Floor structure and substructure in the attic with filling?

Thank you for the information.

I recently had a floor installer on site to hear his opinion.

He gave me the following 2 suggestions/recommendations:
Variant 1: Wet screed

[*]Mineral wool between wooden beams
[*]16 mm OSB
[*]10 mm wood fiberboard (as decoupling, laid floating)
[*]40 mm wet screed
[*]approx. 8 mm floor covering (e.g. click vinyl)

[*]Total construction height: approx. 74 mm

Advantages:
+ cheapest option

Disadvantages:
- high build-up height



Variant 2: Dry screed (2-layer)

[*]Mineral wool between wooden beams
[*]10 mm wood fiberboard (as decoupling, laid floating)
[*]2x18 mm gypsum fiberboards (Knaufprio) (screwed together, loosely laid on wood fiberboard)
[*]approx. 8 mm floor covering (e.g. click vinyl)

[*]Total construction height: approx. 52 mm

Advantages:
+ low build-up height
+ just as stable as wet screed
+ lighter than wet screed

Disadvantages:
- very expensive (2-3 times as expensive as wet screed)



His statement on vinyl flooring with cork:

[*]strongly gaining popularity, offered everywhere
[*]he doesn’t think much of it, because there is no long-term experience (only available for 5 years) and (still) no standard regulations (e.g. how much it’s allowed to bend, etc.)

What do you think about all this??
The problem is also that due to the high beams we have only a fairly low build-up height of about 5 cm. If we go over that, we would have to bite the bullet and make a small step to the adjoining room...

Hello Markus.
The wet screed is not an option at all given the current initial situation!!
Installing a wet screed on a wooden substructure means: bringing significant (!) moisture into the building with its installation. And that is exactly what must be avoided in construction.
In simple terms: this cannot end well. And it will not end well either.
Option 2 sounds proper and will also work.
Rest assured (I speak here from experience): the money you could save with option 1 you will have to invest back into the renovation at least fourfold. I am certainly not a fan of scaremongering.
But the problems you will get "delivered free of charge" into the apartment with the moisture will be significant.
Apart from the load-bearing capacity of the supporting beams, which must first be checked by a structural engineer.
A calcium sulfate screed will load the area with about 74 kg/m², a cement screed with about 95 kg/m².
For most wooden beam ceilings, this is too much, especially since 200 kg/m² are additionally calculated in residential construction for assessment.
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The path you choose remains up to you. As does the responsibility.
Focusing only on an expected saving has financially "broken the neck" of more than one diligent (or naïve) builder. And I know what I am talking about!
Addendum:
If a floor layer talks about normatively regulated deflections with an LVT covering, it means that he wants to convey competence to a technical layperson without actually having it.
The aspect as such is completely nonsensical and irrelevant for a top covering!!
What is normatively regulated is required for PVC planks.
Multilayer modular coverings, as the term goes, are found in DIN EN 16511.
Just for weighing competence.
Regards: KlaRa

Hi KlaRa,

thank you very much for your prompt reply and your clarification. Especially about the wet screed. That already scares me a bit, since the man seemed quite competent.

Anyway, variant 1 is probably out then. Do you know roughly what load I would have with the 2x18 mm gypsum fiberboards (Knaufprio) per m²?

And what do you personally think of the vinyl coming into fashion with cork as impact sound insulation underneath? Can you recommend it without reservation or do you see any significant disadvantages?

