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Community and Q&A

Exposed Frost Protected Slab

Christian Stevens | Posted in Green Building Techniques on

Well be starting construction on our new home in Freeport, ME this Spring, using a Frost Protected Shallow Foundation (with the WarmFörm product) for both the main dwelling and a detached garage/upstairs apartment. The garage slab will be constructed using the skirt insulation specs for an unconditioned space, while the main dwelling will be built on a slab designed for a conditioned space (less foam skirting). The plan is to begin construction on the garage, and move into the upstairs apartment while we finish the main dwelling.  There is a possibility that we won’t have the main dwelling dried in before winter arrives, leaving a FPSF designed for a conditioned space exposed to a Maine winter.  How risky do you think this would be? I plan on up sizing the skirt around the main dwelling as a precaution (say 2 feet of 2” EPS all around), any other ideas to protect the slab should this be a situation we’re confronted with? I’m assuming snow cover would help a bit. The slab will be on a well drained, frost resistant gravel base. Floor plan attached. Thank you

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  1. Expert Member
    Peter Engle | | #1

    There is certainly some risk there. how much risk is difficult to predict. The risk of frost heave is very site dependent. Some factors that would reduce/increase the risk:
    -coastal sites are often much warmer than the climate zone would indicate
    -Well-drained soils are less prone to frost heave than heavy soils.
    -Good site drainage will reduce risk. Wet sites have higher risk. A dry site with ledge close to the surface would have very low risk.
    -If you can provide good site and subsoil drainage, your risk will be significantly reduced. A thick stone base with drain pipes that daylight would be very good protection.

    1. Christian Stevens | | #2

      Thanks, Peter

  2. Expert Member
    Peter Yost | | #3

    Hi Christian -

    seems like the biggest threat would be UV degradation; can you protect for that?


  3. Expert Member
    Zephyr7 | | #4

    If you can get some BLACK poly sheeting you can use that for UV protection. It will also help to keep things a little warm (tenting) if it gets exposure to the sun. Cheap and easy, and probably about the best you can do.


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