Scaffold is described as a temporary structure — and that description is accurate in the sense that it’s erected for a defined period and removed when the work it supports is complete. But temporary doesn’t mean inconsequential. A scaffold that fails isn’t a minor inconvenience. It’s a structural collapse on a live construction site, with potentially fatal consequences for the people working on it and around it.
The design of scaffold structures — the engineering decisions that determine how a scaffold is configured, how it’s tied to the building, what loads it can safely carry, and how it will perform under the conditions it will encounter on site — is what separates a scaffold that can be relied upon from one that carries risk. For developers and principal contractors appointing scaffolding contractors on residential developments and commercial projects, understanding what scaffold design involves in practice is useful context for evaluating whether the contractor they’re appointing is approaching it correctly.
Why Scaffold Design Matters
A scaffold is a structure that carries loads — the weight of the scaffold components themselves, the loads applied by the people working on it, the materials stored on the platforms, and the lateral forces applied by wind. Those loads need to be transferred safely through the scaffold structure to the ground or to the building it’s tied to. When the scaffold is designed correctly, those load paths are understood and the scaffold is configured to carry them safely. When the scaffold isn’t designed correctly, the load paths may be inadequate — and the point at which that inadequacy becomes apparent is when the scaffold is under load.
On straightforward residential scaffold — standard lift heights, conventional tube and fitting or system scaffold, ties at regular intervals to a conventional masonry or concrete structure — the design may be addressed through reference to standard configurations in NASC guidance. On more complex structures — irregular building forms, high-level scaffold with significant wind exposure, loading that exceeds standard assumptions, or ties that can’t be placed at standard intervals — a bespoke design by a competent person is required.
Globe Cambridge’s approach to scaffold design begins with an assessment of the specific requirements of each project — the building form, the height, the access and loading requirements, and the tie opportunities available. Where standard configurations are appropriate, those are applied with reference to current NASC guidance. Where the project requirements fall outside standard configurations, a bespoke design is produced before erection begins.
Ties and the Building Structure
The connection between a scaffold and the building it serves — the tie system — is one of the most critical elements of scaffold design. Ties transfer the lateral loads that wind applies to the scaffold into the building structure, preventing the scaffold from moving or overturning under wind loading. A scaffold that isn’t adequately tied is at risk of collapse under the wind loads it will encounter during its operational life on site.
The tie design for a scaffold needs to reflect the specific characteristics of the building structure it’s connecting to. Ties that work on a traditional masonry wall may not be appropriate for a lightweight cladding system. Ties at standard spacing may not be achievable on a building with limited fixing opportunities. The tie arrangement needs to be determined by the specific building, not applied uniformly from a standard schedule.
On new build residential sites, where the building structure changes as construction progresses — masonry rising, floors being formed, roofing proceeding — the tie arrangement may need to be reviewed and adapted as the programme advances. Globe Cambridge’s seven-day statutory inspection process includes review of the tie arrangement at each inspection, verifying that the ties remain effective as the building and the site conditions around it change.
Load Limits and Platform Design
Every scaffold has a defined load capacity — the maximum load that can be safely applied to each platform and to the scaffold structure as a whole. That load capacity is determined by the scaffold design and needs to be communicated clearly to everyone working on the scaffold. A roofing gang storing materials on a scaffold platform in excess of its design load capacity is creating a risk that may not be immediately apparent but which increases the likelihood of structural failure.
Globe Cambridge issues signed scaffold handover certificates that include the load limits applicable to each section of the scaffold — information that the principal contractor can communicate to every trade working on the structure. Those load limits aren’t nominal figures — they reflect the specific design of the scaffold as erected, including the tie arrangement, the standard of components used, and the configuration of the platforms.
Design Documentation and the Handover Record
The documentation that records a scaffold’s design — the drawings, calculations, and specification that describe how the scaffold should be erected and what it’s designed to carry — is part of what the principal contractor needs to discharge their CDM 2015 responsibilities in relation to the temporary structure. A scaffold erected without design documentation leaves the principal contractor without the evidence that the structure was designed by a competent person, which is a CDM compliance gap as well as a practical safety risk.
Globe Cambridge produces design documentation as a standard part of the scaffold package on projects where bespoke design is required, and references the applicable NASC guidance on projects where standard configurations are used. That documentation is provided to the principal contractor as part of the handover record, giving them the evidence they need that the scaffold has been designed and erected to an appropriate standard.
To discuss scaffold design and erection for your next project, contact Globe Cambridge today.
