Insulation
Crawl Space Insulation Calculator
Insulation for a crawl space, whether it is insulated at the floor above or at the walls.
Result
Where the insulation goes depends on whether the crawl space is vented or sealed. A vented crawl space is insulated at the floor above; a sealed and conditioned one is insulated at the perimeter walls with a ground vapour barrier. Getting this the wrong way round traps moisture and causes rot. 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
Floor or walls?
Floor above if the crawl space is vented to outside. Walls if it is sealed and treated as part of the conditioned building, which also needs a sealed ground vapour barrier.
Is fibreglass suitable down there?
Poorly. It absorbs moisture, sags off the joists and gives rodents a home. Rigid foam or closed cell spray is the usual choice in damp conditions.
The formula
thickness = (target R - existing R) / R-value per inch
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