Incorrect construction method: Drywall and insulation from Knauf?

Hello dear home builders,

We are currently building a townhouse with a developer and are facing a problem with the drywall partitions. According to the construction service description, it is regulated that we simply get metal frame walls with insulation. So far so good!

Regarding the assembly (W111): Profiles from Knauf CW75 (75mm) are used along with a mineral wool insulation from Knauf (40mm). According to Knauf, these must be installed slip-proof as they do not fill the cavity 80%, meaning with a fastening. Our developer says that since this is compression felt, securing is not necessary. We are now quite speechless, as the rooms on both floors adjoin the bathrooms and we are afraid that if the insulation slips, we will hear everything. Knauf wrote to me again that they have had cases where the insulation slipped and therefore they do not provide a warranty if anything should happen.

Does the developer have to comply with Knauf’s installation guidelines here?

We also find it strange that the drywall partitions on the bathroom interior side have an 18mm gypsum board and on the back side 12.5mm. I have not seen any approval from Knauf for such a construction or is that not a problem? Normally, I also know that bathrooms have to be double boarded.

Does anyone know more about this? I would be very grateful.

Best regards Infuso00

... that we simply get sheeted metal construction walls with insulation. ... Knauf CW75 (75mm) and mineral wool insulation from Knauf (40mm). ... and we are afraid that if the insulation slips, we will hear everything. ... Normally, I also know it so that bathrooms have to be double-sheeted.

Single sheeting is in my opinion total rubbish. 12.5mm drywall holds nothing (off) Neither screws for cabinets nor any significant sound insulation. The 40mm mineral wool doesn't help either. I would prefer double sheeting on both sides (each OSB + drywall) here. However, I am not a drywall specialist!

But I have already had some rooms built like this and am very satisfied with it (except for the price).

You can hardly or not at all dictate anything to a developer (if it really is one).

For a wall between the bathroom and the bedroom, I would definitely not include a cavity (resonance chamber for sound, air volume for temperature differences), but an asymmetry of the cladding could already explain that. A double cladding with (hydrophobized!) thinner boards seems more reasonable to me than a single-layer thicker one.

Does the builder have to comply with the installation guidelines from Knauf here?

A builder only has to comply with the aRdT, a general contractor also with their construction service description; manufacturer processing instructions are, in my opinion, legally only recommendations for both.

I do hope a developer also has to adhere to their construction service description. Of course, it will be formulated vaguely enough so that they can always find an excuse in the end. But with my condominium, there was one and the developer largely stuck to it. Regarding the (pre-)wall installations in my bathrooms, this meant double plasterboard (2x12.5mm), but only with gypsum board - no OSB.

I do hope a developer also has to adhere to their construction performance description.

A general contractor does, a developer does not have to have one at all. You are buying a used property from them (even if its construction is still ongoing or even in the future), they do not actually "build" anything for you. A construction performance description can then become part of the purchase contract and guarantee product features, but it can also be entirely absent. Or it can be part of a brochure, but not part of the contract.