Do ventilation ducts need to be insulated?

why did you insulate both the roof and the top floor ceiling? Isn't one of the two enough?

The general contractor extended the thermal envelope up to the top floor ceiling. Since we decided at fairly short notice to move the heating and ventilation to the attic after all, we additionally insulated the roof ourselves as a DIY job.

Hi

The building services belong inside the insulated envelope. In this area, supply and exhaust air should not be insulated either.
After your changes / change requests, I would now consider that as given.

Olli