How to Insulate an Attic

In this video, This Old House general contractor Tom Silva and host Kevin O’Connor explain how to insulate an attic.

Steps:

1. While wearing dust mask and gloves, carry R-38 batts of unfaced fiberglass insulation into the attic.
2. Lay the batts across the ceiling joists, covering the existing insulation.
3. Continue laying down the insulation, making sure the batts are pressed tightly together at all edge and end joints.
4. At the perimeter of the attic, lay the insulation up to the roof rafters, but keep it away from plywood roof sheathing.

Wear a dust mask, goggles, work gloves, a long-sleeve shirt, and long pants to protect your lungs, eyes, and skin from insulation fibers. As This Old House Magazine advises, this gear is essential for getting the job done without discomfort or injury.

Pro Tip: Don’t stand on the joists while working—if you lose your balance, you could crash through the ceiling. Use a piece of plywood or a couple of sturdy, wide boards as a standing surface, and move them around as you work.

Always cut batts to fit around obstructions and penetrations rather than stuffing or cramming them around ducts, piping, and other obstacles. Compressing the insulation crushes the air-trapping pockets in the material, reducing its insulating properties. Place the new layer of batts perpendicular to the old layer to cover any gaps in the lower layer.

As This Old House Magazine advises, covering up soffit vents with batts is a huge no-no—the airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams. Staple plastic or foam baffles to the roof sheathing near the eaves to keep insulation away from the roof’s underside and maintain proper ventilation.

Tools: