ᐅ Insulation with aluminum foil facing installed between the rafters, providing double thermal protection.

Hello everyone,

first some information about the house:

- Built in 1973
- Under-roof membrane: mesh foil. South-west side is crumbly. North-east side not crumbly but with some cracks.
- Rafter spacing: South-west side 20 cm (8 inches). North-east side 15 cm (6 inches). Distance between rafters 65 - 71 cm (26 - 28 inches).
- Ventilation: ventilation bricks at the top on both sides. Nothing visible at the bottom.
Due to the thicker rafters on the south-west side, there is limited ventilation. On the north-east side, probably almost no ventilation at all.
- At least the white roof window is from 2006.

On both sides, aluminum-facing mineral wool insulation was installed between the rafters.
Markings on the insulation: 4 m (13 feet), 60-70 cm (24-28 inches) wide x 10 cm (4 inches) thick. Laid double on top of each other. The first layer has a slight grid pattern on the aluminum facing, the second is smooth.
The first aluminum vapor barrier was stapled between the rafters. The second layer was stapled on the rafters.
The second layer sags slightly inward.

That was the attic. The roof extends down to the upper floor on the north-east side.
The rafters on the upper floor were not insulated. There was only about 4 cm (1.5 inches) thick mineral wool between the rafters and the cladding.
Therefore, I suspect that the attic insulation is not original from 1973.

1) Can I live with this attic insulation setup, or will I have a rotting roof in 20 years?

2) What insulation should I use for the still empty section on the upper floor?
- Fully fill the 15 cm (6 inches) rafter space since there is no ventilation above, and install a vapor retarder with an Sd value of at least 100 on the inside?
- Add 40 mm (1.5 inches) insulation under the rafters?
- Insulate and create an airtight seal for the knee wall as shown in the picture?

Regards,
Andy