After a few hiccups with our supplier, we finally have all the windows installed. It’s amazing how much of a difference that makes to the environment inside the house. I love fresh air, but when it’s blowing the plan-set all over the living room, there can be too much of a good thing.
The installation process went well. Removing an operator here and there helped lighten the load a bit; tri-pane windows are noticeably more heavy than their double-pane counterparts. Installation started out the same as any other house… a level, some cedar shims, fasteners and special low-expansion foam (which remains flexible – this is important!). The first photo shows an installed window in the SIP wall assembly. What you can’t see (translation: what I forgot to take a picture of) is that each window opening was first detailed with a trowel-on elastomeric water-proof membrane, also called the “Weather-Resistive Barrier” or WRB. The most common WRB’s are of the “house-wrap” variety, of which Typar and Tyvek are the most popular. The main detriment to wrapping a WRB around a window/door opening is that it makes it difficult to air-seal on both sides of the membrane. With a trowel-on membrane, it is sealed to the substrate (frame opening) when applied and the window is subsequently sealed to it; far less opportunity for air leakage. The other detail missing is the outermost 2×4 window buck hiding just behind the inside edge of the window frame.
Though not significant, that 2×4 does represent a thermal bridge in the window installation so we chose to isolate it by wrapping the interior of each window opening with polyiso insulation. Two beads of spray-foam and a bead of calking ensure it also becomes part of the vapour-barrier continuation.
Finally, an application of air-sealing tape between the window frame and the foil-faced polyiso completes the air-tight seal.
These pictures also give you a glimpse of the 2×4 service partition. That partition is currently being well-utilized by the electrical, plumbing and HVAC subcontractors, and we’re happy to see that, knowing the alternative would be to carve holes and channels into the OSB vapour-barrier. We have chamfered the sides and top of the service partition around window openings as an architectural detail; this also improves the field of view and the amount of light allowed to enter the rooms.