Reflux valves requirements

This advisory note identifies common non-compliances related to reflux valve installations across NSW. It provides practical guidance for licensed plumbers and contractors in meeting installation requirements.

Last updated:: 28 July 2026

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Note	2/2026
Date issued	June 2026
Last updated	June 2026
For	Licensees and contractors working in the plumbing and construction
Issued by	Building Commission NSW, Practitioner Compliance, Plumbing Team
Scope	Applies to all of NSW

Purpose

This advisory note has been developed in response to non-compliant reflux valve installations identified during Building Commission NSW inspections.

It supports licensed plumbers and contractors to understand the requirements for the installation of reflux valves in NSW in accordance with AS/NZS 3500:2:2026 and the Plumbing Code of Australia 2025 (NSW Variation).

These requirements apply where overflow relief gully (ORG) height requirements cannot be achieved, basement fixtures discharges to a sewage ejector or wet wall, or soffit requirements apply.

Issue

Building Commission NSW has identified a need to remind industry practitioners of the requirements for installing reflux valves, particularly in the following circumstances:

Protection from sewer surcharge is required
Network Utility Operator soffit requirements apply
The required ORG heights cannot be achieved
Basement drainage is connected to a wet wall.

References

Clause requirements

AS/NZS 3500.2:2026

Clause 4.5.2 - Installation

A reflux valve shall be installed where:

the minimum height of the ORG and the lowest fixture specified in Clause 4.6.6.6 cannot be achieved; or
a fixture is located in a basement and discharges to a sewage ejector or wet well and could be affected by a surcharge from a fixture at a higher level.

Plumbing Code of Australia 2025 - NSW C2D4 General requirements

(c) Clause 4.5.2

Insert subclause (c): Soil and waste stacks shall not discharge through a reflux valve except where a reflux valve is installed at the connection to the sewer required with surcharging sewers or where a Network Utility Operator may prescribe soffit requirements.

Note: Where the Network Utility Operator prescribes a reflux valve to be installed for Soffit Requirements, the Network Utility Operator is responsible for the regulation of the reflux valve.

(d) Clause 4.5.3

Delete and insert: Where a surcharge is likely to occur a reflux valve shall be installed immediately downstream of the boundary trap or inspection shaft. The invert of the outlet of the reflux valve shall be installed a minimum of 80mm higher than the invert of the Network Utility Operator ’s system it is connected to.

Note 1: See NSW Figures C2D4a and C2D4b.

Note 2: Where a reflux valve is installed the valve remains the responsibility of the property owner.

Figure C2D4a

**Figure C2D4a**: Example of reflux valve installed 80mm higher than invert of sewer main typically found with shallow connections

Figure C2D4b

**Figure C2D4b**: Example of reflux valve installed 80mm higher than invert of sewer main typically found with deep connections

Regulatory commentary

Soffit and surcharge requirements

The soffit requirement refers to the vertical distance between the controlling surface level on the property (typically the overflow relief gully) and the soffit of the sewer connection point. Network Utility Operators may prescribe minimum soffit height requirements.

In some circumstances, where the required soffit height cannot be achieved, the Network Utility Operator may permit the installation of a reflux valve. For further guidance, refer to Sydney Water and Hunter Water requirements, or contact your local Network Utility Operator.

Network Utility Operators may also be aware of known surcharge conditions within the sewer main infrastructure. Where such conditions exist, a reflux valve must be installed in accordance with NSW Variation C2D4(d).

Refer to the example below showing the location of a reflux valve installed downstream of the inspection shaft or boundary trap, where soffit requirements cannot be met in accordance with Network Utility requirements or where surcharge conditions are known.

Example showing the location of a reflux valve installed downstream of the inspection shaft or boundary trap, where soffit requirements cannot be met in accordance with Network Utility requirements or where surcharge conditions are known.

When overflow relief gully requirements cannot be achieved

Where ORG requirements cannot be achieved, a reflux valve may be installed to protect fixtures that do not meet AS/NZS 3500.2 Clause 4.6.6.6. Consideration must also be given to the requirements of the Plumbing Code of Australia NSW Variation C2D4 (c) which requires that no sanitary drainage or sanitary plumbing is installed upstream of the reflux valve.

NOTE: Where a reflux valve is required for soffit or surcharge purposes and the ORG height requirements of Clauses 4.6.6.6 and 4.6.6.7 cannot be met, an additional reflux valve must be installed at an appropriate location.

For more information, refer to the Overflow relief gully requirements advisory note.

Basement drainage connected to a wet well

Where a fixture is located within a basement and drains to a sewer ejector or wet well and could be affected by a surcharge from a fixture at a higher level, a reflux valve shall be installed to protect the lowest level fixtures from surcharge / blockages.

Information contained within this advisory note refers to codes and standards current at the time at when it was last updated.

Building Commission NSW disclaims any liability (including for negligence) to any person in respect of anything done, or not done, by that person in whole or partial reliance on any of the information in this advisory note.

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