Required width of the bathroom for T-wall solution

I am currently planning my shower bath or bathroom. My architect says we should lay the connections for the washbasins in a kind of pre-wall installation, depth about 15 cm, that is common nowadays. I think that takes up space, especially since the showers are not that big. Wall thickness 11 or 11.5? Is my architect right?

Is my architect right?

Yes. Why do you want to distrust him? There must have been a reason why you chose him. Rhenish greetings

Why do you want to distrust him? There must have been a reason why you chose him

No, I do not distrust him, it was just the question whether this is common nowadays, I built once 10 years ago and at that time all the pipes for washbasins were still installed inside the wall

No offense, but why don’t you start a new thread, or does the question have anything to do with the topic "Required width of the bathroom for T-solution (T-wall)"?

Sorry, I suppose I will do that then.