Industry alert: Metal roofing installation & Condensation Management
Clause VIC E3D2 of the Victorian variations under Volume Three of the NCC, references compliance with SA Handbook 39 for the installation of metal roofing, and states the requirement for the roof sarking, where installed, to extend 25mm into the eaves gutters.
The presence of sarking, and its requirement to extend into the gutter requires practitioners to pay attention to detailing to meet the condensation management provisions of Volume One and Two of the NCC, which contains requirements for the ventilation of roof spaces.
The DtS roof ventilation compliance option requires that a minimum gap of 20mm be maintained across the entire roof space, and ventilation openings within the eave and at the ridge or high level, as shown in Figures 1 and 2. Achieving the minimum 20mm gap needs to consider both the presence of sarking, or similar type material and insulation beneath, in particular between the ceiling insulation and sarking at the heel of a truss.
Figure 1: Pitched roof flat ceiling |
Figure 2: Skillion/Cathedral roof |
As a result, the detailing of the roofing, ventilation and sarking will need to be considered so both the requirements for roofing under Volume Three and the requirements for condensation management under Volumes One or Two of the NCC are met.
In some cases where a particular solution does not meet the DtS provisions under the NCC, for example if the sarking can no longer drain into the eaves gutter, this needs to be designed as a performance solution in accordance with clause A2G2 of the NCC.
While the condensation management provisions for NCC 2022 are not being adopted in Victoria until 1 May 2024, the VBA strongly suggests that practitioners consult with designers, manufacturers and industry groups to discuss appropriate methods of achieving both the roofing and condensation management provisions prior to their adoption so you are prepared for the upcoming changes. The VBA will continue to monitor this matter and engage with stakeholders to provide additional guidance as the need arises.