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Community and Q&A

Under-slab insulation in SoCal (climate zone 3)

SoCalICF | Posted in Energy Efficiency and Durability on


We’re building a new slab-on-grade home in Southern California about 5 miles from the ocean.  Code does not require insulation under the slab.  Is there any reason to consider doing this anyway?


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  1. Expert Member
    ARMANDO COBO | | #1

    I've designed homes in CZ3 that homeowners wanted some insulation under the slab, and we end up installing 4x8 2" rigid foam around the perimeter, under the slab. Also, where you install the foam, depends if you do a 3-pour foundation, monolithic or waffle. Hopefully, there is no termite issues.

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