Build a terraced end house with an additional unit (GÜ) on your own

With 50 pipe (plus 10 mm for installation) only 40 mm of wall remained over a length of about two meters. The wall itself is probably already in place; for a recess, the chance is lost. So the milling machine would have to be used... then the upper two meters of the sand-lime brick would stand on a 40 mm thick base... no way!

In addition: If pipes are installed under plaster, the absence of impact sound insulation in the form of suitable pipe coverings can lead to the transmission of installation noises to the wall and into adjacent rooms that need protection. If a contact-sound-bridge-free under-plaster installation of the pipes cannot be ensured, it is recommended to install the pipes in front of the wall.

If it is really done that way, the craftsman will register his concerns in writing. Rightly so!

You can mess up and panic in any execution In my opinion, this is a completely normal, regularly practiced procedure.

I don't see it that drastically. For example, the plumber will also install the faucet in the guest WC into the wall, so I don’t need a pre-wall there. That wouldn't be a problem for him because the wardrobe is opposite. In the bathroom on the 1st floor, he rather sees an issue with soundproofing.

We want a washbasin cabinet – that cannot be realized with your idea.

It could be, but I don't see the necessity here: even with a 20 cm pre-wall, nothing looks too cramped to me, so in my opinion you can proceed as drawn and shelve my suggestion.

Either we make a continuous 20 cm pre-wall or the 10 cm one.

Or twelve point eight, I don't see the need for a decimeter leap.

That would be possible, but I don't see the necessity here: even with a 20 cm pre-wall, nothing looks too tight to me, so in my opinion you can proceed as drawn and shelve my proposal.

However, in the current floor plan only a 60 cm washbasin is drawn and not an 80 cm one.

If we use the 80 cm one and leave the shower wall at 1.55 m, then with the 20 cm pre-wall we have a passage of about 80 cm.

Now show me how the washbasin should look.

I could also imagine just a pre-wall behind the toilet, where the water connection for the washbasin comes out from the side of the pre-wall and is installed on the surface on the wall. But it depends on the washbasin. Then, for example, the pre-wall for the toilet could be 100 cm wide, and then the 80 cm washbasin comes directly next to it. With Godmorgon from Ikea, that should be possible, for example.