Foundation insulation questions
My wife and I are building a 6000sq’ home just north of Austin, Texas. It is a single story modern ranch type home, principally 2×6 lumber frame with a slab on select fill foundation. We have had a geotechnical and structural engineers design the pad and foundations. Part of the house is on a gentle slope resulting in part of the foundation being somewhat more exposed, in addition the final 12′ of the house at the end of the slope will be cantilevered.
My question is whether the more exposed and the cantilevered parts of the foundation need to be insulated, due to the greater amount of concrete being exposed? The structural engineer said just to put rigid foam insulation on the inside of the concrete forms, but this does not seem to agree with everything that I have read on building science corporation. It also will not prevent heating/cooling by outside air.
The floor on the other side is mostly wood (except for a 5′ wide hallway) and so it seems that the most sensical approach would be to put rigid foam insulation under the subfloor. If so, what thickness should I use?
Last question on this subject, there are 4 board formed concrete walls in the house, with the concrete exposed to the inside and out. The plan is to put rigid insulation in the middle, the question is how much?
Thank you all for your help.
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