I’m building a bathroom addition on my house in Vermont. It’s 10′ x 18′, with the 18′ parallel to the house. Ten feet out the ledge is right at grade, at the house it’s only 9-12″ to ledge. I’ll be pinning a poured concrete wall to the ledge, at grade that wall height will be about a foot up from grade, at the house the wall will be approximately 2′ high. Inside the wall will be tamped gravel, 4″ of rigid insulation, topped by a 4″ concrete slab. My main question is how to keep the 2 traps from freezing. I thought I’d make an insulation box to go under and on all 4 sides of the traps, but I’m wondering if there’s another standard practice for this. I can’t find anything on-line.