ᐅ Is Additional Insulation Needed Beneath Drywall?

Hello everyone,

Our house was built in 2009 and has insulation installed between the rafters (unfortunately, I don’t know the thickness) with a vapor barrier foil installed on top.

Now I want to finish the attic with gypsum boards to create a playroom. For this, I have already installed horizontal battens spaced 30 cm (12 inches) apart. The battens are 24 mm (1 inch) thick. I plan to screw the gypsum boards onto these battens.

My question is: Do I need to install additional insulation between the battens, or is that unnecessary because of the existing insulation between the rafters?

It is not necessary, and I also doubt whether it would be economical. The effort required to save the last liter of oil is usually disproportionately high. Karsten