How do you install a roof vent?
Short answer. To install a box roof vent, locate a spot between rafters high on the slope, cut the opening to the vent's template, loosen the shingles above, slide the vent's flange under the upper courses with the bottom edge over the shingles below, then nail and seal it. A ridge vent is installed differently, over a slot cut along the peak and covered with cap shingles.
Before you start
- Calculate how many vents the attic needs from its floor area and the vent's net free area rating.
- Confirm the attic has soffit intake.
- Do not add box vents to a roof that already has a ridge vent or power fan.
- Work in mild weather with fall protection, and wear soft soled shoes.
Installing a box vent
- Locate: from the attic, pick a bay between rafters within about 3 feet of the ridge measured vertically, and drive a nail up through the deck at the center.
- Mark: on the roof, center the vent's template or base on the nail and trace the opening.
- Cut: cut through the shingles and decking with a utility knife and saw, without cutting rafters.
- Loosen: break the seal on the shingles above and beside the hole, and pull nails in the way.
- Set: slide the vent up so the top and side flanges go under the shingles and the bottom flange lies on top.
- Fasten: nail through the flange where the shingles will cover the heads.
- Seal: apply roofing sealant under loosened tabs and on any exposed nail heads.
Space multiple vents evenly across the slope, typically on the rear of the house so they are less visible.
If you are installing a ridge vent
Remove the ridge caps, cut a continuous slot to the width the vent specifies, stopping short of the ends, install the vent, and nail new cap shingles over it with longer nails.
When to hire it out
Steep, high, or old brittle roofs are dangerous and easy to damage. A professional installation also avoids the most common leak: a flange laid on top of the shingles. See ridge vent vs box vents and roof flashing explained.