Floor Insulation/Raising

[RobH71]

I am in the process of building an extension and what was a ground floor playroom will become my hall way. The existing floor is a concrete slab with minimal insulation and needs to be raised by approximately 70 mm.

I would like UFH but as the insulation is not great would I be heating the ground rather than the screed and with out smashing it out and starting again I don't have a lot of play.

I think my options are UFH in about 70mm of screed or 50 mm insulation and chipboard over and then rads.

Opinions invited.

Read more: https://www.diynot.com/diy/threads/raising-and-improving-floor.571938/#ixzz6w9YsimXq

 

[Deluks]

Thermal tilebacker board, 10mm, then heating pipe in 60mm of screed.

You could maybe use 45mm timber sitting on the concrete, then use JG spreader plates and floorboards over the top.
You would then be able to sit 25 - 30mm of insulation under the spreader plates.

Put something thin between the timber and concrete as a thermal break, laminate flooring underlay or something similar.

 

[RobH71]

I like the sound of the backers boards might just let me get away with screed. Would I put a damp proof membrane in, then backers boards, UFH and then screed ?

 

[Deluks]

The concrete should already have a DPM underneath, but if it's old then probably not.
If the concrete is dry and you don't have damp problems then it should be ok, the foam boards themselves resist the passage of moisture, except around the edges. otherwise a liquid dpm of sorts could be used.