Before a scaffold is erected, the project team needs to know more than its height, length and intended access route. The scaffold configuration, maximum reactions, foundation condition, tie strategy, permanent-structure interfaces and any planned additions all need to describe the same physical arrangement.
Problems arise when those pieces are considered separately. A scaffold designer may calculate leg loads without knowing that standards will sit over a basement. A ground assessment may assume loads that later increase when a loading bay is added. A tie pattern may be designed around masonry that is subsequently removed during façade works. Sheeting or a temporary roof can introduce wind actions that were absent from the original brief.
UK guidance provides controls for each of these issues, but the important engineering task before erection is to join them together and establish a complete load path from the scaffold through its ties, bases and supporting ground or structure.
Scaffolding at Piccadilly Circus in central London. Photo: London Construction Magazine.
Key Takeaway: A scaffold can be correctly designed in isolation and still be unsuitable for the site if the ground, supporting structure, façade, services, attachments or future alterations do not match the assumptions used in that design.
Start With the Design Brief, Not the First Standard
The Health and Safety Executive's scaffolding guidance requires a scaffold either to follow a recognised standard configuration or, where it falls outside such a configuration, to be designed by calculation by a competent person. That decision cannot be made reliably from a sketch showing only scaffold dimensions. The intended use, loading, boarded lifts, access requirements, ties, loading bays, coverings, hoists, temporary roofs and site constraints can all affect whether a standard solution remains applicable.
The current management procedures for temporary works are set out in BS 5975-1:2024. For project teams operating a BS 5975 procedure, the design brief is the point where those requirements and interfaces should be captured before design progresses. LCM's guide to the temporary works design brief covers that process in more detail. For scaffolding, the brief should give the designer enough information to produce not only the scaffold arrangement but the reactions and interface requirements needed by the rest of the project team.
What Should Be Known Before Erection?
| Pre-erection check | Information required | Why it matters |
|---|---|---|
| Design status | Applicable compliance sheet or project-specific scaffold design and check | Confirms the proposed arrangement has an appropriate engineering basis |
| Intended loading | Use, loading class, boarded lifts, material storage and loading-bay requirements | Determines loads transferred through standards, ties and foundations |
| Maximum leg reactions | Design reactions at relevant standards and concentrated-load locations | Allows the ground or supporting structure to be assessed against the actual scaffold loads |
| Foundation | Ground type or structural support, base plates, sole boards and spreader assumptions | Establishes whether the reactions can be carried without unacceptable settlement or failure |
| Subsurface features | Manholes, drains, services, basements, vaults, cellars and previous excavations | A sound-looking surface does not prove the load path beneath it |
| Ties and anchors | Tie positions, required loads, anchor type and actual façade substrate | The design restraint cannot be achieved if the assumed tie position or substrate is unavailable |
| Attachments | Sheeting, netting, hoists, debris chutes, loading bays, fans and temporary roofs | These can materially alter vertical reactions, wind loads or restraint requirements |
| Site interfaces | Excavations, façade works, deliveries, traffic management and public routes | Other operations can undermine foundations or force changes to the designed scaffold arrangement |
| Change control | Defined route for referring alterations back for review | Stops the erected scaffold drifting away from the assumptions used in its design |
Trace the Leg Loads Into the Ground or Supporting Structure
Maximum leg reactions are one of the most useful outputs from a scaffold design because they connect the scaffold calculation to the foundation assessment. Without them, a statement that the pavement, hardstanding or soil is “suitable” has no defined load against which to be checked. The reverse is also true. A calculated leg reaction does not establish that the support beneath it is adequate. The project team still needs to know what the standard actually bears onto, the effective area of the base arrangement and what lies beneath the visible surface.
LCM has examined this interface separately in Scaffold Ground Bearing Capacity: When Does the Ground Need Testing?. Where testing is needed, DCP, LWD and plate bearing testing answer different engineering questions rather than providing interchangeable “pass” results, as explained in our guide to scaffold foundation testing. A scaffold standing on a suspended slab, roof, podium or basement structure requires a different assessment. The issue is no longer simply ground bearing capacity. The supporting structure needs to be checked for the actual concentrated reactions and the complete load path through the permanent works. Depending on the arrangement, load spreading or back-propping may be required.
Manholes, Services and Voids Cannot Be Treated as Drawing Notes
Urban scaffold footprints frequently cross ground containing drainage, utilities, basement structures and historic voids. HSE's HSG47 guidance on underground services sets out the wider requirements for identifying and managing buried-service risk, but scaffold foundation design also needs to consider whether those features can carry, or should be isolated from, concentrated leg reactions. A manhole cover, for example, should not be treated as ordinary hardstanding merely because it is flush with the pavement. The relevant questions include the chamber construction, cover capacity, surrounding ground and whether the scaffold load can be repositioned or engineered around the feature. The same principle applies to basements and vaults. What appears to be a pavement at street level may form the roof of a structural void. The scaffold foundation assessment needs to follow the load below the surface rather than stop at the paving.
The Tie Strategy Has to Match the Actual Façade
Scaffold stability also depends on the restraint assumed by the design. It is therefore not enough to specify a tie pattern without confirming that the required positions and suitable anchorage substrate will actually exist when the scaffold is erected. Window openings, curtain walling, weak masonry, stone façades, planned demolition and façade replacement can all affect where ties can be installed. Where anchor performance forms part of the design, the required verification and testing regime should be established before those ties become structurally necessary. This becomes particularly important on refurbishment projects. A tie may be perfectly adequate on the day the scaffold is erected but cease to provide the intended restraint if the part of the façade receiving it is later removed.
