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