ᐅ Interior finishing with calcium silicate blocks / brick / metal stud framing

Hello everyone,

I’m new to the forum and hope I’m posting in the right section.

I have purchased a condominium that is currently under construction. Since I come from a different engineering discipline, I don’t have much knowledge about interior construction or structural engineering and have only done some preliminary reading so far. The issue is as follows: the builders sent us a letter with the following message (not quoted word for word):

For structural reasons, the non-load-bearing interior walls cannot be made of calcium silicate brick (the building specification states calcium silicate brick or clay brick). Therefore, the interior walls must be constructed from clay bricks with a bulk density of 0.8 kg/dm³ (50 lb/ft³). Alternatively, a metal stud frame (10 cm (4 inches) W110) is explicitly recommended at no additional cost to us.

My first question is whether this explanation is convincing. According to my research, calcium silicate bricks are slightly heavier than clay bricks, but that should not make a significant difference in weight for these narrow interior walls, regardless of whether they are calcium silicate brick or clay brick.

Assuming this is all correct, what do you think of the recommendation for the metal stud frame in terms of sound insulation, stability, and mounting of upper cabinets and similar fixtures? The letter mainly highlighted the advantages of the metal stud frame over clay bricks (W111 offers better sound insulation, easier mounting, simpler renovations, etc.).

I also found out that W111 is the simplest single-layer design. How does its cost compare to clay bricks and calcium silicate bricks? Wouldn’t clay bricks be significantly more expensive? Are they just trying to save money here? Is calcium silicate brick more expensive than clay brick? Is clay brick considerably inferior to calcium silicate brick?

Calcium silicate brick was my clear favorite, so this situation is rather frustrating. I would greatly appreciate it if an expert here on the forum could advise me on what would be the best choice in my case and how to assess the overall situation.

Thank you very much in advance.

Best regards,

Robin

Addendum:

Of course, I meant w111 above. Furthermore, I was informed that the sound insulation value is 45 dB compared to brick (41 dB). After reviewing several tables from Knauf, I concluded that this must be a very simple construction (based on the sound insulation value of 45 dB). This also leads me directly to the topic of fire protection. What are the requirements for a fire resistance rating? Partition walls (according to Section 30 of the building regulations) are specified as F90-AB in our building permit/planning permission. Does this apply to non-load-bearing interior walls?

Are you then also not allowed to install heavy shelves?

Strange reasoning from the homeowners.

I have wondered about that too. Even a filled bathtub should be an issue then. Is it possible or allowed to review the structural calculation?

One might suggest using gypsum boards. However, a builder who is not a complete rookie should not need to be prompted to consider that option. Does your contract situation allow for alternatives without losing your interest?

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Are all the affected interior walls located within your own apartment, or do some of them also border other apartments or common areas such as the hallway?