My radiant floor heated, slab on grade has the insulation like is show in the blueprint, and it works extremely well.
If a person did not like Styrofoam insulation, more permie methods exists.
1) Years ago we had problems with our sawmill twisting out of level, plumb and square due to frost heaving it, so we ended up tossing down 6 inches of sawdust and the problem was gone. An occasional refreshing of the sawdust every few years kept the ground insulated from the cold. Sawdust can be found anywhere.
2) When I do waterlines, Styrofoam is not only expensive, but hard to put into a less than rectangular spot, so I use sheep manure. Think of sheep poo as a natural cob with manure and hay being in convenient pellet form. I spread that over my pipe, then back-fill with soil. This winter we never got above zero for 3 straight weeks, and yet my pipes going to the sheep barns never froze. Other manures do not work as well as sheep poo, so see if you can find a sheep farmer and get some perhaps.
posted 5 months ago
Daniel Ray wrote:6" is really shallow, what are your temperature lows? An insulation skirt around the footing will trap heat from the earth and prevent frost heave.
This is GREAT information, and answers my question perfectly.
It also helps me articulate why I won't insulate underneath the footing.
My only concern is that the footing will be at grade, meaning the foam will be accessible just at the surface, and will get beat up.
I'm sure I can solve it, but would be interesting to hear if anyone else already has.