Sheeting, Hoists and Loading Bays Are Design Inputs
Attachments that are described as “being added later” should still be identified before erection where they are already part of the construction plan. Sheeting and netting change the scaffold's exposure to wind. Loading bays concentrate imposed loads. Hoists introduce additional reactions and anchorage requirements. Temporary roofs create their own gravity and wind actions. Protection fans and cantilever arrangements can also change reactions at selected standards. Designing the access scaffold first and treating those elements as unrelated additions can leave the foundation, tie strategy or local scaffold members based on loads that no longer describe the final arrangement.
Public Highway Constraints Can Change the Engineering
Scaffolding that encroaches onto or over a highway, including the pavement, requires a licence from the relevant highway authority under Section 169 of the Highways Act 1980. HSE includes this requirement in its scaffold guidance. The highway interface is not simply an administrative exercise. Licence conditions, pedestrian clearances, protection arrangements, traffic management, access requirements and restrictions on the available pavement width can affect where standards, beams and protection fans can physically be positioned. Those constraints should reach the scaffold designer before the design is finalised. If a licence condition later forces a standard to move, the resulting bay geometry and foundation reactions may no longer match the original calculation.
Change Control Starts Before the Scaffold Is Built
A useful pre-erection review should consider not only the scaffold required on day one but foreseeable changes during its life. An extra lift, increased loading class, relocated loading bay, new hoist, added sheeting, temporary roof, removed tie, changed cantilever, altered base arrangement or excavation beside the scaffold can all change the assumptions on which the original design or foundation assessment was based.
Where a proposed change affects geometry, loading, restraint, environmental exposure, foundation conditions or the support structure, it should be referred through the project's temporary works procedure before the alteration is implemented. LCM's guide to temporary works change and BS 5975 sign-off explains the wider change-control process. This is more than an inspection issue. An inspection can establish whether the scaffold matches the approved arrangement and remains in suitable condition. It cannot make an unreviewed structural change valid.
The Pre-Erection Questions That Matter
1. Is the proposed scaffold within a recognised standard configuration or does it require bespoke design?
2. Does the design brief describe how the scaffold will actually be used throughout its life?
3. What are the maximum leg reactions at the controlling locations?
4. What ground, slab, roof, pavement or other structure supports those reactions?
5. What base plate, sole-board or spreader arrangement has been assumed?
6. Are basements, vaults, manholes, drainage or buried services present beneath the footprint?
7. What tie loads and tie positions are required, and does the actual façade provide suitable anchorage?
8. Are sheeting, netting, hoists, loading bays, debris chutes, fans or temporary roofs planned?
9. Could excavation, façade removal or other construction work later affect the scaffold's support or restraint?
10. Do highway, pedestrian or logistics constraints conflict with the designed arrangement?
11. Has the required design checking been completed under the project's temporary works procedure?
12. Is there a clear route for referring subsequent changes back for engineering review?
2. Does the design brief describe how the scaffold will actually be used throughout its life?
3. What are the maximum leg reactions at the controlling locations?
4. What ground, slab, roof, pavement or other structure supports those reactions?
5. What base plate, sole-board or spreader arrangement has been assumed?
6. Are basements, vaults, manholes, drainage or buried services present beneath the footprint?
7. What tie loads and tie positions are required, and does the actual façade provide suitable anchorage?
8. Are sheeting, netting, hoists, loading bays, debris chutes, fans or temporary roofs planned?
9. Could excavation, façade removal or other construction work later affect the scaffold's support or restraint?
10. Do highway, pedestrian or logistics constraints conflict with the designed arrangement?
11. Has the required design checking been completed under the project's temporary works procedure?
12. Is there a clear route for referring subsequent changes back for engineering review?
Frequently Asked Questions
Does every scaffold require a bespoke structural design?
No. HSE permits scaffolds to follow a generally recognised standard configuration where the proposed arrangement remains within that configuration's limits. Scaffolds outside those limits require an appropriate bespoke design by a competent person.
No. HSE permits scaffolds to follow a generally recognised standard configuration where the proposed arrangement remains within that configuration's limits. Scaffolds outside those limits require an appropriate bespoke design by a competent person.
Who is responsible for checking the ground beneath scaffolding?
There is no single universal answer for every project. The scaffold designer needs to provide the relevant reactions, while the principal contractor's temporary works arrangements should ensure that the ground or supporting structure is assessed by a competent person and coordinated with the scaffold design.
There is no single universal answer for every project. The scaffold designer needs to provide the relevant reactions, while the principal contractor's temporary works arrangements should ensure that the ground or supporting structure is assessed by a competent person and coordinated with the scaffold design.
Is a Permit to Erect legally required for every scaffold?
There is no nationally prescribed statutory form called a Permit to Erect for every UK scaffold. BS 5975-based project procedures may use formal permits or authorisations as management controls. The exact documentation should follow the project's approved temporary works procedure.
There is no nationally prescribed statutory form called a Permit to Erect for every UK scaffold. BS 5975-based project procedures may use formal permits or authorisations as management controls. The exact documentation should follow the project's approved temporary works procedure.
Does adding sheeting or a hoist require the scaffold to be reviewed?
If the addition was not included in the approved configuration, or it changes loads, wind exposure, ties, foundations or other design assumptions, the design should be reviewed before the modification is made.
If the addition was not included in the approved configuration, or it changes loads, wind exposure, ties, foundations or other design assumptions, the design should be reviewed before the modification is made.
The useful pre-erection question is not simply whether the scaffold drawing has been approved. It is whether the drawing, calculated reactions, foundation assessment, tie arrangement, site conditions and planned use all describe the same scaffold. If one of those inputs changes, the temporary works assessment needs to follow the change.
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Founder & Author, London Construction Magazine | Construction Testing & Investigation Specialist