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Very Recent Passivhaus Article

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I am a big fan of BSC and Passivhaus.......
This is very confusing for me.....
I would love to see the two work together......share knowledge..challenge each other
This is not a contest.
I think the solution is somewhere in the middle... in between BSC and Passivhaus

Asked by John Brooks
Posted Sep 13, 2009 9:35 PM ET


24 Answers

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Thanks for providing a link to John Straube's recent article.

Here is one of Straube's most interesting observations: "Given the standard rates of ventilation and the occurrence of design temperatures of 0 °F (-18 °C) or lower in parts of the United States and Canada, increasing ventilation rates to allow the use of ventilation air as the only means of heating is at best highly restrictive to a design and at worst simply impractical and antithetical to a low-energy house."

I was also interested in Straube's listing of particularly efficient HVAC appliances commonly used in Building America homes:
"The smallest available standard condensing natural gas two-stage furnace with an ECM motor (e.g. Goodman GMH95), a condensing sealed-combustion hotwater heater (such as an AO Smith Vertex, Navien, Quietside, or Viessman VitoDens), an efficient HRV (such as a Fantech VHR704 with an AirCycler controller), Energy Star appliances and all CFL lighting."

Using these appliances, Straube notes that a Building America house uses more energy than a Passivhaus building — but not a lot more — at a lower capital cost. "As can be seen, the source energy consumption, at 158 kWh/m2/yr, exceeds the Passivhaus requirement of 120 kWh/m2/yr. However, for a further investment of under $16,000, a 2 kW PV array can be installed that reduces primary energy consumption to meet the arbitrary (and laudable) Passivhaus energy target. The PV was chosen in this case as it was the least cost approach to achieving the target."

Answered by Martin Holladay, GBA Advisor
Posted Sep 14, 2009 4:05 AM ET


It is a good article.... and I realize that we can not just transplant Passivhaus to North America.
Reality is good.
Maybe I can learn to love PV.

Answered by John Brooks
Posted Sep 14, 2009 7:01 AM ET


It's important to keep in mind that this article is only evaluating the Passivehouse standard in a limited set of climate conditions: DOE Zone 5 and colder (New England, upper mid-west, mountain states and Canada).

If you move a well-sealed R-40 12" wall cellulose house from Maine or Vermont to Philadelphia, the peak heat loss and btu/ft2/yr drop by about 40%. The building behavior and construction tactics in the colder states is very different from the places where most americans live.

Answered by Jesse Thompson
Posted Sep 14, 2009 9:38 AM ET


We do need targets that are climate specific....
As mentioned in another thread.......Sweden has different zones and different targets
In Addition to Extreme Cold....
It is impossible to passive cool in some climates.

Answered by John Brooks
Posted Sep 14, 2009 10:24 AM ET


I'm not sure we need targets that are climate specific, but we do need construction techniques that are climate specific.

The atmosphere doesn't give you a pass to emit more CO2 just because you live in a colder place...

Answered by Jesse Thompson
Posted Sep 14, 2009 12:40 PM ET


I heartily argee that increasing the volume of supply air used to heat a house above the minimum required for health and wellbeing is not a good idea. In Europe 8 litres per person per second (that is 30 m3 per person per hr) is a sensible limit for maintaining indoor relative humidity at suitable levels. This standard of ventialtion compared to other European standards tends to be on the low side.

The suggestion that "so many PH have been ventilated at much higher rates that the PHPP 2007 warns users not to over-ventilate" is a little miss leading - it is not that many PassivHaus homes have been ventilated at higher rates, rather - as I understand it - it is that the PassivHaus standard set a lower ventilation rate than was the norm in Germany at that time when the PassivHaus concept was first developed (in 1991). In order to avoid over ventialtion and to help ensure an adequate indoor relative humidity the notification was introduced to PHPP. (In the UK our regulations still require "over ventilation" as a result of outmoded concerns relating to condensation risk - PassivHaus design results in high surface temperatures which mitigate the risk of condensation.)

