Trying to improve some foundation details
Getting ready to begin a new house and looking to improve some of the weaknesses in the thermal envelope especially in the foundation area, rim joists and where the wall meets the floor system. I will attach pictures below – I am a builder not an architect so please excuse my scribblings.
A quick description of the foundation. Concrete footing, 8” CMU, Closed crawl, 1.5” Thermax on the foundation walls, I Joists floor system, 2×6 wall with 1” Dow SIS. Home is designed for zero entry at each of the three entrances so the crawl space is completely below grade. Looking back should have maybe considered doing this on a slab but that decision was out of my control and at this point too late. Climate zone 3A – Mooresville, NC
We have will have three different conditions on this home:
Condition #1 – Exterior slab butts into the floor system – top of slab is flush with top of floor system. Our current design (Option A) I feel has a weakness where the bottom of the wall meets the floor system. The wall basically sits on top of the masonry and the floor system sits inside. The upside to this detail is the soil below the slab and the slab itself butts into masonry. If we insulate at the rim joists there is essentially a break in our thermal envelope. Was thinking Option B would provide a more continuous thermal envelope. My concern on this detail is the soil and the slab butt into the wood floor system. I was thinking with good flashing – 24” galvanized flashing or a peel and seal bituminous type membrane. Any suggestions for improvement?
Condition #2 – Pretty similar to condition #1 except instead of a slab we have the exterior grade bearing against the floor system. Option A has the soil bearing against the wood frame, siding, etc. which we obviously cannot do per code. Was thinking of extending the masonry portion up flush with the top of the floor system – similar to option A of condition #1 that I was trying to avoid. Any suggestions on how to improve this detail? If I am trying to avoid spray foam – what is the best product to use on the rim joist? Install rigid foam between the I-joists and seal them in?
Condition #3 – Similar to condition #1 but this is where our heat sink floor is (passive solar home). Again as in #1 thought we had a break in our thermal envelope so installed the rim joists and rigid foam under the wall and allowed the exterior slab and the heat sink slab to butt in the rim joists.
Thanks for the thoughts.
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