Retaining walls are more than just a landscaping feature — they're structural elements that hold back soil and water, and getting them wrong can be costly and dangerous. In New Zealand, the qualifications required of a retaining wall builder depend largely on the height of the wall, the materials used, and whether a building consent is needed.
Why Qualifications Matter for Retaining Walls
A poorly built retaining wall can collapse, damage property, and even injure people. Because of this, MBIE Building Performance sets clear rules about who can design and build retaining walls, particularly taller or more complex structures. Understanding these rules helps you hire the right person and protect your investment.
When Is a Building Consent Required?
Under the New Zealand Building Code, retaining walls that retain more than 1.5 metres of ground generally require a building consent. Walls under 1.5 metres may be exempt under Schedule 1 of the Building Act 2004 — but this depends on factors like surcharge loading (e.g., a driveway or building nearby), soil conditions, and proximity to boundaries or other structures.
Always check with your local council before starting work. What looks like a simple low wall may still require consent depending on your site conditions. Your council's building department can confirm whether your project is exempt.
Licensed Building Practitioners (LBPs)
For retaining walls that require a building consent, restricted building work (RBW) rules apply. This means the design and/or construction must be carried out or supervised by a Licensed Building Practitioner (LBP). LBPs are licensed by the Ministry of Business, Innovation and Employment (MBIE) and must demonstrate competency in their area of work.
For retaining walls, the relevant LBP licence classes typically include:
- Site — covers general construction and site work
- Design — for those designing structural elements
Always ask your builder to provide their LBP licence number and check it on the LBP register at lbp.govt.nz.
Engineering Design for Taller or Complex Walls
For walls over 1.5 metres, or walls subject to significant surcharge loads, a Chartered Professional Engineer (CPEng) or similarly qualified structural engineer is typically required to produce the design. The builder then constructs to that specification.
Even for walls under 1.5 metres, if the ground conditions are poor (e.g., expansive clay, high water table) or the wall is near a boundary or structure, engineering input is strongly recommended. BRANZ provides useful technical guidance on retaining wall construction that both builders and homeowners can reference.
What to Look for When Hiring a Retaining Wall Builder
When getting quotes, ask potential builders the following:
- Do you hold a current LBP licence? (Required for consented work)
- Can you provide references or examples of similar retaining wall projects?
- Will you manage the consent process, or is that my responsibility?
- Do you work with a structural engineer for walls over 1.5 metres?
- Are you experienced with the specific material I want? (Timber, concrete block, concrete, stone, or Keystone-style modular blocks all have different requirements)
A reputable builder will be transparent about these points and happy to provide documentation.
Materials and Standards
Retaining walls in NZ are commonly built from:
| Material | Common Use | Notes |
|---|---|---|
| Treated timber (H5) | Garden walls up to ~1.2 m | Must use correctly treated timber per NZ standards |
| Concrete block | Medium to large walls | Often requires engineering |
| Poured concrete | Large or complex walls | Typically engineered |
| Modular block (e.g., Keystone) | Gravity walls | Supplier design guides available |
| Natural stone | Decorative/low walls | Skill-dependent |
Materials and construction must comply with the NZ Building Code, particularly clauses relating to structural stability and drainage. Drainage behind the wall is critical — a blocked or absent drainage layer is one of the most common causes of retaining wall failure.
Drainage and the Building Code
Building Code clause E1 (Surface Water) is relevant to retaining wall drainage. Water pressure behind a wall (hydrostatic pressure) dramatically increases the load on the structure. A qualified builder will ensure adequate drainage — typically a gravel backfill layer and agricultural drain pipe — is incorporated into the design.
When to Call a Professional
You should always engage a qualified retaining wall builder or structural engineer if:
- The wall will be over 1.0 metre high (and especially over 1.5 metres)
- There is a driveway, building, or heavy load near the top of the wall
- The site has poor or unstable soils
- The wall is close to a boundary or neighbouring property
- You are unsure whether consent is needed — check with your council first
For straightforward low garden walls (under 1.0 m, no surcharge, stable ground), a competent handyperson or landscaper may be suitable — but even then, experience with drainage and correct material selection matters.
You can find qualified retaining wall builders in your area on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
