Image Credit: Robin Adair
Image Credit: Robin Adair The insulated concrete form foundation was insulated with an additional 10 inches of expanded polystyrene insulation. Exterior walls include a structural 2x4 wall plus trusses modeled after the Larsen truss. The wall assembly was insulated with a total of 17 1/2 inches of dense-packed cellulose. Windows are supported by bucks made from 3/4-inch plywood, set about 8 inches in from the outside face of the wall.
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At first, the owners of the single-family home at 1102 Temperance Street simply requested the removal of an unwanted balcony.
But renovations often wander in unexpected directions, and by the time the dust settles sometime later this year, Jim Spinney and Holly Ann Knott should have the first certified Passivhaus home in the province of Saskatchewan.
The owners of the 1940s house on Saskatoon’s east side may have had more modest ambitions at the start, but they weren’t counting on the extensive structural decay that their builder, Robin Adair, uncovered as he took the balcony apart.
“They were going to spend a lot of money to fix this,” Adair said. “It was over $100,000, because the rot was right from the foundation to the top of the second floor. They didn’t want to do that. They said they’d build a new building instead. I said, ‘Great, I’ll do it for you, but if I do it, it’s Passivhaus.’ ”
Although Adair has been building high-performance houses since the 1980s, the Temperance Street Passive House is his first attempt at putting his 2014 training in Passivhaus construction to work, and his first try at a certified building.
The new three-level house is a duplex with a pair of 2,358-square-foot residences, one half of the space submitted for certification through Germany’s Passivhaus Institut and the other half built to the same standard but not certified. It’s located just 160 miles northwest of Regina, the community where the ground-breaking forerunner to Passivhaus building, The Saskatchewan Conservation House, was constructed in 1977.
Designed for a punishing climate
Saskatoon usually sees more than 10,600 heating degrees annually, with average January temperatures of 0.5°F above zero (-17.5°C). It’s no place to skimp on insulation or other building details. Adair credits Michael Nemeth for planning the mechanicals and other details using the Passive House Planning Package, calling his work “instrumental.”
The wood-framed building, on a foundation of insulated concrete forms (ICFs), will have four bedrooms and four bathrooms in each unit. Exterior walls start with a structural 2×4 wall sheathed with 5/8-inch spruce plywood, which serves as the air barrier. Seams are taped with Ampacoll XT tape.
On the exterior side of the sheathing is an assembly similar to a Larsen truss wall, consisting of 2x4s separated by webs of 1/2-inch thick plywood, then 5/8-inch tongue-and-groove Agepan DWD fiberboard sheathing, then a rainscreen gap and, finally, HardiPlank fiber-cement siding. The truss wall is 14 inches thick, and both it and the 2×4 structural wall will be insulated with dense-packed cellulose.
The roof is constructed with trusses installed 24 inches on-center, with a 28-inch raised heel providing room for insulation over the exterior walls. Roof pitches are 4-in-12 and 12-in-12. The roof sheathing is 1/2-inch spruce plywood.
Adair says that the costs will total about $195 (Canadian) per square foot, which he estimates is 5% to 10% more than a code-compliant house when comparing a basic shell with windows, but no cladding, trim, or other finish details.
“All the interior and exterior finishes are design details,” he explained, “and how much they cost depends on what you want. You have to be able to compare to a 2×6 wall with fiberglass in it. Yes, the owners were aware that it was going to cost more money, but the other side of that is there are no energy costs, relative to what we would think of as normal here for our climate.”
All-electric design
An electric heater in the ventilation system will heat the house, supplemented by electric in-floor heat in the bathroom and a wall convector in the kitchen, according to Nemeth. Fresh air comes from a Zehnder Novus 300 Passivhaus-certified heat-recovery ventilator, which Nemeth says has heat recovery efficiency of 93%. Ducts are semi-rigid high-density polyethylene.
Because of the design of the roof overhangs and other ventilation features, mechanical cooling wasn’t deemed necessary.
Other details:
- Below-grade insulation: Twelve inches of Type II EPS under the basement slab; 12 inches of PlastiSpan 40 psi underneath the footings; 10 inches of Type II EPS on the exterior of the ICF foundation walls; and 12 inches of Type II EPS on the exterior of the footing.
- Wall and roof insulation: Above-grade walls have a total of 17.5 inches of dense-packed cellulose (R-66). The roof is insulated with 30 inches of loose-fill cellulose (R-100).
- Windows: Gaulhofer Energy Line 85 Plus triple-glazed units. The windows are set about 8 inches in from the outside face of the wall.
- Domestic hot water: Electric-resistance tank heater. A drainwater heat recovery unit should capture about 25% of the energy used to heat the water. When prices come down, a heat-pump water heater could replace the conventional unit.
