The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
The increase in ceiling insulation standards helps prevent heat leakage into the ceiling space, but it does not affect the passage of water vapour. Ceiling insulation excludes more heat from the ceiling cavity, resulting in colder cavity air temperatures. Warmer air can hold more water vapour than cold air. Therefore, colder temperatures in the ceiling cavity lead to an increased risk of condensation.