I guess the question is - does ASHRAE actaully ventilate appropriately? Research into ventilation systems is one of the key area that Dr Fiest is now reviewing - the focus here is comfort rather than just energy saving. It maybe that it does in some cold climates fresh air provision could be reduced to ensure that the RH does not fall below levels of comfort. Does ASHRAE address VOCs in a appropriate manner? Generally, from a European perspective, I would tend to think that this ASHRAE figure is a bit too low.

In a PassivHaus the air leakage rate of 0.6 ach at 50pa within a dwelling addresses hygrothermal problems that have been recognised by the PassivHaus Institut and in Canada (Canadian research suggests an air leakage that is equivalent to less than 0.6 m3 per m2 at 50pa.) Though the two unit are not equivalent they both arrive at a similar zone for the performance target.

How has Straube measured his kWh/m2/yr, has he used the net internal area using the same definitions as used by the PassivHaus Institut? If not then the units can not really be compared. Also have the same primary energy factors been used in both cases? (Straube does not adjust the 120 to reflect his tweaked primary energy factors.) As ever the devil is in the detail. Best Practice PassivHaus achieves less than 70 kWh/m2/yr primary energy use.

Whilst I seek to maintain an open but critical mind you will no doubt apreciate that I have questioned the PassivHaus standard intently and concluded that it is the best standard that I have come accross to date, I hope that my comments are understood in the constructive manner that they is intended.


Answered by Mark Siddall
Posted Sep 16, 2009 2:55 PM ET


Mark Siddall,
I have enjoyed your comments and your perspective.

I have some comments about durability....

Quoting from John Straube's article:
"There is essentially no discussion of durability and little on IAQ in the PH
standard: the effect on the durability of exterior building
materials when the insulation levels rise to the levels used
is not discussed, nor is the need for heightened rain
control requirements, although damaging air leakage
condensation is likely controlled by the very low
acceptable air leakage."

I am only a confused Architect...not a Scientist or someone with Passivhaus training.
As merely an observerver looking at European construction by internet....
I have noticed that European construction does not at first glance APPEAR to have the
"heightened rain control" that we are used to seeing.

It is not in a form that is most familiar to us.
State of the Art North American construction is dominated by housewraps,rigid insulation and peel and stick.....not so in Europe.

What I see in European construction is tongue&groove and shiplap construction....
ventilated claddings and Metal pans for window sills ...
and almost never housewrap, foil-faced polyiso or thick XPS.

It seems to me that "they"(the Euros) employ a different strategy.
If it does get wet ...IT has a better chance of drying than most North American Construction.

I'm glad that John acknowledges the advantage of "the very low acceptable air leakage"

Answered by John Brooks
Posted Sep 16, 2009 4:42 PM ET


Hi John,
Picking up on your first point - if John Straube can read German he may enjoy the PassivHaus Instituts Protokolband documents - they look VERY closely at IAQ, many aspects of energy performance, occupant behaviour etc. - for new build and retrofit.

What do you mean by "heightened rain control"? Rainscreen and the like? Such concepts are common in the UK/Europe. Please expand upon what you mean - thanks.

Timber frame does use external house wrap and internal air barriers /vapour retarders. Tape systems are also available - I presume that this is what you mean by "peel and stick." T&G is not frequently used - in the UK at least - due to cost but this approach comes into its own in high performance buildings by providing a suitable wind/air barrier (depentent upon location.) Where butt jointed boards are used as the air barrier - which again is rarely - tapes are used to seal the joint and ensure that the building is tight whilst the rigid board protects against site abuse from a neglectful sparky or plumber.

Over here there are limits to the thickness of the XPS that you can get [about 100mm] after that you have to use multiple layers which is expensive - due to labour and material costs. Using the 1/3rd, 2/3rd rule - if additional external layers of XPS are to be avoided - this imposes limits to the thermal performance that can be achieved by adding insulation internally. European research warns against the use of external air barriers due to condensation risk - though do I recognise that this was not based upon using XPS as the air barrier.


