Renew roof insulation from 1986?

Well, if you want to go towards passive house standards, it's more like 40 cm. With an old building, you somehow have to compensate for the walls, so a little extra doesn’t hurt. I also have 30 cm 035 and, as Joedreck writes, thick OSB boards underneath for summer heat protection. It’s definitely bearable in this weather, and you hardly have to heat the upper floor in winter.

30cm also seems a bit much to me. An insulation/building materials dealer said that the best price/performance ratio is given at 20cm. Is that correct? Glass wool is cheaper than rock wool, but is it worse or not suitable for pitched roofs? But isn't rock wool + counter battens + OSB3 + gypsum boards a bit too much weight for the roof structure? Can you write me a recommended construction (layer by layer)?

The best P/L based on what? You can't make such a statement, it misses just narrowly, the best P/L has a red roof. The 10 cm more costs maybe 400€ in materials for a row house roof, for 50% better insulation... nothing insulates more cheaply than the roof. (as long as you have space) Only the OSB boards add weight, you should maybe ask someone if you are allowed to put that on. If in doubt, just double the rafters to 30 cm, that will stiffen it properly.

Stone wool is slightly heavier than glass wool. This results in better heat and sound insulation. When it comes to the roof, it’s not just about price/performance in terms of cost. It’s also about hot summers and drafts. Handle it once and never have to touch it again.

So update and many questions from my side. I removed the roof claddings in the attic and the upper floor. Photos are attached.

[*]Under the roof tiles, there is a black tarred? foil. This has a hole in one spot (outlined in orange in the photo). Should I close this hole to prevent water/wind from coming in? [*]The smallest rafter depth is about 16cm, in the upper floor it is about 17 / 17.5cm deep. What insulation depth (stone wool - Klemmrock 035) should I take? 140, 160? Because I was told that I must not stuff the wool completely against the roof so that a ventilation layer exists. My roof construction seems to be ventilated because there is a ventilation grille in the eaves. I would rather not add thickness because I do not want to reduce the room size. On the rafters, I wanted to put drywall 8/9mm? on top. These will be fixed with metal rails that are about 2-3cm deep. Does this mean that I can still take 160 or even 180 wool? Will this construction hold the wool or should I rather take wooden rafters? [*]Previously, the wool was glued onto a cardboard layer with aluminum, see picture. A friend of mine abroad recommended a vapor-permeable foil with aluminum. The pictures are also attached. I have not seen this foil in Germany yet. What do you think of it? [*]In the ceiling between the upper floor and attic, old stone wool is also installed. Should I replace this with new right away and how should I insulate here? The attic floor (not opened yet) is not continuous floor but has a kind of cement beam and on top lies OSB board. [*]How should I best lay the foil between the floors (see photo), I cannot make it completely airtight. [*]What should I do with the eaves, there is space for several layers of wool. Should I seal with the foil only along the inside wall? [*]How should I insulate the ventilation pipes so that no condensation forms there? [*]Is 140 depth sufficient for the energy saving ordinance?

Sorry for the many questions, but I am absolutely new in this matter and have to buy the materials tomorrow / the day after tomorrow and start installation, otherwise it will be quite tight timewise.

Here are more pictures