Yes, in many cases you can pour your own concrete footings for deck posts in New Zealand — but whether you need a building consent first, and whether your site conditions allow DIY, are questions you must answer before you pick up a shovel. Getting this right from the start saves you costly rework and potential legal headaches down the track.
Do You Need a Building Consent?
This is the first question to answer. Under the Building Act 2004, many low-level decks qualify as Schedule 1 exempt work, meaning no building consent is required. As a general guide, a deck that is:
- No more than 1.5 m above the ground at any point
- Not attached to a building in a way that affects its structure
- Not in a special hazard area (flood zone, steep slope, etc.)
…may be exempt. However, exemptions have conditions and your local council has the final say. Always confirm with your council before starting, as rules vary by region and site. You can read more about exempt building work at MBIE Building Performance.
If your deck does require consent, the footings must be designed and inspected to meet the NZ Building Code — and your council will likely require inspections at key stages, including before you pour concrete.
What the NZ Building Code Requires
Deck footings typically need to comply with NZS 3604:2011 (Timber-framed buildings), which sets out footing sizes, depths, and concrete strengths for standard residential construction. Key points include:
- Minimum concrete strength is generally 17.5 MPa for footings, though 20 MPa is commonly used and recommended
- Footing depth must get below the frost line and into stable, undisturbed ground — typically at least 300–450 mm, but deeper on soft or sloping sites
- Footing diameter depends on the load the post carries and the soil bearing capacity — NZS 3604 provides tables to work this out
- In high-wind or seismic zones (much of NZ), additional requirements apply
If your site has poor soil, is on a slope, or is in a liquefaction-prone area, you may need a geotechnical assessment or a structural engineer's input. BRANZ has good guidance on footing design for residential decks.
How to Pour Concrete Footings: Step by Step
1. Mark Out and Dig
Use string lines and a builder's square to mark footing positions accurately. Dig holes to the required depth — a post-hole borer (available to hire from most tool hire shops) makes this much easier. Check the bottom of each hole is firm and undisturbed.
2. Check for Services
Before digging, contact Dial Before You Dig (0800 248 344) to locate any underground pipes, cables, or drains. Hitting a service line is dangerous and expensive.
3. Choose Your Concrete
For small jobs, bagged concrete mix (just add water) from Bunnings or Mitre 10 is convenient. For larger pours, ordering ready-mix concrete is more economical and gives you a consistent, specified strength. Aim for at least 20 MPa.
4. Set Post Anchors or Tubes
Most modern decks use galvanised post anchors (stirrups) cast into the concrete rather than embedding the timber post directly — this keeps timber out of the ground and dramatically extends its life. Set the anchor bolt or stirrup plumb and at the correct height while the concrete is still wet, using a spirit level.
5. Pour and Cure
Fill the hole, rod or vibrate out air pockets, and finish the top with a slight dome to shed water. Keep the concrete damp and protected from direct sun for at least 3–7 days to cure properly. Don't load the footings for at least 7 days, ideally 28 days for full strength.
Materials and Approximate Costs
| Item | Approx. cost (guide only) |
|---|---|
| Bagged concrete mix (20 kg) | $8–$14 per bag |
| Galvanised post anchor/stirrup | $15–$40 each |
| Post-hole borer hire (half day) | $80–$150 |
| Ready-mix concrete (per m³) | $200–$350+ delivered |
Prices are approximate guides only and will vary by region and supplier.
When to Call a Professional
While pouring footings is within reach of a capable DIYer, there are situations where you should engage a qualified deck builder or structural engineer:
- Your deck requires a building consent and council inspections
- The site is sloped, soft, or has poor drainage
- You're in a high-wind or seismic zone and unsure of the load requirements
- The deck will be attached to the house (this can affect the building's structure and weathertightness under NZ Building Code clause E2)
- You're not confident reading NZS 3604 tables or calculating footing sizes
A licensed deck builder will ensure your footings are correctly sized, placed, and documented. You can find qualified local deck builders on tradedirectory.co.nz.
Note: Deck construction is not restricted building work in the same way that electrical or plumbing is, but if your project requires consent, the work must still comply with the Building Code and may need to be carried out or supervised by a Licensed Building Practitioner (LBP).
Safety Notes
- Wet concrete is caustic — wear gloves, eye protection, and waterproof boots
- Deep holes can collapse — never work in an unsupported excavation deeper than 1.5 m
- Always check for underground services before digging
- Review WorkSafe NZ guidance on safe excavation practices
Licensed Building Practitioner (LBP)
