ᐅ Roof Insulation with Vapor Barrier – Counter Battens and Insulation Installation

Hello, I have already read quite a bit here, but I haven't found a definitive answer to my question yet.
I have the following roof construction:
roof tiles, underlay membrane, 160mm (6.3 inches) insulation between rafters, thermal conductivity rating 0.032, vapor retarder.
Now my question is whether it is absolutely necessary to add additional insulation between the counter battens and the drywall panels, or if it is not required.

Best regards and many thanks in advance

unnecessary.

This diminishes the "better" thermal transmittance of the rafters. It is not really necessary, but with a limited 160mm (6 inch) insulation thickness, it cannot hurt either.

Exactly, unnecessary but not completely pointless. I can’t calculate it myself, but here is someone who can. Maybe they will chime in. K.

There is an online U-value calculator (ubakus) that is freely accessible.

With 16cm (6.3 inches) of insulation at WLG 032, the additional 3cm (1.2 inches) between the counter battens and main battens are even necessary to comply with the energy saving regulations (U-value = 0.24). Using only 16cm (6.3 inches) results in 0.25, while adding 3cm (1.2 inches) of WLG 035 insulation brings it down to 0.21.

It is not necessary, but it is often practical to do so. However, adding more insulation inside the vapor retarder would be pointless.