DavidBJ

Thanks all for your replies. - No loads on the floor. Total size of floor being replaced / new to extension is ~45m2. - their proposal is an anhydrite flow screed, not concrete. - afraid not, all in for GF works including extension, chimney removal etc. I’m tending towards asking them to stick to original build-up but maybe switch top layer to flow screed. Thanks all, David

Hello, I’m refurbishing a Victorian terrace including removing chimney to create open plan space at the rear. Existing solid floor is being dug up and replaced to include underfloor heating. Existing quote and spec was hardcore, sand binding, DPM, 150mm concrete slab, 120mm PIR insulation, 75mm sand cement screed. Builders are now suggesting hardcore, sand binding, DPM, 120mm insulation, then 150mm flow screed i.e. no concrete slab. Aside from issues this might create with the heating (less responsive due to thicker top layer), is anyone able to comment on the structure of this build-up? I've seen specs for similar build-ups (i.e. insulation directly onto hardcore instead of slab), but that's when the top slab is 150mm concrete, not flow screed. I'm not convinced in not having a concrete slab somewhere in the flooring structure, but would be good to get some thoughts... Many thanks, David