Foundation insulation

If within the scope of work, foundation walls determined as the thermal boundary can be insulated to a minimum of R-10 and be sealed as explained in the air sealing section of this document. Before starting, confirm that roof runoff, surface water, and groundwater are drained appropriately.

1 Performance criteria

Basement or crawlspace must be brought under the thermal/pressure boundary by installing rigid insulation inside of foundation wall, sealed from subfloor to below grade.

2 Preparation

Primary air leakage should be substantially lowered by sealing gaps at the rim joist, sill, and surface of the foundation wall.

3 Installation

a. For basements assign R-5 or higher foil-faced isocyanurate board listed for exposed use to the foundation wall, full-height; and cut pieces to fit into rim joist and across the sill. Close the gaps in foam board edges at rim and sill, and tape seams in foam board on the wall.

b. For crawlspaces attach R-5 or higher XPS rated for uncovered use in crawlspaces to the foundation wall, to 24 inches below grade; and cut and fit pieces to fit into the rim and across the sill. Seal gaps in foam board edge at rim and sill and tape seams in foam board on the wall.

c. If XPS foam board is installed in a basement beyond the listing for uncovered use, follow a. and cover foam with a thermal barrier.

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