- A condensing clothes dryer means one less penetration in the building envelope and, Nemeth adds, an induction range in the kitchen “offers the performance of gas without the exhaust and makeup-air penalty, not to mention safety.”
- Renewable energy: A roof-mounted photovoltaic (PV) array with a capacity of 4 kilowatts, plus the potential for adding another 3 kW of PV on the garage roof.
- Airtightness: A blower door test on February 2 found an air leakage rate of 0.37 air changes per hour at a pressure difference of 50 pascals — about half of what’s permitted by the Passivhaus standard. As good as that is, Adair says some further tightening is possible.
Advice from an old hand
One of the delights of this project for Adair has been his encounters with Harold Orr, who led the Conservation House project and regularly shows up at the Saskatoon job site where Adair is working.
“I’ll turn around and there’s Harold,” he said. “Great!”
Orr’s team was years ahead of the rest of the construction industry, and the group’s pioneering work in superinsulation and airtight construction eventually led to the creation of the Passivhaus standard by German physicist Dr. Wolfgang Feist. One of Orr’s teammates, the late Rob Dumont, lived in Saskatoon, where he built a superinsulated house of his own.
“That’s his passion,” Adair said of Orr. “He knows that I followed him. I’m overwhelmed by the fact that he does show up. How many people in the world wouldn’t like to be on a site when Harold shows up to see what you’re doing? It’s unbelievable, really.”
Adair says Orr isn’t shy about asking questions and offering what he might do a little differently. “His input has been great,” he said. “He’s been very enthusiastic.”
Adair said he was told it wouldn’t be possible to build a Passivhaus-certified house in Saskatoon’s climate. But according to Nemeth, the release of PHPP 9 in October 2015 was a turning point.
“Up until that point we struggled to meet the Passive House primary energy requirements of 120 kWh/per square meter,” Nemeth said in an email. “PHPP 9 brought the Primary Energy Renewable (PER) alternative path. This allowed us to use the greatly simplified all-electric system. Along with a few other tweaks, PHPP 9 has made it more reasonable to certify a Passive House in Canada’s cold climate.”
Adair hopes the successful completion of the project will encourage other builders and lead to changes in building codes. Another member of his team, Mark Prebble, a Saskatoon real estate agent who has taken Passivhaus training, is filming the construction of the house with hopes of spreading the word in the province.
“It just frustrates me to no end that the developers up here are still building these structures using the lowest cost methods so they can make a lot of money,” he said. “Well, it’s not helping the planet when we do this and that whole mindset has to change. Well, how does that happen? You have to have something the community can see that actually does perform.”
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16 Comments
I'm tremendously curious to
I'm tremendously curious to know what their technique for dense-packing an open truss cellulose wall that thick is.
Are the walls safe from a
Are the walls safe from a vapour perspective?
Also whats the R value for the windows?
Response to Alan B
Alan,
Q. "Are the walls safe from a vapor perspective?"
A. Agepan sheathing is vapor-permeable, so these walls should perform somewhat better (from a vapor perspective) than most double-stud walls. That said, any builder who is worried about winter vapor drive from the interior to the exterior would be well advised to choose a wall assembly that includes a thick layer of exterior rigid foam.
Q. "What's the R-value for the windows?"
A. Typically we talk about the U-factor, not the R-value, of a window. The window manufacturer's web site notes a UW of 0.65 W/(m²K), which meets the Passivhaus recommendation that windows have a UW below 0.8 W/(m²K). (For more information, see Passivhaus window U-factors.)
The metric U-factor of 0.65 W/(m²K) is equivalent to a North American U-factor of 0.114 Btu / ft2 * h * °F.
Thanks Martin
I am unfamiliar with Agepan sheathing, would it be better then plywood/OSB sheathing?
Thanks for converting the windows to U value, i don't know how to do that calculation
Response to Alan B
Alan,
For more information on window U-factors, see All About Glazing Options.
Here is how you convert R-values to U-factors, and vice versa:
R = 1/U
U = 1/R
So U-0.114 = R-8.77
Response to Alan B
Alan,
Q. "I am unfamiliar with Agepan sheathing. Would it be better then plywood/OSB sheathing?"
A. For more information on this issue, see Wall Sheathing Options. There is a discussion of Agepan in the comments section -- see Comment #9 and Comment #16.
Thanks again
I was not clear, i did not know how to convert from to W/(m²K) to U factor
A first.
It will great to see a first passivhaus in the coldest substantially inhabited area of Canada. If they can do it in Saskatchewan then they can do it anywhere in the lower 48. The heating stats will be of great interest to many of us.
Converting units
Metric U-factor (in W/m^2 K) divided by 5.68 = USA U-factor (in Btu/ft^2 h F).
