I am curious about shallow frost free foundations. These are generally a thick foam form filled with cement that has no grade beams or other excavation, except plumbing and electric. Sometimes it is called a raft foundation. The vendors say the cost of excavation, form work, and removal exceeds the cost of a shallow foundation. Do any of you have experience or knowledge about this?

I prefer a complete frost wall. Better performance with minimal additional cost. 42" frost depth in my area.

With either option, look for designs that minimize thermal bridging (for example, from a footing to the interior of an ICF wall).

It's easier to build a FPSF with very low soil loading.

My sons and I finished one near Waterloo Iowa. It's 1080 sq. ft. and I have $11,480 in it which includes $4,500 for the concrete and labor to pour and finish the floor. I do not believe we saved a lot over constructing a stem wall but it was a convenient choice for us considering the limitations of the site. The big ticket items were Fox Blocks at $2,800; high density EPS foam $2,800. It cost me $1,220 for a plumber to put in the drain system and water supply.

Anyone heard of Legalett FPSF system with integrated floor heat (using air in a closed loop, instead of hot water)? I'm interested in the Frost Protected Shallow Foundation idea, and also looking into floor heat options.
Thanks!