If your section has a slope, a bank, or a level change between neighbours, a retaining wall is often the most practical solution. But choosing between timber, concrete, and concrete block can feel overwhelming — each material has genuine strengths and real trade-offs. This guide breaks it all down so you can make a confident, informed decision before calling in a professional.
Why the Choice Really Matters
Retaining walls do a structural job: they hold back soil, manage water movement, and protect your home and neighbours' properties. Get the material wrong and you could end up with a wall that leans, cracks, rots, or fails entirely — sometimes within a few years. In New Zealand, walls over 1.5 metres high (or in certain ground conditions) require a building consent under the NZ Building Code, and the design must meet engineering standards. MBIE Building Performance has clear guidance on when consent is required, and it's worth checking before you start.
Timber Retaining Walls
Timber — typically H5-treated pine — is the most common DIY-friendly retaining wall option in New Zealand. It's relatively affordable, easy to cut and work with, and blends naturally into garden settings.
Pros:
- Lower upfront material cost
- Easier for homeowners to build for low walls (under 1 m)
- Natural, warm appearance that suits most NZ gardens
- Widely available at Bunnings and Mitre 10
Cons:
- Even H5-treated timber has a limited lifespan — typically 15–25 years depending on drainage and soil conditions
- Susceptible to rot if drainage behind the wall is poor
- Not suitable for walls over 1 m without engineering input
- Requires periodic inspection and eventual replacement
Timber walls rely heavily on deadman anchors (horizontal timbers driven back into the bank) for taller sections, and proper drainage aggregate and ag-pipe behind the wall are non-negotiable.
Concrete Retaining Walls
Poured or precast concrete walls are the most robust option available. They're commonly used for taller walls, commercial applications, or anywhere long-term permanence is the priority.
Pros:
- Extremely durable — a well-built concrete wall can last 50+ years
- Handles heavy loads and steep banks confidently
- Low ongoing maintenance once built
- Can be formed into curves or custom shapes
Cons:
- Highest upfront cost of the three options
- Almost always requires professional construction and engineering sign-off
- Formwork and pouring is labour-intensive
- Plain concrete can look industrial — rendering or cladding adds cost
- Difficult and expensive to modify or remove later
For significant walls, BRANZ recommends proper geotechnical assessment of the soil type and drainage conditions before any concrete wall is designed.
Concrete Block Retaining Walls
Concrete block — including both traditional mortared concrete masonry units (CMUs) and modern interlocking segmental retaining wall (SRW) blocks — sits in the middle ground. Products like Allan Block or Firth's Vertica range are popular across New Zealand.
Pros:
- Very durable (30–50+ years with good drainage)
- Attractive, clean appearance — many styles and colours available
- Interlocking SRW blocks can be DIY-friendly for low walls
- Mortared block walls are very strong and can be rendered or painted
- Good flexibility in design and height (with engineering)
Cons:
- More expensive than timber
- Mortared block requires skilled labour
- Interlocking blocks need precise base preparation — errors compound quickly
- Heavier to handle on-site
PlaceMakers and most building merchants stock a good range of block options suited to NZ conditions.
Head-to-Head Comparison
| Criteria | Timber | Concrete (Poured) | Concrete Block |
|---|---|---|---|
| Typical lifespan | 15–25 years | 50+ years | 30–50+ years |
| Relative cost | Lowest | Highest | Mid-range |
| Appearance | Natural/warm | Industrial (can render) | Clean/modern, many styles |
| DIY suitability | Good (low walls) | Poor — needs professionals | Moderate (SRW blocks) |
| Maintenance | Moderate (inspect regularly) | Very low | Low |
| NZ climate suitability | Moderate (drainage critical) | Excellent | Excellent |
| Consent likely needed | Over 1.5 m | Over 1.5 m | Over 1.5 m |
| Engineering required | Over 1 m recommended | Almost always | Over 1 m recommended |
Cost Considerations
As a rough guide only, timber is the most budget-friendly option for materials, but factor in replacement costs over time. Concrete block sits in the mid-range, and poured concrete is typically the most expensive upfront — though its longevity can make it cost-effective over decades. Labour is a significant component for all three; concrete especially so.
Always get at least two or three quotes from qualified retaining wall builders. You can find experienced local professionals on tradedirectory.co.nz.
NZ Building Code and Consent Rules
Under the NZ Building Code, any retaining wall over 1.5 metres in height generally requires a building consent from your local council. Walls on unstable ground, near boundaries, or close to structures may need consent at lower heights. Your council's duty planner can advise on your specific site.
If the wall is part of a larger build or involves significant earthworks, you may also need a Licensed Building Practitioner (LBP) to carry out or supervise the restricted building work. Check the LBP register to verify your builder's credentials.
Drainage: The Factor That Determines Success
Regardless of which material you choose, drainage is the single most important factor in a retaining wall's longevity. Hydrostatic pressure from waterlogged soil is the leading cause of retaining wall failure in New Zealand. Every wall needs:
- A layer of free-draining aggregate (chip or scoria) behind the wall
- A perforated ag-pipe at the base, directed to a legal discharge point
- Weep holes (for mortared block and concrete walls)
Poor drainage will shorten the life of even the best-built wall.
Our Recommendation
For low garden walls (under 1 m) on a budget: Timber is a practical, DIY-friendly choice — just use H5-treated timber, install drainage correctly, and accept you'll likely replace it in 15–20 years.
For mid-height walls (1–1.5 m) where looks matter: Interlocking concrete block (SRW) offers the best balance of durability, appearance, and moderate DIY accessibility. Get a professional to prepare the base and check your work.
For walls over 1.5 m, steep banks, or near structures: Poured concrete or engineer-designed block walls are the only responsible choices. You'll need a building consent, likely an engineer, and a qualified builder. Don't cut corners here — a failing retaining wall is a serious safety hazard and can cause significant property damage.
Whatever you choose, hiring a qualified local retaining wall builder is strongly recommended for anything beyond a simple low garden wall. Find trusted professionals in your area at tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
