Underfloor heating under slate flag stones

Ader1

A house I recently purchased has slate flag stones covering what was the kitchen floor. I will also have the kitchen in this room. The stones are in good conidtion and I've carefully lifted a few and managed it without damaging the stones. There some kind of soil beneath them. I'm thinking of putting down a damp proof course beneath the stones and I'm now thinking about also putting in some underfloor heating; probably electric. Is this possible or workable with the flag stones being almost 2 inches thick at times? Any advice much welcomed.

Captaincodpiece

How much is your budget?

No point in lifting for underfloor heating if you're not going to insulate. By the time you've dug down deep enought for solid insulation and applied a screed floor you might as well run the ufh off the central heating b

Ader1

Thank you. I was lifting initially in order to put down a dpc. You are saying I should insulate too. How dieep do I need to go down for this? Your suggestion to run the ufh off the central heating boiler would then mean having water pipes as opposed to electircity? What kind of cost are we talking about?

onomatopoeia99

I'm installing UFH in my kitchen. It's not the same as yours as under the old floor (which was carpet on top of vinyl on top of lino tiles) is a concrete bed. The system I am using is polypipe overlay, which uses 18mm boards that are routed to allow a plastic pipe containing hot water from the CH to circulate through (there is also a pump that regulates the temperature).

I put a layer of insulation down first onto the concrete, then the UFH boards, then tile backing board and the final layer will be slate tiles (waiting for the electrician and plasterer before I lay those). It has been suggested could have managed without the tile backing board and tiled directly onto the UFH boards as the extra layer will slow the warming of the floor, but it's done now.

Cost of the UFH system was about £700 for something that would cover 12 square metres. It works well, I got it all working just before the weather turned colder and it is so nice walking around in my socks on a warm floor when the heating is on, even with just the featureless grey backing board down.

Ader1

Thanks again. Do you know your type of system would work beneaeth flag stones?

Captaincodpiece

onomatopoeia99 wrote: »

I'm installing UFH in my kitchen. It's not the same as yours as under the old floor (which was carpet on top of vinyl on top of lino tiles) is a concrete bed. The system I am using is polypipe overlay, which uses 18mm boards that are routed to allow a plastic pipe containing hot water from the CH to circulate through (there is also a pump that regulates the temperature).

I put a layer of insulation down first onto the concrete, then the UFH boards, then tile backing board and the final layer will be slate tiles (waiting for the electrician and plasterer before I lay those). It has been suggested could have managed without the tile backing board and tiled directly onto the UFH boards as the extra layer will slow the warming of the floor, but it's done now.

Cost of the UFH system was about £700 for something that would cover 12 square metres. It works well, I got it all working just before the weather turned colder and it is so nice walking around in my socks on a warm floor when the heating is on, even with just the featureless grey backing board down.

What's the total thickness of all that?
I can see its 18mm for the overlay but how much insulation is there, overboard and finished floor?

onomatopoeia99

It will be about two inches all in, which leaves approx a 1" step up from the hallway (I installed engineered oak there without UFH)

Ader1

Some of the flag stones are around 3 inches thick. I was told by a builder today that it would take ages for these to heat up and that the process of them heating up and cooling might make them crack. He didn't advise it under these thick flag stones. Just leave it at some good insulation.

Captaincodpiece

Ader1 wrote: »

Some of the flag stones are around 3 inches thick. I was told by a builder today that it would take ages for these to heat up and that the process of them heating up and cooling might make them crack. He didn't advise it under these thick flag stones. Just leave it at some good insulation.

That's some digging you've got to get 4" solid insulation in then.

MX5huggy

If it's really just soil then you should put a new sub floor in. You're looking at something like 150mm of sub base, 25mm sand blinding, DPM, 100mm concrete, 100mm celotex insulation 75mm of screed with or without wet underfloor pipes, tile adhesive floor, floor covering 75mm for your flags. So half a meter give or take.! Your flags are thick so would be a very slow to respond floor no way would you want electric UF doing this it would never be warm when you want just cost a fortune to run.