How do you install attic vents on a shingle roof?
Short answer. To install a box vent, locate a spot between rafters near the top of the roof, cut the opening to the vent maker's template, slide the vent's upper flange under the shingles above, and nail the flange so the lower edge laps over the shingles below. Exhaust vents should sit within 3 feet of the ridge measured vertically, and they only help if there is soffit intake below.
Before you start
- Calculate how much exhaust the attic needs and read the vent's net free area rating.
- Do not add box vents to an attic that already has a ridge vent or fan.
- Confirm the soffit intake is open; without it, new vents will not help.
- Roof work is dangerous. Use fall protection, avoid hot afternoons when shingles scuff, and avoid cold days when they crack.
Installing a box vent
- Mark from inside: in the attic, pick a bay between rafters near the ridge, away from wiring, and drive a nail up through the deck as a locator.
- Lay out the hole: on the roof, center the vent's template on the nail and mark the opening.
- Cut: set the saw to the deck thickness and cut the opening, staying clear of rafters.
- Loosen shingles: break the seal on the shingles above the hole and pull the nails that would block the flange.
- Set the vent: slide the upper and side flanges under the shingles, with the bottom flange over the shingles below.
- Fasten and seal: nail the flange corners, renail the shingles above, and seal exposed nail heads.
Intake vents
Undereave vents are cut into wood soffit between rafters and screwed in place, with baffles installed inside so insulation does not block them.
Placing several box vents in a row along the back slope keeps them out of view. Compare with ridge venting in ridge vent vs box vents, and see roof flashing explained.