NCC Version:
NCC 2022 – Volume One and Volume Three.
Area of NCC Requirements:
Roof drainage system design, specifically the performance requirements VIC E3P1 to E3P4 for box gutter sizing and overflow capacity, as per AS/NZS 3500.3:2021.
Problem:
The proposed box gutter width (240mm) was less than the Deemed-to-Satisfy (DtS) standard of 300mm, due to building design constraints. Without demonstrating compliance via a performance solution, this could lead to insufficient stormwater flow capacity and potential water ingress, posing risk to property and amenity.
Solution:
A performance solution was developed under Clause A2G2(2)(c) using expert judgment and hydraulic calculations. Despite being narrower, the proposed gutter (240mm wide x 160mm deep) with a matching rainhead exceeds the required flow rate of 51.45 l/s, achieving 61.1 l/s. Installation will comply with AS/NZS 3500.3 standards, including overflow provisions and maintenance measures.
Finalised Report:
The report confirms that the performance solution satisfies all relevant NCC performance requirements (VIC E3P1 to E3P4). The gutter system is compliant, and the solution is valid under NCC 2022 performance provisions.