UFH retrofit (concrete slab)

[Scot2024]

Hi,

I moved into a property which was built in 2019.
I am keen to remove the existing rads and install UFH.

The makeup of the sub-floor (from what I can gather) is concrete slab with 100mm PIR above and then 18mm T&G Chipboard above.

Looking for input as to what is the best course of action for retrofitting UFH here without impacting on floor height.

Thanks

 

[Madrab]

If the sub floor is as you suggest then an overlay system could be a suitable option. Drop the PIR to 80mm, use 20mm insulated overlay boards, then the final floor covering can be laid directly on top of that. Reacts like radiators whereby there is no thermal mass that needs to be kept warm - as in traditional screed based UFH - and heat up times are roughly the same.

 

[Scot2024]

Thanks.

Instead of altering the existing PIR, would i be able to change the chipboard to something like the below photo and route the UFH pipes in this or is it best/needed to use insulated EPS type boards and then chipboard on top?

 

[Madrab]

Potentially yes, the trouble with them is thermal conductivity. Wood is a bad thermal conductor and therefore the heat from them would be limited to the area of the pipe, EPS boards have a alloy spreader layer and that conducts heat out over it's area, that therefore allows a more even heat into and across the final floor covering.

I wouldn't recommend use chipboard on top either, for the same reasons. Either an engineered/real wood or tiled floor can be placed directly on top of the EPS boards or a 6mm cementitious board can be used as a separation layer, as it's thermally conductive.

 

[Scot2024]

Thanks for your comments. So potentially replace the 18mm chipboard with the 20mm EPS boards as a potential option here? I have seen 16mm EPS Boards i think too and then either include the cementitious board or lay tile/wood directly on it? If so, that's probably the best route for me without looking to impact floor height.

 

[Madrab]

Yes, exactly right. The problem with the 16mm boards is that it only allows the use of 12mm PEX, the 20mm allows 16mm Pex so it allows more flexibility with outputs per m2, pipe centres etc.

If the PIR is dropped to 80mm then the 20mm EPS will make that insulation layer back up and then the floor height stays the same - final floor covering dependent.