Weatherization
Considerable detail goes into sealing the homes envelope.
Some very impressive results in tightening the envelope are achieved using dense packed cellulose and sealing air gaps around things like recessed lights.
The best results are achieved when there is complete access to the inside of the walls. When this is possible, plastic sheeting is applied to create a solid vapor barrier, which is seamed and sealed around all sockets, lights, switches, overlaps, etc... Studs in the wall are sealed with caulk.
