What is the proper installation of roof vents?
Short answer. Proper roof vent installation means cutting the opening to the vent maker's size, setting the vent's flange under the shingles above it and over the shingles below so water sheds naturally, nailing it at the marked points, and placing the vents high on the roof at the same height. Sealant is a backup on exposed nail heads, never the main waterproofing.
Static vents, step by step
- Locate the vents near the ridge, usually within 3 feet vertically of the peak, spaced evenly between rafters. Check from the attic that no framing or wiring is in the way.
- Cut the hole to the size printed in the vent instructions. A hole cut too large weakens the deck and leaves the flange unsupported.
- Install shingles up to the bottom of the hole.
- Set the vent so its lower flange laps over those shingles.
- Run the next courses over the top and sides of the flange, trimming shingles around the hood without blocking the louvers.
- Nail the flange where the manufacturer marks it, then seal any exposed nail heads.
What a bad installation looks like
- A flange sitting entirely on top of the shingles, held down by a bead of caulk.
- Vents scattered at different heights, so the lower ones act as intake and pull hot air back in.
- Box vents added next to an existing ridge vent, short circuiting it.
- Bath fan caps with no damper, or a duct simply aimed at a vent instead of connected to its own cap.
Pipes and flues are different
Plumbing vents and appliance flues get their own boots or storm collars, following the same rule: upper shingles over the flashing, flashing over the lower shingles. Metal gas appliance flues also need clearance from combustible materials, so a roofer should coordinate with an HVAC technician when those are moved or replaced.
See roof flashing explained and pipe boot leaks for the details that keep penetrations dry.