Agepan DWD: Building Physics
Hello Alan B and Martin,
Martin, I'm surprised that you'd suggest rigid foam on the outside of the Agepan DWD. We (Tom Gyimesi at 5thC and I at Pinwheel) represent Agepan in Canada and strongly discourage this. First, there's no real purpose: the wall with larson trusses is practically thermal bridge free, the foam would not help with this aspect. Second, the Agepan DWD has a perm rating of ~20, you would have to be very careful to use a product that is more vapour open than the Agepan DWD or else you will introducing condensation in the wall. Further, any strapping attached to the exterior of the hypothetical foam would have more shear momentum to deal with, hence the cladding would have a weaker connection point.
Agepan DWD is specifically designed as wall and roof sheathing to allow vapour movement and thus avoids moisture damages from condensation, which is the main issue with using plywood or OSB sheathing as exterior sheathing in high R-value walls.
Response to Hans Eich
Hans,
You misunderstood my comment (Comment #3). I didn't recommend that anyone build a wall with rigid foam on the exterior side of Agepan sheathing. Rather, I was saying that a builder can choose one of two options: either the Agepan approach (which allows moisture to dry outward) or the rigid foam approach (which keeps the sheathing warm and dry all winter).
If a builder chooses the rigid foam approach, there would be no reason to specify Agepan sheathing, which is quite expensive compared to commonly available sheathing materials like plywood or OSB.
Either approach can work. I sensed from Alan B's question that he was worried about vapor diffusion and moisture accumulation. That's why I suggested the he might prefer the rigid foam approach, since researchers have found that of all studied wall types, those with exterior rigid foam stay the dryest. But there is no evidence that the Agepan approach doesn't work, so (assuming cost is irrelevant) either approach is reasonable.
Evidence?
Hello Martin,
fair. I understand your comment now. We have priced Agepan DWD (in Canada, this may be different in the US) such that it is priced competitive with plywood, all things considered (such as labor to apply another air barrier. When adding foam on the outside of plywood, the system would likely even be more expensive than using Agepan DWD).
As for evidence, Agepan DWD is considered the standard in wood construction in central Europe. It's sort of like a good stage production guy: when he does his job well, no one notices him. Only when he screws up, do people know that he is there. Similar scenario with DWD. It's very commonly used in Central Europe, and if it was failing, it would be noticed.
(Another thing to consider is that anyone working in the trades in Germany, is liable for their work personally for 25 years; meaning a carpenter that uses a product choses the products carefully and Agepan DWD has become the gold standard of exterior sheathing. People even started just calling exterior sheathing DWD, similar to people just calling tissue paper Kleenex.)
But enough of the "product plugging". I just wanted to weigh in on the product, and now would like to step aside for other discussions about this amazing feat of the first PH in SK.
Response to Hans Eich
Hans,
For more information on the ongoing debate about which wall design approach is better -- keeping the sheathing warm and dry with exterior insulation, or allowing water vapor to flow right through the entire wall assembly -- see this article: How to Design a Wall.
Europe has a temperate climate compared to North America.
On has to be careful when recommending materials & practices that work in a European climate for use in North America. The Canadian and US upper midwest are considerably colder in winter than Europe (except the northern half of the Scandinavian peninsula), and the southeastern US has dramatically higher summertime outdoor dew points than anywhere in Europe.
Products like Agepan DWD would fall in the same category as asphalted fiberboard or exterior grade gypsum board from a vapor permeance point of view, and would not meet code in the US as exterior sheathing without "vented cladding" such rainscreened siding, in much of the northern half of the US without a Class-II or tighter vapor retarder on the interior. In US zone 7 (and most of the Canadian midwest- including most of Saskatchewan) even WITH vented cladding it would need a Class-II or tighter vapor retarder somewhere on the interior side of the assembly:
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm
In Zones 1A-3A highly permeable sheathing becomes problematic in air conditioned buildings due to outdoor summertime dew points higher than the room temperatures indoors, leading to mold on the inside of the interior finish walls. In those climates sometimes even OSB or CDX are too vapor permeable for some assemblies.
Bottom line, it doesn't really matter that "...Agepan DWD is considered the standard in wood construction in central Europe", unless the building is actually being built in central Europe (or some similar climate.)
Europe is not North America - agreed...
Hello D Dorsett,
Thanks for weighing in. I agree with what you are saying. It is important to look at the wall as a system. Neglecting to spec proper rain screens (3/4" is not enough) or to look at which materials are being used on the inside can lead to failures. Inverting the vapour drive during hot humid summers is a phenomenon which is rarely encountered in many European countries (although their climate appears to become more drastic too; there have been some very hot summers in recent years in Central Europe).
We can't generalize, which is why we consult on the use of the materials with regard to the specific locations. More and more projects are using Agepan DWD all across Canada (I can't really speak for the US) so more and more data will become available.
Question for Hans Eich
Why isn't 3/4" sufficient for a rainscreen?
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