EPS board for floor build up for UFH

[Male2981]

I am looking to back fill a floor ready for UFH. Currently the floor is suspended, removing this will leave a 400mm gap to back fill. There is a dry concrete slab at the base in good condition. Typically it looks like I should do the following:

Hardcore
Sand
DPM
Concrete Slab
Insulation
UFH Pipes
Screed


Could I backfill with just EPS100 at around 300mm + DPM + pipes + Screed?

 

[freddiemercurystwin]

You could do away with the hardcore and use EPS instead, though you need to make sure you choose a suitable grade designed for domestic floor loads, you would still need a concrete slab.

 

[robinbanks]

You say you've already got a concrete slab; insulate on top of it, insulate round the edges to a height of 40 mm, visqueen (doesn't need a heavy gauge, it's just to stop liquid screed running away), clip UFH pipes to insulation through the visqueen, pour ~40mm liquid self levelling screed

Consider putting your pipe spacings close so you can use a low grade heat system (heat pump) in future even if it's a boiler running it now