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Air Seal Wall Sheathing to the Foundation

January 07, 2021
Read time: 2 mins

One of the biggest air leaks in a house is where the wood meets the concrete

In previous episodes, we installed wall sheathing and taped the seams between the panels. 

This episode focuses on another super-important place to detail the air barrier: where the walls meet the foundation.


Masking a line gives a clean finish

Liz snaps a line about an inch and a half below the wall sheathing and uses duct tape to mask the line.

She masks off about ten feet, and turns to the tubes.

The first bead goes directly under the wall sheathing, to seal the sheathing to the bottom plate. Run additional sealant below to bridge the space between foundation, sill seal gasket, and framing.


Tool the sealant with a plastic spoon and squeegee

The best way to get a clean cove-like fillet bead of sealant is to use a cheap plastic spoon. They are flexible, rounded, and free. 

When the sealant is worked into the upper gaps, the lower edge is smoothed out with a plastic squeegee. 

She works in about three-foot sections, so she can move her whole setup and not have to walk back and forth.  

Working her way down the wall, she squeezes sealant, spoons it in place squeegees the excess, and finally, peels the tape.

When peeling tape off a wet edge like this, pull the tape slightly toward the wet edge, this will fold the sealant back on itself, rather than pulling it down toward the line.

After the first section of wall is done, she begins the next section. Taping the line, sealing the gap, smoothing the surface, and repeating all the way around the house.


—This is the seventh part of a seven-part series on framing, flashing, and sealing a double-wall house. 


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