ᐅ Subfloor Construction Without Screed for Solid Wood Planks – Experiences

My current plan is to have a standard concrete slab under the house; additional insulation is still possible.
Based on my experience with a house that has a basement, I had planned to lay a membrane on the raw subfloor (this time without a basement) as a moisture barrier. On top of that, I would install a joist or cross beam structure with loose-fill insulation in between (cork, perlite, hemp-light clay loose-fill; this is also what the contractor recommended).
I recently consulted a specialist company for these types of insulation materials, and they raised some concerns that the membrane on the raw subfloor might prevent moisture—potentially settling from indoor air in the worst case, through the wooden floorboards and insulation—from properly draining downward because of the membrane.
Their advice was to lay the joists directly on the membrane to protect the wood from direct contact with concrete and moisture, and to place the insulation directly on the raw subfloor instead.
In my opinion, however, this approach might carry the risk that residual moisture could rise from below into the insulation area, just reversing the problem.
One possible solution could be to use foam glass gravel when the concrete slab is first poured; however, I am not sure if my general contractor will implement this or if it actually makes sense.
I thought I had this issue figured out, but since there is no basement under the living areas in this build, it is making me reconsider. Ultimately, I want to avoid screed specifically because of moisture concerns.
Does anyone have more detailed experience or knowledge about this?
@Steffi33, you have a construction like this; could you share your exact setup (membrane, insulation, etc.)? Do you have a basement? What type of concrete slab do you have? What joist height did you use? Sorry for all the questions.

Are you not getting underfloor heating?

Hello, here is a brief overview of the construction... A strip foundation was made for the exterior walls. On top of that, a concrete slab was installed, which is not additionally insulated on the underside. A waterproof membrane was glued and welded onto the raw subfloor (covering the entire area, not just under the joists). For the joist layer, timber beams of about 10x10 cm (4x4 inches) were used, resting on small blocks. Unevenness was compensated with plastic wedges (personally, I wasn’t a big fan of that, but our construction company assured us they will last forever). Between the beams, yellow insulation batts were placed, and finally, the floorboards were installed.

I never considered the idea that condensation could collect on the concrete slab. We don’t have condensation forming on the walls either... would that not be similar? I hope this information is helpful.

Pinky0301 schrieb:

Aren’t you installing underfloor heating?

No, I don’t really like it.

Many thanks @Steffi33 for the information.
It should be something like this here, although I am planning to use insulating gravel.

That is interesting, unusual, and uncommon.

May I ask what advantages you expect from this floor structure?