Insulation between rafters and holes in the roof

Hello everyone,

I have been thinking for some time about converting the attic in my parents' house, and accordingly, I have already clicked through relevant forums quite a bit. With the unpleasant side effect that I am now quite confused about some of the questions due to all the differing opinions.

A few answers in advance to avoid unnecessary follow-up questions:

I am 20 years old and have just finished my apprenticeship – I still want to go to university and therefore prefer to renovate here rather than move out. So I don’t exactly have money to waste, which doesn’t mean I want to do a sloppy job – I just want to clarify the financial situation. There is already an occupied room in the attic, and I would like to extend it to the rest of the attic. I don’t aim to create an energy-saving miracle here but want to somewhat improve the current situation (> 40°C in summer // extreme heating marathons in winter). I would carry out the conversion step by step to even be able to manage it, starting with the south side and then working my way from the east side to the north.

About the project: I would like to install a non-ventilated insulation between the rafters with mineral wool (of course following all the rules of the trade – i.e., a proper vapor barrier, etc.).

First of all, the question arises whether the roofing felt is "too tight" for the insulation material, since it is said that you should always build increasingly vapor-permeable outward. If yes, can I resort to materials like Styrofoam / Styrol, or do you recommend ventilation?

Furthermore, in my specific case, the roofing felt is damaged in several more or less accessible places (a few pictures attached). The roof is watertight, but to exclude moisture penetration of the insulation from outside, I would repair these spots beforehand. Now the question is how best to do this so that no pockets are created where water could accumulate – melting bitumen sheets or sealing with membranes, what do you think is more sensible?

So far so good, that is the issue. I think all further questions will arise accordingly.

Thanks in advance and have a nice Sunday!

Best regards, Dirk M.

Hello,

First of all, I wonder whether the roofing felt is "too tight" for the insulation material,

Yes. Roofing felt hinders diffusion to the outside

For a roof structure like this, you should get professional help. A ventilation gap must be created, as well as proper connections of the vapor barrier, etc.
Before a major damage occurs, you should rather invest in planning and execution

Regards

I also believe that you don't necessarily have to do everything alone. You can do plenty of things, but when it comes to insulation and indirectly ventilation, and if you yourself are not a craftsman or don't have knowledgeable friends, it often ends in problems – even if they only become noticeable years later. Insulation problems in particular can lead to mold infestation, which is certainly no fun. Besides, you emphasized that you don't want to do a botched job. For a start, you can simply consult some specialists in insulation. Just inquire whether you can talk to them. Some are more helpful than you might think. If it concerns your parents' house, they could pitch in a bit of money. The expansion is after all an investment in the future of the house and their son is staying with them longer.