The air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. on a home can be exterior, interior or ideally both. The Airtight Drywall Approach (ADA) adds perimeter caulking or gaskets to the gypsum board installation on exterior walls as an interior air barrier. This is not to be confused in any way with a vapor retarder. While a vapor retarder such as polyethylene or MemBrain installed behind the gypsum board can be installed in an airtight fashion to double as an interior air barrier, the ADA is just about air sealing.