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You can use polystyrene or polyisocyanurate foam board insulation on concrete basement walls. Purchase 8-by-4-foot foam board insulation sections and install them in the basement with the lengths running vertically across the entire wall. Polyisocyanurate foam boards feature built-in vapour and moisture blocks, while polystyrene boards do not. Foam board ranges in R-value depending on it's thickness and density and is considered high-quality insulation when installed correctly.
Measure the height of the basement wall and transfer this mark to the foam board. Hold a straight edge, such as a four foot level, across the foam board at determined mark.
Cut along the edge of the 4-foot level with a utility knife. Bend the foam board at the cut line to snap off the waste material if the knife was not able to cut completely through it.
Run 1/2-inch beads of construction adhesive all over the back of the foam board, especially around the outside edges. Place the foam board vertically on the wall starting at a corner.
Continue running foam board across the entire length of wall following the previous steps, making sure to butt each tightly together.
Place spray foam along the entire bottom and top of the wall. Fill any holes or cracks using the same can of foam. Wait for the foam to expand and dry before shaving off any excess foam using a scraper.
Place insulation tape over each seam where the foam boards butt against each other. Run your hand over the entire length of the tape, making sure it has made full contact with the foam boards.
- For basements that are higher than 8 feet, place full sheets of foam board across the entire bottom wall using construction adhesive. Follow the bottom row of foam board with custom cut portions of the same material. Align all the corners of the top row with the bottom and tape accordingly.
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