How to Handle Rigid Foam and Vapor Barrier Under the Middle of a Basement Slab with Load Bearing Footings?
When insulating a basement slab with a vapor barrier (e.g., 10 mil poly) that will go directly under the slab has a load bearing footing running down the middle of it how should you typically handle the vapor barrier and rigid foam insulation sheets? Virtually every visual example of an insulated basement wall only addresses the slab edge meeting the foundation wall. That part is straightforward. However, there isn’t much attention paid to load bearing footings in the middle of the floor on an insulated basement slab. The house I am building has a 26×40 ft footprint and will have a load bearing footing going down the middle of it for the full length. To detail the rigid foam and vapor barrier should I:
1. Just run the rigid foam and then vapor barrier like the rest of the floor covering the load bearing footings.
a. With this method would I need a higher PSI rated foam such as NGX 400 over the weight-bearing footings than what is used under the non-bearing slab (e.g., NGX 250)?
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