In New Zealand, a homeowner can potentially operate an excavator or dig a hole for a septic tank themselves, but the broader septic system installation is tightly regulated — and the digging is really just the beginning of a complex, consent-driven process. Before you fire up a digger, here's what you need to know.
Understanding the Regulatory Picture
Septic tanks (and their associated drainage fields) are classified as on-site wastewater systems under the NZ Building Code, specifically Clause G13 (Foul Water). Installing a new septic system almost always requires a building consent from your local council, and in many cases a resource consent as well, depending on your district plan and proximity to waterways or boundaries.
You should contact your local council before doing anything — they will tell you exactly what consents are required for your property. Do not assume your situation is exempt. The MBIE Building Performance website has useful guidance on when building consent is required and what Schedule 1 exemptions may apply, though septic system installations are rarely exempt.
What Work Is Legally Restricted?
This is critical: while digging the hole itself is not restricted work, the connection and installation of the wastewater system is. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, drainlaying — which includes connecting a septic tank to your home's drainage and installing the effluent disposal field — is restricted work that must be carried out by a licensed drainlayer or plumber authorised to do drainlaying work.
You can check licensing requirements and find licensed practitioners through the Plumbers Gasfitters & Drainlayers Board. Doing restricted drainlaying work yourself is illegal and can result in fines, plus your council will not issue a code compliance certificate (CCC) for the work.
So Can a Homeowner Dig the Hole?
Technically, yes — excavating the hole for the tank is not restricted work in itself. However, there are several important considerations before you grab the controls of a digger:
- Consent first: Your council may require the excavation to follow an approved design. Digging before consent is granted could mean you dig in the wrong location or to the wrong dimensions.
- Soil assessment: A licensed professional (often a geotechnical engineer or authorised drainlayer) typically needs to assess your soil type and percolation rate to determine the correct tank size and disposal field design. This affects where and how deep you dig.
- Underground services: Before any excavation, you must identify buried services — power, water, gas, and telecommunications lines. Contact Dial Before You Dig (a free NZ service) to get plans of underground infrastructure on your property.
- Excavation depth and shoring: Septic tank holes are often 2–3 metres deep or more. Any excavation deeper than 1.5 metres poses a serious risk of collapse and must be properly shored or battered back to a safe angle. WorkSafe NZ has clear guidelines on excavation safety — this is not something to take lightly.
- Tank access and placement: The tank needs to be positioned correctly for vehicle access (for future pump-outs), setback distances from boundaries and buildings, and connection to both the inlet and outlet lines.
Excavation Safety — Don't Underestimate It
Excavation is one of the most dangerous DIY activities a homeowner can undertake. Soil can collapse without warning, and a cubic metre of soil weighs roughly 1.5 tonnes — enough to be fatal. If you are hiring or operating an excavator yourself:
- Never enter an unsupported trench deeper than 1.5 metres
- Batter (slope) the sides or use trench boxes/shoring
- Keep spoil (excavated soil) well back from the edge
- Have someone present at all times
- Check WorkSafe NZ guidelines for excavation safety before starting
The Practical Approach Most Homeowners Take
Given the complexity, most homeowners find the most cost-effective and legally sound approach is to:
- Engage a licensed drainlayer to design the system and manage consents
- Either have the drainlayer arrange excavation, or hire a local excavation contractor to dig once the design and consent are in place
- Have the licensed drainlayer complete all restricted connection work and arrange inspections
This way, you get a legal, consented installation with a CCC — which matters enormously for insurance and when you sell your property.
| Task | Can Homeowner Do It? | Notes |
|---|---|---|
| Dig the tank hole | Generally yes | Must follow approved design; safety rules apply |
| Operate hired excavator | Yes, if competent | No licence required for own property |
| Connect inlet/outlet drains | No — restricted work | Must be a licensed drainlayer |
| Install effluent disposal field | No — restricted work | Must be a licensed drainlayer |
| Apply for building consent | Yes | But design must meet NZ Building Code G13 |
When to Call a Professional
You should engage a licensed drainlayer from the outset — before any digging begins. They will manage the consent process, design the system to meet NZ Building Code requirements, and carry out all restricted work legally. If you want to save money by doing the excavation yourself, discuss this with your drainlayer first — they may be happy to let you dig once the design is finalised and consented, or they may have good reasons to recommend their own excavation contractor.
You can find qualified local excavators and drainlayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