Answered by Mark Siddall
Posted Sep 17, 2009 12:11 PM ET


On the subject of using XPS. In Europe there are also concerns about the Global Warming Potential of foam insulations (this is why BREEAM, the UKs version of LEED, required that the GWP is less than 5). I understand that in the USA the regulation of the GWP of gasses lags someway behind Europe at this time. There is an illumentating paper on the issue of the GWP of insulants by geographer and climatologist Danny Harvey:


Answered by Mark Siddall
Posted Sep 17, 2009 1:32 PM ET


Concerning "Heightened rain control" I assume that John Straube is saying that we need to take extra precautions with rain contol as we use more and more insulation.

I may have been off base with my perception of what is common "over there"....
here are some examples of what I have looked at:


What I think I see in examples such as above... are assemblies that can dry if they do get wet.
Some of the assemblies in the US have foil faced products on the outside and offer little chance of drying to the outside.

It looks like Both BSC and Passivhaus promote rainscreen and ventilated cladding.

Answered by John Brooks
Posted Sep 17, 2009 2:34 PM ET


As an energy performance standard Passivhaus does not "promote" rainscreen. Rainscreen is widely used in Europe anyway, especially with regard to timber frame. With masonry external wall insulation with a render finish is reasonably common in mainland Europe, in the UK, as Belgium, masonry cavity wall is prevalent - sadly in the UK partial fill cavities tend to be the norm, but full fill is recomended by low energy advocates.

Pavatex is not commonly used, though it has many benefits. I would tend go with protecting materials as best as possible and then if they get wet letting them dry. As I understand it the foils are there to reduce the off gassing of the insulation, which degrades performance over time, rather than controlling moisture - i.e. XPS is already water resistant. The risk of trapping moisture behind the foils, and capillary action at joints wicking moisture towards a timber frame is not a good one.


Answered by Mark Siddall
Posted Sep 18, 2009 2:26 AM ET


I have been wearing my American "Single Family -Stick Frame" Glasses
Are most Passivhauses Masonry construction?
Are most Multi Family?

Answered by John Brooks
Posted Sep 18, 2009 7:50 AM ET


I disagree with John Straub's comparison of ventilation rates between Passive House recommendations and ASHRAE 62.2. First, let's dig down into ASHRAE 62.2. Mr. Straub quotes the ASHRAE standard as "7.5 cfm/person+0.01 cfm/ft2." This is not exactly correct. The actual standard calls for:

0.03cfm/ft2 - 0.02cfm/ft2 ASSUMED INFILTRATION + 7.5cfm/person .

0.02cfm/ft2 assumed infiltration works out to be roughly 3.0ACH50, FIVE TIMES the level of air-tightness required in a Passive House. At ACTUAL Passive House air changes rates of no more than 0.60ACH50, the assumed infiltration should be changed to 0.004cfm/ft2. Thus, for a theoretical 2,000ft2 Passive House, the ASHRAE 62.2 ventilation rate would be:

(0.03-0.004)*2000 + 7.5*4 = 82cfm

This compares very favorably to Mr. Straub's quoted "Passive House" ventilation rate of 80cfm for the theoretical house. I would say that ASHRAE 62.2 and Passive House are in near-perfect agreement on ventilation rates!

Answered by John Semmelhack
Posted Sep 18, 2009 2:42 PM ET


Regarding Mr. Straub's writing on supplying heating through the ventilation air in Passive Houses, we should dig a little further into the history of the development of Passive House. Passive House was developed for the German climates as an exercise in both very low energy buildings AND construction economy. Dr. Feist found that when he increased the performance of the building shell to a certain level, he would be able to deliver all of the needed heat via the ventilation air supply, thereby eliminating the need for a separate heating distribution system (radiators are common in German buildings). Also, since the peak heat demand is so low, the heat could be pulled from the energy efficient water heater, thereby saving the purchase of a boiler or furnace. This is called "Tunneling through the cost barrier" (see http://www.natcap.org/sitepages/pid61.php). This clever bit of design is only economical because of Germany's climate - a relatively high winter design temperature combined with relatively high heating degree days.

