ᐅ Roof insulation: modifying existing insulation in a single-family house, energy standard 55

Hello everyone,

Here is the situation:

A house built in 1998 (prefabricated timber frame construction) is being renovated into a single-family home 55ee. According to the energy consultation, I need to install the following in my roof:
-> Roof insulation: 24 cm (9.5 inches) with thermal conductivity 0.032 in the rafters + 4 cm (1.6 inches) with thermal conductivity 0.022 (PU) under the rafters.

The rafters are currently only 20 cm (7.9 inches) deep, and there is already insulation installed. This means my current setup is: 20 cm (7.9 inches) insulation in the rafters + 4 cm (1.6 inches) under the rafters.
I have attached a photo.

Questions:
1. Is it possible to determine the insulation value of the existing insulation later on, or should I expect to have to remove what is already there?
2. Expanding the rafters doesn’t seem practical to me. Is there a way to achieve the required insulation values with the current setup of 20 cm (7.9 inches) rafters + 4 cm (1.6 inches) under the rafters using different insulation materials, or would it be more sensible to increase the 4 cm (1.6 inches) under the rafters?

I would really appreciate your opinions!

Regards!

JJDTE123 schrieb:

1. Is it possible to determine the insulation value of my existing insulation afterwards, or should I expect that I will need 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 thermal conductivity class (WLG) of 32. It is very unlikely that WLG 32 insulation was installed back then.

JJDTE123 schrieb:

2. Expanding the rafters doesn’t make much sense to me right now. Is it possible to achieve the required insulation value with a setup of 20 cm (8 inches) rafters plus 4 cm (1.5 inches) counter battens using different insulation materials? Or would it be more sensible to increase the thickness of the 4 cm (1.5 inches) counter battens?

You could use PUR (polyurethane) insulation, which provides significantly better thermal performance.

What is the overall roof structure planned? PUR insulation with aluminum foil facing for the 4 cm (1.5 inches) layer as a vapor barrier? What material are you using for the WLG 22 layer? PUR with aluminum foil facing usually only achieves WLG 23. What does the energy consultant say?

The existing insulation probably has a thermal conductivity of 0.040 W/(m·K). What makes me suspicious is the 4 cm (1.6 inches). Could that possibly be a necessary air gap? Otherwise, you wouldn’t install 24 cm (9.5 inches) there. What is the overall construction like? Apart from that, mineral wool and rigid polyurethane foam is rather unpleasant...