Electric underfloor heating

[Christian McArdle]

I am currently installing my kitchen. It is a Edwardian terrace (i.e. looks Victorian). Unusually, the floor construction is suspended wooden on the same level as the principal rooms. This is bad, because I want a slate floor, which (to my mind) implies some sort of heating to take the edge off the cold floor. (Space heating by radiators).

So, what is the minimum thickness I could make a slate floor complete with underfloor heating, so I don't get too much of a step up from the back room? The floorboards are currently layed with hardboard. It took me ten minutes to remove a square 25cm by 25cm, it is so well affixed. I don't fancy removing any more of it.

Alternatively, should I bite the bullet, go for a substantial step up and install wet underfloor and insulation to replace the radiators?

Christian.

[RichardS]

We've got exactly the same arrangement - don't know whether the suspended wooden floor was put in when the house was renovated about 16 years ago, but it's the same level as rest of house. Come to think of it, some of the neighbours might have a step down to the kitchen. I'll have a look next time I',m round there.

Anyway, previous occupant of the house had ceramic tiles put in - think they're also laid on top of hardboard and then floorboards.

Problem is that they have cracked right across the room in a couple of places, due to slight deflection of the underlying floor, I think.

Therefore if I was replacing the floor (and we'd thought about slate) then I'd want to take the lot up and stick some particularly meaty, flat external WBP ply down, fix down firmly and then lay on top of that. I'd also want to make damned sure that the ventilation was chipper, and the joists & flooring treated first - if you get dry rot in that lot then you're buggered as you can't get access to sort it out.

Don't know about UFH. Our floor isn't that cold - the really cold ones are solid concrete floors, IMHO.

Of course you could bit the bullet & replace with a well insulated insulated concrete floor, and the whole wet UFH enchilada. Don't know whether it's feasible to do that and leave a 1ft (covered) channel all the way around for routing pipework, cables and to maintain ventilation?

cheers Richard

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[Christian McArdle]

Sounds like too much work to dig up the old stuff, although the ply on top might be good. The kitchen units are already going in. I can't live without a kitchen any longer and only have a couple of weekends free to fit it. The floor will probably be done in 3 or 4 month's time. I can allow height now when adjusting the units, appliances, and worksurface height if I know how thick the floor will be. I won't be tiling under the units.

So, in terms of height, we have:

4mm hardboard (can't be bothered to remove). 6mm WBP plywood 3mm heat resistant compound 3mm Underfloor heating 4mm Flexible floor tile adhesive 10mm Slate

Giving a total of 30mm. That's going to be one annoying step, unfortunately.

I've no idea what heat resistant compound is, but I'm told I need it. No idea how thick it is really.

Christian.

[Earl Kella]

unfortunately.

----- Original Message ----- From: "Christian McArdle" Newsgroups: uk.d-i-y Sent: Monday, August 11, 2003 4:27 PM Subject: Re: Electric underfloor heating

unfortunately.

Just done this to my Kitchen. Wooden floor (but with access underneath through cellar) followed by tile backer board - 10mm thick - and on top of this Wickes under floor heater 400W with slate tiles on top, about 10mm.

The tile backer board is really to stop the heat going through the floor boards and you don't need the heating compound with this. Can't remember where from but I can find out if you want to email me at rokella at eurobell dot co dot uk.

If I was to do it again I'd maybe get the 800W version because they take a long time to heat up although hold the heat for quite a long time afterwards. Either that or leave the floor on constantly as it is fairly cheap apparently - obviously it's been off since installation and testing in April.

As Andy said, I wonder now if I really need it as we wear slippers about the place, but what the hell it's a neat feature that I point out to all who enter. BTW don't rely on this to heat the room - it's only to take the edge off the tiles.

Cheers

Earl

(I don't check this ng regularly so you may not get a quick response if desired!)

[The Natural Philosopher]

About 30 miles?

You can make a screed floor as thick as you want. Ideal is about 10-12" from teh soil, with hardcore, sansd blinding, screed, Damp proof membrane, insulation, then pipes-in-screed. Or wires I guess.

[Christian McArdle]

Unfortunately, I don't fancy installing a concrete floor to a kitchen that has already been fitted. Such a solution may well be regarded as somewhat disruptive.

Christian.

[IMM]

unfortunately.

Slate has the highest "admittance" of any masonry material. Well worth installing on floors and especially in eco/solar applications.

[Christian McArdle]

Sounds interesting, I'll give it a look. It would have to be really thin, though. I forgot about the windows in the kitchen. In true Edwardian style, they go down quite low. The standard worktop height is already above the architrave and, in fact, will be just touching the sash beading. I'm happy to raise the floor a little if the integrated appliances can still fit under the surface, though. The floor won't be going under there, so I can make a little down ramp.

Christian.

[Christian McArdle]

It looks like it would be too thick. You need 15mm pipe, 18mm plywood and what looks like about another 15mm of insulation below the pipe. I don't think I'd get the integrated appliances in under that. I'll measure it up, though. I can't (i.e. won't) lift the floorboards or get access underneath.

Any idea of how much a suitable system would cost if it does fit? The room is a galley, 5m by 1.4m, widening for the last metre to 2.6m (I could live with just heating the central strip, though). What bits would I need, manifolds, etc?

I'm also worried about how wet heating would work in practice. I only really intend to use the electric underfloor as a "boost" setting about half an hour before intending to cook. Would a wet system have a longer response time, especially with 18mm of ply insulating the tiles from the pipes?

Christian.

[Christian McArdle]

I think I may have found the wrong system on their website. I'm not laying laminate, but slate tiling. What material would be required between the overlay panels and the tile adhesive?

If I can use 6mm WPB ply, then I get:

4mm hardboard 0mm plastic membrane 18mm overlay panel 6mm WBP ply 4mm flexible floor tile adhesive 10mm slate

Giving 42mm thickness, which is 12mm more than electric, but may just be doable.

Christian.