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We have had underfloor heating installed in a kitchen - dining extension that has been built on our house. We have yet to install the final floor covering. We were going to to use engineered oak and engineered timber does seem to be very commonly used, but how efficient is this at transfering heat in practice? We are also considering slate, tile or stone, surely this would be a much better conductor of heat and therefore ultimately a more economic option in terms of running costs. This seems such a basic question, but I can't find anything written on this topic.
best is a hard surface, like stone / slate / ceramic / porcelain, or even polished concrete
other surfaces will insulate to a degree, with a deep shaggy carpet being the worst option.
Timber is workable, as long as it is well bonded to the screed, and a relatively thin timber (9-12mm)
on a practical note, porcelain tiles require less maintenance than stone / slate etc, as these can take up spillages and stains etc.
we have porcelain throughout a new kitchen dining extension over UFH, and a reclaimed parquet (about 10mm thick) bonded to the living room screed. all works well, but the porcelain reacts a little quicker.
we chose not to use a tile finish in the living room, as we wanted to avoid being tempted to cover it with rugs - which doesn't help the UFH. The timber is just that little bit 'warmer' aesthetically, so we have no rugs.
I second that - in the underfloor heating loop under oak floors in my house I had to raise the loop temp in order to transfer the heat through well. With the flagstone and cobbled floors the loop temp works well at a much lower temp...I use the underfloor downstairs under the stone floors and not much at all upstairs now.
I have a mixture of engineered oak, stone, carpet and tiles over UFH. The engineerd oak is 21mm thick secret nailed to "joists" with Osma profile insulation with foil heat spreader between. No additional OSB or anything like that under it. You can only do that with 21mm thick, the thinner engineered oak needs more support. It works ok but I wouldn't put it in a kitchen. Too much risk of it getting wet/damaged/stained. Go for a nice stone or tiled floor and keep the oak for the dining room. I would avoid slate as I hear it's quite soft and scratches easily.
For engineered oak try Woods of Wales http://www.woodsofwales.co.uk/ and http://www.woodsofwales.co.uk/ExampleFloors.htm . I picked up lots of samples from different suppliers at the self build shows and called and drove all around East Anglia to visit suppliers to get more. Then my builder got me a sample from them and it looked so much better. Ask for a sample with an Osmo hard wax oil finish. I'm told it can be recoated without the repaired areas showing up as much as other finishes. Not had to do that myself yet.
We've now discovered that we can't use tiles due to construction of sub floor - it has timber joists laid on top of solid insulated slab, with 50mm kingspan between the joists. The UFH and a thin screed (about 40mm) lay on top of the kingspan. The result is some extra slab insulation, a nice fixing for secret nails, but a rather flexible screed.
So we're back to engineered timber, so, C Watters, it is a relief to hear that it works.
We also intend to use 21mm. Joiner has recommended using an low insulation underlay (Duralay heatflow) to avoid direct timber to screed contact (which he has previously found causes twisting to the timber floor). Also some noise reduction benefit. Any thoughts on this?
Can you clarify.. does the screed cover the joists or is it just between them? Presumably the screed is just between the joists which is why you can't have tiles. Pity the builder didn't ask what floor covering you wanted before he decided how to do the UFH.
Duralay heatflow isn't a bad choice as an underlay but is an underlay necessasy? Our wood floor isn't over screed so I can't comment on the noise issue. We just get local creaking from some of the nails. Check with the UFH company what they recommend. Duralay heatflow has a TOG of 0.75 which is quite low sho should be ok.
When was the screed done? You should allow plenty of time for it to dry before laying a wood floor of any sort. The normal rule is 1 day per mm so in your case 6 weeks+. It sounds like your joiner might have had a problem previously because he's not allowed enough time for the screed to dry and humidity levels to settle. The underlay might have been acting as a vapour barrier which is why it worked. One trick is to put a rubber car mat down on the screed overnight. If if it's damp underneath next day it's too soon - however that's not the best way - better to use a meter to check humidity levels.
Interesting sugestion that it could have been a humidity issue rather than due to direct heat contact. Screed has been down for over two months so should be dry by now
obviously a bit late for mick43, but it seems a much simpler solution to install UFH in screed and then glue the timber down. there are glues specifically for this application and have seen one installed and was very impressed. Saves all the bother of joists, laying the UFH between them etc etc. Also allows any flooring finish. Not sure of any downsides to this option?
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