Insulation under or above concrete slab

[Steveb21]

I have a floor (above a basement) which is constructed using Block and Beams. Under the B&B will be 25mm of insulation, Rockwool RWA45. Above will be 25mm Celotex rigid board, membrane sheet, UFH pipes and then 50mm of liquid screed.

To the side of the area in question is backfill (around the basement and original property). Would it be best practice to have 100mm of Celotex PIR under the concrete slab, or on top?

So:

50mm Liquid Screed
UFH Pipes
Concrete Slab
Membrane
100mm of Insulation
DPM
Sand
Hardcore
Earth


or:

50mm Liquid Screed
UFH Pipes
Membrane
100mm of Insulation
Concrete Slab
DPM
Sand
Hardcore
Earth

 

[noseall]

I have a floor (above a basement) which is constructed using Block and Beams. Under the B&B will be 25mm of insulation, Rockwool RWA45. Above will be 25mm Celotex rigid board, membrane sheet, UFH pipes and then 50mm of liquid screed.

To the side of the area in question is backfill (around the basement and original property). Would it be best practice to have 100mm of Celotex PIR under the concrete slab, or on top?

So:

50mm Liquid Screed
UFH Pipes
Concrete Slab
Membrane
100mm of Insulation
DPM
Sand
Hardcore
Earth


or:

50mm Liquid Screed
UFH Pipes
Membrane
100mm of Insulation
Concrete Slab
DPM
Sand
Hardcore
Earth

Second option for UFH except the membrane goes down before the insulation.