FPSF haunch Detail
Nutting out details for a future Frost protected shallow foundation, has anyone ever done something like this with success?
EPS underneath the footings and slab per the usual guidelines. Board form the sides and apply insulation after stripping. The detail that I’m wondering about is creating the slab haunch in the center. It seems like a headache to detail the foam around a crushed stone haunch, so how about setting all the subslab foam on a level pad, and then piling the crushed stone on top of that, after vapor barrier? I have some concerns about damaging the vapor barrier. Could protect it with cement board? I’ve done FPSP with a foam haunch under the slab, but it seems like that’s expensive and unnecessary from a thermal perspective
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Short answer: yes, using this system: https://warmform.com/. They recommend using additional foam as the interior fill but we used gravel and it worked well. Vapor barrier should go above the gravel.
On a project about to start we will use WarmForm but instead of EPS for the sub-slab insulation we're using Glavel, for a similar end result to what you describe.
Out of curiosity, without derailing the question at hand too much... Do you replace all the gravel with glavel, or just the center of slab foam? I got some info from them and the quote was really not so bad. I'm not sure if it would be easier or more difficult to work with than gravel.
It's my first project using Glavel (or possibly AeroAggregates) and the builder is new to high performance so we're taking it easy on this one, but the idea is to use a crushed stone base layer with Glavel above that--in blue on this drawing: