In most cases, no — installing a backflow prevention valve on a drain is considered restricted work under New Zealand law and must be carried out by a licensed professional. However, understanding exactly why, and what the rules are, will help you make the right call and avoid costly mistakes or compliance issues down the track.
What Is a Backflow Prevention Valve?
A backflow prevention valve (sometimes called a non-return valve or check valve) is a device fitted to a drain or pipe that allows wastewater or stormwater to flow in one direction only. It prevents sewage or floodwater from flowing back into your home through floor drains, toilets, or other fixtures — a very real risk in low-lying areas or during heavy rainfall events, which are increasingly common across New Zealand.
These valves are typically installed in:
- Subfloor drainage or basement floor drains
- Stormwater connections prone to surcharging
- Sewer lateral lines where council mains can back up
Is This Restricted Work in New Zealand?
Yes. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, any work that connects to, modifies, or installs components within a sanitary drain or stormwater drain is classified as restricted drainlaying work. This means it must be performed by — or directly supervised by — a Licensed Drainlayer registered with the Plumbers Gasfitters & Drainlayers Board (PGDB).
Carrying out restricted work yourself (or hiring an unlicensed person) is illegal and can result in:
- Fines for you and the person doing the work
- Insurance complications if something goes wrong
- Issues when selling your property
- Potential health and safety risks
The only exception is if you are the owner-occupier doing work on your own home — but even then, the rules are nuanced. Owner-occupiers may do some minor plumbing work, but drainlaying on sanitary or stormwater systems is generally not included in those exemptions. Always check with the PGDB before proceeding.
Does It Need a Building Consent?
This depends on the scope of work. Some minor drainage work falls under Schedule 1 of the Building Act 2004 as exempt from building consent, but connecting or modifying a drain that ties into the public network or involves structural changes may well require consent. Always check with your local council before starting any drainage work — requirements vary by region and the nature of the job.
For guidance on the Building Code and consent requirements, visit MBIE Building Performance.
What About the NZ Building Code?
Backflow prevention in drainage systems is addressed under NZ Building Code Clause G13 (Foul Water) and Clause E1 (Surface Water). These clauses set performance requirements for preventing the backflow of foul water or stormwater into buildings. Any installation must comply with these clauses, which is another reason licensed professionals are required — they understand how to meet code requirements and can issue the necessary Certificate of Compliance.
You can find more information on these standards through BRANZ, New Zealand's building research authority.
What Can a Homeowner Do?
While the installation itself is restricted, there are things you can do as a homeowner:
- Identify the problem — notice signs of backflow such as gurgling drains, sewage smells, or water backing up through floor drains
- Research your options — understand the types of valves available (flap valves, gate valves, combination units) before talking to a tradesperson
- Prepare the site — clear access to the area where work is needed
- Talk to your council — find out if your area is prone to sewer surcharging and whether they have any subsidy or support schemes
Choosing the Right Valve and Tradesperson
A licensed drainlayer will assess your specific situation and recommend the right type of backflow prevention device. Common options include:
| Valve Type | Best For | Notes |
|---|---|---|
| Flap (check) valve | Sewer laterals, floor drains | Simple, low maintenance |
| Gate valve | Stormwater lines | Manual operation required |
| Combination valve | High-risk properties | Flap + gate combined |
Products from suppliers like Bunnings, Mitre 10, or PlaceMakers are widely available, but selecting and installing the correct valve for your drain type must be done by a licensed professional.
Safety Note
Working around drainage systems carries real health risks — exposure to raw sewage can cause serious illness. Even if you were legally permitted to do this work yourself, appropriate personal protective equipment (PPE) including gloves, eye protection, and respiratory protection would be essential. For guidance on safe work practices, refer to WorkSafe NZ.
When to Call a Professional
Call a licensed drainlayer if you:
- Have experienced sewage or stormwater backing up into your home
- Want to install or replace a backflow prevention valve on any drain
- Are unsure whether your existing valve is working correctly
- Are buying or selling a property and want drainage compliance confirmed
A qualified local drainlayer can assess your drainage system, recommend the right solution, carry out the work legally, and provide the paperwork you need. You can find licensed drainlayers in your area right here on tradedirectory.co.nz.