Do You Need a PS1 for Plumbing and Drainage?

There is often confusion around whether a PS1 Design Producer Statement is required for plumbing and drainage design, particularly on commercial projects.

The short answer is: not necessarily.

Based on our review of Auckland Council and MBIE Building Performance guidance, there is no blanket requirement for a PS1 simply because a project includes plumbing or drainage work, or because the building is commercial.

MBIE describes a producer statement as a professional opinion that a Building Consent Authority may rely upon when determining whether it has reasonable grounds to establish Building Code compliance. Producer statements have no particular status under the Building Act and are typically used for specialist or engineering work where they assist Council with its assessment.

When does the council need a PS1 for Plumbing and Drainage?

It largely comes down to the complexity of the design and the evidence available to demonstrate compliance.

For a relatively straightforward plumbing and drainage system, compliance may be readily demonstrated through drawings, specifications and the applicable Acceptable Solution or other recognised compliance pathway.

For more complex or specifically engineered systems, Council may seek additional assurance from a suitably qualified designer. A PS1 provides one mechanism for doing this.

Importantly, G12 Water Supplies and G13 Foul Water establish the performance requirements that the building work must meet. They do not themselves create a blanket requirement for a PS1.

If a PS1 isn't mandatory, why engage a hydraulic consultant?

This is where the distinction between requiring a PS1 and benefiting from a proper hydraulic design becomes important.

For many commercial projects, the main reason for engaging a hydraulic consultant isn't simply to obtain a PS1. It is to establish a coordinated and compliant plumbing and drainage design before construction starts.

Where plumbing or drainage alterations are known to be required, completing the hydraulic design early allows potential compliance and coordination issues to be identified before they become expensive site problems.

Depending on the project, the design may need to demonstrate matters such as:

- appropriate sizing and configuration of water supply systems

- suitable backflow prevention

- appropriate foul water pipework and drainage arrangements

- adequate venting

- appropriate management of wastewater and overflow

- coordination with architectural, structural and other building services.

G12 addresses matters including adequate water supply, contamination, leakage, scalding and potable water protection, while G13 requires adequate plumbing and drainage for the safe disposal of foul water.

Council still needs sufficient information to establish compliance with these requirements, regardless of whether a PS1 accompanies the design.

Why should I hire a hydraulics engineer?

A coordinated hydraulic design also gives the client a defined scope to tender.

Instead of asking several plumbers to independently interpret what is required and price potentially different solutions, each contractor can price the same drawings and specification.

That generally makes tender comparisons clearer and reduces ambiguity around what each contractor has allowed for.

It also shifts important design decisions out of the construction phase, where changes are typically harder to coordinate and more disruptive.

Can my plumber design the plumbing and drainage system?

For straightforward work, plumbing and drainage design does not necessarily need to originate from a consulting engineer simply because a building consent is required.

However, Council still needs appropriate documentation and evidence demonstrating that the proposed and completed work complies with the consent and relevant Building Code requirements.

Auckland Council, for example, uses a specific PS3 Plumbing form completed by a certifying plumber to confirm specified plumbing work has been constructed in accordance with the consented documents and relevant requirements.

A PS3 should not be confused with a PS1. A PS1 relates to design assurance, whereas a PS3 relates to construction.

The takeaway

A PS1 is not automatically required for plumbing and drainage work. What is required is sufficient evidence for Council to establish that the proposed work complies with the Building Code.

For simple projects, that evidence may be relatively straightforward.

For larger or more complex commercial projects, engaging a hydraulic consultant early can provide considerably more value than simply producing a PS1. It establishes the design, identifies compliance and coordination issues before construction and gives contractors a common set of documents against which to tender.

In other words:

The value of hydraulic design isn't the PS1. The value is getting the plumbing and drainage design resolved before construction starts.

Need Clarity on Your Next Commercial Project?

Don't let plumbing and drainage design become a costly roadblock on site. Whether you're navigating Council requirements or need a fully coordinated hydraulic design before your tender phase, our experts can help.

Get in touch with our hydraulic engineering team today to discuss your project requirements.