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AS/NZS 3500.3: Stormwater drainage

AS/NZS 3500.3 is the Australian standard for residential stormwater drainage. Covers roof, surface and subsoil drainage. Licensed plumber work, not builder-DIY.

By Dan Waring. Last updated 12 May 2026. Verified 12 May 2026.

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AS/NZS 3500.3 is the Australian and New Zealand standard for stormwater drainage on plumbed buildings. Part 3 of the AS/NZS 3500 plumbing and drainage series, it specifies design, materials, installation and testing requirements for roof drainage (gutters, downpipes, valleys, overflows), surface drainage (paved areas, pits, channels), and subsoil drainage, up to the point of discharge. The current edition is AS/NZS 3500.3:2025, published 17 April 2025 and mandatory as the deemed-to-satisfy path for new work commenced on or after 20 October 2025 (verified 2026-05-12, Standards Australia; VBA).

Also known as: AS 3500.3, AS/NZS 3500 Part 3, the stormwater drainage standard.

Category: Plumbing.

What it covers

  • Roof drainage: gutter and downpipe sizing based on the design rainfall intensity at the site (Bureau of Meteorology data), valley gutter rules, eaves gutter falls, overflow provisions
  • Surface drainage: paved area falls, pits, channels, kerb adaptors
  • Subsoil drainage: subfloor and retaining wall drainage where moisture risk is present (typically via an agricultural drain)
  • Connection to the point of discharge: the kerb, channel, on-site absorption system, or other approved discharge point at the property boundary

It does not cover sanitary drainage (Part 2) or water services (Part 1).

Where it sits in the regulation

NCC 2022 Volume Two clause H2D6 (Roof and wall cladding) makes AS/NZS 3500.3 the deemed-to-satisfy path for gutters and downpipes on Class 1 and Class 10 buildings (verified 2026-05-12, ABCB NCC H2). NCC 2022 Volume Three (Plumbing Code of Australia) calls up AS/NZS 3500.3 as the DTS path across all building classes.

Plumber-gated work

Sizing and certifying stormwater drainage is licensed plumber work in every Australian state and territory. The builder’s role is to engage the plumber early enough for downpipe positions and stormwater drain runs to inform slab set-out, confirm a current state plumbing licence, and file the Certificate of Compliance before occupancy. Builders do not size stormwater systems themselves: the calculation depends on local rainfall intensity, catchment area, and outlet hydraulics, all of which sit inside Part 3.

Relationship to AS 4654.2

On flat or low-pitch membrane roofs (decks, balconies, parapeted roofs), AS 4654.2 governs the membrane and the membrane-side detailing of the waste outlet (upstand, clamping, flashing). AS/NZS 3500.3 picks up from the connection downstream, sizing the downpipe and discharge line. The two standards are read together: a membrane outlet that meets AS 4654.2 but discharges into an undersized downpipe under AS/NZS 3500.3 still fails the system.

References

  1. Standards Australia, Spotlight on: AS/NZS 3500 Plumbing and Drainage Standards Series, 2025 Updates. https://www.standards.org.au/blog/spotlight-on-as-nzs-3500 (verified 2026-05-12).
  2. Australian Building Codes Board, NCC 2022 Volume Two, Part H2 Damp and weatherproofing. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h2-damp-and-weatherproofing (verified 2026-05-12).
  3. Victorian Building Authority (Building and Plumbing Commission), Updated plumbing and drainage standards (AS/NZS 3500 series). https://www.vba.vic.gov.au/plumbing/plumbing-regulatory-framework/updated-plumbing-and-drainage-standards-asnzs-3500-series (verified 2026-05-12).

See also

Last updated: 2026-05-12. Verified: 2026-05-12.

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