Partially insulating a cold roof - is that a good idea?

Hello,

background: our construction company built a cold roof (KFW 55). So, vapor barrier, rock wool. I don’t know if this is normal, on the wool under the boards (diffusion-open) you can find droplets of condensation water. Some boards therefore look wet and slightly moldy. The construction company advised us against installing OSB boards. But we are also not allowed to insulate anything, because "no air exchange takes place and only problems are to be expected. We would then lose the warranty. The attic may only be insulated if it is heated and ventilated." I don’t understand the latter, is that correct? I assumed the more the whole house including the roof is insulated, the better. Now I would like to at least insulate the wall on one side (gable). I want to mount a couple of shelves there later. So the spot will be hard to access later. The question is whether that makes sense if the rest of the roof remains uninsulated? If that lowers the difference between the outside temperature and the inside by a few degrees, that’s fine with me. Or is it only worthwhile if you insulate the attic completely with insulation wool and the vapor barrier? Is there anyone professional who could give me a tip? Thank you very much in advance!

Hello!

Unfortunately, I am not an expert, but I am also thinking about the insulation of my own cold roof (ventilated) and do not understand your contradictory statements here and there.
A cold roof is usually not insulated, right!? Why do you talk about a vapor barrier and mineral wool? At the same time about “diffusion-open,” which is not the case with a vapor barrier!?

Your photo also shows no insulation. Am I the only one who doesn’t understand the connection? :(

I have described what the ceiling of the upper floor looks like:
-Rigips
-Vapor barrier
-Insulation wool
-Boards spaced about 5 mm apart for diffusion

That means this is the floor of the attic. Now it's about the rest: gable and slopes. The temperature in winter is almost exactly the same as outside.

I described what the ceiling of the upper floor looks like: -Drywall -Vapor barrier -Insulation wool -Boards spaced about 5 mm apart for diffusion That means the floor of the attic is like this. Now it's about the rest: gable and slopes. The temperature in winter is almost exactly the same as outside.

That is also planned and fine. If you now insulate one gable side (internal insulation as planned and calculated?), nothing will change with the cold roof. Either insulate the entire attic completely and professionally or not at all. You also have a KfW 55 house. That won't work if only a few square meters of the exterior walls fit and the windows are only single-glazed or the remaining walls have the insulation level of a wooden hut.

However, I do not understand why the ceiling is built to be "diffusion-open" towards the top and not airtight (e.g., with OSB)! According to my previous understanding, this can lead to problems especially with unventilated roofs, as condensation water can form/accumulate in the upper ceiling. This, in turn, could be mitigated if the roof were additionally insulated!?

I thought so. I would have dared to insulate it completely, I don't understand the construction company's resistance to it: "only if it is heated". Unfortunately, I am dependent on this, at least as long as the warranty is still valid. Otherwise, I will lose it.