Mr. Straub is correct to point out that this technique is not economical in many of our climates for small residential buildings. However, as far as I know, Dr. Feist is not dogmatic on the heating via supply air issue (except, perhaps in German and similar climates). He acknowledges that different heating systems will be more appropriate in certain locations.

Answered by John Semmelhack
Posted Sep 18, 2009 3:04 PM ET


John Semmelhack,
Thanks for the clarification on the ASHRAE standard.

Dr. Fiest is certainly not dogmatic about heating strategies. The most economic method may be heating via fresh air, in a central European climate, but other strategies can be employed and are not frowned upon. Watch these videos to hear from Dr. Fiest himself.


Answered by Mark Siddall
Posted Sep 19, 2009 8:40 AM ET


Mark Siddall,
The Dr. Feist interviews are Very, Very Good.
Thank you for taking time to share your Passivhaus knowledge and resources.

Answered by John Brooks
Posted Sep 19, 2009 11:20 AM ET


Some other corrections that need to be made to John Straub's article - he states, "The floor area is measured by total conditioned area inside the cladding. The basement is only considered at 60% of its actual area because it is not considered living space in the German standards. Why, I can't understand; perhaps Germans don't build basements you can live in like a modern basement in North America." This is not correct.

The PHPP 2007 states that "The treated floor area is calculated based on the German Floor Area Ordinance...It refers to the floor area which is inside the thermal envelope." In North American terms, this means the treated floor area should be measured drywall to drywall, not outside cladding to outside cladding. In addition, the PHPP goes on to discuss other parts of the inside of buildings that are NOT to be considered part of the treated floor area: stairs, double height spaces, mechanical chases, large columns, and so on.

Regarding basements, my take is that if the basement is finished as a living space, then it would counted at 100%. If it's an unfinished basement inside the thermal envelope, it should be counted as 60%.

This is important when we look back, for example, at the primary energy comparison given in the article. The theoretical 2,000sf house needs to have at least 160sf of floor area backed out of the calculations (roughly 130sf for the exterior walls and 30sf for a stairway). This would lead to a revised primary energy result of 171.8kWh/m2, and would require a 2.3kW PV system in order to get down to the Passive House maximum of 120kWh/m2 at a cost of roughly $18,500.

As Mark Siddal noted elsewhere, best practice Passive House projects are achieving roughly 70kWh/m2 primary energy, without any PV. The theoretical house from the article would need a 4.6kW PV system to get down to 70kWh/m2 at a cost of about $37,000.

Answered by John Semmelhack
Posted Sep 19, 2009 9:52 PM ET


Hmmm. You'd think that, as a science driven organisation, BSC would ensure that they use the same datum points and interrogate the differences between both PassivHaus and the Building America standards - arguably this a fundamental a requirement of science driven approach that seeks to be fair and dispassionate. The more John pulls at the fabric of this BSC article, addressing many of the issues that I raised but digging into in more crarefully considered detail, the more worrying this becomes. This is not the science led approach that I have come to expect from BSC - which on the face of it is rather disappointing.

In the context of scientific debate BSC deserve the benefit of the doubt, so I guess that this article currently shows that we are all fallible and can make errors. However, now that these discrepancies have been exposed, and addressed in some detail - thus assisting BSC's understanding of fundamental concepts that influence PassivHaus design and its integration with US standards - I for one hope that BSC will take the opportunity to revise the article so that these distortions are addressed. Being a science driven organisation I am sure that, in the interests of good scientific endevour and debate, they will be happy to oblige - unless of course BSC can offer a suitable rebuttle (which of course I would also be interested in reading and reflecting upon).


