For most straightforward residential excavation work, you can dig up to 1.5 metres deep without a building consent under Schedule 1 of the Building Act 2004 — but this comes with important conditions. The moment your dig is near a boundary, an existing structure, a slope, or any services, the rules tighten considerably and you may need consent or professional input regardless of depth.
The Key Rule: Schedule 1 Exemptions
NZ's Building Act 2004 includes a list of exempt building work (commonly called Schedule 1 exemptions) that doesn't require a building consent. For excavation, the general exemption allows earthworks up to 1.5 m deep, provided the excavation:
- Is not within the distance equal to its depth from any building foundation or boundary (e.g., a 1.2 m deep trench must be at least 1.2 m from a foundation or boundary)
- Does not affect the stability of neighbouring land or structures
- Is not on a steep or unstable site
- Does not involve retaining more than 1.5 m of ground (retaining walls over 1.5 m generally require consent)
Always confirm the current exemptions with your local council, as they can impose additional requirements beyond the national Building Code. You can also check the official guidance at MBIE Building Performance.
Retaining Walls and Excavation Together
If your excavation involves building a retaining wall, the consent threshold is typically:
| Retaining Wall Height | Consent Required? |
|---|---|
| Up to 1.5 m (no surcharge) | Generally exempt |
| Over 1.5 m | Building consent usually required |
| Any height near a boundary or with surcharge (e.g., driveway, building load above) | Check with council |
A surcharge means any extra load above the retained soil — like a vehicle, fence, or building — which significantly increases the forces on a retaining wall and can trigger consent requirements even at lower heights.
Underground Services: Dig Safe First
Before you put a spade in the ground, you must locate underground services. Striking a gas line, water main, or power cable can be fatal and is your legal responsibility.
- Contact Dial Before You Dig (beforeudig.co.nz) to get service plans for your area
- Check with your local council and network utility operators
- Hand-dig carefully within 500 mm of any marked service
WorkSafe NZ has clear guidance on excavation safety, including requirements for shoring and safe access in trenches deeper than 1.5 m.
When Depth Alone Isn't the Only Factor
Even a shallow dig can require consent or professional involvement if:
- Soil type is poor — peat, fill, or expansive clay can make even modest excavation risky
- You're on a slope — cuts into hillsides can destabilise land and trigger the NZ Building Code's Clause B1 (Structure) and Clause E1 (Surface Water) requirements
- You're near a waterway — regional councils often have rules under the Resource Management Act (RMA) about earthworks near streams, wetlands, or the coast. This is separate from building consent and may require a resource consent
- Volume of spoil — some councils set limits on the total volume of earth moved before an RMA consent is needed
- Heritage or contaminated sites — additional rules may apply
Always check with both your local territorial authority (TA) and your regional council, as they have overlapping but different roles.
Trenching for Plumbing and Drainage
If you're digging to lay drainage or connect to the public sewer, be aware that drainlaying is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006. Any connection to the public wastewater or stormwater network must be carried out by — or under the supervision of — a licensed drainlayer. Check licensing at the Plumbers Gasfitters & Drainlayers Board.
You may be able to dig the trench yourself, but the actual pipe connections and sign-off must be done by a licensed professional.
Electrical Cables Underground
If your excavation is anywhere near underground electrical cables, treat every cable as live. Electrical work is restricted under the Electricity Act — only a registered electrician can work on or connect electrical cables. Find registered electricians through the Electrical Workers Registration Board.
When to Call a Professional
You should engage a qualified tradesperson or engineer before digging if:
- Your excavation will exceed 1.5 m in depth
- You're working on a sloped, unstable, or filled site
- The dig is close to any building foundation, boundary, or retaining structure
- You need a resource consent for earthworks near a waterway
- The project involves drainage, gas, or electrical connections
- You're unsure about soil stability or groundwater
For larger earthmoving projects, a geotechnical engineer may need to assess the site. A Licensed Building Practitioner (LBP) can help ensure your project meets the NZ Building Code — find one at Licensed Building Practitioners.
For hands-on earthmoving work, you can find qualified local earthmoving contractors right here on tradedirectory.co.nz.
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