Underfloor heating

[john fraser]

It's been some time since I've posted here, but I'm relying on the accumulated expertise still being here. I'm contemplating a new house with UFH and a recycled timber floor. I've been advised that this may not be a good idea as the moisture content of recycled flooring might not go together too well with UFH. Any opinions on this statement? If it's true, how difficult would it be to reduce the moisture gradient in recycled flooring? TIA. Jayeff

[G&M]

Providing it's safe, you could just not nail/screw the floor down for a month or two whilst the UFH dries the flooring out.

[The Natural Philosopher]

Even with wood laminated ply flooring, I get at least 0.1% expansion in the summer humidity as against the ultra low humidity of cold winter air heated by the UFH.

You may expect 0.1% expansion along the grain and as much as 1% across it. On a 4 meter room that is 40mm overall. Plus warping and cupping on no quarter sawn planks.

Plus a slight reduction in UFH capability due to the insulation properties of the wood. To an extent you can compensate by better insulating the floor below the heating elements, but it will result in higher floor temps for the same heating.

Going by my experience, if its a new build and you can do the room and floor insulation to building standards level, there won't be so much heat needed that it will seriously screw up the floor, BUT you WILL need to work out how to take care of the wood movement.

The simple way out is what I did - 'Kahrs' wood laminate stuff. You can't see it especially well, but this is what it turned out like

think its doable wit real wood planks, but at a price. If you lay timber joists across the floor and then plank em 'floating' transversely - do this in summer when internal humidity is highest - and cover the edges with at least 25mm of skirting you can probably get way with it - the floor will shrink a bit, and will tend to cup upwards at the edges, in winter, but should hold up well.

If you go the extremely expensive way and lay real solid joists in there and have a suspended floor, its again doable, but insulation below becomes more tricky than a solid floor.

FWIW our floors get up to maybe 30C absolute maximum: The house insulation is enough to make that all we need, for room temps of about

22C in coldest winters. If its that bad we light the fires anyway!