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Where does a vapor barrier go in a frost protected shallow foundation?

Dale Luhman | Posted in Green Building Techniques on

we have a high water table and want to put in a frost protected shallow foundation in an unheated garage. however,

in holladay article “polyethylene under concrete slabs” martin says to put vapor barrier directly under the concrete slab. his layers are concrete, vapor barrier, 2″ rigid insulation, 4″ crushed stone-no fines.

in revised builders guide to frost protected shallow foundations for unheated buildings, figure 7 layers are concrete, non-frost susceptible fill, rigid insulation, 6″ minimum sand/gravel layer.

so in a frost protected shall foundation, it seems like having a vapor barrier would be good. should a 10 mil vapor barrier be placed between the concrete and the non-frost susceptible fill?

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  1. Expert Member
    Malcolm Taylor | | #1


    Martin (and BSC's) advice doesn't change. Regardless which other layers you have, the vapour-barrier is always best situated directly below the concrete slab.

    1. Dale Luhman | | #2

      thanks. thats what i thought, but since it was not clear in blending the two articles i wanted to double check.

  2. Deleted | | #3


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