The trim on this job is combed spruce, which came primed on four sides. The sill is a 2x4, beveled on both edges at 15 degrees, sitting on top of a 2x6 apron with a matching bevel and a 3„4-inch-by- 3„4-inch rabbet on the bottom to receive the siding. Once we have the windows on site, we measure and cut all the trim packages, then carefully treat all the raw wood surfaces with a good exterior primer, followed by top coats. We do the painting all at once, racking up the pieces to dry, so that the installation can proceed without interruption. We also prebend all the cap flashings.
I fasten the head trim with 3 1„4-inch double-dipped galvanized casing nails. On top I add the secondary cap flashing, sealing it to the building paper with flashing tape. I then nail on the sill; at this point the window is ready for siding installation.
Note the 1 3„4-inch-by-3„4-inch pressure-treated plywood "butter boards" installed along the sides of the window. The siding butts against these strips, where it's bedded in a generous bead of caulk.
To prevent wicking, the siding gets held off the cap flashing by the height of the end dam. The 1x4 side trim follows the siding, covering the ends at the butter boards and nearly flushing out with the head trim. Foam backer rod and acrylic caulk or low-expansion spray foam seal the window to the rough opening on the inside.
Kyle Dunkley is a foreman with Konstant Construction in Victoria, B.C., and a regular presenter at JLC Live.