Yes, you can use a hand auger to dig retaining wall post holes yourself — and for many straightforward residential projects it's a perfectly practical choice. Whether it's the right tool for your job depends on your soil type, the depth and diameter of holes required, and whether your retaining wall needs a building consent.
What Is a Hand Auger and How Does It Work?
A hand auger (sometimes called a post-hole borer) is a manual digging tool with a helical blade that bores into the ground as you twist it. You can hire petrol-powered one- or two-person augers from most hire centres, or use a manual T-bar style for shallower, lighter work. For retaining wall posts, a powered auger is almost always the better choice — manual versions become very hard work beyond about 600 mm depth.
When a Hand Auger Works Well
A hand or hire auger is well-suited to retaining wall post holes when:
- Soil is loose to medium: Sandy loam, soft clay, or topsoil without significant rock or tree roots.
- Holes are 150–300 mm in diameter and up to around 1.2–1.5 m deep.
- Access is tight: Augers are far more manoeuvrable than excavators in narrow side passages or established gardens.
- The wall is low-risk: Walls under 1.5 m retaining height are more likely to fall under Schedule 1 exemptions (see consent section below).
When an Auger Isn't the Right Tool
There are situations where you should reconsider:
- Rocky or compacted ground: Augers can hit rock, boulders, or hard clay pan and simply stop. Forcing them risks injury.
- Deep holes: Posts for taller walls may need holes 1.5 m or deeper — this is exhausting and potentially dangerous with a hand tool.
- Unstable or waterlogged soil: Hole walls can collapse before you get the post in.
- Large-diameter holes: Anything over 350 mm is better suited to a tracked auger or excavator.
- Tree roots: Roots can bind the auger blade and cause sudden kickback — a real injury risk.
NZ Building Consent — Do You Need One?
This is critical. In New Zealand, retaining walls are regulated under the NZ Building Code, and many require a building consent from your local council. Under Schedule 1 of the Building Act 2004, some retaining walls are exempt from consent — but the rules are specific:
- Walls retaining up to 1.5 m of ground may be exempt, provided they don't support a surcharge (like a driveway, building, or slope above) and aren't near a boundary or drainage.
- Any wall retaining more than 1.5 m almost certainly needs consent.
- Walls near property boundaries, slopes, or with surcharge loads may need consent regardless of height.
Always check with your local council before you start digging. The rules vary by district and site conditions. You can find general guidance at MBIE Building Performance.
If consent is required, the wall design must meet NZS 3604 (for timber-framed construction) or be engineer-designed. Post hole depth, diameter, and concrete embedment will be specified — and you must dig to those specs exactly.
Choosing the Right Auger Size
Post hole diameter should generally be 2–3 times the post width. As a rough guide:
| Post Size | Minimum Hole Diameter | Typical Depth |
|---|---|---|
| 100 × 100 mm | 200–250 mm | 600–900 mm |
| 125 × 125 mm | 250–300 mm | 750–1000 mm |
| 150 × 150 mm | 300–350 mm | 900–1200 mm+ |
Always confirm hole dimensions with your engineer or council-approved plans if consent is involved.
Step-by-Step: Digging Post Holes with an Auger
- Mark out your post positions using string lines and pegs. Double-check spacing and alignment.
- Call Before You Dig — contact Dial Before You Dig (0800 248 344) or check with your council to locate any underground services. Striking a gas line or power cable is extremely dangerous.
- Set up the auger and start slowly, keeping it vertical. Use a spirit level to check plumb as you go.
- Clear spoil regularly — lift the auger every 200–300 mm to remove soil. This prevents binding.
- Check depth with a tape measure or marked rod.
- Place your post and concrete promptly — holes can collapse or fill with water if left open.
Safety First
Powered augers can cause serious injury if they strike a root or rock and kick back suddenly. Always:
- Use two people on a petrol auger — never operate alone.
- Wear steel-capped boots, gloves, and safety glasses.
- Keep bystanders and children well clear.
- Never wrap clothing or loose items around the auger shaft.
- Check WorkSafe NZ guidelines for safe use of powered tools.
When to Call a Professional
While digging post holes is DIY-friendly in good conditions, there are times to bring in a qualified retaining wall builder:
- Your wall needs a building consent or engineer's design.
- Ground conditions are unknown, rocky, or unstable.
- The site has poor drainage or is on a slope.
- You're unsure about post sizing, concrete mix, or embedment depth.
- The wall is near a boundary, building, or drainage line.
A licensed builder or retaining wall specialist will ensure the wall is structurally sound and compliant with the NZ Building Code. You can find experienced local retaining wall builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
