Is partial insulation of the roof sensible?

Hello everyone,
unfortunately I have a problem and can't really make progress even with Google and hope to get some help from you.
I bought a house from the 70s and am currently having the bathroom upstairs renovated. In this process, the bathroom fitter removed the knee wall and stripped the sloped ceiling of the drywall. Now the question is, does it make sense to newly insulate the sloped ceiling and the ceiling in the bathroom with a vapor barrier, or would that lead to mold growth in the adjacent staircase where I would rather not remove the drywall and insulate again because I would create a thermal bridge?
On the opposite side is the children's room, where I will have a Velux window installed... here the question naturally also arises whether I should insulate the sloped ceiling anew since half of the slope is already open for the installation of the window anyway. However, this would mean that I would also have to remove the knee wall, which is made of Ytong, to get to the knee wall of the roof. Honestly, that's too much effort for me because there are so many other construction sites.

I would be very happy to receive an answer from you. Thank you very much in advance,

Wilhelm

We know decisively too little about your house to give you significantly more meaningful answers than "42" ;-)

:-D ok. I hear that quite often. Being a builder is really difficult. The different trades are already getting stressed out. What other information do I need to provide so that a meaningful assessment can be made? The rafters are 15cm thick on the slope, I have more space in the ceiling. Now there is this outdated insulation in there, which has been eaten up by rats, so I would very much like to replace it anyway, but if I end up causing more damage than good, of course I question it. Thanks

Roof is carpenter construction, made of softwood grade II, with wooden sheathing on top

:-D ok. I hear that often. Being the builder is really difficult. The different trades are also getting frustrated. What other information do I need to provide so that a meaningful assessment can be made?

In short: everything—uncompromisingly, no ifs or buts. You have several threads "running" here—in all of them it apparently escaped you that no one can read your mind. All your questions are very poorly illustrated, so neither a helpful reader nor a craftsman you hire can develop any strategies for solutions. Create an overview as a basis for clarity: floor plans (of all floors), sections (at least one, parallel to the gable). Being an advisor or contractor for someone like you, THAT is really difficult!

Hello 11ANT,
thank you for your candid response. It seems you haven’t missed the fact that I have hardly any experience when it comes to renovating a house. You read something here, something else there, and in a third article something completely different again. Of course, that doesn’t help in knowing how to approach problems. However, as the renovation progresses, I realize that it really isn’t rocket science.
Regarding my question here, I would have expected a simple answer: "yes, of course, you can do it if you adjust the insulation in the next two or three years, because if you use insulation with varying effectiveness, condensation can form due to thermal bridges and your roof timbers will mold," or "no, absolutely not, because you’ll cause yourself more problems because of issue x than you solve," or "yes, just do it, mold won’t form that quickly."
It really isn’t that complex.... of course, no one can look inside my head and sometimes I might assume things a reader naturally wouldn’t know. For that, I do apologize...

And since you mention my other questions: an experienced electrician knows what a [Kasten] costs nowadays. You always get ripped off everywhere and all the time, so I just wanted to ask how much a [Sicherungkasten] costs. If someone asks me what a used BMW from 2010 costs, I can also say that 30,000 euros is too much, no matter what the equipment is.

Still, many thanks to everyone who takes the time to respond to my questions.
Have a nice evening