Replacing a cracked plastic drain pipe under your driveway sounds like a straightforward DIY job, but in New Zealand the rules around drainlaying are strict — and getting it wrong can be costly. Whether you can legally do the work yourself depends on what type of drain it is, where it sits on your property, and what the NZ Building Code requires. Read on to understand your options before you pick up a shovel.
What Type of Drain Is It?
The first thing to establish is what the pipe actually does, because this determines whether the work is restricted drainlaying under NZ law.
- Stormwater drain – carries rainwater runoff from your roof, driveway, or yard to a soakpit, stream, or council stormwater system.
- Sanitary drain – carries wastewater from your toilets, sinks, showers, and appliances to the public sewer or an on-site treatment system.
- Subsoil drain – a perforated pipe that manages groundwater around foundations.
If you're unsure which type you have, check your property's drainage plans (often held by your local council) or have a licensed drainlayer inspect it before doing anything.
What Is Restricted Drainlaying Work in NZ?
Under the Plumbers, Gasfitters, and Drainlayers Act 2006, drainlaying is restricted work in New Zealand. This means that connecting to, disconnecting from, or altering any sanitary drain or stormwater drain that connects to a public system must be carried out — or supervised — by a licensed drainlayer.
The Plumbers Gasfitters & Drainlayers Board (PGDB) enforces these rules. Doing restricted drainlaying work without a licence can result in fines and, more importantly, leaves you liable if the work causes damage or fails a council inspection.
As a homeowner, you are generally NOT permitted to:
- Replace or repair any section of sanitary drain (even on your own property)
- Alter connections to the public stormwater or sewer network
- Carry out work that requires a building consent involving drainage
What Can a Homeowner Do?
There is a narrow exception under the Act that allows owner-occupiers to carry out certain drainlaying work on their own property — but only for sanitary plumbing (not drains), and the rules are specific. For drainlaying proper, the exemption is very limited.
What you can typically do without a licence:
- Dig to expose the pipe to assess the damage
- Clear a blockage using a drain rod or high-pressure water jetter (no cutting or joining pipes)
- Replace a subsoil drain that does not connect to the public system (check with your council first)
Always confirm with your local council what is permitted in your area before starting any work.
The Driveway Complication
When a drain runs under a driveway, the job becomes more complex for several reasons:
- Breaking up the driveway surface (concrete or asphalt) requires care to avoid damaging the pipe further or undermining the sub-base.
- Pipe bedding and backfill must meet the NZ Building Code and relevant standards (typically manufacturer specs for the pipe material and relevant NZ Standards for drainage installation — check with your council or drainlayer for the applicable standard) to prevent future cracking from vehicle loads.
- Compaction of backfill is critical — poorly compacted fill under a driveway will cause the surface to sink.
- A building consent may be required depending on the scope of work and your council's requirements. Check with your local council or visit MBIE Building Performance for guidance on Schedule 1 exemptions.
Choosing the Right Replacement Pipe
If a licensed drainlayer is carrying out the work, they will specify the correct pipe. Common options for under-driveway installations include:
| Pipe Type | Typical Use | Notes |
|---|---|---|
| uPVC (solid) | Sanitary & stormwater drains | Most common; check pressure rating for depth |
| HDPE | High-load or trenchless applications | Flexible; suits directional drilling |
| Perforated uPVC | Subsoil drainage | Not suitable for sanitary use |
Your drainlayer will select the appropriate SN (stiffness) class for the depth and vehicle loading above the pipe. Suppliers such as Placemakers and Mitre 10 stock a range of drainage pipe, but always confirm the specification with your tradesperson first.
Could Pipe Relining Be an Option?
If the crack is not a full collapse, pipe relining (inserting a resin-impregnated liner into the existing pipe) may be possible without digging up your driveway at all. This is a specialist job carried out by licensed drainlayers with the right equipment, but it can save significant cost and disruption. Ask your drainlayer whether relining is suitable for your situation.
When to Call a Professional
For virtually any work on a cracked drain pipe under your driveway, you should engage a licensed drainlayer. This is especially true if:
- The pipe is a sanitary or stormwater drain connecting to the public network
- The damage is extensive or the pipe has collapsed
- A building consent is required
- You need the driveway reinstated to a trafficable standard
A licensed drainlayer will also arrange any required inspections and sign off the work correctly, protecting you legally. You can find qualified local drainlayers on tradedirectory.co.nz. Always check that your tradesperson holds a current licence via the PGDB licence register.
Safety Note
Excavation work carries serious risks. Trenches can collapse without warning, and underground services (gas, water, power, telecoms) may be present near your drain. Before any digging, call Before U Dig (0800 248 344) to locate underground services. Never enter an unsupported trench deeper than 1.5 metres — this is a WorkSafe NZ requirement.
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