Exterior Finishing: Windows, Doors, Siding, and Trim
Exterior Finishing: Windows, Doors, Siding, and Trim
This domain tests weatherproofing and finish installation. The goal is to shed water outward and allow wall assemblies to dry.
Core rules
- Install weather-resistive barrier shingle-fashion, lapping upper courses over lower. Flash rough openings before installing windows or doors.
- A sloped sill pan, sill flashing, jamb flashing, and head flashing work together; sealant is a supplement, not the primary flashing.
- Integrate window and door flanges with the barrier and siding in the correct layer order. Head flashing must lap over side flashing.
- Keep siding clear of roofs and soil; follow manufacturer clearance and fastening rules, and allow movement at ends and joints.
- Back-prime or seal trim cut ends, especially at the bottom, and maintain a drainage gap where required.
Worked example
For a flanged window, install the barrier, set a sloped sill pan, place the window plumb and square, then flash the jambs and head. The head flashing goes over the upper flange and under the barrier above. Siding then laps over the flashing. Reversing this order-siding first, then caulk-traps water.
Traps
Using caulk instead of flashing, reverse-lapping the barrier, and leaving siding tight to a roof or deck are frequent errors. Also do not seal the bottom of a wall cavity that is designed to drain.