How to Seal a Roof Vent

Roof vents are the most common points of failure on a sloped roof. Every plumbing stack or exhaust vent requires a rubber boot to bridge the gap between the pipe and the shingles, and over time, that rubber degrades under the sun's UV rays. When you see water stains on your ceiling, there is a very high probability that a weathered vent boot is the culprit. Addressing this early prevents rot in your roof deck and mold in your attic insulation. A well-sealed vent uses a combination of integrated flashing, properly placed nails, and high-grade exterior sealant to ensure that water is directed away from the penetration point and down the slope of the roof, rather than into your home.

1. Check Before You Touch. Carefully lift the shingles overlapping the top edge of the vent flashing. Check for cracks, curling, or nails that have backed out of the roof deck.
2. Clean the Foundation. Remove any moss, leaves, or old, cracked caulk around the base of the flashing. Use a stiff putty knife to scrape away loose debris without damaging the shingles.
3. Plug the Leak Points. If you find nails that are pulling up or leaving holes in the flashing, remove them or tap them flush. Apply a dab of roof-grade sealant over every exposed nail head.
4. Inject Under the Flange. Lift the edges of the flashing where possible and inject a bead of sealant underneath. Press the flashing firmly back down to ensure a compression seal.
5. Patch the Rubber Boot. If the rubber gasket around the pipe is cracked, apply a specialized rubberized roof patch directly over the cracked area. Smooth it out with a gloved finger to create a tapered, waterproof edge.
6. Restore the Roof Deck. Lower the shingles back into position over the top flange of the vent flashing. Secure them with a small dab of roofing cement under the edges to hold them against wind lift.