Yes, in many cases you can build a simple garden shed on a concrete slab yourself — but whether you need a building consent, and what rules apply, depends on the size and location of the shed. Getting this right before you start will save you headaches (and potential fines) down the track.
Do You Need a Building Consent?
Under the New Zealand Building Code, some small sheds are exempt from building consent under Schedule 1 of the Building Act 2004. As a general guide, a single-storey detached outbuilding (like a garden shed) may be exempt if it:
- Has a floor area of 10 m² or less, or
- Is up to 30 m² if it meets specific conditions — including being single-storey, not used for habitation, and not located in a high wind or flood-prone zone.
However, exemptions have conditions and your local council may have additional rules (such as district plan setback requirements from boundaries). Always confirm with your local council before you start — don't rely solely on general guidance. You can find more detail on exempt building work at MBIE Building Performance.
Planning Your Concrete Slab
A solid, level concrete slab is the foundation of a good shed. Here's what to consider:
- Thickness: A typical garden shed slab is 100 mm thick, with a thickened edge beam (around 200–300 mm deep) around the perimeter for extra support.
- Reinforcing: Use 665 mesh reinforcing (or as specified) laid in the centre of the slab. This helps control cracking.
- Sub-base: Compact a layer of AP20 or AP40 crushed aggregate (at least 75–100 mm) beneath the slab for drainage and stability.
- Moisture barrier: Lay a polythene DPM (damp-proof membrane) — typically 0.25 mm — over the sub-base before pouring to prevent moisture rising through the slab.
- Drainage: Make sure the site drains away from the slab. Poor drainage is a common cause of damp sheds.
If you're not confident with concrete work, consider hiring a concretor for the slab and doing the shed framing yourself.
Framing the Shed
For a simple timber-framed shed, standard practice follows the principles of NZS 3604:2011 (Timber-framed buildings), even if your shed doesn't formally require consent. This standard covers stud spacing, bracing, and connection details that make for a sturdy, wind-resistant structure.
Key framing tips:
- Use H3.2 treated timber for framing in contact with or close to the ground or concrete, and H1.2 for wall framing above ground.
- Space wall studs at 600 mm centres for standard cladding.
- Anchor the bottom plate to the slab using chemical anchors or cast-in bolts — don't just sit the frame on the concrete.
- Brace the walls adequately for your wind zone. New Zealand has significant wind loading requirements, especially in exposed or coastal areas.
Cladding and Roofing
Popular cladding options for DIY sheds include Colorsteel or Zincalume corrugated iron, fibre cement sheet (such as products from James Hardie), or treated plywood. For roofing, corrugated steel is the most common and DIY-friendly choice.
- Ensure your roof pitch allows adequate water runoff — a minimum of 5° for metal roofing is typical, though steeper is better.
- Install roof underlay beneath the roofing iron to manage condensation.
- Make sure guttering and downpipes direct water away from the slab and foundation.
What About Electrical Work?
If you want power in your shed, electrical wiring is restricted work in New Zealand and must be carried out by a registered electrician — you cannot do this yourself. This includes installing a sub-board, running cables, and connecting to the mains. Check the Electrical Workers Registration Board (EWRB) for more information on what's restricted. A simple extension cord run from the house is not a permanent wiring solution and can be a fire hazard.
Health, Safety and Site Considerations
- Wear appropriate PPE when mixing or pouring concrete (gloves, eye protection, boots).
- Be aware of underground services before digging — contact Dial Before You Dig ((check the current number at their website)) to locate pipes and cables.
- Check your district plan for setback distances from boundaries, as these vary by council.
- If your property is in a flood-prone, high-wind, or coastal zone, additional requirements may apply. Check with your council and refer to BRANZ for technical guidance.
When to Call a Professional
While a simple shed is a great DIY project, consider hiring a qualified builder if:
- Your shed exceeds the consent-exempt size thresholds.
- The site has poor ground conditions, significant slope, or drainage issues.
- You're unsure about wind bracing requirements for your area.
- A building consent is required — a Licensed Building Practitioner (LBP) may need to carry out or supervise certain work. See Licensed Building Practitioners for details.
- You want electrical power connected to the shed.
You can find qualified local builders and concretors on tradedirectory.co.nz.
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