Floating installation of OSB boards on wooden beam ceiling

Hello,

in our old building from the late 1950s, I have ripped out the nailed floorboards and want to install a 25mm thick OSB/4 board (glued with tongue and groove) floating after leveling the joists. The decoupling between joists and OSB should be done using 10mm hemp felt. The joist spacing is on average 570mm, joist width is 115mm, joist height is currently not verifiable (the ceiling joists on the same floor have about 120mm height). The total construction height is a maximum of 40mm, i.e., the OSB board will be filled with 2mm and then 2.5mm linoleum will be fully glued on top.

The goal of this measure is to reduce impact sound into the floor below and to reduce walking noise in the kitchen. Since we have already addressed impact sound transmission in the floor below through extensive decoupled suspended ceiling, the pure walking noise reduction in our own apartment is a priority.

My question is quite simple:
Am I shooting myself in the foot with decoupling by hemp felt if the hemp felt compresses differently due to the load of the loaded kitchen cabinets and the board arches slightly upwards in the unloaded area of the walkways, thereby causing unwanted additional walking noise?

I have considered two variants of floating installation of OSB boards:
Variant 1: On the one hand, I separate the permanently loaded areas from the pure walkways by separate boards and edge insulation strips. A kind of OSB board puzzle.
Variant 2: On the other hand, I lay 2500x1250 large OSB boards so that they are mostly loaded on both sides.

Is there a more sensible third variant (e.g. screwing instead of floating; floating with a different decoupling than hemp felt?) or a modification of my two variants?

Thank you for your support.

Hello Joachim.
You describe an interesting initial situation!
Basically, compromises have to be made with sound insulation in timber construction methods.
Sound insulation to the extent of solid construction would be illusory.
I would build up in two layers since the distances between the support beams are quite far apart.
Bond the lower OSB layer without intermediate insulation and screw it to the support beams with Spax screws after height leveling and equalization.
One layer of impact sound insulation based on glass wool (for preventive fire protection), on top of this lay another OSB layer at right angles to the first level, floating and bonding the edges.
This will work if sufficient construction height is available.
However, you will only control the low frequencies through mass.
Mass that we achieve well in solid construction, but not in timber construction!
-----------------------------
Regards: KlaRa

Perhaps you could also vary the substructure as a compensation for the different loads. So, place the hemp felt with varying thicknesses on the support beams. However, KlaRa's variant will provide better sound insulation (two-mass system) and be more stable. Nevertheless, I would question the hardness, i.e., the spring rate, of the impact sound insulation in the intermediate layer and, if necessary, recalculate how many millimeters your kitchen cabinets would then sink.

Hello and thanks to both of you,

I want to take up two keywords and probably derive a better third option for myself:

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da die Abstände der Tragbalken ziemlich weit auseinander liegen.


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Also den Hanffilz unterschiedlich stark auf die Trägerbalken legen... Jedoch würde ich die Härte, also Federrate, der Trittschalldämmung in der Zwischenlage hinterfragen, und ggf. nachrechnen, wie viele Millimeter deine Küchenschränke dann einsinken würden.

Since I have to level anyway, I will do that with construction solid wood screwed on both sides (40 x 80mm ok?) and thereby reduce the beam spacing.

I will go with a 5mm hemp felt mat over the entire area, which should still contribute to decoupling and the compression under the load of the kitchen cabinets will also be lower. (For 20mm hemp felt mat the manufacturer specifies an average compressibility of 3.2mm). It is extremely important to me that I do not create hollow spaces in the walking area due to the different compression of the impact sound mat from the heavy kitchen cabinets, which would additionally cause noise development.

Would that be a sensible approach?

Unfortunately, I have a maximum total build-up height of 40mm available. Unfortunately, that is not enough for a two-layer OSB construction with intermediate insulation.

Hello, are there any new insights on this? I am also currently in the process of reorganizing a covering on a wooden beam ceiling. My idea: 3 - 5 mm recycling rubber, 16mm OSB then 16mm MDF screwed offset. The structure should lie floating on the rubber. What is your assessment? Thanks and best regards Olli

Hello questioner.
One thought must be abandoned with timber construction (and that is what we are writing about here): that we can achieve sound insulation like in solid construction!
Ceiling timber constructions always have the disadvantages that
a) the vibration-damping mass is missing and
b) that cavities/panels between the load-bearing beams amplify the sound.
That means we first need a decoupling between the load-distribution layer (here: OSB boards) and load-bearing beams, whereby a hemp felt with high compaction is certainly a good choice, but also an 8mm thick rubber granulate mat (e.g. REGUPOL).
Separating an area with (heavy) kitchen build-up from the walking surface, that makes no sense!
This insulation strip must be secured against slipping on the load-bearing beam (gluing or nailing so that the nail head is recessed clearly below the surface of the insulation strip).
What few consider: all these insulating materials do damp, but at certain frequencies they let sound through. Unavoidable and material-specific, related to the insulating material.
Regarding the load distribution layer:
16mm OSB then 16mm MDF screwed in staggered, well, that is recommended nowhere, I wouldn’t do it that way either. As soon as we firmly connect two different materials, there is automatically the risk of a bimetal effect with temperature and humidity changes. Warping of the usable surface will be the unpleasant consequence.
Better: use 2 OSB boards, wood chipboards or suitable gypsum fiber boards (e.g. KNAUF Brio or Fermacell boards).
The paneling is now the last part of the structure.
Only mass helps here, and no light insulation materials for filling. After laying (and secured against accidental slipping) a sieve protection (otherwise the floor below will have no dust-free future), take a suitable mineral filling material with appropriate density.
But finally, a reminder:
You can do it as well as possible, but an optimal impact and structure-borne soundproofing is not achievable with timber construction!
Regards: KlaRa