When your drains are failing, you generally have two options: drain relining (fixing the pipe from the inside) or drain replacement (digging it up and starting fresh). Both solve the same underlying problem, but they work in very different ways, suit different situations, and come with different price tags and disruption levels. Here's what every NZ homeowner should know.
What Is Drain Relining?
Drain relining — sometimes called cured-in-place pipe (CIPP) lining — is a trenchless repair method. A flexible liner saturated with resin is inserted into the damaged pipe, inflated to press against the pipe walls, and then cured (hardened) in place using hot water, steam, or UV light. The result is a smooth, jointless new pipe inside your old one.
Because there's no need to dig a trench, relining is far less disruptive. Your garden, driveway, or concrete path stays largely intact. Most residential relining jobs can be completed in a single day.
Relining works well when:
- The pipe has cracks, fractures, or root intrusion but is still structurally sound enough to hold its shape
- The pipe is in a difficult-to-access location (under a slab, driveway, or landscaping)
- You want to minimise disruption and reinstatement costs
- The pipe diameter is within the range the relining equipment can handle (typically 75 mm to 300 mm for residential work)
Limitations of relining:
- It slightly reduces the internal diameter of the pipe (usually by a few millimetres)
- It cannot fix a pipe that has completely collapsed or is severely misaligned
- Not all pipe materials or configurations are suitable — your drainlayer will assess this first
- Access points (usually existing manholes or small excavations) are still needed at each end
What Is Drain Replacement?
Drain replacement is the traditional approach: excavate the ground above the pipe, remove the old pipe entirely, and install new pipe in its place. In New Zealand, replacement pipes are commonly PVC (uPVC), which is durable, smooth-bore, and resistant to root intrusion.
Replacement is more disruptive — trenches need to be dug, surfaces broken up, and then reinstated afterwards — but it gives you a completely new pipe with a full design life (often 50+ years for uPVC).
Replacement is usually the better choice when:
- The pipe has collapsed, is severely offset, or has major structural failure
- The pipe is badly corroded (common in older clay or cast-iron pipes)
- The drain layout needs to be changed or upgraded
- Tree roots have caused repeated blockages and relining won't address the root cause
- The pipe is too small and needs upsizing
How Do They Compare?
| Factor | Drain Relining | Drain Replacement |
|---|---|---|
| Excavation required | Minimal or none | Yes — full trench |
| Disruption to property | Low | High |
| Typical job duration | Hours to 1 day | 1–3+ days |
| Suitable for collapsed pipes | No | Yes |
| Pipe diameter reduction | Small (a few mm) | None (new pipe) |
| Reinstatement costs | Low | Can be significant |
| Approximate cost guide | Higher per metre, lower overall | Lower per metre, higher overall |
| Lifespan of repair | 50+ years (manufacturer dependent) | 50+ years (uPVC) |
Note: Costs vary significantly by location, pipe depth, access, and pipe length. Always get at least two or three quotes from licensed drainlayers.
The Diagnosis Step: CCTV Drain Inspection
Before any repair, a reputable drainlayer will carry out a CCTV drain inspection — a small camera is fed through the pipe to identify exactly what's wrong and where. This is essential: it tells the tradesperson whether relining is viable or whether replacement is the only real option. Don't skip this step, and be wary of anyone who quotes for relining without inspecting the pipe first.
Consents and Regulations in New Zealand
Drainlaying work in New Zealand is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006. This means it must be carried out by (or under the supervision of) a licensed drainlayer registered with the Plumbers Gasfitters & Drainlayers Board (PGDB). Homeowners are not permitted to carry out drainlaying work themselves.
Whether a building consent is required depends on the scope of work and your local council's interpretation of Schedule 1 of the Building Act. Minor like-for-like drain repairs may be exempt, but any significant alteration or new drain installation is likely to need consent. Always check with your local council before work begins — don't rely on assumptions.
For guidance on the Building Code requirements relating to drainage (particularly clauses G13 — foul water, and E1 — surface water), visit MBIE Building Performance.
When to Call a Professional
All drainlaying work — whether relining or replacement — must be done by a licensed drainlayer. If you notice slow drains, gurgling sounds, sewage smells, wet patches in your garden, or repeated blockages, don't delay. Left untreated, a failing drain can cause serious damage to your property's foundations and create health hazards.
You can find qualified, local drain cleaning and drainlaying professionals on tradedirectory.co.nz. Always ask to see their PGDB licence and request a written quote that includes the CCTV inspection report.
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