In simplest terms, a wall is a six-sided box consisting of a horizontal top plate, a horizontal bottom plate, and vertical side studs, with a gypsum board and wall sheathing back, all fastened together to create a wall cavity that is typically filled with insulation when this wall is part of the building’s exterior shell. If air is allowed to flow through the wall cavity, i.e., if the wall cavity is not air tight, the flowing air can reduce the insulation’s effectiveness. If the wall cavity is not airtight, convective loops can also develop within wall cavities, due to temperature differences between the inside and outside surfaces and top and bottom sections of the wall. These convective loops can encourage more air flow, further reducing insulation effectiveness and potentially resulting in moisture problems.

To ensure the optimum energy performance and moisture management of the whole house, all of the wall components should be connected to the each other and to the ceiling and floor in a way that creates a continuous and complete air barrier system.

Gypsum board drywall is an air barrier material (BSC 2009). The taping of drywall seams results in a plane of airtightness at the field of the wall. However, several steps must be taken
to use this material properly to create a continuous and complete air barrier system. To do this, it is important to create air barrier continuity at the perimeter of drywall assemblies as well as at all penetrations through the drywall. Air barrier continuity at the perimeter of drywall assemblies is achieved by sealing the edges of the drywall to solid framing materials. This requires a continuous bead of sealant along:

• all exterior wall bottom and top plates,
• all top plates at insulated ceilings,
• rough opening perimeters,  
• both sides of the first interior stud of partition walls (BSC 2009).

This air sealing can be achieved by applying caulk, glue, or strips of foam gasket material to the surface of the top plates, bottom plates, and framing around doors and windows before installing the drywall. This would typically be done by the drywall installer. This task should be included in the contract for the appropriate trade depending on the workflow at the specific job site.

How to Air Seal the Sheetrock to the Top Plate

1. Apply a continuous bead of caulk or glue or staple a strip of compressible foam gasket material along the top plate along all exterior walls and all interior walls.
2. Install drywall over caulk, glue, or gasket material. Mud and tape drywall. 

Figure 1 - A pliable foam gasket material is stapled along the top plate prior to installing drywall

Figure 2 - A continuous bead of caulk or glue is applied to the top plates on exterior walls and interior walls that intersect insulated ceilings, as well as rough openings around doors and windows, prior to installing drywall

Figure 3 - Sealing the drywall to the top plate is one step in forming a continuous, complete air barrier in the home’s exterior shell