Insulate beneath concrete slabs regardless of climate
Use 2-in. of XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. (R-10) in all but the warmest climates
When detailing a concrete slab on grade, add insulation at the perimeter and beneath the slab. This is useful even in warm, humid climates. Here, insulation beneath the slab isolates the living space from cool below-grade temperatures. This reduces the chance that warm, humid air will condense on cool concrete floors. In Florida and the southern-most parts of Texas, Louisiana, Alabama, and Georgia you could drop back to 1-in. or R-5.
Exterior insulation needs protection from the elements. Choose materials that are nontoxic and durable. In termite prone areas, prevent infestations by installing a termite barrier, which protects the insulation from insect and moisture damage.
Learn more in the Green Building Encyclopedia:
Further Resources
Building Science Corp.
Primer on problems with concrete slabs and how to prevent them:
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