Wet UFH - insulation advice

Ben88 · 30 Nov 2019

Notch7 said:
Whether you have underfloor heating or not, insulated floors make a much more cosy home than just cold concrete.

Bear in mind you will need to dig up not just the floor, but a bit of soil too. You need type 1, sand blinding, dpm, concrete slab, insulation, screed.

Breaking up the concrete itself isnt too bad, its probably a couple of days work for 1man. Another day or so for the reduced dig.
If you have room you might want a grab lorry instead of a skip -it might work out dearer than a skip for the quantity if you only need one skip, but you havent got to load a skip. Or get a low skip, or one with a door. Running up a scaffold plank into a skip is quite hard.

Id be guessing at 2no 8 yard skips if you dig out 300mm or so.....in which case a grab will be best.

And you need a whacker plate for the type 1 as its needs compacting.

In terms of underfloor heating, I found a plumber who did it for a labour price and I supplied the underfloor heating kit. Underfloor heating firms can charge an awful lot for supply and install.

Thanks Notch, very helpful.

The £7.5k quote I had was for digging floor out, type 1, sand, DPM, 100mm celotex, concrete and screed with UFH included.

Doing the dig myself saves me about £5k - builder and plumber will do the making good for £2.5k - that sounds okay to me.

I have zero building skills or knowledge so can do essentially manual labour but very little making good.

MeldrewsMate · 1 Dec 2019

I have fitted the Polyplumb retro-fit system which will raise the height from the concrete slab by about 20mm. It was expensive, but much cheaper than the £7500 you quoted. This system uses 12mm pipe, so the maximum loop length is about 80m. Their kitchen/diner is also about 35m2, and has 3 loops. I can vouch for it's effectiveness in warming the area, but not its true running cost vs one with proper underfloor insulation. I take issue with your rough heat calculation, it's more probably half that figure as UFH allows comfort levels to be achieved with lower air temperatures.

UFH takes a long time to heat up, so you will need to install two heating zones in the house, one for UFH, the other for the rads - failure to do this will mean bedroom rads coming on at 4am when the UFH is calling for heat.

Ben88 · 1 Dec 2019

MeldrewsMate said:
I have fitted the Polyplumb retro-fit system which will raise the height from the concrete slab by about 20mm. It was expensive, but much cheaper than the £7500 you quoted. This system uses 12mm pipe, so the maximum loop length is about 80m. Their kitchen/diner is also about 35m2, and has 3 loops. I can vouch for it's effectiveness in warming the area, but not its true running cost vs one with proper underfloor insulation. I take issue with your rough heat calculation, it's more probably half that figure as UFH allows comfort levels to be achieved with lower air temperatures.

UFH takes a long time to heat up, so you will need to install two heating zones in the house, one for UFH, the other for the rads - failure to do this will mean bedroom rads coming on at 4am when the UFH is calling for heat.

Thanks for your response. This sounds promising but a few follow ups if you don’t mind.

1) With only a 20mm build-up, what floor covering did they have? They can’t have had much room for any insulation, if any at all?!

2) My heat calculation was done by a website. I put in floor construction, size and glazing area, along with whether we have insulation in the roof/cavity etc. I’m not sure what else I can say other than that was the figure it spat out...

On the zones, that’s fine. The UFH will have stats on the walls in those rooms. The radiators already have a separate stat which we can move from room to room.

MeldrewsMate · 21 Dec 2019

Ben88 said:
Thanks for your response. This sounds promising but a few follow ups if you don’t mind.

1) With only a 20mm build-up, what floor covering did they have? They can’t have had much room for any insulation, if any at all?!...

They had 10mm thick ceramic/porcelain tiles, no insulation laid below the required 'asbestos' former that the 12mm pipe clips into. This is a cement based board with slots routed in. See Polyplumb website for further explanation.

John D v2.0 · 22 Dec 2019

Ben88 said:
If I’m losing 10% through the floor on a £800 per year gas bill,

If you don't insulate it would be a lot more than going down, concrete conducts heat away a lot better than the air in the room.
Radiators are actually more efficient in a poorly insulated room as the whole radiator is in the room heating the air rather than chased into and heating an externally facing surface.
And even then, you can still see the outline of radiators on a thermal imaging camera from outside in an old house.

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Wet UFH - insulation advice

Ben88

MeldrewsMate

Ben88

MeldrewsMate

John D v2.0

DIYnot Local

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