Underfloor Heating - Insulation under slab not on top

[Jono_UK]

Hi,

I am in the final stages of building an extension. I have now decided I would like wet underfloor heating. The problem is the extention is built with the 100mm insulation underneath the slab and not on the top.

I still need to put a 50mm screed down.

Am I able to install wet underfloor heating? How would it fix to the concrete slab (I know it is normally cliped into the insulation)

Could I use the waffle matting to fix the pipes into instead of clipping? The insulation is below the slab and all around it's edges.

Any advice would be great. Jono.

 

[Garfeild]

You need the insulation underneath the pipework,it will not work properly laying pipework directly on top of concrete,you need to reflect the heat upwards.

 

[Jono_UK]

I have 5omm to play with within the screed. Could I put another layer of insulation down and then wet underfloor then the screed?

Or could I benefit from the pipes heating up the whole concrete slab as well as the screed? The slab is very well insulated with 100mm insulation under and around it. If I could turn back the clock I would have done it correctly and had the insulation above.

All I need to know is is it at all possible?

 

[clf-gas]

If you've got 50mm from slab too finnished floor level then your laughing.
18mm insulated overlay boards on top of slab, piperun in pre routed grooves, 6mm ply over the top if laying tile or laminate floor, or 18mm caber flooring if laying carpet.

the 100mm insulation under 100mm slab, the building inspector would have had you do anyhow.

How've you ended up 50+mm below FFL anyway

PS, dont go down the route of putting pipe on slab, or you'll have to turn it on now to be warm for christmas, and i dont mean next

 

[dunny]

If you've got 50mm from slab too finnished floor level then your laughing.
18mm insulated overlay boards on top of slab, piperun in pre routed grooves, 6mm ply over the top if laying tile or laminate floor, or 18mm caber flooring if laying carpet.

the 100mm insulation under 100mm slab, the building inspector would have had you do anyhow.

How've you ended up 50+mm below FFL anyway

My post along similar lines from yesterday seems to have disppeared. I checked my levels today and I have 60mm to finished floor level. I will be using 18mm solid wood and 22mm stone. So with the polyplumb stuff it looks like I will have enough, just.

Seem reasonable??

 

[clf-gas]

Spot on mate, could go with 15mm pipe then,

 

[dunny]

Spot on mate, could go with 15mm pipe then,

I am in Lancs, nr Ormksirk - how about you??

D

 

[clf-gas]

Opposite side, near Rochdale.

 

[dunny]

Well thanks for your help so far.....