Waterproofing
Back on the roof, remove the shingles surrounding the opening
to allow for waterproofing measures (i.e. flashing, tar paper). Don't
skimp here, roof windows are vulnerable to leaking if not installed
properly.
Before fastening the window to the roof framing, consider putting down
ice and water protection, in the roll form, or more messy but less expensive,
roofing tar. Anchor the window according to the manufacturer's directions.
NOTE: Nailing/screwing the flashing in the incorrect place may
cause water to leak in. As an added measure, put down ice and water
protection again, this time over the window flange. Add roofing felt
over the protection and caulk where it butts up against the window.
Start at the bottom of the window
with the step flashing, install a shingle, then flashing, etc. Overlap
the flashing as you work toward the top. The manufacturer may include
additional waterproofing channel flashing or framing.