Question
How do I build (detail) an insulated shallow foundation with a (wet) radiant slab?
I know how to insulate a shallow foundation but I am not sure if I still insulate under the slab ( with inclusive geo- liquid in slab) and how far outside around the slab to insulate with the 2" rigid insulation. Our frost depth up here in Iowa is 48". Thank You Charles Schwab AIA
Answer
The first part is easy - yes you insulate under the slab.
The second part depends on which county you are designing for and a few other factors. The chart and associated info needed is in 2009 R403.3.
If in doubt contact the building department as they have the ultimate say and can require more than what the code says.
