Retrofit Wet Underfloor Heating - Insulation Thickness/Material

[JamieB3009]

Hello,

I am currently having an extension built and have also got a price to install wet UFH in both the extension and also the existing property at the same time. Existing property is 2001 built. The builder has dug a couple of trial holes in the existing floor and found it is a 50mm screed on top of a block and beam floor using thermalite blocks. We have approx 35mm additional height to play with before the front door thresholds are breached. The UFH contractor is suggesting that 30mm kingspan thermafloor on top of the existing thermalite blocks, followed by a 50mm liquid screed containing the pipes will be sufficient for the system to work properly.

I am a little bit uncertain - does anyone have any experience or advice as to whether this will be effective?

Thanks

 

[Mr Chibs]

If you are embedding pipes you really want 50-75mm of screed, with a good chunk of insulation underneath it 100/150mm.

30mm of insulation won't work as well as the recommended amount.

You may be better looking at an overlay system where you have insulated pipe trays and you click the pipe in, then use appropriate floor type.
Have a search on here, there is plenty of info.


Good luck.

 

[robinbanks]

Your builder is not correct. You're carrying out a major renovation of a thermal element and are required to get building control approval for the works. You need to demonstrate that your floor achieves a U value of 0.25, and 30mm of insulation doesn't achieve that with kingspan. Maybe if it's aerogel or VIP, but I didn't run that number. Also, do check you truly have thermalite block, as there is a big difference between the lambda of a dense concrete block vs thermalite..

You don't need 50mm of screed for your buildup, you could probably get away with 35. All in an overlay system may meet thermal requirements better though I personally feel that screed makes for a better heat spreader.

If you're serious about upgrading, take the block and beam out and put 150mm of ground supported insulation, or remount the beams lower

 

[JamieB3009]

Thanks for the reply and the advice.

As far as I can see they are thermalite blocks when sticking a camera down (see attached photos). Would the 35mm screed you mention include the pipes within it? In terms of ground supported insulation, how would this work as it is just loose ground? I assume this would need compacting, mot type 1 adding and a vapour barrier (effectively turning it into a solid floor)?

Thanks,

Jamie

 

[robinbanks]

Yep, they look like some form of aerated block- thermally a lot better than dense. Speak to your screed supplier, but additives can be used to permit thinner screeds and yes, the pipes would be in-screed. Yes, I was mooting creation of a ground supported, insulated slab

You might be able to lose a bit off your door heights if you're prepared to modify/replace the frames and doors - look at every option