How to Install a New Gable Vent in an Attic

Build a square frame into the attic using 2 x 4s and nails or screws so that you can attach it to the gable end studs. Build the frame so that it will have at least a 1/8-inch clearance on all sides, including the top and bottom.

Outfit your drill with a long bit extension. Drill some 3/8-inch holes to the outside to help you locate all the corners of the opening once outside.

Snap some chalk lines on the holes you made from inside the attic to outline the vent opening. Place a bi-metal blade in your reciprocating saw and cut out the outline following the chalk line.

Center the vent's body over the opening you made and trace the outline of the flange with a marker. If there's no flange to trace, use the trim that you plan to use. Determine the depth you will need to cut in the exterior wall and set your circular saw. Remove the piece that you cut out so that the flange will lie flat against the sheathing.

Flash all sides of the vent frame with building paper, making sure the upper pieces overlap the bottom pieces so that the top covers the metal cap. Secure the paper in place with a staple. Make sure that the new paper overlaps the old paper by 2 inches.

Apply caulk to each strip and insert it under the siding on all sides. Fold overlapping paper before shoving it into the opening.

Push a metal cap flashing under the building paper and the exterior wall at the top of the vent opening. Apply a good amount of caulk under the flange and put the vent in place by pushing the top under the metal cap flashing.

Secure the vent after you check to make sure it is plumb with some nails or screws placed in all sides. Make any additional repairs like replacing shingles or adding trim so that the vent matches the rest of the house.