Retaining walls are a fact of life for many New Zealand homeowners — our hilly terrain and variable soils mean that keeping the land in place is often a priority. But with several materials to choose from, it can be hard to know where to start. This guide breaks down the most common options so you can make a confident, informed decision.
Why Material Choice Matters
The "best" retaining wall material isn't one-size-fits-all. The right choice depends on your wall height, the soil type and load behind it, your budget, how it needs to look, and whether it requires a Building Consent. In New Zealand, any retaining wall over 1.5 metres high (or one that retains soil near a boundary, driveway, or structure) generally requires a Building Consent under the NZ Building Code. Always check with your local council before starting work.
Concrete Blocks (Segmental Retaining Walls)
Concrete block or segmental retaining walls are one of the most popular choices in NZ, and for good reason. Products like Allan Block or similar interlocking systems are widely available at Bunnings and Mitre 10, and they're designed for DIY-friendly installation at lower heights.
Pros:
- Durable and low maintenance
- Good range of styles and colours
- Interlocking systems are relatively straightforward to lay for walls under 1 m
- Handles NZ's wet winters well when properly drained
Cons:
- Taller walls require engineering input and geogrid reinforcement
- Can look utilitarian without landscaping
For walls over 1 m, always consult a professional — the engineering behind drainage and reinforcement is critical.
Timber (Treated Pine)
Treated timber retaining walls are a classic NZ choice, particularly for garden terracing and walls up to around 1 m high. H5-treated pine is the minimum standard for in-ground contact in NZ, as it resists rot and borer in our damp conditions.
Pros:
- Cost-effective for smaller walls
- Natural, warm appearance that suits NZ gardens
- Relatively easy for competent DIYers
Cons:
- Lifespan is shorter than concrete or stone — expect 15–25 years depending on conditions
- Requires deadmen (horizontal anchors) for taller walls
- Not suitable for walls retaining heavy loads or near structures
Timber is best suited to garden beds and low terracing rather than structural retaining situations.
Poured Concrete or Concrete Block (Structural)
For serious retaining jobs — steep banks, driveways, or walls over 1.5 m — poured concrete or reinforced concrete block walls are the gold standard. These are engineered structures that must be designed to comply with NZS 3604 or specific engineering standards, and they almost always require a Building Consent.
Pros:
- Extremely strong and long-lasting
- Can handle surcharge loads (vehicles, buildings)
- Can be finished with plaster or cladding for a clean look
Cons:
- Higher cost
- Requires professional design and construction
- Not a DIY project at any meaningful height
BRANZ has useful technical guidance on retaining wall construction and drainage requirements that both homeowners and builders should be aware of.
Natural Stone
Dry-stack or mortared stone walls are beautiful and can last generations when built correctly. Schist, basalt, and river stone are all used around NZ.
Pros:
- Excellent aesthetics — suits rural and heritage properties
- Very long lifespan
- Dry-stack walls allow natural drainage
Cons:
- Labour-intensive and expensive
- Requires skill to build well
- Sourcing quality stone can be difficult depending on your region
Gabion Baskets
Gabion walls — wire mesh cages filled with rock — are increasingly popular in NZ for their modern industrial look and excellent drainage properties. They're particularly well-suited to areas with high rainfall or poor drainage.
Pros:
- Excellent drainage (reduces hydrostatic pressure)
- Flexible — handles ground movement well
- Distinctive, contemporary appearance
Cons:
- Wire mesh can corrode over time if not galvanised or PVC-coated
- Filling and placing cages is hard work
- Not always suitable for tight urban sections
Material Comparison at a Glance
| Material | Typical Height Limit (DIY) | Durability | Relative Cost | Consent Likely? |
|---|---|---|---|---|
| Concrete blocks (segmental) | Up to ~1 m | High | Moderate | Over 1.5 m |
| Treated timber | Up to ~1 m | Moderate | Low–Moderate | Over 1.5 m |
| Poured/reinforced concrete | Engineer required | Very High | High | Almost always |
| Natural stone | Varies | Very High | High | Over 1.5 m |
| Gabion baskets | Up to ~1 m (DIY) | High | Moderate | Over 1.5 m |
Cost and height guidance is general only — always confirm with your local council and a qualified professional.
Drainage: The Hidden Key to Any Retaining Wall
No matter which material you choose, drainage is the most critical factor in retaining wall performance. Hydrostatic pressure from waterlogged soil is the number one cause of retaining wall failure in NZ. Every wall needs adequate drainage behind it — typically a layer of free-draining gravel and agricultural pipe (ag-pipe) at the base, with weep holes or outlets at regular intervals.
NZ's MBIE Building Performance guidance and your local council's technical requirements will specify drainage standards for consented walls.
When to Call a Professional
You should always engage a qualified retaining wall builder or structural engineer if:
- Your wall will be over 1 m high (and certainly over 1.5 m)
- The wall is near a boundary, building, or driveway
- You're on a steep or unstable slope
- The soil is clay-heavy, expansive, or poorly draining
- A Building Consent is required
Building consent work must be carried out by or under the supervision of a Licensed Building Practitioner (LBP). Getting it wrong can be costly — and dangerous. You can find qualified local retaining wall builders on tradedirectory.co.nz.