ᐅ Insulation between rafters, insulation beneath rafters (PIR), vapor barrier film

Hello everyone,

We bought a house built in 1964 and now want to insulate and renovate the roof.
There is an underlay membrane and 12cm (5 inches) of insulation, probably glass wool, which will be removed.
Everything will be replaced with:

Insulation between rafters: wood fiber insulation board Steicoflex 036, 120mm (4.7 inches)
Vapor retarder, counter battens
Insulation beneath rafters: PIR BauderECO S 60mm (2.4 inches)
OSB or gypsum board

With this combination of insulation materials, I calculate a U-value of 0.23, which would be below the legal minimum requirement.
I also have an example reaching 0.18 but it would take up too much space.

Question: Is this insulation setup appropriate, or could there be issues with the insulation beneath the rafters?

Thanks in advance for your responses.
Best regards,
Martin W.

Why is the vapor retarder placed between the insulation layers?
It should be installed on the warm side, from the interior toward the exterior, in front of the insulation. Alternatively, glued OSB boards can also serve as a vapor retarder.

From inside to outside:
OSB -> 60 mm (2.4 inches) PIR -> vapor retarder -> wood fiber insulation
the principle of "tight on the inside, open on the outside" is basically fulfilled.
I also consider it sensible to plan the vapor retarder behind the PIR at this point. Physically/theoretically, the vapor retarder foil would not strictly be necessary, as this function is already more than fulfilled by the OSB and PIR. However, the 60 mm (2.4 inches) PIR should be regarded as an installation layer with penetrations and leaks due to electrical outlets, spotlights, cables, hangers, etc., and therefore an airtight layer should be installed behind it. To ensure airtightness, placing the foil at this point, directly beneath the rafters, is optimal; it can also serve as a vapor retarder.