How to Insulate a Basement Floor
Uninsulated basements provide a major avenue for home heat loss. Placing rigid foam insulation underneath the foundation thermally isolates it from the cold ground to stop heat from being drawn out of the home. If you are insulating an existing home, the best you can do is put the rigid foam over the floor and cover it with plywood. Does this Spark an idea?
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Things You'll Need
- 2" EPS rigid foam insulation
- 1" XPS rigid foam insulation
- Mesh tape
- Mastic
- 1/2" plywood sheets
- Masonry nails
- Hammer
- Drill
- Screws
Instructions
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New Construction
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1
Pour the foundation footings and stemwalls.
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2
Cut the rigid foam insulation to fit vertically along the stemwall. The insulation must be wide enough to reach from the footing to where the top of the slab will be.
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3
Cut a 30-degree angle along the top side of the insulation. This will create a thermal break between the slab and foundation wall to better prevent heat loss--it means that only the top part of the slab will touch the foundation wall.
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4
Place the insulation along the stemwall with the angled cut up and on the inside, away from the stemwall.
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5
Lay more rigid foam insulation horizontally between the vertical insulation. Pour the concrete floor over the insulation.
Existing Construction
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6
Lay 1" XPS rigid foam over the basement floor. Seal the joints between the sheets with mastic and mesh tape to prevent air leaking through.
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7
Cover the foam with a layer of 1/2" plywood and fasten the plywood to the concrete floor.
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8
Lay a second 1/2" plywood layer over the first and screw the two layers together.
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9
Cover the plywood floor with your desired covering or leave it as is.
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