The Shell

Location and orientation of the house on the lot was chosen not only for passive solar heat gain, but to make best use of the terrain for drainage, to limit the cutting of mature trees as much as possible and to ensure a quality of life for occupants with a mix of privacy and usable outdoor space.

By Mike Reynolds

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After the land was cleared, compacted gravel was brought in to bring the site to a workable level. The house sits at about grade at the north side, but needed about 3.5 feet of fill at the south to level the building site. Compacted gravel was tamped in stages every foot and a half to ensure a solid base. A retaining wall was built using rocks from the site to hold the compacted gravel and future slab in place.

Footing forms were well secured to avoid a blow out during the concrete pour, including lots of braces to hold the weight of the concrete so forms don’t bend. Three runs of 2×6s easily held concrete and insulation, and after forms were removed, that wood was used for framing.

All plumbing and other infrastructure [water pipes, drains, radon stack, central vac, power conduits, etc.] was put in place next, belowthe coming insulation and concrete. Insulated water pipes were used for greater energy efficiency, and to contribute points for LEED certification.

After all the plumbing was in place, eight inches of Roxul rigid insulation was installed on every surface. Roxul engineers recommended high-density EPS foam under the footing, as Roxul has not yet been tested against the weight of a footing and load-bearing wall, but Roxul Comfortboard CIS [more dense than Comfortboard IS] panels were used below the main slab. Comfortboard is convenient to work with as it cuts easily and stays securely in place without slipping, allowing for tight clean joints. The joints of panels were overlapped as well to further reduce heat loss.

Building the walls: The REMOTE System
The wall construction follows the principles of the ‘REMOTE’ wall - Residential Exterior Membrane Outside-insulation Technique - a high-performance building envelope developed by the Cold Climate Housing Research Centre in Alaska. Walls are framed conventionally with 2×6s and sheathing; stud cavities are still insulated with batts, but most of the insulation is on the outside of the sheathing.

This type of design allows vapour and air barriers to be sandwiched in between layers of insulation to protect their continuity. And in the case of polyethylene vapour barriers in such a variable climate as we have in Canada, they perform better on an annual basis when they are about 1/3 into the wall assembly instead of right behind drywall. With the Edelweiss House we have opted to omit the 6 mil poly entirely, its role being filled instead by an exterior moisture-permeable airtight weather barrier (Delta Vent SA) and an interior vapour retarder primer from Benjamin Moore. Vapour retarder primers stop twice the moisture required by building code, but allow walls to dry a bit to the interior during summer months, which is a growing concern among building scientists in terms of summer condensation damage as most homes now are air conditioned.

Siding installation
Whatever your wall assembly is, in order for it to last it has to be able to dry. The Edelweiss House exterior is finished with FSC-certified pre-stained wood siding from Riopel. Siding should protect your interior layers from wind, precipitation and humidity, and it must be able to dry. In order to do so, air and water must be able to move freely behind it so any water that penetrates can drain out, and humidity can escape.

Our weather barrier is covered by 3/4” vertical furring strips, giving ample room for drying. From the bottom, air flows up behind siding and into the soffit, joining air venting through the roof.

Building the roof
We opted for a green roof on this house, for a couple of reasons. Curb appeal would be one, we liked the idea of walking up to an open area of flowers and clover more so than a large sheet of metal, which was the other option. Green roofs can be quite a bit more work but have enormous benefits, mostly in urban areas.

Here in the woods there is no great need for it, but in dense urban centers a green roof offers habitat for birds and insects, and in commercial applications on office buildings they can give people access to green space that isn’t always easy to find in a downtown core.  They can be beneficial for heating and cooling, and though the cost is higher than other roofing systems, the life span is much longer.  The most destructive force on roofing materials is actually not precipitation, but UV rays. Once you cover membranes and they are no longer exposed, it is hard to really put a life span on it, because as evidenced by landfills, plastic underground just does not breakdown at a pace that we need worry about.

Mike Reynolds is a former home builder, a LEED for Homes Green Rater, and the editor of Ecohome.net.

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