Retaining walls in New Zealand come in two broad categories: garden retaining walls (low, decorative, and often consent-exempt) and structural retaining walls (engineered to hold back significant earth loads, often requiring building consent). Understanding which type you need is important — get it wrong and you could face safety risks, council issues, or costly remediation work.
What Is a Garden Retaining Wall?
A garden retaining wall is typically a low-height wall used to create raised garden beds, define landscaping features, or manage minor changes in ground level. These walls are generally:
- Up to 1.5 metres high (the common consent-exemption threshold under Schedule 1 of the Building Act 2004, though conditions apply)
- Not supporting any additional load from structures, driveways, or buildings above
- Built from timber sleepers, concrete blocks, natural stone, or brick
- Designed primarily for aesthetics and light earth retention
Because they retain relatively little soil and carry no surcharge loads, garden retaining walls are lower risk. However, even a modest wall can fail if poorly built, so good construction practice still matters.
What Is a Structural Retaining Wall?
A structural retaining wall is engineered to resist significant lateral earth pressure, often where:
- The wall is over 1.5 metres high
- There is a surcharge load above the retained soil — such as a driveway, vehicle traffic, a building foundation, or a slope
- The wall forms part of a building's foundation system
- Ground conditions are poor (expansive soils, high water table, or fill material)
Structural retaining walls must be designed to handle these forces safely over their lifetime. They are commonly built from reinforced concrete, concrete block masonry, timber pole systems, or segmental retaining wall systems with geogrid reinforcement. An engineer's input is typically required.
Key Differences at a Glance
| Feature | Garden Retaining Wall | Structural Retaining Wall |
|---|---|---|
| Typical height | Under 1.5 m | Often over 1.5 m |
| Surcharge loads | None | Driveways, buildings, slopes |
| Engineering required | Usually not | Yes — typically a structural engineer |
| Building consent | Often exempt (check with council) | Usually required |
| Common materials | Timber sleepers, stone, block | Reinforced concrete, engineered block |
| Risk level | Lower | Higher |
Building Consent and the NZ Building Code
In New Zealand, whether your retaining wall needs building consent depends on several factors. Under Schedule 1 of the Building Act 2004, retaining walls that retain no more than 1.5 metres of ground and do not support any surcharge from structures or vehicles may be exempt from consent — but this is not automatic. Conditions apply, and your local council has the final say.
If your wall exceeds 1.5 metres, sits near a boundary, retains a slope above a building, or supports any additional load, you will almost certainly need consent. The MBIE Building Performance website has clear guidance on consent exemptions and the Building Code requirements that apply.
Retaining walls must also comply with NZS 3604 where applicable, and in some cases with specific geotechnical or structural standards. BRANZ publishes useful technical guidance on retaining wall construction for New Zealand conditions.
Always check with your local council before starting work. Rules can vary by district, and some councils have additional requirements around walls near boundaries or in flood-prone or steep-terrain areas.
Materials Commonly Used in NZ
Garden Retaining Walls
- Treated timber sleepers (H5 treated for ground contact)
- Concrete masonry blocks (e.g., standard besser blocks)
- Natural stone or schist (popular in Central Otago and Marlborough)
- Brick
Structural Retaining Walls
- Reinforced concrete (poured in situ)
- Engineered segmental block systems with geogrid reinforcement
- Timber pole walls (large diameter, engineer-specified)
- Gabion baskets (wire cages filled with rock)
Products from suppliers like Sika and Ardex are commonly used for waterproofing and adhesion in concrete retaining wall construction. Building materials are widely available at Bunnings, Mitre 10, and PlaceMakers.
Drainage: Critical for Both Types
One of the most common causes of retaining wall failure in New Zealand is poor drainage. Water build-up behind a wall dramatically increases the pressure it must resist. Both garden and structural walls need:
- Coarse aggregate backfill directly behind the wall
- Ag pipe (agricultural drainage pipe) at the base to carry water away
- Weep holes or gaps to allow water to escape
NZ's variable climate — from wet West Coast winters to Auckland's heavy summer downpours — makes drainage planning essential.
When to Call a Professional
You should engage a qualified retaining wall builder or structural engineer if:
- Your wall will be over 1.5 metres high
- There is any structure, driveway, or significant slope above the wall
- You are on a steep or unstable site
- You are unsure about soil conditions or drainage
- Building consent is required
Retaining wall failures can be dangerous and expensive. A licensed builder or specialist contractor will ensure the wall is designed and built to last. You can find qualified retaining wall builders in your area on tradedirectory.co.nz.
For consent-required work, your builder may need to be a Licensed Building Practitioner (LBP) to carry out or supervise restricted building work.
Licensed Building Practitioner (LBP)
