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Blue Heron EcoHaus: Adding Walls and Roof

The double-stud exterior walls are modeled on those developed by Saskatchewan superinsulation pioneer Rob Dumont

Double-stud exterior walls reduce thermal bridging through the frame and provide room for ample amounts of insulation. Framing techniques are relatively straightforward.
Image Credit: All photos (except photo of Dumont's house): Kent Earle
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Double-stud exterior walls reduce thermal bridging through the frame and provide room for ample amounts of insulation. Framing techniques are relatively straightforward.
Image Credit: All photos (except photo of Dumont's house): Kent Earle
Exterior walls consist of two parallel 2x4 walls with an 8-inch space between them. Both 2x4 walls are framed 16 inches on center and have a double bottom plate to accommodate a 1 1/2-inch thick concrete floor. The inner wall is load-bearing. The south-facing wall includes three very large windows and a door that will lead to a patio. The windows let in winter sunlight for heat. All four exterior walls are now framed. Roof overhangs are 48 inches wide, allowing complete summer shading and optimum winter solar gain. The overhangs are far wider than the norm in the area.

Editor’s note: Kent Earle and his wife, Darcie, write a blog called Blue Heron EcoHaus, documenting their journey “from urbanites to ruralites” and the construction of a superinsulated house on the Canadian prairies. Their previous blog on GBA was called Dealing With Really Bad Water. The blog below was originally published in July 2015. (A complete list of Kent Earle’s GBA blogs is provided in the “Related articles” sidebar below.)

The day following the completion of the excavation, backfill, grading, and dirt hauling, Taylor and Curtis with EcoSmart got to work framing the double-stud exterior walls. We had chosen to use the “deep wall system” originally developed by Rob Dumont, a local Saskatoon engineer who is widely recognized as one of the pioneers of superinsulated green building. He has been a major inspiration to the owner of EcoSmart Developments, Murray Guy.

Dumont had been one of primary engineers in creating the Saskatchewan Conservation House – which is one of the original homes that inspired the German Passivhaus movement. Rob Dumont built his own home in 1992 using his deep wall system. It was considered to be the most energy efficient house in the world at the time.

Rob Dumont’s home in Saskatoon. [Photo credit: Michael Henry]

Dumont developed this superinsulated wall system and Peter Amerongen from Edmonton, Alberta, has been perfecting it over the past few years, using it in the Riverdale NetZero and the Mill Creek NetZero homes, among others. To my knowledge, no one since Dumont himself has built another home in Saskatchewan using this type of wall system. I’ve written about this wall system previously, but now we were going to see it come to life before our eyes.

Taylor and Curtis had of course never built this type of wall before, but they had done extensive research and were very motivated. This wall system includes two parallel 2×4 walls, spaced 16 inches apart, thereby creating an 8-inch void between each 2×4 wall. There is no need to offset the studs as the large void, which will be filled with dense-packed cellulose (recycled newspaper), has no thermal bridging whatsoever.

We elected to space the 2x4s at 16-inch centers for both the interior and exterior walls. It is possible to space the non-loading bearing wall at 24-inch centers, but when attaching the wood siding to the exterior wall (our non-load bearing wall), this might be a little more tricky.

Of course this wall system takes a bit longer to construct then your typical stick-framed house, as each wall needs to be built twice. What the guys did was to lay the lumber one on top of the other to ensure that the spacing was appropriate. The studs were nailed together with a double bottom plate (we will be pouring 1 1/2 inches of concrete for the main floor, so another bottom plate was needed in for securing the drywall) and a double top plate. The two walls were then secured to a 16-inch-wide 3/8-inch OSB header and footer, and tipped up into place using wall jacks. The walls were then glued and nailed into place and sheathed on the outside.

The first day they framed the west wall, which is 30 feet long. Honestly, the excitement of seeing a wall could not be contained that day.

On day two they framed the north side, which is a 48-foot wall with minimal penetrations — one window in a bedroom, one in the hall for ventilation, and the back door.

Day three was the west wall, again 30 feet long, which included three large windows. (Energy efficiency geeks will note that there is minimal benefit to large windows on the east side and there is risk of overheating in the spring and fall.) However, these windows look onto an amazing river view that we had to enjoy. The windows will have glazing with a special coating designed to reduce heat gain (more on that later).

On day four they ambitiously completed our southern wall, our primary 48-foot wall. This wall has three massive windows — each more then 10 feet wide — and a patio door to the deck. This side of the house looks onto a beautiful southern view across the river valley. The windows will also be a source of heat gain in the wintertime.

Next would come the interior walls and roof. Suddenly, this was looking like a house!

The importance of roof overhangs

The roof is what really gives a house its personality. In A Pattern Language, Christopher Alexander writes, “The roof plays a primal role in our lives. The most primitive buildings are nothing but a roof. If the roof is hidden, if its presence cannot be felt around the building, or if it cannot be used, then people will lack a fundamental sense of shelter.”

We had really debated about doing a house without overhangs. When scouring design sites, we had seen a lot of examples of houses without overhangs.

I really like the look of some of the vernacular houses we saw, and we came very close to building something along these lines. However, we were talked out of it — or perhaps, talked into proper overhangs, by our engineering team from Integrated Design. They were very adamantly against the “no overhang” aesthetic that we were drawn to. Granted, they had some valid points including: adequate shading in the summer, protecting the siding and windows from rain and excessive moisture, and keeping water away from the foundation. Grudgingly, I did some of my own research, and, dammit, they were right.

Our favorite house is called the “Stockily in Balsthal” by Pascal Flammel Arkitekten. Now those are overhangs. This house is just so badass. (Granted, this house has very large windows on the gable ends that have absolutely no shading — which would certainly lead to overheating).

Our house is only a bungalow, so we could not have as crazy intense overhangs as this place — but still it served as good inspiration, and also got some good eye-rolls from the engineers, especially when we would tell them, “Well, if we can’t build a house without overhangs, then we want this!”

After playing around with solar studies (using a computer program) and tracing the path of the sun at our GPS location, we found that the optimal overhang width — one that would give complete shading in the summer, ultimate solar gain in the winter, and still look badass — was a 48-inch overhang. Most roof overhangs in this part of the country are 12 inches to 20 inches wide, so 48 inches is quite a statement. I loved that fact that it balanced the aesthetics with the practicality of overhangs.

But I was not sure how this would really look until the guys got the rafters up and in place. At 38 feet wide and nearly 20 feet tall, the truss company had to send a special truck out to deliver them. I took that as a good sign that these were going to be unique.

One Comment

  1. User avater
    Elden Lindamood | | #1

    Badass overhangs
    I have never heard anyone describe overhangs as "badass" before. Made me chuckle. I think I'll have to add that to my lexicon.

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