As air rises on its way toward the attic, it often finds a path through recessed lighting fixtures. Remove the trim pieces and seal around the edges with caulk. Better yet, replace the lights with UL-approved airtight fixtures.

Drop ceilings are another common path, since they hide cracks, gaps, and penetrations in the original ceiling. Remove the ceiling tiles and fill cracks and gaps with silicone caulk. Seal around any penetrations with non-expanding foam.