OK…. This is slightly complicated, but I’m going to try and cover all the steps we use to perform air sealing and insulation in one. My preferred method of air sealing is using the OSB sheathing on the exterior wall and ceiling drywall above as my air barrier. This said, it is important to seal all connections between floor plates, vertical stud to sheathing connections and wall partitions/penetration in the ceiling. The best way to approach this is by drawing an imaginary line all around the perimeter of the home and seal all known areas of leakage in this plane. My system is a bit redundant, because I also use an airtight drywall approach when installing drywall (continuous perimeter adhesive application around walls, windows & doors) as drywall is being installed.
Sealing begins with using a high quality silicone or acoustical caulk along all bottom plate, king & jack studs, and double top plate. I then ‘picture frame’ the stud cavities with closed cell spray foam. Finally all the partitions and penatrations in the attic are sealed with closed cell foam to give me a continuous air barrier on all six sides of the home.