Renew roof insulation from 1986?

But then I have about 1cm ventilation layer. Isn't that too little? Manufacturers say 3-4cm.

Now I have spoken with several dealers. None have Rockwool stone wool in stock. One recommended the Knauf Insulation UNIFIT TI 135 U instead of Rockwool, and instead of the expensive Rockwool Intello Climate Plus and the adhesive tapes, they recommended the Knauf LDS2. That sounds interesting, but now I am unsure. The stone wool or the glass wool after all?

Well, before nothing happens, then glass wool. It's probably a bit cheaper too

I found the stone wool at the hardware store, in stock and not expensive. But the following open questions still remain. It would be good if you could answer them for me.

[*] I am taking 14 + 4, is that a problem because of the 20% rule violation?
[*] I cannot take 16er because then I would have 1cm ventilation layer, so 14 is correct?
[*] Which vapor barrier foil + tape + model can you recommend? So exact model / designation. Because the Knauf is not much cheaper than the Rockwool RockTect Intello climate Plus.
[*] Are the tapes / adhesives from Rockwool good, or better from Knauf? Am I allowed / supposed to then take the tapes / adhesives from one manufacturer and foil from another?

Sorry for the many questions.

Sign up at U-Wert dot net. There you can fiddle around a bit regarding issues with occurring condensate, etc.

I wouldn’t worry about tape and such. It just needs to stick. The important thing is the wall connections. Otherwise, air will blow through there.

Regarding the exact foil, I cannot give you any advice. At that time, I looked for my personal optimum, which was with OSB boards. As a layman, I therefore don’t know more than you.

Personally, I wouldn’t have any concerns about the 1cm. But I can understand that you want to be on the safe side.

On the one hand, you are only bound by the Energy Saving Ordinance if you renovate more than 10% of the component.
Which does not apply in your case, as you are not touching the roof covering at all.

This means you just must not make it worse.
Replacing existing insulation is often completely pointless when it comes to the insulating ability of the building material. Doubling the rafters and additionally insulating was already suggested.

Summer thermal protection is generally achieved with double cladding using 12.5mm gypsum board. Here, the mass is what matters, so OSB is not sufficient protection, or only in combination with gypsum board.
Double cladding is in any case to be installed on a wooden structure.