Had a mechanical company design my floor heat in my shop. They recommended to put tie the PEX above the rebar closer to the top of the slab, rather than the bottom of it. Reason being it makes for a more efficient heat transfer into the shop. Cement guys don't like it as they have to be more careful when working the concrete, but it is your shop. Don't forget to put a vapour barrier underneath the insulation as well. My shop heats very efficiently and I really like the floor heat.We are planning on having a heated floor running PEX every foot on top of 2 inch high density foam and 15 mm rebar at 12 in if I do spray foam it'll be two or three in and probably R-20 bats walls are 2 by 8 construction.
Like the idea of running drainage tile out a side hill but worried that mice or rats me use it as an entry way
Thought about running foam between the strapping on the outside but it would be a bit of a job now that the tin is already done could possibly pull the corners off or a couple of sheets and slide foam between the two by four strapping. Will have to look into this.