Window Detail
Triple pane window is installed over sill flashing & weather resistant membrane and then taped.
Then there is a 2×4 ripped to the thickness of 1 layer of rigid roxul around the window offset about 3″. This holds a layer of rigid roxul tight against the window frame and provides a nailing & flashing surface. The second layer of rigid roxul covers up the 2×4 resulting in a thermal bridge free detail. Borate treated 2×4 strapping on flat hold the 2 layers of rigid roxul in place. Also shown here is the wall connection to the foundation. You can see the dimple board drainage layer with a self adhered flashing at the top and the rigid roxul over top. On the left of the lower picture (above) you can see how the rigid roxul is held in place with temporary bracing via leaning 2x4s before the install of permanent strapping and long screws.
You can see the head flashing at the top of window. This is nailed into the 2×4 ripped strip offset above the window. Wood trim is installed at jambs and sill flashing with end dams. What is left is the siding nailed into the strapping (not shown).
On the inside headers are installed at the floor joist level. Air barrier wrap can be seen surrounding the window head and jamb.
The windows are installed through the interior side of the window frame rather than with the common flange. Sill self adhered flashing can be seen with the air barrier membrane properly lapped. Tape from the window frame to the structure and rod & caulk will be provided in future (not shown).
The head and jamb are shown here.
Compared to a typical window installation there are some differences here. The membrane wraps are similar but the air barrier membrane needs to be taped at all seams. The window is flangeless and is mounted with side-mounted screws. There is a 2×4 nailing strip offset at head and jamb and the 2 layers of exterior rigid roxul is a new addition to the conventional sequence of installation. The 2×4 strapping on flat is larger than the standard and the required extra long screws must penetrate the 2×4 strapping, 2 layers of rigid roxul, plywood sheathing, and at least 1.5″ into the stud. This takes some skill as the studs can’t be seen and must be hit. Also, the screws should be angled upward slightly. This is due to the nature of long screws which tend to sag from the weight of the siding if installed horizontally. The angled installation slightly up mimics the final resting ‘sag’ of the screw such that there is no movement of the siding after install. Any screws that miss their mark are to be left in place. This avoids penetrations of the air barrier if these screws were removed.
Doors are installed similarly to windows. A 2×4 ripped is offset at jamb and head. The door frame rests on plywood spacers and is glued/sealed with adhesive foam. The frame is over a self-adhered flashing at sill which itself sits above rigid EPS at concrete foundation.
As mentioned in part 1 of the series this wall detail takes a high vapour permeance or breathable approach in contrast with a more vapour closed system such as traditional 6 mil poly, spray foam insulation, or SIPS panel.
The South facing sunshades on the Langley Passive House are permanent, sized to reject the overheating summer sun while allowing passage of the winter sun through the windows to heat the home, and fit the architectural style of the home.
The Langley Passive house is a ‘split-insulated’ wall assembley pioneered by RDH Building Engineering for the BC climate. This strategy is described in the Building Enclosure Design Guide (HPO 2011) and Guide for Designing Energy Efficiency Building Enclosures (FPInnovations 2013) both by RDH.
