Retroactively optimize soundproofing of interior walls

Hello,

we are dissatisfied with two interior walls regarding sound insulation. One is a wall between the bathroom (the shower is against the wall) and the bedroom, the other wall is between the bedroom and the living room (here you can hear, for example, the running TV very clearly).

The wall structure is as follows: on both sides 12.5 mm drywall (GKB) and 12 mm OSB, 6x8 cm KVH studs, 8 cm cavity filled with 6 cm stone wool.

There are now two options, either a double-shell wall solution from the bedroom side (i.e., building a similar wall with a gap to the existing one) or opening the current wall from one side (bedroom) again and, instead of the stone wool, filling the 8 cm deep cavities with sand-lime bricks (7 or 7.1 cm thick) for more mass.

The disadvantage of the first option is, of course, that many things have to be changed, e.g., light switches, sockets, flooring adjustments, etc.

These are the two options my builder who built the house suggested to me.

Can anyone contribute something on what is more sensible and what provides better sound insulation?

The question is first of all why the sound is transmitted so massively. What does the connection to the ceiling and floor look like? Is the floor/the ceiling properly decoupled?

What will help little is to put a second wall in front of the existing one. The sound will then probably continue to be transmitted easily via the aforementioned weak points.

Hello Jacob,

I can only agree with my predecessor. First, the actual cause of the poor sound insulation should be clarified. Because both filling in the wall and constructing a second wall involve a lot of effort. In the end, however, neither brings anything if the sound is transmitted, for example, via connections to the wall, floor, or ceiling that are not decoupled.

One more tip:
If it is about constructing a new wall, I would recommend a mounting wall with a cladding made of gypsum fiber boards. Because that provides an additional benefit in sound insulation.

I always read sound-decoupled construction. What does that actually mean? I do think it was built that way.

Well, I only know how it was done with us: KVH 6x8 cm frame on the floor with an anti-rattle underlay (UW sealing tape), the same on the ceiling, a few centimeters of air left to the walls, and the room insulated with mineral wool. The OSB and drywall panels were placed a few millimeters away from the floor/wall/ceiling, and the gap/joint was sealed with acrylic. Laminate flooring was laid with the appropriate distance to the wall, and the skirting boards were screwed to the wall with about 1 mm of air above the laminate floor.

In the ground floor it was quite fiddly because we have visible ceiling beams; it was quite a lot of cutting around the beams or cutting out those parts... I wouldn’t be surprised if there is one or the other spot where an OSB or drywall panel meets a ceiling beam...