Scaffolding that sinks into soft ground is one of the most common — and most dangerous — stability problems on residential building sites in New Zealand. The good news is that with the right base preparation and load-spreading equipment, you can keep your scaffold level, stable, and safe throughout your project.
Why Scaffolding Sinks — and Why It Matters
Scaffolding frames concentrate a significant amount of weight onto a very small footprint. When that load is applied to soft garden soil, lawn, or recently disturbed ground, the legs can punch through the surface and cause the entire structure to lean or collapse. This is not just a nuisance — a collapsing scaffold is a serious injury risk. WorkSafe NZ lists falls from height as one of the leading causes of serious harm in the construction industry, and an unstable scaffold base is a key contributing factor.
Use Proper Base Plates
Every scaffolding standard (upright leg) should sit on a base plate — a flat steel plate that spreads the load over a larger area than the tube alone. Most hired or purchased scaffold systems include base plates as standard. If yours didn't come with them, do not proceed without sourcing them first.
Base plates alone are not enough on soft ground. They need something solid underneath them.
Lay Sole Boards (Mudsills) Under the Base Plates
A sole board (sometimes called a mudsill) is a flat timber board placed under the base plate to spread the load even further across the soil. This is the single most effective way to prevent sinking.
What to use as a sole board
- Scaffold-grade timber sole boards — typically 50 mm thick hardwood or LVL timber, at least 200–225 mm wide and long enough to span at least two base plates where frames are close together
- Scaffold hire companies often supply these — ask when you hire your gear
- Avoid using thin ply, pallet timber, or soft untreated pine, as these can split or compress under load
How to position sole boards
- Clear away any loose mulch, bark, or soft topsoil from the area where the scaffold will stand
- Lay the sole board flat on the firmest ground available
- Place the base plate centrally on the sole board
- Adjust the screw jack (the threaded foot inside the base plate) to level the standard — never extend a screw jack more than the manufacturer's recommended maximum (commonly around 300 mm, but always check your specific equipment)
- Ensure the board cannot slide or tip — on sloped ground, you may need to cut a small level platform
Prepare the Ground Beneath
If the soil is very soft — for example, freshly dug garden beds, waterlogged clay, or sandy loam — sole boards alone may not be enough. Consider these additional steps:
- Compact the soil with a hand tamper or plate compactor before setting up
- Add a layer of compacted gravel (GAP 20 or similar) under the sole boards for drainage and a firmer bearing surface
- Avoid setting up over underground services, irrigation lines, or recently backfilled trenches — these areas are prone to sudden settlement
- After heavy rain, always re-check that the scaffold has not shifted or settled before climbing it
Check for Level Regularly
Once the scaffold is erected, use a spirit level on the horizontal ledgers to confirm the structure is plumb and level. Recheck after the first day of use, after any significant rain, and at the start of each working day. If a leg has sunk even slightly, the whole structure must be unloaded and re-levelled before anyone climbs it.
Tie-Offs and Outriggers on Soft Ground
On soft or uneven ground, outrigger bases (stabiliser feet that extend the footprint of the scaffold) can significantly improve stability. These are especially useful for tower scaffolds on residential sites. Ensure any ties to the building structure are also correctly installed — a scaffold that cannot sink but can tip is equally dangerous.
NZ Regulations and Standards
In New Zealand, scaffolding over 5 metres in height must be erected, altered, or dismantled by a certificated scaffolder under the Health and Safety at Work Act 2015 and associated regulations. Even for lower scaffolds, the person erecting the structure must be competent to do so safely. The relevant standard is NZS 4576 (Guidelines for Scaffolding), which covers ground bearing requirements. Always check with WorkSafe NZ if you are unsure about your obligations, and refer to BRANZ for good practice guidance on temporary structures.
If your project requires a building consent, your local council may also have requirements around site safety and temporary structures — confirm with them directly.
When to Call a Professional
If your scaffold is over 5 metres high, on a steep or unstable slope, near an excavation, or you are simply not confident in the ground conditions, hire a certificated scaffolder. A professional will assess the ground bearing capacity, specify the correct sole board and base plate arrangement, and ensure the structure meets all legal requirements. Getting it wrong can be fatal. You can find qualified local scaffolders on tradedirectory.co.nz.
Even for lower DIY scaffolds, if the ground is waterlogged, recently disturbed, or you notice any movement after erection, stop work and get expert advice before continuing.
