We are restoring a barn/oast. The lower floor of the granary is
currently a concrete base (unknown provenance) with 3 courses of
bricks and then a suspended wooden floor.
We want to put down a solid oak floor - 2cm thick, tongue & grooved
all round with under-floor heating. Planks are about 15cm wide...
The supplier says that there may be problems with humidity and that
the floor could not be floating as it is too big (19ft x 30ft). We
could dig up the floor and make it solid (hardcore/screed etc.) but
that is expensive, but it would control the humidity issues. The
flooring is all kept at constant humidity & temperature (about 17C &
8% I think) in sealed stores locally.
What (hopefully helpful) suggestions could people make? We are
particularly keen to hear from people who have laid solid wood floors
on underfloor heating either at ground or upper floor levels.
Many thanks etc.
A wooden floor will shrink using UFH pipes. It can be done and insulation
will have to be fitted beneath the pipes. I assume you mean humidity from
water vapour rising from the concrete floor. A poly membrane can be laid
over this sub floor in case water vapour rises from this. And "maybe"
insulation over that.
It is a commercial well ventilated building, so probably will not have poly
membrane under the concrete, never mind insulation.
The best way is to gig up and relay the existing floor. But by doing this
you disturb the foundations. Barn conversions are famous for sucking your
money once a floor is being laid as the existing foundations (sometimes
none, being on earth) start to shift. Barn conversions have a high
percentage of abandonment as the foundations suck in your money. So try and
stick with what you have, and don't disturb the foundations/walls. Keep it
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I don't think the size would be a problem as long as the boards are not
continuously fixed (glued). You *will* get gaps, though, and the "sealed
stores" of timber are most likely to vary from pack to pack and even
board to board. What humidity is the supplier talking about? Timber
moisture content/fluctuation, that in the void, what? I wouldn't
consider heating under a timber floor, it seems a recipe for an
I've had a look at BroadLeaf Timber who reckon they will guarantee
their wood laid over a solid unfloor-heated floor...
Well they have identified the best possible way to ensure the smallest
But experience shows that the range of humidity between heating on
(winter) and off (summer) will still cause some movement.
Using narrow planks and bolting em down hard will help...but be prepared
for the odd one to look bad.
I have a fully floating oak faced ply laminate floor that is 40ft x 18
ft...with a fireplace in teh middel...and underfloor heating. It did
need a bit of adjusting as it swelled but the overall movement is less
thah 10 mm.
Right. First off you will be throwing heat away unless you insulate
between the heating and the ground.
Secondly, IMHO you will spend FAR less on not digging up, but simply
filling the void underneath with DPM, inuslation, wire mesh with plastic
UFH pipe tie wrapped to it, and screed. My floor has 50mm polystyrene
and about 100mm of reinforced screed.
This costs, but it means your UFH pipework is cast in, and is part of
the cost of the new subfloor. Make sure your screeder will work to a
dead flat finish, and if possible don;t let him mix his own screed - get
it ready mixed in a truck sop its all identical, otherwise you will have
to do as I did and level the floor afterwards...
When I looked at UFH for suspended floors, the cost of the insulation
and trays was steep. Its cheaper to re-lay the floor.
As to whether you can lay un-laminated oak on that - I'd be a tad
dubious. I went with a Kahrs laminate. If I get rich I will relay oak
well, thats me. Except it wasn't SOLID wood. it as oak faced ply, and it
SWELLED in the summer humidity. It does NOT look as good as oak floor
boards - its too even in color and surface finish. But it does work
WELL. I have just fitted oak skirting to cover the expansion gaps and a
bit of flexible frame sealer where it abuts to brickwork, and it's now
very nice indeed.
The serious problem is that in winter, with cold air being heated by the
UFH at ground level the wood humidity is VERY low, but in summer, warm
wet air sits around and is not heated at all. You can expect maybe 1-2%
expansion across the grain. And significant cupping and warping of all
non quarter sawn (solid) sections. What this probably means is you have
to lay either with T & G style boards and expect cracks in winter
between them. Or let it fully float and cover some fairly large gaps at
the edge - maybe up to an inch - with skirting and beading. I reiterate,
because its counter intuitive, that *inside*, the wood will swell in
SUMMER, and shrink in WINTER.
I would not even consider NOT making the floor solid. UFH for suspended
floors is way more expensive than the cost of filling in the existing.
BTW everybody who came over the holiday simply loved the feel. It is the
best way to heat, bar none.
Well really its two rooms that don't have a wall between them.
Imagine a 6.5m x 14m space.
Now cut a block out of the middle about 3m long and extending all the
way across apart from a 2 meter passageway...and fill it with a porch,
stairwall and two inglenook fires back to back...and thats it really.
I must put up some pikkies sometime.
I wrote a section for the SelfBuild FAQ on this as it is such a popular
question, worth taking a read of that.
IMHO ... you should never use solid wood flooring over UFH ... it will cup,
and shrink - for sure.
The best is engineered construction flooring, i.e. all wood (not
photolaminate) with a 5mm or7mm hardwood veneer on surface.
So finish is exactly the same as solid oak, can be sanded the same number of
times as solid wood .. but the base has multiple layers, much like birch
plywood ... very dimensionally stable.
For an example take a look at:
Hope that helps
Tad more expensive than Kahrs - see www.kahrs.se.
I can vouch for teh fact that this stufff works as advertised.
I can also vouch for the fact that it does not look (quite) like solid
Tain't bad tho.
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