In many cases, minor excavation near a boundary fence does not require a building consent — but that doesn't mean you can simply dig wherever you like. NZ Building Code rules, Schedule 1 exemptions, neighbour obligations, and site-specific conditions all play a role. Getting this wrong can damage your neighbour's property, undermine foundations, or expose you to serious liability.
What the NZ Building Code Says
The NZ Building Code (administered by MBIE Building Performance) sets out requirements for excavation work under Clause B1 (Structure) and Clause E1 (Surface Water). Any excavation must not:
- Undermine the stability of your own or a neighbouring structure
- Redirect stormwater or cause flooding onto adjoining land
- Damage retaining walls, foundations, or services on or near the boundary
Even if your excavation is exempt from building consent, it must still comply with the Building Code. Non-compliance can result in enforcement action by your local council.
When Is Building Consent Required?
Under Schedule 1 of the Building Act 2004, some excavation work is exempt from building consent. As a general guide:
- Shallow, small-scale excavation (e.g., garden beds, fence post holes) on flat, stable ground away from structures is typically exempt.
- Retaining walls are exempt if they retain no more than 1.5 metres of ground — but this threshold can be lower near boundaries or where surcharge loads (like vehicles or buildings) are present.
- Any excavation that affects an existing retaining wall, foundation, or structure on or near the boundary is very likely to require consent.
Important: Schedule 1 exemptions are not a blanket free pass. Your local council is the authority on what requires consent in your area. Always check with them before starting work — rules can vary and site conditions matter enormously.
The 1.5-Metre Boundary Rule
A commonly misunderstood principle relates to lateral support. Under NZ common law and the Building Code, you must not remove the natural support that your land provides to your neighbour's land or structures. As a practical rule of thumb used in the industry:
- If you excavate within 1.5 metres of a boundary, or to a depth greater than 1.5 metres anywhere on your section, you are more likely to need a building consent and an engineer's assessment.
- Excavation near a boundary fence that sits close to a house foundation, retaining wall, or driveway on the neighbouring property carries significant risk and almost certainly warrants professional input.
This is a guide only — consult your council and a qualified engineer for your specific situation.
Neighbour Obligations and the Law
Beyond the Building Code, you have legal obligations to your neighbour under common law (the right of lateral support). If your excavation causes their fence, retaining wall, or land to subside or collapse, you may be liable for the full cost of repairs — regardless of whether you had consent.
Best practice is to:
- Talk to your neighbour before starting any significant excavation near the shared boundary
- Give reasonable notice and document the existing condition of the fence and their land (photos are useful)
- Consider whether a Licensed Building Practitioner (LBP) or structural engineer should assess the work first
Underground Services — A Critical Safety Check
Before any excavation, you must identify underground services. Buried power cables, gas lines, water pipes, and telecommunications cables can all run close to boundary fences. Striking a live cable or gas line is potentially fatal.
- Contact Dial Before You Dig (0800 248 344 or www.beforeudig.co.nz) to get service plans for your site — this is free and strongly recommended
- Check with your local council and network utility operators
- WorkSafe NZ has guidance on safe excavation practices, including shoring requirements for trenches deeper than 1.5 metres
Machinery and Excavator Safety Near Fences
Operating an excavator close to a boundary fence requires care:
- Assess the ground conditions — soft, wet, or recently disturbed soil increases the risk of collapse
- Keep the excavator bucket and boom clear of the fence structure to avoid accidental damage
- Never allow personnel in a trench deeper than 1.5 metres without appropriate shoring or battering — this is a WorkSafe NZ requirement
- Be aware of the machine's swing radius relative to the fence and any overhead lines
When to Call a Professional
You should engage a qualified tradesperson or engineer if:
- The excavation is deeper than 1.5 metres or within 1.5 metres of the boundary
- There are existing structures (retaining walls, foundations, buildings) on or near the boundary
- The ground is unstable, sloped, or waterlogged
- You are unsure whether building consent is required
- Underground services are present or unconfirmed
A Licensed Building Practitioner (LBP) can carry out or supervise restricted building work. Find qualified local excavation contractors and LBPs on tradedirectory.co.nz. For structural assessments, a Chartered Professional Engineer (CPEng) is the appropriate expert.
For any work that disturbs water supply, wastewater, or drainage connections, a licensed drainlayer registered with the Plumbers, Gasfitters and Drainlayers Board must be involved — this is restricted work under NZ law.
Licensed Building Practitioner (LBP)
