How to Vent a Shed-style Roof

Determine the pitch of the roof by: using the level to mark a plumb line on the face of a gable-end fascia; placing the pivot point (spot at the base of the right triangle) of a speed square at the bottom of the plumb line with the backside of the right triangle on the plumb line; and reading the pitch where the bottom of the fascia passes through the slot at the bottom of the speed square (common rafter scale).

Buy two, right-triangle vents with the same pitch as your roof. Get the correct orientation since one needs to face right while the other faces left.

Measure the three sides of one vent, minus the flange or frame, and draw an outline of it on each gable end. Lay this out so the angled side of the vent follows the angled underside of the roof line. Keep the angled line just below the top framing member of the half-gable.

Cut out the sheathing inside the lines you drew in step three, using the saw. Set the saw cut depth to match the thickness of the sheathing so you don't cut through any framing. If there are no framing components in the way, or the thickness of the vent will allow you to set the vent in the opening and nail it in place through the flange, then go on to step six.

Remove existing framing that will not allow the vent to fit all the way into the opening. Add new framing around the inside of the opening creating a box for the vent to fit into by cutting the two-by-four lumber into lengths that fit between the remaining framing components and fastening them in place with the two-inch deck screws.

Apply a bead of silicone caulk all around the back of the flange of each right-triangle vent. Place the vents into the holes and fasten in place by driving nails or screws through the flanges and into the sheathing.

Fit the siding to the edges of each vent frame or over the top, depending on your vent type.