underfloor heat in workshop

What sort of max point load are you expecting?

Usually in a domestic setting you put the ufh into the screed.

However I have worked on industrial slabs where they ufh is in the main structural slab tied to the mesh. Slab needs to be a bit thicker to compensate but I can't remember any major issues. Pipes are approx 16mm diameter and the aggregate size 20mm so didn't cause concern.

You could add an extra layer of mesh to sandwich the pipes to be belt and braces where the point loads are expected.

Insulation is an absolute must because ufh is run at lower temperatures. Especially so if it's in a thicker concrete slab instead of a thinner screed.

Only worth it if you are using the workshop a lot, underfloor is great but very slow to respond to demand for heat. Money spent on insulation on other parts will have a faster return. The idea of lying on a heated floor does appeal though!

Hot water tubes in concrete slabs are one of the most efficient ways to transfer heat. Also, inexpensive materials, relatively simple design, and versatile for using solar, biomass, heat pump or any other heat source.

How warm are you going to keep the shop? and is it going to be heated all the time, and insulated? If the ground temp (average annual temp) is close to the temp you'll keep the shop, then there is little to be gained from insulation under the concrete. Here, perimeter insulation is critical.

As Mo said, the slowness is a big drawback. Running the tubes too long is another big problem, but easy to avoid. It's easy to spend a lot of money on an overly complex system that doesn't work any better than simple one. If you're not going to install it yourself, that is another big factor.

You need to be looking at something like this https://www.kingspan.com/gb/en/prod...-insulation-boards/kingspan-greenguard-gg700/

What heating system?

Ive heated quite a few commercial spaces now. If you ever want to fit anything to the floor you will live in fear of hitting a pipe. Unless you have endless low grade water at say 30 degrees I’d insulate the roof and chuck a 40kw volcano blow heater in each corner. Yes you get a heat spike for the first half hr but then it will recycle the heat in roof for rest of day.

Also good for air movement in summer…