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Recessed wood framed floor system level with frost wall?

user-7031237 | Posted in Green Building Techniques on

We have an existing building with a concrete slab with interior insulated poured frost walls in zone 6A Southern Maine.
Planning an addition using again interior insulated poured frost walls at the same elevation as the existing frost walls. But in the addition we want a low height crawl space for plumbing & storage with a wood framed floor finishing out roughly the same elevation as the existing concrete slab or top of existing frost walls.
How do we connect I Joists to the inside of the poured wall?
1) create a 4″ ledge in the top of the poured wall?
2) bolt a LVL ledger to the inside of the poured wall similar to deck construction, then use joist hangers on it?
3) What about condensation with the lumber directly against the concrete and insulation on the interior? Bituthane between the lumber and concrete?

Any thoughts or experiences would be appreciated, Thanks! Tom W.

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Replies

  1. Expert Member
    Michael Maines | | #1

    Tom, you just missed a very similar question posted a few days ago: https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/104876/interior-formed-shelf-support-floor-joists-p.

    I've done many of these with a shelf, but on my next one I'm going to try Malcolm's approach of casting in a pressure treated ledger, possibly with foam behind it, and installing the joists on hangers. If you don't have waterproofing on the frost wall exterior and a capillary break over the footer, it would be a good idea to wrap the back of the ledger with Vycor (or other peel-and-stick) to block water movement. The Vycor and insulation should prevent significant condensation, but for another level of protection (and energy efficiency) you could add high-density foam under the ledger.

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