Yes, in many cases you can build a small retaining wall yourself without hiring an earthmover — but whether you need professional help depends on the wall's height, your site conditions, and New Zealand's building consent rules. Get these factors wrong and you risk an unstable wall, property damage, or a structure that doesn't comply with the NZ Building Code.
What Does an Earthmover Actually Do?
An earthmover (also called an excavator operator or earthworks contractor) uses machinery such as excavators and bobcats to cut into slopes, remove spoil, and prepare a level, stable base for a retaining wall. For small walls on flat or gently sloping sections, you may be able to do this preparation by hand with a spade and wheelbarrow. For larger cuts — particularly anything over about 500 mm deep or on steep or unstable ground — earthmoving machinery makes the job far safer and more practical.
NZ Building Consent Rules for Retaining Walls
This is the most important thing to get right before you start digging. Under the NZ Building Code and the Building Act 2004, retaining walls are subject to consent requirements based on height and surcharge (what's sitting above the wall).
Schedule 1 of the Building Act lists exemptions — work that doesn't need a building consent. As a general guide:
- A retaining wall up to 1.5 m high that does not support a surcharge (e.g., no driveway, building, or heavy load above it) is typically exempt from building consent.
- Any wall over 1.5 m, or one that retains soil near a building, boundary, or driveway, will almost certainly require a building consent and may need engineering sign-off.
Important: These thresholds can vary depending on your local council and site-specific conditions. Always confirm with your local council before starting work. You can find general guidance at MBIE Building Performance.
DIY-Friendly Retaining Wall Options
For walls under 1.5 m that don't require consent, several materials suit a confident DIYer:
Timber Sleepers
Treated timber sleepers (H5 treated for ground contact) are popular and widely available at Bunnings and Mitre 10. They're relatively easy to cut and stack, and suit a range of garden styles.
Concrete Blocks and Segmental Retaining Wall Blocks
Interlocking segmental retaining wall blocks (such as Allan Block-style products) are designed for DIY installation. They use a batter (slight backward lean) and geogrid reinforcement for taller runs. Follow the manufacturer's specifications carefully — these systems are engineered products.
Natural Stone
Dry-stacked schist or basalt can look great and drain well, but requires skill to build stably. Best suited to low garden walls.
Key Steps for a DIY Retaining Wall
- Check consent requirements with your council first.
- Mark out and excavate your base trench — typically 150–200 mm deep for the first course, on firm, undisturbed ground.
- Install drainage — a perforated ag-pipe behind the wall with free-draining gravel backfill is essential to prevent hydrostatic pressure building up and pushing the wall over.
- Build level and plumb (or with the correct batter for your block system).
- Backfill in layers, compacting as you go.
Proper drainage is the single most common thing DIYers get wrong. A wall without drainage will eventually fail.
When Do You Actually Need an Earthmover?
You'll likely need to hire an earthmover or earthworks contractor when:
- The cut is deeper than about 500 mm or the volume of soil is large
- The ground is hard clay, rock, or unstable fill
- You're working on a steep slope where manual excavation is unsafe
- The site has limited access for wheelbarrows and manual tools
- You need to remove large quantities of spoil from site
For anything requiring a building consent, your council may also require the earthworks to be carried out to a specific standard, and an engineer may need to inspect the foundation conditions.
Do You Need an Engineer?
For walls over 1.5 m, near boundaries, or supporting a surcharge, a geotechnical or structural engineer is typically required. They'll assess soil bearing capacity, design the wall, and may need to inspect during construction. This is not optional — it's a safety and legal requirement. BRANZ has useful guidance on retaining wall construction principles.
Safety Considerations
- Never work in an unsupported trench deeper than 1.5 m — this is a serious risk of collapse and a WorkSafe NZ requirement.
- Be aware of underground services (water, gas, power) before digging. Call Before U Dig (0800 248 344) to locate services.
- Wet weather can destabilise excavations quickly — don't leave open cuts unprotected.
When to Call a Professional
Call a qualified earthmover or retaining wall contractor if your wall is over 1.5 m, your site is steep or has poor soil, you need a building consent, or you simply want the job done right the first time. A professional will have the machinery, experience, and knowledge of local conditions to build a wall that lasts. You can find experienced local earthmoving and retaining wall contractors on tradedirectory.co.nz.
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