| To | Licensees / Contractors / the Plumbing and Drainage Industry |
| From | Building Construction Compliance, Plumbing Team, Parramatta |
| Date | June 2023 |
| Scope | Applies to all metropolitan and regional areas in New South Wales. |
Issue
To clarify the requirements when drainage pipework has been installed internal or external to a building in ground considered to be “other than stable ground”.
Code detail
The PCA 2022 is available to be viewed on the Australian Building Codes Board (ABCB) website. Part C2 prescribes the minimum performance requirements for sanitary drainage systems
Plumbing Code of Australia (PCA) 2022
C2P7 – Damage
- A sanitary drainage system must avoid damage from root penetration, super imposed loads or ground movement.
To comply with the above Performance Requirement the Deemed-to-Satisfy requirements prescribes the following:
AS/NZS3500.2 – Sanitary plumbing and drainage
Clause 5.6 – Drains other than stable ground
Where drains are to be laid in filled, unstable or water-charged ground, methods of support and bedding shall be designed to withstand and suit the ground conditions.
Regulatory Commentary and Requirements:
Filled, unstable¹ or water-charged ground requires a suitably qualified expert to confirm the suitability of the drains to be installed in the ground considered to be other than stable via the below options:
Note ¹ – Unstable ground although not defined in the AS/NZS 3500.0 Glossary, can be reasonably assumed to mean instances of highly reactive type soils, ground prone to slippage, or where relevant authorities such as Subsidence NSW have conditions in place relevant to the installation of drainage systems (ie Flexible Joints in Drains).
Filled Ground:
If the filled ground has been compacted and has been deemed adequate to continuously support the drain by a suitably qualified expert, a letter to the regulator is to be supplied outlining their qualifications and including a statement verifying that:-
“The filled ground in the immediate area of and/or under the sanitary drainage pipework will continuously support the drain and accommodate the loads of the surrounding ground and is considered stable”.
Unstable Ground:
If the unstable ground has been assessed and has been deemed adequate to continuously support the drain by a suitably qualified expert, a letter to the regulator is to be supplied outlining their qualifications and including a statement verifying that:-
“The unstable ground in the immediate area of / under the sanitary drainage pipework will continuously support the drain and accommodate the loads of the surrounding ground and is considered stable. The drain requires no provisions such as flexible joints, or similar to counteract or accommodate unstable ground or reactive soils.”
Water-charged Ground:
If the water-charged ground has assessed and been deemed adequate to continuously support the drain by a suitably qualified expert, a letter to the regulator is to be supplied outlining their qualifications and including a statement verifying that:-
“The water-charged ground in the immediate area of / under the sanitary drainage pipework will continuously support the drain and accommodate the loads of the surrounding ground and is considered stable”.
Performance Solution:
If the filled, unstable or water-charged ground has been assessed by a suitably qualified expert, and deemed unsuitable to support the pipework, a method to support the drainage is required to be determined by a suitably qualified expert.
Any engineered solution to support the pipework (ie pier and beam, or other engineered support solutions) must be submitted as a Performance Solution.
Any engineered solution to counteract or accommodate unstable ground or reactive soil conditions via the use of flexible joints or similar must be submitted as a Performance Solution. See the Fair Trading Technical Advisory Note on Flexible Joints in Drains for more information.
Note:
Information contained within this document is current as of June 2023 and refers to codes and standards current at the time of writing.
NSW Fair Trading 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.