Connecting a new downpipe to your stormwater drain is a common home improvement task in New Zealand — but it's not entirely a DIY job. Some parts of the work are straightforward for a capable homeowner, while other parts are legally restricted and must be carried out by a licensed drainlayer. Getting this wrong can result in fines, failed inspections, or serious drainage problems down the track.
Understanding the Rules: What's Restricted Work?
In New Zealand, drainlaying is a licensed trade regulated by the Plumbers, Gasfitters and Drainlayers Board (PGDB). Under the Plumbers, Gasfitters, and Drainlayers Act 2006, any work that connects to or modifies a below-ground drainage system — including stormwater drains — is considered restricted drainlaying work. This means it must be performed (or directly supervised) by a licensed drainlayer.
Connecting a downpipe to an underground stormwater drain almost always falls into this category. If you dig down and make a new connection into an existing underground pipe, that is restricted work — full stop.
What Can a Homeowner Do?
While the underground connection itself is restricted, there are tasks a homeowner can legally carry out:
- Replacing an existing above-ground downpipe with the same size and configuration (like-for-like replacement)
- Repositioning or extending above-ground downpipe runs before they enter the ground
- Clearing blockages in above-ground sections
- Installing a rainwater diverter or above-ground rain barrel/tank connection
- Preparing the site — marking out, digging, and backfilling — though the actual pipe connection must be made by a licensed drainlayer
If you're unsure where the above-ground work ends and the restricted underground work begins, it's always safer to ask a licensed drainlayer.
Does This Work Need a Building Consent?
This depends on the scope of work. Under Schedule 1 of the Building Act 2004, some minor drainage work is exempt from building consent — but the exemptions are specific and have conditions. For example, connecting to an existing stormwater system may be exempt if it's minor maintenance or repair, but a new connection point to the underground network may require consent.
Always check with your local council before starting work. Requirements vary between territorial authorities, and getting it wrong can cause problems when you sell your home or make an insurance claim. The MBIE Building Performance website has useful guidance on consent exemptions.
NZ Building Code Compliance
Stormwater drainage in New Zealand must comply with NZS 4404 (Land Development and Subdivision) and the NZ Building Code, particularly Clause E1 (Surface Water). The key requirements include:
- Stormwater must be directed away from buildings and neighbouring properties
- Connections must not allow stormwater to enter the sanitary sewer system (cross-connection is illegal and can result in significant fines)
- Pipes must be laid at the correct fall (gradient) to ensure self-cleansing flow — typically a minimum of 1:60 for stormwater laterals, though your council may specify differently
- Materials must be fit for purpose (uPVC is the most common choice in NZ)
| Pipe Size | Common Use | Minimum Fall |
|---|---|---|
| 100mm uPVC | Single downpipe connection | 1:60 |
| 150mm uPVC | Multiple downpipes or larger catchment | 1:100 |
Note: Always confirm pipe sizing and fall requirements with your licensed drainlayer or council.
Typical Process for a New Downpipe Connection
- Plan the route — identify where the downpipe will connect to the underground stormwater system
- Check for existing services — contact Dial Before You Dig to locate underground cables and pipes
- Engage a licensed drainlayer — they will make the underground connection, ensure correct fall, and issue the required Certificate of Compliance (CoC)
- Install above-ground downpipe — this can often be done by the homeowner or a builder
- Inspection and sign-off — your council may require an inspection before backfilling
Materials You'll Need (Above-Ground Work)
For the above-ground downpipe sections, common materials available from Bunnings or Mitre 10 include:
- uPVC downpipe (typically 80mm round or 65×50mm rectangular in NZ)
- Downpipe brackets and clips
- Offsets and elbows to navigate around obstacles
- Downpipe shoes or adaptors to transition to underground pipe
- Solvent cement for uPVC joints
Always match the pipe diameter to your existing system and check compatibility with your drainlayer before purchasing.
When to Call a Professional
You must engage a licensed drainlayer for:
- Any connection into an underground stormwater drain
- Laying new underground stormwater pipework
- Any work that requires a building consent
- Situations where you're unsure whether stormwater and sewer lines are correctly separated
A licensed drainlayer will also issue a Certificate of Compliance, which is an important legal document for your property records. You can find qualified, local drainlayers on tradedirectory.co.nz.
Safety note: Always locate underground services before any digging. Striking a buried electrical cable or gas line can be fatal. Contact Dial Before You Dig and follow WorkSafe NZ safe excavation guidelines.