I am doing a diy hydronic heating system in a house I bought in the mountains. For the main part of the house I am using 3/4" x 9" strips of plywood with spacing for the tracks of the 1/2" pex. Above that I have a 1/8" sheet of plywood to keep the pex in place until I am ready for the hardwood flooring. Overall height including the new hardwood is 1 1/4" increase in the floor height.
The question I have is around the bathroom, kitchen and entryway. We were thinking that instead of doing something similar and then using hardiebacker and tile we would do a poured and polished concrete slab for these locations. The concern I have is about if I would be able to have 1.25" thickness in the slab, would that be thick enough to not have the tubes project through the floor and still have a warm floor? I was thinking of using GFRC but not sure if that would do anything better or not. I also do not think that the 1/2" above the pex would allow for any rebar to be put in. I may be able to use a thinner wire mesh.