The wall-to-foundation interface is a critical location for maintaining continuity of air, vapor, and moisture barriers in the building envelope. This article outlines best practices for properly detailing these transitions in residential and commercial construction.
Why This Transition Matters
This junction often includes dissimilar materials—concrete, wood, or steel—and is exposed to ground moisture, settlement, and air infiltration. Failure to seal this interface can result in bulk water intrusion, thermal bridging, and indoor air quality issues due to radon or soil gas infiltration.
Transition Detailing Methods
- Use fluid-applied membranes that bridge from slab edge or foundation wall to sheathing
- Install flexible transition membranes over concrete or CMU, lapped under WRB or CI layers
- Where rigid foam is used at the foundation, integrate sealant or tape joints at board edges
- Seal sill plates to concrete with gasket tape and apply sealant beads around anchor bolts
Vapor Control and Climate Considerations
In cold climates, a vapor retarder may be needed on the interior face of the wall assembly. In mixed or humid climates, use vapor-open air barriers on the exterior and ensure drainage and drying potential. For slab-on-grade homes, include a polyethylene vapor barrier below the slab and seal its edge to the vertical foundation membrane.
Quality Control and Field Testing
Mock up this transition before full construction and inspect for full adhesion and continuity. Use blower door testing with pressurization diagnostics to identify leakage paths at sill plates and wall-footing junctions. Photograph and document membrane overlap lengths and sealant types used for project records.
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