ᐅ Underfloor Heating Beneath Wood Plank Flooring

As I said, I didn’t install it myself, but both the timber supplier (who sells solid oak planks up to 20mm (0.8 inches) thick) and the installer (who built the staircase for us) don’t see any problem with it. Whether it’s ideal is another question, but it is definitely possible!

Precisely glued, traditional and “open” floorboards are installed on a UKo, as the original poster describes, and that simply doesn’t work... One should also read until the end.

spochtsfreund schrieb:
We are also getting full-length solid Douglas fir floorboards with underfloor heating, which will be glued directly onto the screed.

Theodorius schrieb:
I would like to have a floor that is as warm as possible and natural, because it should be breathable.

Breathable? What exactly is supposed to breathe and where?

Theodorius schrieb:
From what I have seen, floorboards are installed on a special substructure..

Installation method A: screwed onto a subframe or raised floor
Installation method B: fully glued with suitable parquet adhesive

Both are possible; neither is mandatory. In the US and other countries, method A is very common.

Theodorius schrieb:
I would like to have a floor made of natural wood that is as warm and breathable as possible.

I’m not sure what you mean by breathable. Wood can absorb and release some moisture in the air for buffering, but you still need to ventilate the room properly. A wooden floor feels warm mainly if it is well insulated against the ground. Without proper insulation and waterproofing, it can feel cold and drafty – although this is less of a concern in new construction.

Theodorius schrieb:
Wooden planks. Maybe even spruce/fir.

Wood is not a good conductor of heat. For planks, I would recommend not going too thick, more around 20mm (0.8 inches). Spruce, fir, and pine are often thicker because they are softer and also have worse heat conductivity compared to, for example, oak.
Compared to a floor heating system embedded in screed with tiles on top, you probably need to slightly increase the flow temperature for wood planks. So when combined with a heat pump, planks are not ideal, but with a gas boiler this is usually not a problem.

Theodorius schrieb:
But how do you design such a floor together with underfloor heating?

Not much differently than without heating. A substructure with insulation mats in between, but not flush with the top edge of the joists—slightly lower instead. Then lay the heating pipes in the remaining space, not in a spiral shape but rather in continuous parallel runs (flow and return next to each other). At the transition points to the next joist bay, cut out notches in the joists to accommodate the pipes. To improve heat distribution, use metal heat distribution plates. Ready-made systems are available, and sometimes special insulation mats are required, but usually natural fiber boards or other natural materials are used. Search engines are your friend.

Nordlys schrieb:
That’s impossible. Period.

If you have absolutely no ... no ... I’ll refrain from commenting. Just this much: Actually, no, it’s possible. Period.

dertill schrieb:
Not much different than without. Substructure with insulation mats in the gap, just not flush with the top edge, but slightly below. On top, in the remaining gap, lay the heating pipes not in a spiral shape, but in straight runs back and forth (supply and return side by side). At the crossing points to the next gap, notch the beams of the substructure. Use metal heat distribution plates for better heat transfer.

How funny. My first spontaneous thought would have been "that won’t work," but then yesterday during a coffee break, I absentmindedly came up with exactly this kind of construction, even though I had never seen it before. Logical ideas always seem to converge somehow.

I was just about to suggest it, and lo and behold: it already exists. You never know...

Technical question: Are such floorboards still nailed to the substructure like in the old days? And couldn’t the heat distribution plates simply be one large, thin aluminum sheet that also runs over the substructure beams? You could just nail or screw it down, right?

chand1986 schrieb:
Are these floorboards still nailed to the substructure like in the old days?

They are concealed screwed into the tongue at a 45-degree angle. Special screws with drill tips are available for this, for example, Assy-Plus decking screws.

For underfloor heating with raised floors, there are ready-made systems available, as @dertill mentioned. For example, the Thermolutz System Econom-Flex.

There is also a YouTube video demonstrating the concealed screwing method...