Unvented small crawl space details for helical pile foundation
I’ve done some reading here on GBA and Building Science Corp. I am hoping I’ve understood the details and just wondered if I could sanity check and get any inputs from yourselves.
Climate 4c. A small 300sqft new cabin with a small 4-6” gap to grade under the floor. Floor structure is a steel perimeter frame with infilled timber joists floor sat on helical screw piles.
We can’t build any higher nor can we pour a concrete slab for various reasons.
– – 2” second hand rigid foam insulation laid on top of a thin gravel layer over the levelled earth, I understand insulation here doesn’t offer much benefit but I think code wants to see it and it’s a small area so not very costly
– – Heavy gauge poly laid onto insulation with seems sealed and taped
– – Insert helical piles through the poly and insulation then seal the poly at each penetration with a gasket
– – Bring poly up the perimeter and seal to the steel perimeter beam
– – 2” rigid foam insulation vertically at perimeter to the top of floor level encasing the steel beam at the outside and bury into the ground 6” or so to get below frost depth (the face of insulation would in turn sit plumb with our proposed 2” of exterior insulation on the walls above)
– – Protect exterior insulation with cement board or edpm
– – Introduce conditioned air to the mini crawl space and add an extraction point via our HRV
– – No plumbing in the space which can instead go directly out the back wall
Your thoughts welcome. Thank you
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