Will wooden logs withstand the load when pouring concrete underfloor heating?

Hello Paul! The truth is, pouring screed on a wooden floor is not the best option in your case. Moreover, designs have long been developed that allow dispensing with screed. For example, floors in which heat is distributed over profiled heat-conducting plates, which simultaneously serve as mounting elements and contribute to a uniform temperature distribution under the surface of the floor covering.

You can buy a ready-made kit with insulation, which simply unfolds on the floor, or you can save a little and buy only heat-conducting plates and lay them on the rails. Since you have already made thermal insulation, the second option is more suitable for you. How it looks is seen in the photographs: two options for sets, and layout on rails.

More details can be found here this and in this articles on our website.