Answered by Mark Siddall
Posted Sep 20, 2009 10:22 AM ET


Sorry everyone, I was too hasty in my last reply regarding corrections to the floor area of the "BSC" house. We actually need to back out about 130sf in exterior wall area from EACH FLOOR (assuming an average wall depth of 12"), in addition to about 30sf for a stairway. This would lead to a treated floor area (using PHPP 2007) of about 1,710sf (158.9m2).

This brings the primary energy use up to 184.9kWh/m2, over 50% more than the Passive House maximum. It would take a 2.7kW PV system to get the house down to the Passive House maximum of 120kWh/m2, at a cost of about $21,600, and a 4.8kW PV system to get the house down to the level that the better built examples of Passive Houses are achieving (70kWh/m2), at a cost of about $38,400.

Answered by John Semmelhack
Posted Sep 21, 2009 7:42 AM ET


John Straube's latest on this subject...http://www.buildingscience.com/documents/insights/bsi-026-passivhaus-becomes-active-further-commentary-on-passivhaus

Answered by Garth Sproule 7B
Posted Oct 6, 2009 12:17 AM ET


Thanks for the link. I'm re-posting the link to make it easier to click:
"Further Commentary on Passivhaus."

Answered by Martin Holladay, GBA Advisor
Posted Oct 6, 2009 3:39 AM ET


thanks Garth,
I am glad to see the discussion continue
BSC, Passivhaus and PHIUS are all excellent resources
Here are some recent comments by Katrin

Answered by John Brooks
Posted Oct 6, 2009 5:59 AM ET


John Brooks started this thread with the speculation that: "the solution is somewhere in the middle... in between BSC and Passivhaus"

From my experience with the two organizations, that's an odd statement. While Passivhaus is a narrow, highly-prescriptive methodology for building extremely energy-efficient homes, BSC promulgates the science behind efficient and durable construction to encourage smart innovation (as well as recommending certain building strategies for various climate zones).

If John is referring to the one Straube article comparing the super-efficient PH approach to the highly-efficient Building America approach which includes some site-generated power, then I'll state flatly that the "solution" is NOT somewhere between those two options.

I'm much more inclined to suggest that, if there is a solution to building responsibly amidst today's global crises, it lies well outside the one-dimensional spectrum between those two widely discussed options. In fact, there are many dimensions to housing that are being explored and implemented, including (but not limited to) building very small, co-housing and other village-based or shared habitat, natural building, "green" building (whatever that means), sustainable building, biophilic architecture, regenerative architecture, permaculture, etc...

We must not forget that efficiency, as we understand it, is largely an industrial value. Nature is profligate yet self-sustaining, balanced and wholesome. Taking industrial efficiency to its apogee, or relying on (allegedly) benign technological "fixes" to the mess that industrial technology has created for us is thinking well inside the box that has brought global human culture (and the rest of life) to the brink.

Unless we break free of the paradigms that have brought us to this precarious moment in time, speaking of "solutions" is little more than an addict's hope for a better fix. We are so imbued with the Technological Program, it so underlies and infuses every element of modern human culture, that few even notice that it's the very air we breathe - and that air has become toxic.

There are, in fact, no technological "solutions" to our current catastrophe. The technological engine is driving us, with increasing velocity, to the cliff. Any pretense to the contrary is a form of denial, the necessary response of the addict. Our science and technology is an epiphenomenon of our mindset, and as long as that mindset is built upon the Newtonian mechanistic universe, Cartesian dualism and Darwinian struggle for survival - upon an abstraction and reduction of the world rather than an immersion within it - we will continue to destroy what we claim to love.

Answered by Robert Riversong
Posted Oct 6, 2009 12:53 PM ET


For those interested in the ongoing debate between two schools of technological "improvement" in housing, Marc Rosenbaum and David White have just posted a response to BSC 25 at: http://www.passivehouse.us/bulletinBoard/viewtopic.php?f=5&t=227#p833

Answered by Robert Riversong
Posted Oct 12, 2009 4:29 PM ET

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