A critical issue in roof drainage system is making sure that adequate overflow measures are put in place to prevent backflow into the premises. We’ve put together this information to assist Rollsec customers in their compliance with Building Code of Australia (BCA).

View our downloadable brochure for information on different overflow solutions in detail.

The National Construction Code 2016 (NCC2016) – New Overflow Requirements

The NCC2016 Volume 2 contains overflow requirements for domestic eaves gutters. Performance requirements require a Class 1 (e.g. domestic residence) or Class 10 (e.g. open carport) as per the construction practices described in section 3.5.2 of the NCC2016, or by designing in compliance with AS/NZS3500.3 or AS/NZS3500.5, or a Performance Solution as described in the NCC.

Gutter Overflow Design

The two design options available for overflow systems are:

  1. Continuous system: This type of overflow design services the entire gutter (e.g. slotted gutter and/or controlled back gap using spacers).
  2. Dedicated system – A specific overflow structure made for the purpose (e.g. using a rainwater head).

Meeting BCA design requirements may be achieved by designs using either or both types of construction.

Responsibilities of Designers

The designer is responsible for the design of an appropriate rainwater system which allows adequate drainage according to site needs. The designer may be an architect, a builder, a hydraulic engineer, a home owner, or a roofing or guttering contractor.

The design and installation of any rainwater system must comply with the NCC2016 requirements of the Building Code of Australia and Australian Standards AS/NZS 3500.3 Plumbing and Drainage, Stormwater Drainage or AS/NZS 3500.5 Plumbing and Drainage, Housing Installations.

Responsibilities of the Installer

It is the installer’s responsibility to ensure the rainwater system is installed as per the requirements of a BCA compliant design.

Please note: Adequate fall towards the downpipes must be given to gutters. (A minimum of 1 in 500 for eaves and external gutters and 1 in 200 for internal gutters applies.)

Installers must ensure that the correct number of downpipes of sufficient size are installed, in compliance with BCA requirements, and that downpipes are debris-free and able to function correctly.

Maintenance Considerations

Regular maintenance is the best practice way to ensure your drainage is in good condition. Downpipes must be cleared of debris. Gutters must be regularly cleaned to prevent the build-up of debris, fungus or any other materials that could risk overflow. (Gutter guards are a good all-round preventative option for keeping guttering and downpipes clear.)

Need Some Help?

If you’d like some help with design, installation or compliance issues, just ask Rollsec. We’re your local specialists for all types of roofing materials supplies in Brisbane. Ask us about guttering, downpipes, flashings, and steel roofing. Our experts will be happy to help, so call us or contact us online.

Information extracted from the NCC2016 Volume 2 and is relevant for Queensland.