Underfloor heating on wooden beam ceiling

We are slowly approaching the floor construction... (as is usually the case, some things came to light during the demolition that we will now also do, although originally not planned. But since we are doing everything ourselves, the (additional) financial expense is manageable and time plays only a subordinate role for us)

Are the door lintels really raised that comfortably?

No, we raised all the lintels. But this only concerned the 1st floor, so it was "only" 4 lintels. The mentioned 10-12 cm of space is to the balcony door, which should remain in place, so it is the limiting factor, but it will certainly be enough.

Now another question about the floor construction is on my mind: Actually, we wanted to level the areas between the beams with leveling fill, then lay 22mm thick OSB boards on which the underfloor heating system (Zewotherm ZEWO Klimaboden) will be installed. To reduce the typical vibrations of a wooden beam ceiling, we wanted to fasten the OSB boards to the wooden beams with long screws.

A friend has now advised us against screwing down the OSB boards, as it does not improve the vibration properties and spreads loud walking noises to the floor below.

His opinion/experience is that the vibrations of the ceiling can only be reduced by more mass and he would therefore fill the spaces between the beams with clay or even concrete slabs...

Of course, I am aware that with a wooden beam ceiling certain compromises must be made regarding footstep noise and also vibrations, so I would like to hear your experiences and tips for a sensible floor construction!

Would a two-layer structure possibly make sense (e.g. OSB boards screwed to the beams, then an insulating layer to reduce footstep noise transmission and on top of that, laid floating fermacell screed boards)?

Thanks in advance

Regards

His opinion/experience is that the vibrations of the ceiling can only be reduced by adding more mass, and therefore he would fill the spaces between the beams with clay or even concrete slabs...

And what is supposed to hold this immense weight?

Vibrations are reduced with springy mounting. I always have the feeling in this forum that impact sound is imagined to be the same as airborne sound, just with a different direction of radiation. But impact sound is not a secondary vibration hitting a component through the air. Rather, it is mechanical at the moment of generation. To damp it out in mass or stiffness requires completely different calibers (more precisely: inappropriate ones, as in this proposal).

I would rather seek my solution in dissipating the "impact energy" and avoiding force locking between the components and their assembly.

"Heavy stuff" does not belong in the spaces between the beams, but rather on top of them. Here again it seems to me that one basically imagines a wooden beam ceiling as a horizontal prefab wall.

Hello questioner.
Of course, I am honored that you value my opinion!
Regarding Part 1: the height leveling
A compensating fill always serves for surface equalization. For example, when the subfloor is very uneven or the tolerance limits of the angle deviation are not acceptable. Then the floor is "crooked."
However, with exposed supporting beams that do not meet these flatness requirements, a different approach is taken. Here, the future load distribution plane (a floorboard, OSB, or chipboard sheets) must be aligned level. This can only be achieved after leveling the beam position heightwise and then by shimming with cut-to-size wooden wedges glued (!!) onto the supporting beams.
A 22mm thick OSB board installation, on which the thermal insulation board from Zewotherm is laid, can indeed be a solution.
Part 2: the load distribution plane
However, the decisive factor for the thickness of the boards or OSB sheets is the spacing of the supporting beams. At a 45cm/50cm spacing, 22mm thickness is sufficient. Otherwise, they bend too much under load.
(Quote) "To reduce the typical vibrations for a timber beam ceiling, we wanted to fasten the OSB boards to the wooden beams with long screws."
Answer: Well, better leave that alone!
On the height-aligned supporting beams, we attach as thick as possible fleece strips with a bottom bead of glue (or better: stapler), on which the OSB boards rest floating. Otherwise, we create sound bridges "free of charge" into the building through the screws.
It is true that with timber construction, one must give up on optimal impact sound insulation.
Part 3: soundproofing between the framework
Concrete slabs between the framework? Well, I will leave that open for evaluation with common sense.
From pure theory, that may be correct. But practically, this is impossible to accomplish!
However, the compartments should actually be filled with dry, dust-free mineral materials of high density. Building material suppliers will certainly offer suitable materials.
A two-layer structure would of course always be better than a single-layer one, but that depends on the given construction height.
Then, on the supporting beams, one could also lay 19mm boards, mineral wool impact sound insulation on top (ideal for timber construction), and then the 22mm OSB boards with the system plate of the underfloor heating manufacturer.
The thinner the upper load distribution plane is, the more likely it is to vibrate.
For example, no musician would want to work with as thick skins as possible on drums. Only thin membranes vibrate well. Just like thin gypsum fiberboards ....
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I hope I was able to shed a little light into the darkness!
Regards: KlaRa

Thank you for your detailed and competent explanation, KlaRa!

We also want to install a bathroom in our house from the 1930s with wooden ceilings in a now "normal" room.

By how many cm will the floor be higher in the end with tiles if I want to build everything properly from the joists up and seal it?

With such projects, you always have to pay attention to the door heights and lintels.

Hello unknown questioner. Primarily, the question should be directed to a structural engineer regarding which loads are generally possible with the given support beam dimensions. I do not mention this without reason; it must (!!) be clarified beforehand. Without considering the wedge-shaped shims for height adjustment, 19mm will be required for the load distribution layer (on support beams), on top of which a mineral wool insulation layer, e.g., "Floorrock GP" with 30mm (total: 49mm), 22mm OSB board as load distribution layer (total: 71mm) + alternative sealing + tile adhesive + tiles = 15mm, then we arrive at approximately 86mm installation height. You could save some height only if you reduced the impact sound insulation from 30mm to 20mm. At the expense of impact sound protection, of course. Between 80 and 95mm installation height will always be required when roughly considering the structure! ------------------ Greetings from the desk KlaRa

Hello KlaRa,

first of all, thank you again for your detailed explanation(s)!

On the ground floor, the floor consists of vault stones between T-beams. In the past, wooden beams (according to the building description, sleeper beams) were laid and fixed over these T-beams, which took over the load distribution.

Now we have removed the entire floor structure and are considering what new load distribution layer would be sensible so that the vault stones do not have to bear any load?

We actually want to fill the spaces between the T-beams with leveling fill and then lay screed boards with a thickness of 30mm + 10mm wood fiber (for thermal insulation downwards/basement).

The question is whether this is suitable as a load distribution layer?

Thank you very much in advance!

Best regards + enjoy the rest of the weekend