When a drain starts causing problems — slow drainage, bad smells, or soggy patches in the garden — a licensed drainlayer will carry out a thorough assessment before recommending a fix. The decision to repair or replace a drain pipe comes down to the type, extent, and location of the damage, the age and material of the pipe, and what the NZ Building Code requires for your situation.
The First Step: CCTV Drain Inspection
The most reliable diagnostic tool in a modern drainlayer's kit is a CCTV drain camera. A small waterproof camera is fed through the pipe, sending live footage to a screen above ground. This lets the drainlayer see exactly what's going on without unnecessary digging.
A CCTV inspection can reveal:
- Cracks or fractures in the pipe wall
- Root intrusion from nearby trees or shrubs
- Pipe displacement or joint separation (common in older clay pipes after ground movement)
- Blockages from grease, debris, or collapsed sections
- Corrosion or deterioration of the pipe material
- Bellying (a sag in the pipe that holds water and waste)
The footage is usually recorded so the drainlayer can review it and share it with you. A good drainlayer will walk you through what they found and explain their reasoning clearly.
Key Factors in the Repair-vs-Replace Decision
1. Extent and Severity of Damage
A single small crack or a localised root intrusion at one joint may be suitable for a spot repair — either excavating just that section or using a pipe relining technique where a resin-impregnated liner is cured in place inside the existing pipe. However, if damage is spread across multiple sections, or if the pipe has collapsed, replacement is almost always the better long-term option.
2. Pipe Material and Age
Older NZ homes often have clay (earthenware) or concrete pipes, which are brittle and prone to cracking, root intrusion, and joint failure over time. Modern installations use uPVC pipe, which is more durable and resistant to root intrusion. If a clay or concrete pipe is already showing widespread deterioration, a drainlayer will often recommend full replacement with uPVC rather than repeated patch repairs.
3. Pipe Gradient and Alignment
Drains must fall at the correct gradient to flow properly — typically around 1:60 for a 100 mm drain (though the correct gradient requirements should be confirmed against the applicable NZ standard and your drainlayer's advice, as requirements can vary), though this can vary. If a CCTV inspection or a water flow test reveals that the pipe has settled, shifted, or bellied out of alignment, no amount of patching will fix the underlying drainage problem. In these cases, replacement and re-laying to the correct fall is the only real solution.
4. Location and Access
Some pipes run under concrete slabs, driveways, or close to building foundations. The cost and disruption of excavation can sometimes make pipe relining a more practical option, even for moderate damage, because it avoids major earthworks. Your drainlayer will weigh up the access difficulty against the long-term reliability of each option.
5. NZ Building Code Compliance
Any drain repair or replacement must comply with the NZ Building Code, particularly Clause G13 (Foul Water), which sets out requirements for drainage systems. If your existing drain doesn't meet current standards — for example, it's undersized or poorly graded — a replacement gives the opportunity to bring everything up to code. Your drainlayer will advise whether a building consent is required; many drain repairs fall under Schedule 1 exemptions, but you should always confirm this with your local council.
Common Assessment Methods at a Glance
| Method | What It Reveals | Repair or Replace Indicator |
|---|---|---|
| CCTV camera inspection | Cracks, roots, displacement, collapse | Localised = repair; widespread = replace |
| Water flow / dye test | Blockages, leaks, gradient issues | Poor flow despite clearing = replace |
| Ground probe / surface inspection | Soft spots, subsidence, wet patches | Subsidence often means replace |
| Pipe material check | Age and type of pipe | Old clay/concrete = lean toward replace |
Repair Options a Drainlayer Might Recommend
- Spot excavation and section replacement — digging up just the damaged section and splicing in new uPVC pipe
- Pipe relining (CIPP) — cured-in-place pipe lining inserted without major excavation; good for pipes in difficult locations
- Root cutting and jetting — high-pressure water jetting to clear roots and debris, sometimes combined with a root-inhibiting treatment
- Joint resealing — for minor joint leaks where the pipe itself is otherwise sound
When to Call a Professional
Drainlaying is restricted work in New Zealand. Under the Plumbers, Gasfitters and Drainlayers Board (PGDB), only a licensed drainlayer (or someone working under their supervision) can legally carry out work on sanitary drains and stormwater connections. This protects public health and ensures work is done to the correct standard.
Call a licensed drainlayer if you notice:
- Persistent slow drainage or gurgling sounds
- Sewage smells inside or outside your home
- Wet or sunken patches in your lawn or garden
- Cracks appearing in paths or driveways near drain lines
- Repeated blockages that keep coming back
Attempting to repair or replace drain pipes yourself is not only illegal for restricted work — it can also create serious health hazards and may void your home insurance. You can find qualified, local drainlayers on tradedirectory.co.nz.
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