Extruded foam over slab
I have an existing pole barn that I’m converting to a workshop. Since this building will be heated I would like to insulate the existing slab which is pitched to middle so that it could be washed down back in the day. I will be putting down a layer of plastic with treated sleepers over it ripped from 1 1/2” at the end to 2 1/2” in the middle and then covered with plywood . If I use 1 1/2” XPS will the 1” air gap in the middle be inefficient? Am I better off having someone spray open cell spray foam that fills the void completely? Thank you.
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