking the more expensive path is not always an indication that the path doesn't make environmental sense. But in this case, I think it's hard to justify the retrofit approach, because the Passivhaus standard is so demanding.

    After a lot of careful demolition, you are usually left with a foundation and some framing. If the foundation is damp, as it often is, it will require expensive measures to make it dry. If the framing doesn't meet modern structural requirements, and it often doesn't, the framing will have to be beefed up.

    Everything else is usually new: new wiring, new plumbing, new HVAC, new insulation (of course), new siding, new roofing, and new windows. All of those new materials have embodied energy.

    If you start with a bulldozer, you have a clean building site, and your air sealing task is infinitely easier. You might even be able to re-use the foundation.

    There's not that much embodied energy in framing wood in any case.

  83. StevenL | | #83

    passive House or net zero
    "In Europe, builders interested in energy efficiency are gravitating to the Passivhaus standard..Meanwhile, American researchers — and a few American builders — have developed a fascination with the idea of the net-zero-energy house.."

    Look .... the European Union is about 27 countries and the Americas are about 35 countries OK? In Germany and Scandinavia there is a lot of interests in PH but that means less than one percent of the new housing stock is going for that standard (hard to find figures) and net zero has followers in all of Europe.
    In short the USA is way, way, waaaaay behind in construction tech -- you have LEED which is a very poor multi level marketing rip off of BRE(EAM).

    Apart from the "strawman" opening this is a good article.

  84. User avater GBA Editor
    Martin Holladay | | #84

    Response to Steven L
    Steven L,
    I certainly agree with you that most American builders have nothing to brag about when it comes to energy efficiency. My intent was never to beat the drum for American superiority -- quite the contrary.

    Far more Passivhaus buildings have been built in Europe than in the U.S. The market penetration of Passivhaus buildings is particularly high in Austria and Germany, where they now make up a significant percentage of new residential construction. (I'm not sure of the most recent data on German housing starts, but in Austria, Passivhaus buildings now represent 25% of new construction; see http://www.oesterreichhaus.at/en/ig-passivhaus .)

    Of course, the vast majority of Europeans live in older buildings, not Passivhaus buildings; the same can be said for Americans.

  85. Chris Vlcek | | #85

    PHPP energy modelling
    One of the huge benefits of the Passive House approach is in the Passive House Planning Package (PHPP) itself. It is a comprehensive spreadsheet program that has been rigorously developed & tested in Europe. It does take considerable effort to wrap one's head around, but as Marc R. pointed out, there is an 'ah ha' appreciation for the entire building system that results. The energy analysis will impact design decisions positively, whether or not the Passive House standards are achieved. The software cost is quite low in order to make it available. But I do hope that is becomes integrated with a more user-friendly interface, so it will have a greater potential for users to make conscious energy-use decisions easier in the design phase.

  86. User avater GBA Editor
    Martin Holladay | | #86

    On PHPP
    Chris Vlcek,
    I agree; in a previous blog, I noted that the "PHPP software is a subtle, accurate, and incredibly useful design tool."

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