How to Insulate an Attic Ceiling Between Rafters

Lay a piece of insulation into the first space between rafters, with the vapor barrier facing either up or down, depending on your needs. Place a second piece of insulation directly in front of the first piece with the two ends butted tight together. Slide the insulation underneath any wiring that runs through the attic. Continue laying insulation until you reach the end of the attic or a heat-producing object such as a light fixture, chimney or exhaust fan.

Measure the distance from the end of the installed insulation to the end of the attic or heat-producing object. Lay a piece of insulation flat with the vapor barrier facing up. Measure the insulation to the previously noted length and mark it with a pencil. Subtract three inches from the measurement if the insulation is being installed next to a heat-producing object.

Cut the insulation at the mark with a utility knife. Lay the insulation into the opening with one end butted up tight against the end of the insulation laid behind it. Continue laying insulation between rafters until all spaces are filled.

Lay the second layer of insulation perpendicular across the first layer. Peel off the vapor barrier of each piece of insulation used in the second layer. Maintain the three-inch gap between insulation and heat-producing objects. Tuck the second layer of insulation under the roof joists, but keep it from touching the plywood ceiling.