ᐅ Opinions on Interior Roof Insulation

Hello everyone,

We are about to renovate a house from 1980 with a pitched roof.
1.5 floors plus an attic used as storage, possibly later converted into a playroom or office (private).

Now I am wondering how to approach insulation.

Currently, the roof is constructed as follows:

- Roof tiles
- Air gap
- Delta membrane
- Glass wool insulation

The Delta membrane is now porous and partly damaged. The glass wool insulation is also not in its best condition in some places.

The first roofer suggested a complete re-roofing with external (above-rafter) insulation.
Costs around 16,000-18,000 euros.

Since the roof is still in good condition, I currently consider this unnecessary.
We will remove everything from the inside, so we have good access.

I am considering three options:

Option 1:

**Install a vapor-permeable underlay membrane afterward**
1 = Rafters, possibly with additional battens
2 = Insulation material
3 = Vapor-permeable underlay membrane fixed on the sides with battens
4 = Roof battens
5 = Vapor retarder

Option 2:
Skip the underlay membrane and instead increase the air gap slightly.

Option 3:
Remove the roof tiles as DIY, install the underlay membrane, then put the roof tiles back on.
Then proceed as in Option 1.

I tend to go with Option 1.

Does anyone have experience or advice?