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Design & Installation of "High Front" Eaves Gutter Systems

Building Designers, Builders, Certifiers & Installers should be aware of the provisions of The Building Code of Australia 2009 Part 3.5.2.4 (d) for "high front" gutters which states:

"Where high-fronted gutters are installed, provision must be made to avoid any overflow back into the roof or building structure by incorporating overflow measures or the like".

The eaves gutters form part of the of the roof drainage system which is required to comply with the National Plumbing and Drainage Code AS/NZS 3500.3 -2003

Building Designers should take into consideration the roof drainage requirements of AS/NZS 3500.3.2003 during the design process, including the correct number of downpipes and adequate stormwater drainage provision for the residence.

Roof Plumbers / Installers are required to install the rainwater components that form the roof drainage system in accordance with the requirements of AS/NZS 3500.3.2003. The process for designing the roof drainage system can be found in Figure 3.4 (page 27) of the standard which includes selecting overflow measures.

The overflow measures can be specifically located overflows or continuous overflows. AS/NZS3500.3.2003 Appendix G provides some informative examples of overflow measures.

In regions of high rainfall intensity a combination of overflow methods may be required for the roof drainage system to be compliant.

As a design principle, the overflow provisions should not be less than the capacity of the downpipes. Gutter manufacturers are able to provide technical advice on their products.

Suggested overflow measures include:

• Slotted front of gutter (subject to adequate capacity of slots)
• Inverted downpipe nozzle at high points in the gutter but set at a level below the fascia top.
• Stop ends cut down to a lower level to act as a weir.
• Gutter installed such that the gutter front is below the top of the fascia allowing overtopping of the gutter

1. Yes, high front gutter products comply with the provisions of the BCA 2009 and are required to be installed as part of the roof drainage system designed in accordance with Australian Standards.

Q. What has changed in the BCA 2009 that relates to high front eaves gutters?

1. The only change in BCA 2009 applicable to high front eaves gutters is the removal of the reference to "slotted" gutters in relation to overflow measures. (The exclusive reference to slots as an overflow provision has been removed from BCA 2009.)

Q. Can I still use high front slotted gutters?

1. Yes, "slots" in high front gutters are one of the options available to provide overflow measures as required by the standard.

Q. What are overflow measures?

1. The standard AS/NZS3500.3.2003 requires roof drainage systems designs to include selecting overflow measures. The installer / roof plumber should select overflow measures as per Figure 3.4 (page 27) of the standard. The overflow measures are intended to prevent any overflow back into the roof or building structure.

1. "Slots" may be adequate in many applications; in some applications a combination of overflow methods may be required for the roof drainage system to be compliant with the BCA.
   
   As slot size and frequency varies from manufacturer to manufacturer,
   Gutter manufacturers should be consulted regarding the slot overflow capacity of their high front gutters.

Q. What other overflow options are available?

1. Suggested overflow measures include:

1. Inverted downpipe nozzle at high points in the gutter but set at a level below the fascia top.
2. Stop ends cut down to a lower level to act as a weir.
3. Gutter installed such that the gutter front is below the top of the fascia allowing overtopping of the gutter.

Q. How are overflow measures calculated?

1. SSA HB 39 provides guidance on the design of overflow measures. As a design principle, the overflow measures should not be less than the capacity of the downpipes.

1. No, overflow measures can be specifically located overflows or continuous overflows. AS/NZS3500.3.2003 Appendix G provides some informative (non-mandatory) suggested examples of overflow measures.

Q. What about the buildings designer?

1. Building Designers should take into consideration the roof drainage requirements of AS/NZS 3500.3.2003 during the design process, including the correct number of downpipes and adequate stormwater drainage provision for the residence.

Australian Steel Institute PO Box 6366 North Sydney NSW 2059 P: (02) 9931 6666 F: (02) 9931 6633 www.steel.org.au