In this video, This Old House general contractor Tom Silva shows how to super-insulate an attic.
1. Apply closed-cell spray foam insulation to the underside of the roof sheathing, filling the spaces between roof rafters.
2. Once the foam cures, use a reciprocating saw to trim the excess foam flush with the rafters.
3. Cover the insulated attic roof with ½-inch-thick drywall.