How to Add Air Vents to Garages

Calculate the number of vents you need for the garage by measuring the length and width of the garage floor and multiplying them together to determine the square footage. Divide the square footage by 150, because you want one vent for every 150 square feet of space.

Drive a nail through the roof where the first vent is being installed. Place the nail 2 to 3 feet down from the peak of the roof, centered in between two roof rafters. Space the vents evenly along the roof in order to provide the best ventilation.

Climb up to the roof and locate the nail. Look for an area where the shingles are raised.

Draw a circle on the roof that is the same diameter as the inside of the vent, keeping the circle centered over the nail.

Cut the shingles along the circle with a utility knife, then pry them off the roof with a pry bar.

Cut a hole in the roof where you removed the shingles with a reciprocating saw.

Remove the roofing nails from the shingles around the top of the circle by prying the shingles up and pulling out the nails. This will enable you to slide the top of the roof vent underneath the shingles.

Apply a thick bead of roofing cement to the shingles along the bottom edge of the circle.

Slide the top of the flashing for the roof vent underneath the shingles around the top of the hole, and push the bottom of the vent into the roofing cement. The flashing is the flat part around the base of the vent.

Nail the roof vent to the roof with galvanized roofing nails, then seal the vent with clear silicone adhesive. Place the adhesive along the joint where the flashing meets the shingles, and on top of the galvanized nails.

Nail the shingles around the top of the vent to the roof where you removed the original roofing nails. The nails will go through the shingles and the flashing, and into the roof sheathing.

Install the other vents using the same technique.