My brother and I share a brick garage on our family's property in Pennsylvania that has a 1970s concrete floor. We were thinking of tearing it out and putting in radiant heat so it's more usable in winter. If we go 10 inches down for insulation and tubing, it drops us below the foundation line. I'm trying to keep the cost down by doing as much of the work ourselves as possible but I don't want to end up with a cracked wall. What's the lowest safe depth you would recommend without undercutting the footing?