Engineering check for an NCC 2025 Performance Solution (A2G2) against Volume One F1P1(3) or Volume Two H2P1(2): vertical piped overflows are outside AS/NZS 3500.3:2025 (Clause 3.7.7.2 Note 3)
AS/NZS 3500.3, which NCC 2025 calls up for box gutters (Volume One F1D3, Volume Two H2D6(1)(a)), does not cover vertical piped overflows, so one needs a Performance Solution under A2G2, assessed against F1P1(3) for Class 2 to 9 buildings or H2P1(2) and (3)(b) for Class 1 and 10; this check gives that assessment a starting figure.
An engineering check, not the Standard's deemed-to-satisfy method. Use it to understand a design or to support a Performance Solution under NCC 2025 A2G2.