Slots/openings in aerated concrete KfW 40

How about concealed cisterns? 60 cm wide, 14 cm deep in a 42 cm wall.

What is the alternative? Built-up and clad with drywall.

Just as a side note to control freaks. You usually hire a masonry company because it is their profession to build houses, and therefore you don't let the all-round service "nothing is impossible for cash upfront" handle it. We never asked ourselves the above questions and simply let the people do their job.

Just as a side note to control freaks. You basically hire a masonry company because it is their profession to build houses, and therefore you don’t let the all-round service of "impossible is nothing, pay in cash on the spot" handle it. We never asked ourselves the above questions and simply let the people do their job.

Just because it’s a masonry company doesn’t mean everything is okay. I shudder just thinking about our plastering company. Not only were they bankrupt themselves afterwards, they probably contributed significantly to the general contractor eventually throwing in the towel because he had to deal with the legal disputes and warranties. The damage alone to us was probably five figures.

Just as a side note to control freaks. You usually hire a masonry company because it is their profession to build houses, and therefore you don’t let the all-around service "Nothing doesn't work" get done for cash on the spot. We never asked ourselves the above questions and simply let the people do their job.

That's true. So far, we are also satisfied. A little control never hurts ;)

What is the alternative? Build a frame and clad it with drywall.

An alternative would have been a facing wall (made of Ytong).