Yes, in many situations a New Zealand homeowner can legally build a retaining wall under 1.5 metres without a building consent — but there are important conditions attached. Getting this wrong can be costly and even dangerous, so it pays to understand the rules before you pick up a shovel.
The Building Consent Exemption Explained
Under Schedule 1 of the Building Act 2004, certain low-risk building work is exempt from requiring a building consent. Retaining walls fall into this category only if the wall:
- Retains ground to a height of less than 1.5 metres, and
- Does not support any surcharge (extra load) such as a vehicle, building, or structure above it, and
- Does not affect neighbouring property or a public space.
If all three conditions are met, you generally do not need a building consent. However, always confirm this with your local council before starting — district plans, resource consents, and site-specific conditions can add extra requirements that override the Schedule 1 exemption. You can read more about consent exemptions at MBIE Building Performance.
When You Still Need Consent (Even Under 1.5 m)
Don't assume the exemption automatically applies. You may still need consent if:
- The wall is near a boundary and could affect a neighbour's land or drainage
- There is a vehicle crossing, driveway, or structure above the retained area
- Your district plan has specific rules (some councils require consent for walls over 1 m)
- The site is on unstable or steep ground, or in a flood or erosion zone
- The wall is part of a larger earthworks project that requires resource consent
Ring your local council's duty planner or building department — it's a free call and can save you a lot of grief.
Does It Still Need to Meet the Building Code?
Absolutely. Even exempt work must comply with the New Zealand Building Code. For retaining walls, the key clauses are:
- B1 (Structure): The wall must be structurally sound and able to handle the loads placed on it.
- B2 (Durability): Materials must be durable for their intended life — typically 50 years for permanent structures.
- E1 (Surface Water): Drainage behind the wall must be managed to prevent water build-up and hydrostatic pressure.
For timber retaining walls, NZS 3604 provides guidance on construction standards. For concrete block or concrete walls, engineering principles apply. BRANZ publishes good technical guidance on retaining wall construction that's worth reading.
Common Retaining Wall Types for DIY
| Wall Type | Typical DIY Suitability | Key Consideration |
|---|---|---|
| Timber sleeper | Good for walls up to ~1 m | Use H5-treated timber; install deadmen anchors |
| Concrete block (dry-stack or mortared) | Moderate | Needs good drainage and a solid base |
| Gabion baskets | Good | Requires compacted fill and drainage |
| Poured concrete | Harder — consider a pro | Formwork and reinforcing can be complex |
Key Construction Tips
Drainage is Critical
Poor drainage is the number one cause of retaining wall failure. Always install agricultural drain coil (ag pipe) at the base of the wall, wrapped in geotextile fabric, and backfill with free-draining gravel (not clay). Weep holes in the wall face also help relieve pressure.
Use the Right Materials
Timber must be H5 treated for in-ground contact. Using untreated or H3 timber in the ground will lead to premature rot. Check with your local Mitre 10, PlaceMakers, or Bunnings for the correct treated timber grades.
Batter and Deadmen
Timber walls should lean slightly into the bank (batter) and use deadmen — horizontal timbers buried into the bank — to anchor the wall against overturning. As a rough guide, install deadmen every 1.2–1.5 m along the wall.
Solid Foundations
Dig down to firm, undisturbed ground for your base. A wall built on loose or poorly compacted soil is a wall waiting to fail.
Safety Considerations
Earthworks and retaining walls carry real risks — cave-ins, wall collapse, and falling material can cause serious injury. WorkSafe NZ has guidance on safe excavation practices. Never work in an unsupported trench deeper than 1.5 m, and always be aware of underground services (water, gas, electrical) before digging. Call Before U Dig (0800 248 344) to locate services.
When to Call a Professional
While a sub-1.5 m wall can be a satisfying DIY project, there are times when hiring a qualified builder or engineer is the smart move:
- The wall is close to the maximum height or near a boundary
- The ground is unstable, wet, or on a slope
- There's a structure, driveway, or vehicle load above the wall
- You're unsure about drainage or structural design
- The project is part of larger earthworks
For anything that needs engineering sign-off, you'll want a Licensed Building Practitioner (LBP). You can find qualified local builders and tradespeople on tradedirectory.co.nz. Check LBP registration at Licensed Building Practitioners.