Roof insulation modify existing insulation single-family house 55

Hello everyone,

following situation:

House built in 1998 (prefabricated house with timber frame construction) is being converted into a single-family house 55ee. Now, according to the energy consultation, I am supposed to install the following in my roof:
-> Roof insulation: 24 cm WLG 032 in rafters + 4 cm WLG 022 (PU) under rafters

The rafters currently only have 20 cm and there is already insulation installed in them. This means my current setup is: 20 cm in rafters + 4 cm under rafters
I have attached a picture.

Questions:
1. Is it possible to find out the insulation value of my existing insulation afterwards, or do I have to expect to remove the existing insulation anyway?
2. Expanding the rafters doesn't really make sense to me now, is there a possibility to achieve the setup 20 cm rafters + 4 cm under rafters with different insulation values or would it be more advisable to expand the 4 cm under rafters?

I would be very happy about your opinions!

Regards!

1. Is it possible to determine the insulation value of my existing insulation afterwards, or do I have to expect to remove the existing insulation anyway?

If the insulation is already 25 years old, you can be 99% sure that it definitely does not have a WLG 32. It is very unlikely that 32 insulation was installed back then.

2. Extending the rafters doesn't really make sense to me now, is there a way to achieve the build-up of 20 cm rafters + 4 cm counter rafters with different insulation values or would it be more sensible to extend the 4 cm counter rafters?

You could put in PUR insulation. It insulates significantly better.

How is the entire roof structure planned? PUR insulation with aluminum foil for the 4 cm as a barrier? What material are you using for WLG 22 – PUR with aluminum foil only has WLG 23. What does the energy consultant say?

The existing insulation certainly has 0.040 WLG. What makes me suspicious is the 4 cm. Could that possibly be a necessary air layer? Because then you wouldn’t actually be installing 24 cm. What does the overall structure look like? Apart from that, mineral wool and PUR is just disgusting...