The Exterior Walls

The exterior walls of the net zero ready house will be made from a double stud wall filled with blown in insulation. The double stud wall is basically two traditionally framed walls placed a few inches apart which create a space in between for an extra thick layer of insulation. The exterior wall of the double stud wall will be the load bearing wall and will be made from 2 x 6 studs spaced at 24 inches apart. The interior, non-load bearing wall will be constructed of 2 x 4 studs also spaced at 24 inches apart.

A vapour barrier and drywall are attached to the interior wall. House wrap and siding are attached to the exterior wall. In between the interior and exterior surfaces will be 12.5 inches of insulation, likely dense packed cellulose with an R value of 3.8 R/inch, giving the walls an R-value about 47.5.

The double stud wall seems to be the most cost effective way of achieving the desired high R value. Using other methods and materials, such as ICFs or SIPS, may have resulted in somewhat thinner walls but would have been much more expensive.

The frame for the house will likely be prefabricated in sections by a factory framing shop, then transported by truck and assembled at the build site. The Europeans have got this down to a super efficient, highly customizable, assembly line. Here's a video:



I'm not sure how it's done here in Toronto but we'll find out soon enough.

Goodbye garage

Word is from someone on the PAL review panel that the inverted slope driveway on the original plans is not going to get approval. Toronto is apparently trying to discourage this type of driveway because of potential drainage problems (an inverted slope driveway guides water towards the house leading to possible flooding problems if drainage is not carefully installed and maintained) but regardless, in this case, the slope of the driveway would have been too steep anyway.

The driveway/garage, then, has been replaced with a full basement and a parking pad.

Some other minor changes from the original include front window layout and backyard wall/patio layout.

One concern with the new front window area is the increased amount of summer heat it will allow into the house. Some type of exterior shading device will have to be built to prevent overheating.

The Basement

The last post discussed the three main requirements for a basement foundation with respect to energy efficiency: insulation, water barrier, vapour barrier.

Let's look at the cross section for the basement to see how those factors will be addressed in this Toronto net zero house.

Let's start with the walls.

The main structural component of the wall will be built up of concrete filled ICF blocks. What's an ICF?

ICF or Insulated Concrete Forms, are hollow foam blocks (think styrofoam) which can be fitted together somewhat like building blocks to form walls. Concrete is then poured into the continuous hollow chamber inside the blocks. Once the concrete cures, you've got an insulated, structural wall. The blocks have a foam wall thickness of 2.75 inches (insulation value of ~R27, pretty good already for a basement wall but even more insulation will be added later) which surround a 4 inch core of concrete (almost no insulation value).

Check out the video below to get a better idea of what ICFs are about:



ICFs can be used to build the whole house but they tend to cost more per square foot than building with traditional wood frame so in the case of Adrian's house, he'll only be using them for the basement foundation. To get a fully waterproof, vapour proof, high R-value basement, though, just the ICFs alone will not be enough.

On the outside surface, the surface facing earth, there will be a waterproof membrane applied to it. Sitting against the waterproof membrane will be a dimple membrane which will allow any water which makes its way to the wall to flow down around the footing to the weeping tile where it will drain away. Thus there should be no hydrostatic pressure against the wall and no water penetration through the wall.

On the inside surface of the ICF wall, a 2x4 frame will be built right against it to support more insulation, probably rockwool batte, and drywall. This will provide an additional ~R14 making a total insulation value of ~R41 for the basement walls. Now that level of insulation is something you're not going to find in standard construction.

The floor will be composed of a bottom gravel layer which will hold drainage/venting pipes for water and radon gas. The gravel will be spread out level to the top of the footings.

The next layer of the floor will be a 5.25 inch thick layer of polyurethane foam ( total ~R36) then a water barrier then a 2 inch poured concrete slab. This should be more than adequate to keep water out of the concrete slab and prevent it from seeping up to the basement floor.

Constructed properly, this should result in a very warm, dry and highly energy efficient basement.