House renovation - underfloor heating

t8010789

I’m in the middle of ripping up the suspended wooden floor in our 1950s house, I then plan to have underfloor heating installed. There seems to be several ways in which we can go about this process. We have a 300mm between the top of the concrete subfloor (original and not damp proofed) and the top of what was the floor boards. We would need to put a dpm down and lap it up the walls below any insulation we put down but would you consider building up the level with hardcore and a blinding of sand or insulate the lot? I have seen Dpms that you paint onto the floors/walls but not sure if that would be a sensible option. Any thoughts would be appreciated.

Dudda

Because you have 300mm to play with you can use cheaper eps insulation instead of the more expensive pir insulation. EPS isn't as good thermally as PIR so you need more depth to achieve the same performance but this works to your advantage in this case.

Radon DPM taped and continued up walls and taped to the DPC in the walls if you can find them. Then 225mm EPS and 75mm screen with the under floor heating.

t8010789

Thanks dudda, that’s along the lines of what I had in mind.

I have attached a sketch of what you have suggested, my sketch misses a couple of things but it gives a good overview. You will see that the dpm goes up past the dpc and I believe this will be deemed ‘bridged’, it could be possible that damp could find its way into the wall? A couple of builders have suggested putting in a radon barrier/sump but we are in a low level area and it would be retrofit so not going to seal 100%, is it regs though?

Dudda

Ya that's fine. Normally I'd say yes to putting in a radon sump but it has to go below the radon barrier and you're putting the radon barrier on top of the existing sub floor so you'd have to cut a trench out of the existing slab. I wouldn't like to go messing with the existing slab. If you go messing putting the radon sump in the insulation you're creating a cold bridge. You don't have to put it in by law.

I will say that for anyone else reading this googling about floor build ups and finding this you should put a Radon sump in if possible. I'd recommend it 99% of the time and this is the 1% I wouldn't.

BryanF

Edge insulation (as much as) you can to reduce heat loss from the slab into the existing walls

Vote4Napoleon

BryanF wrote:

Edge insulation (as much as) you can to reduce heat loss from the slab into the existing walls

And apparently into the foundations 2. That's what a plumber who does work for a big UFH and A2W HP supplier says.

BryanF

Refer to Part L TGD building regs