Hello Markus.
Which load-bearing capacity is possible with 2x18 mm gypsum fiber boards (Knaufprio) per m² is not only a question of the prefabricated screed (this is the general term for all dry systems) but primarily a question of the joist spacing. And look: in a country where even cucumber sizes are standardized, there is not a single regulation that specifies such joist spacings based on live loads.
Only one regulation from Austria was helpful in this regard until about 8 years ago, and it has since been withdrawn.
However, it can be assumed that 2 x 18mm OSB boards or BRIO18, if these elements are not screwed to each other and with a joist spacing <50cm, a superimposed load of 2kN/m² is consistently possible without problems.
The so-called impact sound insulation between the boards must not be too thick, otherwise the whole surface becomes ductile when walked on and is subjected to bending stress. Personally, I would proceed as follows here:
On the 1st element level (which can be screwed to the joists)
1 layer of "Regupol(R) Sound 47", on this a layer of paper as a separation layer, and on top of that the second layer of Brio or similar.
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(Quote) "And what do you personally think of the vinyl with cork underneath as impact sound insulation that is becoming fashionable?"
Answer:
Especially LVTs have had the greatest growth among flooring types not only since 2017.
They come for gluing or fixing to a substrate, equipped with a click system (that's probably what we're talking about?) and as loose-laid variants with heavy backing.
The cork on the back cannot really serve as a "serious impact sound insulation"! Likewise, when installed below the carrier board it is not helpful for increasing walking comfort. It is a "crunch protection" when the elements are laid directly on a cement screed and there are still sand grains on the surface... nothing more!
It is of little use but not harmful. That is how I would put it....
I see no disadvantages!
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Good luck with the purchase and installation: KlaRa

Hi KlaRa,

first of all, thank you very much for your detailed response. It is nice that there are people like you who are willing to share their knowledge with laypeople and also have the patience for it.

Unfortunately, I still don’t fully understand exactly how you would proceed. Could you please describe the individual layers again very precisely step by step for a layperson, including exact names of the products?

The recommendation I received was:

[*]Mineral wool laid between wooden beams (200 mm high)

[*]10 mm wood fiberboard (as decoupling, laid floating on the beams)
[*]2x18 mm gypsum fiberboards (Brio 18) (screwed together, loosely laid on wood fiberboard)
[*]approx. 8mm floor covering (e.g. click vinyl) on gypsum fiberboards

How exactly would you change this now? For example:
- Do you mean something like "Regupol(R) Sound 47" as a replacement for the 10mm wood fiberboard? And is the Regupol then simply laid loose on the beams?
- What kind of paper is that, which you would lay as a separating layer between what?
- What is the first layer you would screw onto the beams?

Wishing you a nice Sunday,
Markus

Hello Markus. Before I say goodbye for the weekend, a quick note: Laying mineral wool between wooden beams (200 mm high) is possible. However, the impact sound insulation improves with increasing mass. Mineral wool doesn't offer much here; a PERLITE fill would be better. But the choice depends on how much weight the rafters below can support. You wouldn't want the whole thing to fall into the room after the ceiling rafters below have come loose.

10 mm wood fiberboard (as decoupling, laid floating on the beams): how is that supposed to work, how can this layer be protected against unintended changes in position in the coming years? You can nail thicker fleece strips (e.g. 30 mm thick) onto the beam layer, making sure the nail heads are well covered (not sticking out). That would work. On top of that, OSB boards laid floating in double layers, screwed together and glued tongue-and-groove. This would create decoupling above the fleece strips (on the beams). Or it doesn't matter whether it's OSB or 2x18 mm gypsum fiberboards (Brio 18).

(Quote) "How exactly would you change this now? For example: - Do you mean the "Regupol(R) Sound 47" as a replacement for the 10 mm wood fiberboard? And is the Regupol then simply laid loose on the beams?" Answer: Nail fleece strips on the beam layer, lay one layer of OSB or BRIO on it, then lay the REGUPOL mat floating on top, and again lay the second layer of BRIO or OSB on top, glued tongue-and-groove. (Quote) "What kind of paper is that, which you would lay as separating layer between what?" Answer: It doesn't matter. Newspaper sheets or wrapping paper, possibly also waste paper (used as slip sheet, earlier also used under wet screeds). The main thing is that slipping between the layers is possible, so there are no stresses that could ultimately cause warping of the usable surface (floor area). The mineral wool in the cavities, the fleece strips on the wooden beams, and the REGUPOL mat will together provide quite some sound insulation. Although the values of the individual layers should not be added mathematically, it works. Finally, my note again: Sound insulation like that in solid construction can never be achieved to the same extent in timber construction. --------------------------- Logging off: KlaRa