Additional roof insulation (built in 78)

Hello everyone,

we are currently renovating an upper floor under the roof. The house dates from 1978, so the existing insulation is not very generous. Now the question is whether something can still be done without completely redoing everything (unfortunately, the budget is not sufficient for that).

The roof currently looks like this:


The old panels are to be removed and then either new ones or drywall (then of course wallpapered) installed. For that, I would add additional battens to reduce the distance, which is still too large. Possibly also replace the old ones at the same time, depending on the situation. Currently, the insulation consists of about 16cm of glass wool (foil-coated). On the rafters below the tiles there is a Delta foil. Now the question is whether it is possible to increase the insulation somewhat. The battens running crosswise in the picture are 58mm deep, so I would have put 50mm insulation (glass wool, rock wool?) in there. Does that make sense? What about a vapor barrier? Where would I install it? Any other suggestions?

Thanks in advance for your answers

Now the question arises whether it is possible to reinforce the insulation a bit more. The slats running crosswise in the picture are 58mm deep, so I would have put 50mm insulation (glass wool, stone wool?) in there. Does that make sense?

With an existing 16 cm mineral wool layer, it makes sense to reinforce it. If 58mm slats are already there, you can use those as well. I would rather take 60mm insulation and press it firmly. With that thickness, it's best to use 032, which only costs a little more. Glass or stone wool... glass wool is simply cheaper, stone wool should keep the heat outside a bit better in summer, but only minimally. Neither is wrong.

What about a vapor barrier? Where would I install it?

With 16 cm existing thickness and aluminum facing on the inside, you can do without an additional vapor barrier on the inside—but I would not recommend that, especially since the aluminum facing is already visibly damaged. Ideally, remove/destroy the aluminum facing, install new insulation, and place a vapor barrier foil INSIDE, then gypsum board over that.

Other suggestions?

Even if the money WERE there, I would leave the old insulation in place and only reinforce it as described.