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Should we insulate under a slab even in an unconditioned space?

archy21 | Posted in Energy Efficiency and Durability on

We have a +/- 3,000 sq. ft. maintenance building we are designing which is mostly unconditioned space on a concrete slab (there are a couple offices in one area). The primary goal of the slab is to provide a durable and flat work surface for relatively precise vehicle and equipment maintenance. There is always the chance that the building could be re-purposed in the future and insulated and conditioned. We are in climate zone 4. Is the slab less prone to cracking if we install +/- 2″ continuous insulation underneath? or even just 2″ at perimeter?

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  1. GBA Editor
    Martin Holladay | | #1

    I don't think the slab will be less prone to cracking if you insulate underneath it; other factors are more important, including placing concrete with the correct slump (in other words, without too much water) and keeping the slab damp after it is placed until the concrete is cured.

    However, if there is any chance at all that the building might be conditioned some day, now is the time to install subslab foam. It will never be easier or cheaper to insulate the slab than right now.

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