Building a low natural stone retaining wall is a rewarding DIY project that can add real character to a NZ garden. With the right preparation, materials, and technique, most homeowners can tackle a wall up to around 600–800 mm high — but there are important rules around building consent and drainage you need to understand before you start.
Do You Need a Building Consent?
In New Zealand, retaining walls are regulated under the NZ Building Code and the Building Act 2004. Under Schedule 1 exemptions, a retaining wall that retains less than 1.5 metres of ground and does not support a surcharge (such as a driveway, vehicle load, or building) may be exempt from building consent. However, this threshold can vary depending on your site conditions, soil type, and local council rules.
Always check with your local council before starting work. Some councils have additional requirements, particularly on steep or unstable land. You can find general guidance at MBIE Building Performance.
Choosing Your Stone
Natural stone walls have been built in NZ for generations, and there are several good options:
- Schist – popular in Central Otago and the South Island; attractive and durable
- Basalt/volcanic rock – common in Auckland and Waikato; very hard-wearing
- Greywacke – widely available across NZ; a solid, dense option
- Limestone – softer and easier to work with, suits certain garden styles
For a dry-stack wall (no mortar), choose stones with relatively flat faces so they bed together well. For a mortared wall, you have more flexibility with irregular shapes. Dry-stack is generally preferred for low garden walls as it allows natural drainage and is more forgiving to build.
Source stone locally where possible — landscape suppliers, quarries, and some garden centres stock natural stone. Buying locally reduces cost and ensures the stone suits your regional climate.
What You'll Need
| Item | Purpose |
|---|---|
| Natural stone (various sizes) | Wall structure |
| Compactable gravel/AP20 | Base and backfill drainage |
| Geotextile fabric | Prevents soil migration into drainage |
| Builder's line and pegs | Keeping the wall straight and level |
| Rubber mallet and chisel | Shaping stones |
| Spade and wheelbarrow | Excavation and moving material |
| Spirit level | Checking level and batter |
Step-by-Step: Building a Dry-Stack Stone Wall
1. Plan and Mark Out
Mark the wall line with pegs and string. Decide on the batter (the slight backward lean into the bank) — aim for roughly 25–50 mm of lean for every 300 mm of height. This lean is critical for stability.
2. Excavate the Base
Dig a trench at least 200–300 mm deep and slightly wider than your largest base stones. The footing must sit on firm, undisturbed ground. Remove any soft or organic material.
3. Lay a Gravel Base
Add 100–150 mm of compacted AP20 gravel to the trench. This provides a stable, free-draining foundation. Compact it firmly with a hand tamper or plate compactor.
4. Lay the First Course
Choose your largest, flattest stones for the base course. Set them firmly into the gravel, ensuring they are level side-to-side and angled slightly back into the bank. These base stones do the most work, so take your time.
5. Build Up the Courses
As you build each course:
- Stagger the joints — never line up vertical joints between courses (this is called "running bond" and is essential for strength)
- Use tie stones (long stones running back into the bank) every 1–1.5 metres to anchor the wall
- Fill gaps with smaller stones and rubble, but avoid large voids
- Maintain your batter angle as you go up
6. Install Drainage Behind the Wall
This is one of the most important steps. Poor drainage is the number one cause of retaining wall failure in NZ, especially given our heavy rainfall events. Line the back of the excavation with geotextile fabric, then backfill with free-draining gravel (AP20 or similar) for at least 300 mm behind the wall. This prevents hydrostatic pressure building up and pushing the wall over. You can find more on drainage requirements in BRANZ guidance.
7. Cap the Wall
Finish with a course of flat cap stones to give the wall a tidy, finished look and help shed water away from the top.
Key Tips for NZ Conditions
- Earthquake zone awareness: NZ sits on an active fault system. In higher seismic zones (check with your council), even low walls may need engineering input.
- Expansive soils: Some NZ soils, particularly volcanic clays in Auckland, swell when wet. Good drainage is even more critical in these areas.
- Frost: In alpine and inland South Island areas, frost heave can shift stones over time. A deeper, well-compacted base helps.
When to Call a Professional
You should engage a qualified retaining wall builder or structural engineer if:
- Your wall will be 900 mm or taller, or close to the 1.5 m consent threshold
- The wall will support a surcharge such as a driveway, deck, or building
- Your site has unstable, steep, or waterlogged ground
- You are in a high seismic zone or on land with known geological issues
- You are unsure whether consent is required
A licensed building practitioner (LBP) may be required for certain restricted building work. Check Licensed Building Practitioners for more information. You can find experienced local retaining wall builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
