Interior wall: aerated concrete or lightweight construction?

Hello community,

I am currently facing a problem and hope you can give me some guidance! Here is the situation:

I am currently renovating a four-unit house with a general contractor in order to rent it out afterward. I will not be living in it myself. There is a general contractor agreement (with a fixed price) with contractor XY in which all executions were specified. Among other things, it was also stipulated that all interior walls are to be built in solid construction (calcium silicate or aerated concrete).

The house is currently in an advanced state of construction. However, some partition walls still need to be installed in the attic. Two rooms will be created there: a bedroom and a study/storage/walk-in closet or whatever. The contractor now wants to build these partition walls in the attic using lightweight construction (stud framework, insulation, etc.) and not in solid construction as stated in the contract. However, I insist that it be executed in aerated concrete as outlined in the contract.
Of course, I can imagine why the contractor would prefer to build it in lightweight construction, since the costs for a lightweight wall can be significantly lower than for a solid wall. The contractor claims that the lightweight wall is much better than the aerated concrete wall. This discussion went back and forth for about two weeks and I have continued to say that I want a solid wall. The contractor didn’t seem very agreeable and kept trying to persuade me to choose the other wall. So far without success.

In a phone call yesterday, I was told that it is structurally not possible to place a wall in aerated concrete there at all and that therefore they must use the lightweight wall. However, I consider this absolutely wrong since aerated concrete is very light on the one hand and the ceiling below is also a massive concrete slab. The spans there are also absolutely small. Of course, one would have to look very closely at the static calculations at this point, but I’ll skip that now.

For me, the solid wall is simply clearly much more high-quality and better. Just thinking about the sound of a lightweight wall when knocking on it, I definitely want the solid wall. On the other hand, I can of course also be relaxed since I will not live in the apartments myself...

I would like to hear your opinions on this. Which type of wall would you prefer? Are there advantages or disadvantages? Is it maybe not so bad to install a lightweight wall after all?

I look forward to feedback!

If lightweight partition wall, then please double-sheathed with OSB or composite board and gypsum (especially since it will be a rental apartment!). There is not much against lightweight construction at first, as far as how sound-transmitting it is depends, in my opinion, on how well the drywaller knows what he is doing. Aerated concrete is also not exactly the soundproofing king. I, as a wooden house owner, can't say much against drywall partitions. Are these walls between 2 apartments? If yes, the BU should calculate the sound insulation verification for it!

Talk to him about gypsum wallboards - they only have a thickness of 10 mm, but they also have good sound insulation properties and do not need to be plastered, only filled.

I would like to hear your opinions on this.

Better not: there will be many, and the majority will say that only sand-lime brick would be suitable, and not even aerated concrete. However, I only see the walls between the sleeping and storage rooms of the same maisonette as suitable for using lightweight walls here; and I see no advantage in this case, because it only plays out parallel to the roof slope, whereas the affected walls stand almost completely orthogonal to it.

since the costs for a lightweight wall can be significantly lower than for a solid wall.

Not in this case, because the advantage lies at the labor cost level – specifically where the wall is angled at the top. In my experience, this topic will have been settled for you a long time ago in this forum, if the singer dispute between the factions in 2021 flared up properly again on page 14.

Hello everyone and many thanks in advance for the responses,

to explain the attachment. There are three maisonette apartments, separated from each other by a solid 24.5 cm sand-lime brick wall. This only concerns the walls within the apartments. As I understand it here, a lightweight partition wall can also provide a certain level of sound insulation and be of high quality. I will speak with the building contractor again today and then make a decision.

make it out of stone. when the tenant screws his TV to the wall, he doesn't think, he just does it. certainly, it also works in drywall, but not with the hardware store anchors.