Your choice of wall assembly will not only affect the energy efficiency and the longevity of your home but will also affect the air quality through the presence of moisture and mould in your wall. A small investment into this wall assembly will provide benefits to not only the operating costs but more importantly the air quality and longevity of your home.
The wall assembly is comprised of the cladding, framing structure, insulation and air/vapour barrier. When considering the best wall assembly for your home the following issues need to be addressed: how do you prevent water from getting in, how do you keep air from getting out, how do you establish insulation levels as high as possible and how do you construct the wall assembly to increase its ability to dry out in the event water gets in?
One challenge of our traditional wall assembly is that almost ¼ of the wall is comprised of wood that has an R-value of 1.5/inch thus degrading the effectiveness of the R-value of the wall. This leaves only ¾ of the wall to shove our insulation into. The framing lumber acts as a thermal bridge. Since we are limited by how much insulation we can shove between the wood studs, the next generation of wall assemblies will involve moving insulation to the outside of the wall. This will greatly reduce the thermal bridging and moisture in the wall assembly whilst increasing the energy efficiency, longevity and health of the home.
Most of us are familiar with the poly plastic sheeting placed between the insulation and the drywall. This traditional approach has the poly performing two functions: the air barrier and the vapour barrier. Unfortunately, this poly can trap moisture inside the wall assembly. A better approach would be to move the air barrier to the outside of the home sandwiched between the plywood sheathing and exterior rigid insulation. Removing the poly will allow any moisture that penetrates the wall assembly to dry to either the interior or exterior. Since moisture promotes mould, a wall assembly that remains dry will be healthier for its occupants. Cutting edge builders embrace positive change.
Joe Lstiburek a world-renowned building science expert has coined this wall, the “Perfect Wall.” Any builder familiar with building science will be able to advise you on the best wall assembly for your current and future needs.