Category Archives: Air Sealing

Mudsills – Where the Framing Meets the Foundation

The framing meets the foundation at the mudsill and the space between them can be the cause of serious air leaks which transport moisture and waste heating/cooling energy. In order to insure an airtight crawl space we made a tight seal between the mudsill and the top of the foundation by placing polyethylene sheeting between the mud sill and the top of the foundation.

The mud sill assembly starts with a 1/4″ closed-cell polyethylene foam gasket directly over the rough surface of foundation wall concrete. The gasket fills gaps and protects the 10mil poly sheeting strips which are placed on top of the gasket. The pressure treated mud sill is then placed over the poly sheeting.

The tough poly sheeting over the top of the foundation acts as a capillary break and vapor barrier preventing moisture in the concrete foundation walls from wicking into the interior wooden structure or evaporating into the interior crawlspace area.

Photos showing the inside foundation wall edge flashing sealed with foam and roof edge flashing screwed to the plastic ICF web. This cap acts as the interior side air seal

Inspection is a constant activity at our job site …but this guy looks confused.

The exposed flap of poly sheeting will be sealed to the exterior sheathing to create a durable air seal at this critical foundation to framing intersection. Next, we begin the crawl space girders and joists.