Scaffold planks on a working platform must overlap by a minimum of 300 mm over each bearer or transom in New Zealand. This is a well-established requirement under NZ scaffolding practice and is consistent with the guidance set out by WorkSafe NZ, which oversees health and safety on construction sites. Getting this right is not just a technicality — an under-lapped plank can tip, slide, or collapse under load, causing serious injury or death.
Why the 300 mm Minimum Matters
The 300 mm overlap rule exists to ensure planks cannot easily tip or shift when a worker steps near the end. If the overlap is too short, the plank acts like a see-saw over the support, and the unsupported end can lift suddenly. A 300 mm bearing gives enough contact area to resist tipping under normal working loads, including the weight of a person, tools, and materials.
Key point: The 300 mm is a minimum, not a target. Where site conditions allow, a slightly longer overlap adds an extra margin of safety.
Maximum Overhang at the Ends
Just as important as the overlap over supports is the overhang beyond the last support at each end of a plank. Planks should not overhang the end bearer by more than four times the plank thickness. For a typical 50 mm thick timber scaffold plank, that means a maximum overhang of around 200 mm. An excessive overhang creates a trip hazard and a tipping risk.
If you are using proprietary steel or aluminium decking systems, always follow the manufacturer's specific instructions, as these may differ from timber plank rules.
Plank Thickness and Grading
In New Zealand, traditional timber scaffold planks are typically:
- 50 mm thick × 225 mm wide (nominal)
- Graded to a structural standard suitable for scaffolding use
- Free from large knots, splits, or decay that could reduce strength
Always inspect planks before use. Reject any plank that is cracked along its length, heavily notched, or shows signs of rot. WorkSafe NZ guidance makes clear that defective planks must be removed from service immediately.
Span Between Supports
The maximum span between supports depends on plank thickness and the load the platform will carry. As a general guide for 50 mm timber planks:
| Platform Load Class | Max Span Between Supports |
|---|---|
| Light duty (e.g. painting) | Up to 2.4 m |
| General duty | Up to 2.1 m |
| Heavy duty (materials, masonry) | Up to 1.8 m or less |
These are indicative figures only. Always refer to the specific scaffolding design or the manufacturer's data for the planks and system you are using. For anything beyond a basic low-level platform, a competent scaffolder should determine the correct span.
Securing the Planks
Planks must be secured against displacement — this means they should not be able to slide along their length or lift in the wind. Common methods include:
- Cleats nailed or screwed to the underside at each end
- Proprietary clips or hooks on system scaffold decking
- Lashing with wire or scaffold ties where cleats are not practical
Do not rely on plank weight alone to keep them in place, especially at height or in exposed, windy conditions — a common situation on many NZ coastal and hillside sites.
Gaps Between Planks
Planks laid side by side on a platform should have no gaps greater than 25 mm between them. Larger gaps are a trip hazard and can allow tools or debris to fall onto people below. If a gap cannot be avoided, it must be covered or the area below must be barricaded.
NZ Regulations and Standards
Scaffolding in New Zealand is governed by the Health and Safety at Work Act 2015 and associated regulations. WorkSafe NZ publishes approved codes of practice and guidance on scaffolding that set out these requirements in detail. For scaffold over 5 metres in height, a licensed scaffolder (holding a relevant certificate of competence) is required to erect, alter, or dismantle the structure. This is restricted work — it is not something a homeowner should attempt at that height.
For more information on building work and safety obligations, MBIE Building Performance is a useful reference for understanding where scaffolding intersects with building consent requirements.
When to Call a Professional
While a homeowner may be able to set up a very basic, low-level hop-up or trestle platform for minor tasks, any scaffold over 5 metres high must be erected by a licensed scaffolder under NZ law. Even below that height, if you are unsure about plank grading, span calculations, or how to secure the structure safely, it is always worth getting a professional involved.
A qualified scaffolder will ensure:
- Correct plank overlap and overhang at every level
- Proper guardrails and toe boards
- Safe access and egress
- Compliance with WorkSafe NZ requirements
You can find licensed local scaffolders on tradedirectory.co.nz to get quotes and check credentials before work begins.
