In many situations, yes — a homeowner can excavate a small retaining wall footing themselves in New Zealand. However, whether you need a building consent, how deep you can safely dig, and what's underneath the ground are all critical factors that can quickly turn a simple weekend job into a serious legal or safety issue. Here's what you need to know before you pick up a spade.
What Does NZ Law Say About Retaining Walls?
Under the NZ Building Code and the Building Act 2004, retaining walls are classified as building work. Whether your project needs a building consent depends primarily on the height of the wall:
- Retaining walls up to 1.5 metres in height that do not support a surcharge (such as a driveway, vehicle load, or building) may be exempt from consent under Schedule 1 of the Building Act. Confirm with your council how height is measured for your specific wall type, as this can vary.
- Walls over 1.5 metres, or any wall retaining a surcharge, will almost certainly require a building consent.
Always confirm with your local council before starting work — exemptions can vary depending on your site conditions, proximity to boundaries, and local district plan rules. You can find general guidance at MBIE Building Performance.
Is Excavating the Footing Itself Restricted Work?
Excavation for a small retaining wall footing is not classified as restricted building work (RBW) in the same way that structural, weathertight, or certain other building work is. This means a competent homeowner can legally do the digging themselves. However, keep in mind:
- If a building consent is required, the overall project must comply with the consent conditions, and inspections will be needed at key stages.
- If the wall design requires an engineer's input (common for walls over 1 m or on unstable ground), the engineer's specifications will dictate footing dimensions and depth.
- Excavation near existing structures, retaining walls, or boundaries can undermine foundations — take care and seek advice if in doubt.
Understanding Footing Depth and Soil Conditions
The depth of your footing excavation depends on the wall type, height, and your soil. As a general guide:
| Wall Height | Typical Footing Depth | Notes |
|---|---|---|
| Up to 600 mm | 200–300 mm | Firm, stable soil assumed |
| 600 mm – 1 m | 300–500 mm | May need engineer input |
| 1 m – 1.5 m | 500 mm+ | Engineer recommended |
| Over 1.5 m | Consent & engineer required | Not DIY footing excavation |
These are indicative figures only — always follow your engineer's or manufacturer's specifications. Soil type matters enormously: clay, fill, sandy, or expansive soils all behave differently. BRANZ has useful guidance on soil and foundation behaviour for homeowners.
Practical Steps for DIY Footing Excavation
1. Check for Underground Services
Before you dig anything, contact Dial Before You Dig (0800 248 344 or dialbeforeyoudig.co.nz) to identify any buried pipes, cables, or drains. Striking a gas line or power cable is extremely dangerous and potentially fatal.
2. Confirm Your Consent Requirements
Contact your local council's building department with your wall dimensions and site details. Don't assume you're exempt — confirm it in writing where possible.
3. Mark Out and Measure Carefully
Use string lines and pegs to mark the footing trench. Ensure it's level and correctly positioned. A footing that's out of alignment will cause problems for the entire wall.
4. Excavate Safely
- Keep trench walls as vertical as possible and don't undercut them.
- For trenches deeper than 1.5 metres, WorkSafe NZ guidance indicates that shoring, benching, or battered sides should be considered — this depth is unusual for a small retaining wall footing but worth knowing.
- Remove spoil well away from the trench edge to avoid it collapsing back in.
- Never work alone in a trench.
5. Check the Base
Once at depth, the base of the trench should be firm and undisturbed natural ground. If you hit soft, wet, or loose fill material, stop and get professional advice before proceeding.
Tools You'll Need
For a small footing trench, most homeowners can manage with:
- Spade and mattock for hand digging
- Wheelbarrow for spoil removal
- String line, spirit level, and tape measure
- Compactor plate (hireable from most hire shops) if you need to compact the base
For longer or harder ground, a mini excavator hire is worth considering — many hire companies offer these with a brief operator induction. Check Bunnings or Mitre 10 for tool hire options, or search local hire companies.
When to Call a Professional
You should engage a qualified excavator operator or builder if:
- The wall is over 1 metre high or retains a surcharge load
- Your site has sloping ground, unstable soil, or fill
- You're working near existing foundations, drainage, or boundaries
- The ground is too hard for hand digging and you're unfamiliar with machinery
- A building consent is required and you're unsure of the process
- An engineer has specified particular footing dimensions or methods
For walls requiring consent, the building work may need to be carried out or supervised by a Licensed Building Practitioner (LBP). Always check with your council what's required for your specific project.
You can find qualified local excavators and builders on tradedirectory.co.nz to get the job done safely and to code.
Licensed Building Practitioner (LBP)
