Scaffold Technical Guide • Projecting Access • No Ground Support Below
What Is a Cantilever Scaffold?
A cantilever scaffold is a scaffold arrangement where part of the working platform projects beyond its direct support. Instead of being fully supported from the ground below, the projecting section is carried by cantilever tubes, needle beams, brackets or system components that transfer load back into the main scaffold, structure or support arrangement.
Cantilever scaffold layout
Definition
What is a cantilever scaffold?
A cantilever scaffold is a temporary access scaffold where the working platform, scaffold bay or access section projects out beyond its direct vertical support. The cantilevered part is not fully supported by standards taken down to the ground below the working area. Instead, the load is transferred back through needles, cantilever beams, brackets, ties, anchors, support tubes or another verified support arrangement.
Cantilever scaffolds are normally considered where normal base support is not practical because of an obstruction, fragile surface, pavement restriction, conservatory, lower roof, watercourse, basement void, restricted ground bearing or a section of building where standards cannot be safely founded.
Technical Layout
How a cantilever scaffold is built
The projecting section is usually supported by cantilever needles, steel beams, tube-and-fitting arrangements, proprietary brackets or system scaffold components. The inner end must be restrained so the cantilever cannot rotate, pull out, deflect excessively or overload the support structure. The platform, standards, ledgers, transoms, bracing and ties are then arranged around that support method.
Needle beams or cantilever tubes project from the support side and carry the outer scaffold load.
The backspan, anchorage or restraint arrangement prevents uplift, rotation and movement of the projecting section.
Standards may sit on the cantilever support members rather than bearing directly onto the ground below.
Ledgers connect the standards and form the scaffold lift along the length of the cantilevered bay.
Transoms support the scaffold boards and tie the scaffold across its width.
Bracing helps keep the scaffold rigid and reduces sway or distortion in the cantilevered bay.
Use Cases
When is a cantilever scaffold used?
A cantilever scaffold is used when the scaffold has to project over an area that cannot be loaded from below. The purpose is to create access to the workface without placing standards directly under the projecting platform.
Used where conservatories, roofs, extensions, plant, walls or other obstructions prevent standard base support.
Useful where the ground below cannot take standards, sole boards or base plates in the normal way.
Can be considered where base standards would obstruct the area below or cannot be positioned safely.
Used where a section of the elevation needs access but the direct ground line is unavailable.
Load Path
The critical point is how the load gets back to support
Cantilever scaffold planning is mainly about load path. The platform load, operative load, material load and self-weight of the scaffold must be transferred through the cantilever member and back into a support capable of taking the reactions. The further the projection extends, the greater the bending, uplift and restraint demand becomes.
- Projection: the distance the scaffold projects beyond its support line.
- Backspan: the section behind the support line used to restrain the cantilever.
- Reaction: the force transferred back into the support structure, ties, anchors or scaffold frame.
- Uplift: the tendency of the inner end to lift when the outer end is loaded.
- Deflection: downward movement of the cantilevered section under load.
- Platform loading: the intended duty, number of operatives, tools and materials on the scaffold.
Planning
What needs to be checked before installing one?
A cantilever scaffold should not be treated as a normal elevation scaffold with a projecting platform added at the end. The cantilever arrangement should be considered around projection, support condition, restraint, anchorage, bay size, lift arrangement, platform loading, working height, edge protection and the structure receiving the load.
- Support structure: the structure or scaffold supporting the cantilever must be suitable for the reactions.
- Needle or beam size: the cantilever member must suit the span, projection, backspan and load.
- Anchorage or restraint: ties, anchors, couplers, kentledge or backpropping must suit the load path where used.
- Bay size: standards, ledgers and transoms should be spaced to suit the cantilever arrangement.
- Working platform: scaffold boards, guardrails, midrails, toe boards and platform gaps must be considered.
- Deflection and movement: the arrangement should avoid excessive movement under use.
- Design requirement: outside recognised standard configurations, bespoke design is required.
Technical References
Cantilever scaffold guidance references
The key technical question is whether the cantilever arrangement fits a standard scaffold configuration or needs a specific scaffold design. Because a cantilever changes the load path and introduces bending, uplift and restraint forces, design input is often more likely than it would be for a straightforward independent tied scaffold.
NASC TG20:21 is the main good-practice reference for many tube-and-fitting scaffold arrangements where the scaffold fits standard guidance.
BS EN 12811-1 is the key performance standard commonly referenced for access and working scaffolds.
NASC TG21:20 is relevant where the cantilever scaffold needs design input or falls outside standard arrangements.
NASC TG4:25 becomes relevant where ties, anchors or anchorage systems form part of the cantilever restraint or stability arrangement.
Limitations
When might a cantilever scaffold not be suitable?
A cantilever scaffold is useful when the ground below cannot be used, but it is not always the best access method. It may be unsuitable where the support structure cannot accept the reactions, where the required projection is too large, where platform loading is high, where restraint cannot be verified or where another access method creates a simpler load path.
- Weak support: the receiving structure may not be suitable for cantilever reactions.
- Large projection: longer projections increase bending, deflection and uplift demand.
- Heavy loading: material storage on a cantilevered platform can change the design requirement.
- Unclear restraint: the scaffold should not rely on unverified restraint or assumed anchorage.
- Better alternatives: a tower, MEWP, designed independent scaffold, beam scaffold or other access method may be more suitable.
FAQ
Cantilever scaffold questions
Is a cantilever scaffold freestanding?
No. A cantilever scaffold relies on load being transferred back through a support, restraint or anchorage arrangement. The projecting section is not simply standing on the ground below.
Does every cantilever scaffold need design input?
Normally, yes. TG20:21 covers limited cantilever arrangements; those outside recognised standard configurations require competent design and calculations.
What is a cantilever needle?
A cantilever needle is the projecting support member that carries the scaffold load outward from the support line and transfers that load back into the restraint or support arrangement.
Can scaffold boards simply be extended out beyond the scaffold?
No. A proper cantilever arrangement needs suitable structural support. Extending boards without a checked support and restraint arrangement is not the same as a cantilever scaffold.
Need a cantilever scaffold assessed?
BlackFox Scaffolding can assess whether a cantilever scaffold is the right access method where ground support is restricted, an obstruction prevents normal standards or the working platform needs to project beyond the support line.