Insulation
Basement Insulation Calculator
Insulation for basement walls and rim joists, where moisture decides the material.
Result
Basement walls are below grade and damp. Rigid or closed cell foam against the concrete keeps warm indoor air away from the cold surface where it would otherwise condense. Fibreglass batts directly against a foundation wall are a recipe for mould. Required R-values are set by climate zone and by local energy code, and they differ for attics, walls and floors. The figures offered here are common code minimums rather than recommendations, and a minimum is a floor, not a target.
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About this calculator
Why not just use batts?
Because warm humid air reaches the cold concrete through them and condenses. Foam in contact with the wall keeps the dew point inside the insulation where no liquid water forms.
Do rim joists matter?
Considerably. They are a large uninsulated area with direct contact to outside, and sealing and insulating them is one of the cheapest comfort improvements in an older house.
The formula
thickness = (target R - existing R) / R-value per inch
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