Is the drywall installer allowed to smoke?

I hope the drywall installer is sensible enough to find another construction site with a different client, where you can open the windows if necessary. :p

Does he speak German? Or can he only say 'hello' and 'bye'?

For me, it was over with smoking inside after the interior plastering.
Talk and find a compromise (smoking at the window, for example)

or don't think about it for 2 weeks and switch off your head. It will probably stick little to nothing on the GK boards.

Still, it doesn't have to be that way

It also has to do with respect. As the client, you are also the house owner and not a guest at the landlord's.

First of all, it must be clarified whether you have bought a house from a general contractor. In this case, he is the client and the house rights lie with him. I would not make a fuss about the drywall work yet. Better to get good work. After all, there is a lot of ventilation anyway, a door/window is always open, etc. When it comes to interior finishing and paint, it should then stop.

Our painter smokes, and I think the tiler does too. We both kindly asked them to take their smoke breaks on the terrace or in front of the house (including an ashtray and a temporary shelter in the garden ;-)). It was no problem at all; they immediately understood. Both also know that we are moving in with a child. In the entrance area, we also have a note with all sorts of things (phone numbers, info about the coffee machine, etc.), where it is also mentioned again. You can phrase it nicely.

You yourself write, "My house is also your house," so let him smoke. Some need nicotine for good work performance, just like others need alcohol. He will not be spending months on the construction site. Nothing will "stick" there either. Of course, the windows should be open. Not that he can’t see his work because of all the smoke. :D