How to Insulate a Garage Roof

Install temporary braces to hold the insulation batts in place. You're going to staple the batts to the roof joists, but until you do so, you need something to hold the insulation in place. You can nail wooden tack strips across the joists every few feet, or you can use bar clamps, clamped to the joists. Tack up the strips or attach the bar clamps every 4 feet the length of one joist space.

Position your scaffold at the end of the garage, between two joists. Unroll the first insulation batt and fit it between the joists. Lift it up over your tack strips or bar clamps.

Staple the paper flange on either side of the insulation batt to the joist, using the staple gun. Place a staple every few inches until you've stapled the length of the batt. Move your scaffold if you need to in order to reach all of the insulation batt.

Repeat these first three steps as needed to fill the joist spaces with insulation batts. Move the tacking strips or bar clamps and your scaffold after you staple in each batt.

Cut insulation away from electrical outlets. Cut the insulation with a razor knife. Seal the cut edges to the edge of the electrical box with duct tape to seal out drafts.