The last time we were on the roof, it was to install some valley flashing. This time we’re going to hop over to the other side and flash a dormer.
First, we’ll strip away the layers—
and begin at the beginning, with a couple of courses of roofing membrane and the drip edge flashing.
Step by step dormer flashing:
- Roofing underlayment can be installed on the roof, but hold it back from the roof wall joint.
- Cover the connections with peel and stick membrane and then fold the synthetic underlayment up the wall also.
- Underlayment and peel and stick should go higher than the step flashing, for easier verification.
- Install shingles to the base of the dormer, notching the end piece appropriately.
- Lay a bead of roofing cement along the top of the shingle course just below the dormer and bed the base flashing into it.
- The first piece of step flashing should turn the corner and extend over the base flashing.
- Nail it through the shingle into the roof to avoid wood movement problems between roof and wall.
- The next shingle extends below the previous step flashing.
- And the next step flashing goes on top, aligned above the next shingle. And so on … Continuing up the side of the dormer.
- At the top, fold a closure flashing with a piece of sheet metal that can tuck into the crotch where roof meets soffit. You can bed it in roofing cement.
- The next row of shingles can slip under the closure flashing.
- Finally, you can install the house wrap over the top of the step flashing and base flashing.
Now, you’ve got a roof/wall joint that won’t leak into you good-night’s sleep.
—Technical assistance from: Doug Horgan (BOWA), Dan Whitmore (Hammer & Hand), and Matt Jackson (The Timber Tailor) | 3D Modeling: Matt Jackson and Dan Morrison | Music: As I Figure by Kevin MacLeod | Produced by: Dan Morrison