Previously, I described the unique wall system we designed for this house: a vapour-permeable wall using conventional materials and construction techniques. This week I got to see the wall go from drawings to real life as work began on the external portion of the wall (the internal portion is simple mineral wool batt insulation sandwiched between 2×6″ studs).
The first step was to put a layer of house wrap over the plywood sheathing. This particular house wrap is vapour-permeable but does not allow liquid water to pass. It is meant to protect the sheathing from any rain that might make it behind the cladding. It wasn’t necessary in our case since we have a 3-inch thick layer of mineral wool insulation between the sheathing and the cladding and we had already planned to put house wrap on the outside of those layers, but code requires it and since the membrane is vapour-permeable we didn’t feel it was worth the effort to get out of doing it.
Next, vertical 2 x 2 furring strips were nailed to the studs, and strips of 1.5″ thick Roxul Comfortboard were cut and fitted between them. One of the many advantages of mineral wool insulation is that it is not as “squishy” as fibreglass insulation and is therefore much easier to cut. More importantly, mineral wool does not loose insulative effectiveness when compressed. So the guys could make sure it fit nice and tight between the studs.
Next, horizontal 2×2″ furring strips were nailed to the vertical strips, and another layer of 1.5″ Comfortboard was placed between them.
The whole thing was then covered with a sheet of house wrap. This was taped to flaps of housewrap that had been laid under the sill plate (bottom of the wall) and the top plate during the framing process. The end result is the entire wall of insulation plus furring strips is encased in housewrap. Even though mineral wool is unaffected by moisture, the furring strips will probably appreciate staying dry.
The board and batten siding will be attached to the horizontal furring strips. In order for the guys to see them when the time comes (since they are covered in house wrap), special staples were placed along the nailing lines. The staples come with a rubber flange to seal up the hole created by the staple. The bright green colour makes them especially visible. They also used these to mark the window and door openings.
The walls are now ready for the windows to be installed. I can’t wait to see my beautiful windows out of the box!