A freestanding deck is self-supporting, meaning it sits entirely on its own posts and footings rather than being bolted to your house framing. This approach avoids potential moisture and weathertightness issues at the house wall, and can simplify consent requirements in some cases — though you'll still need to check with your local council before you start.
Do You Need a Building Consent?
In New Zealand, many low decks are exempt from building consent under Schedule 1 of the Building Act 2004, but the exemption has strict conditions. As a general guide, a freestanding deck may be exempt if it is no more than 1.5 metres above ground level and the total area doesn't exceed certain thresholds — but these rules can vary and councils interpret them differently. Always confirm with your local council before starting. You can find general guidance at MBIE Building Performance.
If your deck requires consent, the work must comply with NZS 3604:2011 (Timber Framed Buildings) and the NZ Building Code, particularly clause B1 (Structure).
Plan Your Deck Layout
Before picking up a tool, sketch your deck to scale and decide:
- Deck dimensions — length, width, and finished height above ground
- Timber species and treatment — use H3.2 treated timber for framing above ground, and H4 or H5 treated timber for any timber in or near the ground
- Post spacing — typically 1.8 m to 2.4 m centres, depending on bearer and joist spans (refer to NZS 3604 span tables)
- Decking board direction — this affects joist layout
- Access and steps — factor these into your footing plan
Footings: The Foundation of a Freestanding Deck
Because there's no house to share the load, every post needs its own solid footing. Common options in NZ include:
- Concrete pad footings — poured in situ, sized to suit the load and soil type
- Screw piles — increasingly popular, fast to install, and less disruptive to the ground
- Precast concrete piles — suitable for lower decks on stable ground
Footing depth and size depend on your soil bearing capacity and local frost depth (relevant in colder South Island and Central Plateau areas). If you're unsure about your soil, a geotechnical assessment or advice from a structural engineer may be needed. BRANZ publishes useful guidance on ground conditions and timber construction.
Setting Out Footings
Use batter boards and string lines to establish a square layout. Check squareness by measuring diagonals — they should be equal. Mark footing centres clearly before digging.
Posts
For a freestanding deck, posts transfer all loads to the footings. Use H4 treated timber where posts are set into or close to the ground, or H3.2 where posts sit on a metal post base above a concrete footing (the preferred method for longevity). Common post sizes are 100×100 mm or 150×150 mm — check NZS 3604 for the correct size based on your deck height and tributary area.
Secure posts to footings using galvanised or stainless steel post bases — never embed untreated or H3.2 timber directly into concrete.
Bearers
Bearers run horizontally between posts and support the joists above. They are typically bolted to the sides of posts or seated in post caps. Common bearer sizes range from 140×45 mm to 190×45 mm (or doubled up), depending on span. Use the NZS 3604 span tables to confirm the correct size for your spacing and load.
All connections should use galvanised or stainless steel hardware — especially important in coastal NZ environments where salt air accelerates corrosion.
Joists
Joists span between bearers and carry the decking boards. Typical joist sizes are 140×45 mm or 190×45 mm at 400–600 mm centres. Fix joists using joist hangers or direct fixing to bearers, following the hardware manufacturer's specifications.
Leave a small gap (around 3–5 mm) between joists and any adjacent structure to allow drainage and airflow — good ventilation under the deck is essential in NZ's varied climate to prevent moisture build-up and timber decay.
Decking Boards
Once the frame is complete, lay your decking boards across the joists. Popular NZ options include:
- Treated pine (H3.2) — affordable and widely available at Bunnings, Mitre 10, and PlaceMakers
- Hardwoods (e.g., kwila/merbau) — durable but check sourcing for sustainability
- Composite decking — low maintenance, good for wet NZ conditions
Leave a 3–6 mm gap between boards for drainage and expansion.
Bracing and Stability
A freestanding deck must be laterally braced — without attachment to the house, it can rack sideways. Options include:
- Diagonal timber bracing between posts
- Steel flat strap bracing
- Knee bracing from posts to bearers
Your bracing design should follow NZS 3604 requirements or be specified by a structural engineer if your deck is large or elevated.
When to Call a Professional
While a confident DIYer can tackle a low freestanding deck, consider hiring a qualified Licensed Building Practitioner (LBP) for:
- Decks that require a building consent (restricted building work requiring an LBP)
- Any deck requiring a building consent
- Complex sites — sloping ground, poor soil, or coastal exposure
- Structural design questions
You can verify an LBP's licence at Licensed Building Practitioners. To find a qualified local deck builder, search tradedirectory.co.nz for professionals in your area.
Safety note: Working at height carries real risk. Use appropriate scaffolding or edge protection, and follow WorkSafe NZ guidelines for working safely on elevated structures.
Licensed Building Practitioner (LBP)
