Replacing a broken gully trap might look like a straightforward dig-and-swap job, but in New Zealand it is classified as restricted drainlaying work under the Plumbers, Gasfitters, and Drainlayers Act 2006. In most cases, you will need a licensed drainlayer to carry out the work legally. Here is what you need to know before you pick up a spade.
What Is a Gully Trap and Why Does It Matter?
A gully trap is a small, water-sealed fitting installed at ground level where household wastewater pipes (from laundry tubs, washing machines, kitchen sinks, and sometimes showers) discharge into the underground drainage system. The water seal inside the trap prevents foul sewer gases from escaping back into your home or yard. When a gully trap cracks, blocks, or collapses, it can cause:
- Foul odours around the property
- Wastewater overflowing onto the ground (a health hazard)
- Loss of the water seal, allowing sewer gas into living areas
- Non-compliance with the NZ Building Code (particularly Clause G13 – Foul Water)
Because gully traps are a direct part of your property's foul-water drainage system, any work on them is taken seriously by regulators.
Is Replacing a Gully Trap Restricted Work in NZ?
Yes. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, drainlaying work — which includes replacing, altering, or connecting any fitting that forms part of a sanitary drainage system — is restricted work. Only a person who is:
- A licensed drainlayer (or licensed plumber with drainlaying scope), or
- Working under the direct supervision of one,
may legally carry out this work. This is enforced by the Plumbers Gasfitters & Drainlayers Board (PGDB), which is the licensing authority for the trade in New Zealand.
Doing this work yourself without a licence — or hiring an unlicensed person — is an offence that can result in fines and may also void your home insurance or create liability issues if something goes wrong.
What Can a Homeowner Legally Do?
While you cannot replace the gully trap itself, there are a few things you can do as a homeowner:
- Clear a blocked gully trap — removing debris, leaves, or a surface blockage is generally considered maintenance rather than drainlaying work.
- Fit a gully trap cover or grate — replacing a plastic or metal cover/grate on an existing, intact trap is typically fine.
- Dig to expose the trap — you can do the preparatory digging to expose the broken trap, which may save on labour costs, but leave the actual fitting replacement to the licensed tradesperson.
- Identify and document the problem — take photos and note where the trap is located to help your drainlayer quote accurately.
If you are unsure whether a specific task crosses into restricted work, contact the PGDB for clarification before starting.
Do You Need a Building Consent?
Replacing a like-for-like gully trap in the same location is generally considered maintenance or repair and may fall under Schedule 1 of the Building Act 2004 as exempt building work — meaning a building consent may not be required. However, this depends on the scope of work and your local council's interpretation.
Always check with your local council before starting, as exemptions can vary and some councils require notification even for exempt work. You can find general guidance on building consent exemptions at MBIE Building Performance.
Regardless of consent, the work must still comply with the NZ Building Code, particularly Clause G13 (Foul Water), and must be carried out by a licensed drainlayer.
What Does the Job Typically Involve?
A licensed drainlayer replacing a gully trap will generally:
- Excavate around the existing trap (if not already done)
- Cut out the broken fitting from the drain line
- Install a new PVC or ceramic gully trap, correctly bedded and aligned
- Reinstate the connection to the underground drain
- Test the water seal and check for leaks
- Backfill and reinstate the surface
- Issue a Certificate of Compliance (CoC) confirming the work meets the NZ Building Code
The Certificate of Compliance is an important document — keep it with your property records.
How Much Might It Cost? (Rough Guide Only)
As a very rough guide, a straightforward gully trap replacement by a licensed drainlayer might range from a few hundred dollars upward, depending on access difficulty, depth, pipe material, and your region. Get at least two quotes from licensed drainlayers. You can find qualified local drainlayers on tradedirectory.co.nz.
When to Call a Professional
Call a licensed drainlayer promptly if you notice:
- Wastewater pooling around the gully trap or overflowing onto the ground
- Cracked, sunken, or collapsed trap body
- Persistent foul smells near the trap even after cleaning
- Slow drainage from multiple fixtures that empty to the gully
Delaying repairs can lead to ground contamination, health risks, and more expensive damage to the underground drain line. A licensed drainlayer can also check whether the surrounding pipework has been affected.
Safety note: Wastewater contains harmful bacteria and pathogens. Wear gloves and wash hands thoroughly if you handle anything near an open gully trap, and keep children and pets away from the area until repairs are complete. If you suspect a sewer gas smell inside your home, ventilate immediately and seek professional advice.