Ytong vs. KS - Construction manager insists on Ytong because of wrong order

Hi everyone,

we are currently building our detached house. The exterior walls are made of Hebel/Ytong 36.5cm aerated concrete. Originally, we planned to have all interior walls built with sand-lime bricks. The builder then pushed us to do everything on the ground floor with aerated concrete and only use sand-lime bricks on the upper floor where the bedrooms are located. I wanted sand-lime bricks mainly because of their high density and sound insulation, as I want good soundproofing between the bedrooms (3 girls). Now the site manager obviously ordered Ytong, although sand-lime bricks are also specified in the structural plan. More precisely, it says: KSL-P 12-1.60/DbM SFK12, raw density=1.5kg/dm3, sigma0=1.80MN/m2 fk=5.50MN/m2. His mistake is relatively clear. Of course, he now wants to sell the Ytong. He said the PPF 0.5 Ytong anyway has the higher density and is better at sound insulation than sand-lime bricks. I’m not really familiar with this and would like to hear your opinion. Should I insist on the sand-lime brick construction? Thanks.

He obviously wants to sell the Ytong now.
He said the PPF 0.5 Ytong already has the higher density and is better for soundproofing than the sand-lime brick.
Should I insist on the sand-lime brick version?

Honestly, I wouldn’t even argue about it or stress over the values etc. The whole thing is a bit transparent. He’ll probably come up with the "time factor" if you reject it – new order delays everything and so on.

I would insist on what is planned.

Thank you! You are actually right. It is also indicated like that in the structural plan. Even if it is only the interior walls on the upper floor, it has all been calculated with that. For this reason alone, I would be reluctant to just change it like that.

I am sure that there are still a few pallets of KS lying around at the local building materials dealer, and the quantity should not pose a transport problem for a shell builder.

we are currently building our single-family house. The exterior walls are made of Hebel/Ytong 36.5cm aerated concrete. Originally, we planned to have all interior walls built with sand-lime brick. The developer then pressured us to do everything on the ground floor with aerated concrete and only use sand-lime brick on the upper floor where the bedrooms are located.
I wanted to use sand-lime brick mainly because of the high density and sound insulation, as I want good soundproofing between the bedrooms (3 girls).
Now the site manager obviously ordered Ytong, although sand-lime brick is also specified in the structural plan. [...] Should I insist on the sand-lime brick execution?

Absolutely: yes!
Even if it is somewhat unclear in . The principle is quite simple: don't put heavy on light. This applies especially when and where the walls do not line up exactly on top of each other (and also as far as we are partly talking about non-load-bearing walls here).
Aerated concrete and sand-lime brick are clearly not equivalent in their properties in the sense that they could be exchanged for each other.
The contractor wants to build something different here than what the structural engineer signed off on. This is not a "minor offense." Apart from that, the rascal is supposed to deliver what you ordered according to your construction contract. That and nothing else – even if it were the same price – he should procure from his supplier.

Even if it may sound dramatic, it apparently cannot be said often and clearly enough: the "site manager" of the contractor is, from the perspective of interests, an "opposing" site manager. His job is to protect his employer from delays and complaints – which from his point of view may come at unlimited cost to your interests. If you have already been so clumsy as not to put your own site manager in place of the contractor’s "site manager" as the client, you should at least now show a clear stance and a firm line to fulfill the construction contract as agreed. Call fouls, show a yellow card. Not like this!

It’s best to schedule two additional appointments with the accompanying construction expert right away. Experience shows that such attempts to test your uncertainty and/or kindness are unlikely to be the last.

I would insist on ks just because of the sound.