screed to suit ufh

paulmallon

anyone any thoughts on what the minimum concrete screed depth should be for under floor heating. Also what is the recommended floor insulation. I M putting down 60 mm foil backed with 75mm screed

yop

Paul, I have 100mm of kingspan on the floor, then the UFH pipes, then 75mm on the ground floor.
Upstairs I have 25mm of kingspan, UFH pipes and 25mm of screed.

Salem

Hey yop,
Any reason for the 100mm kingspan or did you just put it in cause you could ?

paulmallon

25 upstairs?
any reason for this? i am putting 75 upstairs.
what spacing is your ufh pipes?

yop

Salem, the way I look at it is that the more insulation the less heat loss. That is the main reasoning.

Paul - 25mm upstairs for weight bearing reasons, with a timber frame you cannot obviously use hollow core so the only alternative was the strenghten the ceiling joists and use only 25mm of screed upstairs.

Mellor

yop wrote:

Salem, the way I look at it is that the more insulation the less heat loss. That is the main reasoning.

Paul - 25mm upstairs for weight bearing reasons, with a timber frame you cannot obviously use hollow core so the only alternative was the strenghten the ceiling joists and use only 25mm of screed upstairs.

how long is thefloor down, 25 is below recomended standard for a floating screed, have you any problems with cracking, probably can't tell with a finished floor on.

yop

Mellor- The floor is down now about 8 months, no issues with cracking, the screed is poured between battens, the screed is not used a "final floor" but more as a heat container. The timber rests on the battens I have down not the screed.

Mellor

Ok, so the screed isn't bearing any load at all. Thens its fine. Its only if its structural that cracking might be an issue

ircoha

yop wrote:

Salem, the way I look at it is that the more insulation the less heat loss. That is the main reasoning.

Paul - 25mm upstairs for weight bearing reasons, with a timber frame you cannot obviously use hollow core so the only alternative was the strenghten the ceiling joists and use only 25mm of screed upstairs.

Would u mind explaining this please

Thanks

I think that Yop is referring to a precast concrete floor, good for UFH upstairs in Block & Brick type houses, too heavy for Timber frame (well not unless you have some extra strong timbers in the walls).

yop

Ircoha - Yip, you cannot have precast flooring for obvious reasons in a timber frame house.

corkonian0110

Gents,

In terms of the underfloor heating in the ground floor and building by timer frame as I will be starting soon - is it better to have the UFH down and screeded before the TF kit arrives?

jc

ddea

In reply to original query we have used 50mm foil backed insulation with 50mm screed. Would ideally have liked to have more for both but we were advised by architect, builder and plumber that this was standard and would work perfectly.

yop

Corkonian110 - It depends really, if you are doing it youself as in my case it was going to be slow to do so I left it until the kit was up.
If you are getting your plumber to do it then you can suggest this to him, it would surely save hell of a lot of time and work when there is no final floors to put down at the end!
If your getting a private company to do it and have both floors with UFH I don;'t know will they do 2 trips to install the UFH. Suppose sure ask them!

Mellor

50mm is below the standard recomended thickness for a screed over insulation. I'd be a little worried that by three professionals all suggested differently.

corkonian0110

Cheers Yop - will be tackling it myself so will play it by ear.
Nice blog by the way, a must read for most self builders!

yop

I wud have thought that 75mm would be the minimum from what I have read. Strage they are saying 50mm

Mellor

The minimun is 65mm, but 75 is very common.

starman100

The brother is putting down UFH in his new house, upstairs he has 50mm Kingspan then he is putting 50mm of screed on top (pre-cast floor).

Does anyone know if you need a special screed mix to cope with the temperature variations, he was on about some additive you can add to the mix but sounds like extra hassle to me?

yop

Yes there is a mix but I know few who have put it in. Standard screed is spot on