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Roof drainage: gutters, downpipes and overflow

Editions covered: NCC 2022 (current in most states), NCC 2025 (WA, VIC, ACT), NCC 2019 noted · Last reviewed 22 October 2026

When a gutter overflows into the eave or the wall, it is usually for one of three reasons: the gutter has too little fall, there are too few downpipes, or there is no overflow path. This guide sets out the NCC rules for houses and Class 10 structures, with clauses, and shows where Victoria and WA go their own way.

Which edition? NCC 2022 applies in NSW, QLD, SA (building), TAS and the NT. NCC 2025 applies in WA, VIC and the ACT from 1 May 2026. The NCC 2025 references AS/NZS 3500.3:2025, where the NCC 2022 references the 2021 edition.

Where the rules are

  • NCC 2022 Volume Two H2P1 and H2D6(1): gutters and downpipes can follow either AS/NZS 3500.3 or ABCB Housing Provisions Part 7.4.
  • H2D6(3): Part 7.4 can only be used if the roof drainage connects to a stormwater system that meets H2D2. It does not cover box gutters. Box gutters need AS/NZS 3500.3 or a performance solution (see also HP 7.4.1).
  • AS/NZS 3500.3 Plumbing and drainage: Stormwater drainage: we cite this Standard and don't reproduce it. Ask the app for the clause on box gutter sizing, sumps and falls.

Key requirements (Housing Provisions Part 7.4)

  1. Materials (HP 7.4.2):
    • Metal gutters and downpipes are made to AS/NZS 2179.1, and UPVC to AS 1273.
    • All materials are compatible with the roofing upstream (7.2.2(2)).
    • No lead where the roof is part of a drinking-water catchment.
  2. Sizing (HP 7.4.3): eaves gutters are sized from Tables 7.4.3a to 7.4.3c, using the 5-minute rainfall intensity for your area (Table 7.4.3d):
    • A 5% annual exceedance probability (AEP) storm for the gutter itself.
    • A 1% AEP storm for the overflow measures.
  3. Eaves gutter installation (HP 7.4.4(1)):
    • A fall of not less than 1:500.
    • Brackets fixed at stop ends and corners, and at no more than 1.2 m centres.
    • Overflow measures that can handle the overflow volumes in Tables 7.4.4a and 7.4.4b.
    • Under 7.4.4(5), overflow measures aren't needed for a verandah or eave wider than 450 mm that is unlined, or raked with lining sloping away.
  4. Valley gutters (HP 7.4.4(4)):
    • Only on roofs pitched over 12.5 degrees.
    • At least 15 mm freeboard and side angles of at least 12.5 degrees.
    • Sheet width and depth from Table 7.4.4c.
    • On flatter roofs, valleys are designed as box gutters.
  5. Downpipes (HP 7.4.5): each downpipe serves no more than 12 m of gutter, and downpipes sit as close as possible to valley gutters.
  6. Overflow measures (HP 7.4.6 and 7.4.7):
    • Continuous options: front-face slotted gutters, a controlled back gap (a permanent 10 mm spacer at each bracket), or a front bead set at least 10 mm below the top of the fascia.
    • Dedicated options at each downpipe: an end-stop weir (not where the end stop is against a wall), an inverted nozzle, a front-face weir, or a rainhead. Each has minimum sizes and set-downs.
  7. Roof sheeting into the gutter (HP Part 7.2):
    • Minimum pitches are 5 degrees for corrugated, 2 degrees for trapezoidal and close-pitched trapezoidal, and 1 degree for concealed-fixed profiles (7.2.3).
    • Sheets overhang into the eaves gutter by at least 50 mm (7.2.8).
    • End laps are 150 mm above 15 degrees and 200 mm between 5 and 15 degrees (7.2.6).

NCC 2019 difference: gutters and downpipes sat in Part 3.5.3 (3.5.3.3 to 3.5.3.5). The 2022 rewrite added the overflow tables and lined up the storm probabilities with AS/NZS 3500.3:2021.

How the states differ

  • Victoria:
    • VIC H2D6(1) requires gutters and downpipes to follow AS/NZS 3500.3, and the Part 7.4 route doesn't apply in Victoria.
    • Roof drainage is "roofing (stormwater) work" under the Plumbing Regulations 2018, reg 25.
    • Reg 26 says a licensed or registered plumber doing that work "must comply with the requirements of Victorian variation VIC Part E3" of the Plumbing Code.
    • VIC E3D2 (NCC Volume Three) calls up AS/NZS 3500.3 and SA HB 39.
  • Western Australia:
    • NCC 2022 Amendment 1 added WA 7.4.3(a), WA 7.4.4(1) and WA 7.4.5(c). Eaves gutters can be sized to AS/NZS 3500.3, and the 1:500 fall applies unless the gutter is designed to that Standard.
    • WA H10D1 lets eaves-gutter overflow follow Part 7.4.
    • The NCC 2025 Housing Provisions keep the WA clauses. The explanatory note says WA allows a 95 × 45 mm rectangular downpipe under its AS/NZS 3500.3:2021 variation.
  • New South Wales: "roof plumbing work" (gutters, downpipes, roof flashings and roof coverings, other than tiles, slates and glass and similar) is defined in the Home Building Act 1989, Sch 1. It is excluded from "plumbing and drainage work" under the Plumbing and Drainage Act 2011, s 4(5)(d). The NCC rules above apply as normal.
  • Queensland: under the Plumbing and Drainage Act 2018, s 80, gutters, downpipes and stormwater must not be connected to a sanitary drain or an on-site sewage facility.
  • SA, TAS, the ACT and the NT: the Housing Provisions 2022 schedules list no variation to Part 7.4. SA moved its Plumbing Code (Volume Three) to NCC 2025 from 1 May 2026.

Ask the app

Upload a photo of the gutter, sump or overflow, or ask:

  • "What is the minimum fall for an eaves gutter?"
  • "Can I design a box gutter using the Housing Provisions?"
  • "How many downpipes do I need for 20 m of gutter?"
  • "What overflow does a gutter need in Victoria?"
  • "What's the minimum pitch for corrugated roofing?"

Ask a roof plumbing question · Roofing · Plumbing

Related checklists

This is general guidance, not a compliance check. Always check your approved plans, the edition that applies to your permit and any local stormwater rules, and confirm details with your certifier, building surveyor or plumbing regulator.

Based on content from the National Construction Code 2022 and 2025 (NCC Volumes Two and Three and the ABCB Housing Provisions), provided by the Australian Building Codes Board under the CC BY 4.0 licence. The ABCB does not endorse this guide. Based on content from the New South Wales Legislation website at 14 October 2026. For the latest information on New South Wales Government legislation please go to https://www.legislation.nsw.gov.au. The standards the NCC references are cited and explained in our own words, not reproduced.