Yes, in many cases a homeowner can hire a petrol or electric auger to drill holes for timber deck posts — it's a practical and cost-effective approach for a DIY deck build. However, before you fire up the machine, there are several important steps around building consents, ground conditions, and safe operation that you need to work through first.
Do You Need a Building Consent?
This is the first question to answer before you dig a single hole. In New Zealand, many decks are exempt from building consent under Schedule 1 of the Building Act 2004, but only if they meet specific criteria — typically a deck no more than 1.5 m above ground level and not attached to a building in a way that affects its structure.
However, the rules can vary depending on your local council, site conditions, and whether the deck is attached to the house. Always confirm with your local council before starting work. You can find general guidance on exempt building work at MBIE Building Performance.
If consent is required, your post sizes, hole depths, and concrete specifications will be set out in the approved plans — and you must build to those specs.
Choosing the Right Auger for the Job
Hired augers come in several styles:
- One-person hand-held augers – suitable for softer soils and smaller diameter holes (up to around 150–200 mm)
- Two-person augers – better for harder ground and larger holes
- Tractor-mounted or skid-steer augers – for large projects or very hard ground; these require a machine operator
For a typical residential deck, a two-person petrol auger with a 200–300 mm bit is the most common hire choice. You'll find these at most hire centres, including those associated with Bunnings and Mitre 10.
Match your auger bit diameter to your post size. A 100×100 mm post typically needs a hole at least 200–250 mm in diameter to allow for concrete backfill around it.
How Deep Should the Holes Be?
Post hole depth is critical for structural stability and to resist frost heave and soil movement. As a general guide:
| Post height above ground | Minimum hole depth |
|---|---|
| Up to 1.0 m | 450–600 mm |
| 1.0 m – 1.8 m | 600–750 mm |
| Over 1.8 m | Engineer's advice recommended |
These are indicative figures only. Your actual depth should be based on your specific design, soil type, and any consent conditions. NZS 3604:2011 (Timber-framed buildings) provides guidance on foundation requirements for standard residential structures — check with your council or a Licensed Building Practitioner if you're unsure.
Timber Post Selection
For in-ground or near-ground contact, you must use H5-treated timber to comply with the NZ Building Code. H5 treatment is rated for ground contact and provides protection against rot and borer. Using H4 or lower-grade timber in the ground is not acceptable and will void any warranty or consent compliance.
Look for the treatment grade stamped on the timber when purchasing from PlaceMakers or similar suppliers.
Call Before You Dig — Underground Services
This is non-negotiable. Before operating any auger, you must contact Dial Before You Dig (0800 248 344 or beforeudig.co.nz) to identify underground services including gas pipes, water mains, electrical cables, and telecommunications lines. Striking a buried service can be fatal and is a serious legal liability.
WorkSafe NZ has clear guidance on excavation safety — read it before you start.
Operating the Auger Safely
- Wear PPE: steel-capped boots, gloves, safety glasses, and hearing protection
- Never operate alone — always have a second person present
- Keep bystanders, especially children, well clear of the work area
- If the auger bit strikes a rock or root and kicks back, release the handles immediately — do not try to hold on
- Work slowly and clear spoil regularly to prevent the bit binding
- On slopes, take extra care with footing and machine stability
Backfilling with Concrete
Once your posts are positioned and checked for plumb (use a spirit level on two faces), backfill with concrete — not just soil. A bagged rapid-set or general-purpose concrete mix works well for post footings — follow the manufacturer's instructions for mixing ratios. Allow the concrete to cure fully before loading the posts.
For decks requiring consent, your approved plans will specify the required concrete strength — confirm this with your designer or council.
When to Call a Professional
Consider hiring a qualified earthmover or post-hole contractor if:
- Your ground is very hard, rocky, or has heavy clay that resists hand-held augers
- You need holes deeper than 750 mm
- The site is on a slope or has unstable soil
- Your deck requires a building consent and you're not confident interpreting the plans
- You encounter unexpected underground services or obstacles
A professional earthmover will have the right machinery to get the job done quickly and safely. You can find experienced local earthmoving contractors on tradedirectory.co.nz.
For the structural and carpentry work, an LBP-licensed builder should carry out or supervise any restricted building work if your deck requires consent.
Site Safe
