How to Flash a Plumbing Vent at the Roof Line

Plumbing vent pipes may become a source of leaks in your roof, unless you properly install flashing around them. The flashing must sit under the shingles above the vent pipe, and above the shingles below the vent pipe, to keep a watertight seal. A rubber boot, which comes with the vent pipe’s flange, completes the watertight seal, as it keeps water from leaking between the space between the flashing and the vent pipe.

Pry bar
Vent pipe flashing
Chalk
Utility knife
Roofing nails
Hammer
Roofing compound
Flashing rubber boot

Instructions

- 1
  Pry up any roofing nails holding the bottom edge of the shingles above the plumbing vent pipe. Lift up the bottom of the shingles and slide the flashing over the vent pipe.
- 2
  Lower the shingles over the metal flashing to see how the shingles fit. Using a piece of chalk, mark where the shingles sit on the raised portion of the flashing.
- 3
  Lift up on the flashing to slide it off the vent pipe. Use a utility knife to trim the shingles along the chalk line you marked. Slide the flashing back over the vent pipe and under the shingles above it, testing that the shingles sit flat against the flashing.
- 4
  Drive roofing nails through the edges of the flashing, except where the flashing sits under the shingles. Lift up the shingles and apply roofing compound to the flashing where it meets the shingles. Press down on the shingles to adhere them to the flashing.
- 5
  Slide the flashing’s rubber boot over the vent pipe. Press on the boot until it sits firmly against the flashing, forming a watertight seal.

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