guest-blogsheader image
0 Helpful?

Blue Heron EcoHaus: Adding Walls and Roof

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

Posted on May 16 2016 by Kent Earle

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 GBAGreenBuildingAdvisor.com 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 PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. 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 2x4 walls, spaced 16 inches apart, thereby creating an 8-inch void between each 2x4 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 bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. 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 plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical 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 glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. with a special coating designed to reduce heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. (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 DesignBuilding design in which different components of design, such as the building envelope, window placement and glazings, and mechanical systems are considered together. High-performance buildings and renovations can be created cost-effectively using integrated design, since higher costs one place can often be paid for through savings elsewhere, for example by improving the performance of the building envelope, the heating and cooling systems can be downsized, or even eliminated.. 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.


Tags: , , , ,

Image Credits:

  1. All photos (except photo of Dumont's house): Kent Earle

1.
May 26, 2016 4:37 PM ET

Badass overhangs
by Elden Lindamood

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


Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!