An overflow relief gully (ORG) is an essential element of the drainage system and unless there is an exemption, at least one shall be installed in a drain. It is intended to provide relief in the event of sewage surcharge, which is particularly important for the protection of property. There are specific requirements for an ORG and these are set out in the standard for sanitary plumbing and drainage, AS/NZS 3500 Part 2.

An ORG is to be located:

1. within the property boundary
2. external to the building
3. so that the top of the gully is accessible
4. positioned where any discharge will be noticeable.

The top of the gully must not be enclosed and must have clear access for more than 2m above the grate. Discharging points over the ORG must also be carefully considered as not to affect the grate’s ability to be released in the event of a surcharge. The standard also provides alternative locations where it is not possible to conform to these requirements, for example, located within a building or recessed within an external wall. These alternatives should only be used in circumstances where it is impracticable to meet the four main requirements.

ORG heights are critical in terms of providing effective relief from sewage surcharge and to avoid excess water from entering the drainage system. The minimum height between the top of the overflow gully riser and the lowest fixture connected to the drain is 150mm and must be maintained at all times. The lowest fixture includes a floor waste gully. This is intended to prevent sewage from entering the building.

The minimum height between the top of the overflow of the ORG riser and the finished surface level shall be 75mm, except where the gully riser is located in a path or a paved area. In this case, it shall finish at a level to prevent ponding and ingress of water. Plumbers and drainers must also be aware of ORGs in flood-affected areas.

The standard provides that in areas subject to known flooding, the inlet to a sanitary plumbing and drainage system shall be positioned at least 150mm above the declared flood level. The inlet could likely be the top of the ORG. It is therefore important to know what the declared flood level is for the property you are working on. Plumbers and drainers ought to know what the declared flood level is for the property before starting work. This will ensure compliance with the standard and avoid the possibility of enforcement action for non-compliance. For information about flood levels, please contact the local government.

Diagram 1 – Typical Overflow Relief Gully installation

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Example of an ORG riser located in a path or a paved area

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Example of a failure allowing the ingress of water.

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Example of a ORG riser allowing for turf, the turf being the ‘Finished Surface Level’.

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Did you know...

• construction workers are 6 times more likely to die from suicide than an accident at work
• we lose a construction worker every second day to suicide
• suicide rates are 80% higher than the general working age population in construction.

​​​​​​These are very troubling statistics, but what can we do to help?

MATES provides suicide prevention through community development programs on sites, and by supporting workers in need through case management and a 24/7 helpline. They support the construction industry in Queensland, New South Wales, South Australia and Western Australia, the Energy industry in Queensland and New South Wales, and nationally to the Mining industry.

MATES was established in response to a major report on suicide (the ‘AISRAP Report’) within the Queensland commercial building and construction industry. The report found that suicide rates in the industry were higher than the Australian average for men, and youth suicide within the industry could be as much as 2.38 times more common than among other young Australian men.

The MATES program is based on the simple idea that suicide is everyone’s business. Everyone in the industry must play their part to improve the mental health and well-being of workers and reduce suicide in the building and construction industry.

Working for the construction industry in general, MATES is independent of employers and unions, and never works directly for an employer. Programs are delivered across the industry regardless of employer or union affiliation.

If you or someone you know is doing it tough, the MATES Helpline is available 24/7 on 1300 642 111 or check out the Mates in Construction website for more information about how they can help you.