Hi Everyone, I am planning to build a cottage around Montreal, Canada. Usual foundation depth is 4' but I know I can do the FPSF frost protected shallow foundation and use ICF's just 16" high or deep?? I also know I need to insulate under the slab but what about the footing do you also insulate under the footing? Any other ideas or ICF company's I should look at?? Thank you Enviroman

Environman, We are starting a FPSF project next week. We will be setting two courses of 16" tall ICF on 6AA stone. The blocks will have 4" showing above grade. The concrete will be held down to 28" and the inside will have 4" of foam removed for the slab to pour over to the top of the block. There will be 2" of foam laying flat along the exterior extending out 2'. I will try to get some pictures once we get started.

With ICFs for the stemwall, you can skip the insulation under the footing because there aren't any significant thermal short circuits. However, the building would perform a little better with some insulation under the footing.

The biggest problem with that, however, is getting building dept. approval for foam under the footing. See, the standard FPSF details don't show it, so the bldg. dept. may not allow it without a stamped drawing from a PE. Most foundation engineers, however, would understand that the foam is strong enough (they make foams rated up to 100psi). So I'm saying that it's probably not worth the hassle and extra engineering cost if you're dealing with a picky bldg. dept.

You don't need footings with FPSF - just a monolithic, thickened edge slab around grade level or below. Foam under it (extending past the edges), stack ICFs on top of it.

Jonr, You are absolutely right that a monoslab is the best and least expensive way to do FPSF. On a sloped site, or if you just have to have a crawlspace, then a stemwall can be appropriate. Again, the standard FPSF details don't show foam under the bearing wall (except for unheated structures), but it is desirable and possible. http://oikos.com/esb/43/foundations.html