A site-led perspective on BS 5975 design responsibility
The Temporary Works Designer role under BS 5975 is often seen as one of the most clearly defined duty holder positions, with a structured beginning, deliverable, and endpoint. However, this clarity can lead to a critical gap between design intent and site reality, particularly when designs are developed against incomplete briefs or without an understanding of installation constraints. This article examines why the role is frequently misunderstood in practice and how this creates delivery risk on construction projects.
The Temporary Works Designer role is misunderstood because compliance is often interpreted as meeting the brief, rather than ensuring the design is buildable, accessible, and executable under real site conditions.
The Complete Design Illusion in Temporary Works
Under BS 5975, the Temporary Works Designer is responsible for producing a safe and suitable design based on the information provided. In practice, however, the role is often treated as a defined transaction: a brief is issued, a design is produced, and the responsibility is considered discharged.
This creates a structural weakness in the system. The design may be technically compliant, but the underlying assumptions (including access, sequencing, loading methodology, and installation practicality) are frequently untested. Where the brief is incomplete, expedited, or commercially driven, the resulting design reflects those limitations.
As a result, projects can reach site with a complete design that cannot be executed safely or efficiently. The misunderstanding lies in assuming that design completion equates to delivery readiness, when in reality the two are not the same.
Under BS 5975, the Temporary Works Designer is responsible for producing a safe and suitable design based on the information provided. In practice, however, the role is often treated as a defined transaction: a brief is issued, a design is produced, and the responsibility is considered discharged.
This creates a structural weakness in the system. The design may be technically compliant, but the underlying assumptions (including access, sequencing, loading methodology, and installation practicality) are frequently untested. Where the brief is incomplete, expedited, or commercially driven, the resulting design reflects those limitations.
As a result, projects can reach site with a complete design that cannot be executed safely or efficiently. The misunderstanding lies in assuming that design completion equates to delivery readiness, when in reality the two are not the same.
The Designer Role: Clear Boundaries, Hidden Risk
Compared to other BS 5975 duty holders, the designer’s role appears relatively straightforward. It has a defined start and finish, with clear outputs. This lack of ambiguity is often seen as a strength.
However, this bookended nature can encourage a narrow interpretation of responsibility. The focus becomes delivering the required calculations and drawings, rather than interrogating whether the design can actually be implemented.
Other roles (such as Temporary Works Coordinator or Supervisor) inherently deal with uncertainty and evolving site conditions. The designer, by contrast, can remain detached from the execution phase, unless there is deliberate engagement beyond the minimum requirement.
Compared to other BS 5975 duty holders, the designer’s role appears relatively straightforward. It has a defined start and finish, with clear outputs. This lack of ambiguity is often seen as a strength.
However, this bookended nature can encourage a narrow interpretation of responsibility. The focus becomes delivering the required calculations and drawings, rather than interrogating whether the design can actually be implemented.
Other roles (such as Temporary Works Coordinator or Supervisor) inherently deal with uncertainty and evolving site conditions. The designer, by contrast, can remain detached from the execution phase, unless there is deliberate engagement beyond the minimum requirement.
Site Reality: Where Design Assumptions Fail
From a site perspective, the gap between design and delivery is often most visible during installation and testing.
With over 15 years of experience in temporary works installation and structural testing, it is clear that many design issues do not arise from incorrect calculations, but from incorrect assumptions about how the works will be executed.
A common example involves the preloading of temporary steel structures. Designs may specify preload forces to be applied through threaded bars or jacking systems, assuming that the system can be installed and loaded as designed.
In reality, several critical factors are often overlooked:
The result is a compliant design that cannot be executed. On site, this leads to redesign, workarounds, or unsafe practices; all of which introduce risk, delay, and commercial pressure.
In many cases, the underlying issue is not engineering complexity, but a lack of understanding of how the system will be built, accessed, and tested.
From a site perspective, the gap between design and delivery is often most visible during installation and testing.
With over 15 years of experience in temporary works installation and structural testing, it is clear that many design issues do not arise from incorrect calculations, but from incorrect assumptions about how the works will be executed.
A common example involves the preloading of temporary steel structures. Designs may specify preload forces to be applied through threaded bars or jacking systems, assuming that the system can be installed and loaded as designed.
In reality, several critical factors are often overlooked:
- Access constraints: There may be no physical space for operatives to position jacks or torque equipment
- Equipment limitations: The specified preload may require equipment that cannot be accommodated within the geometry of the structure
- Installation sequence: The order of assembly may prevent the preload from being applied after installation
- Human factors: There may be no safe way for operatives to reach or operate the system
The result is a compliant design that cannot be executed. On site, this leads to redesign, workarounds, or unsafe practices; all of which introduce risk, delay, and commercial pressure.
In many cases, the underlying issue is not engineering complexity, but a lack of understanding of how the system will be built, accessed, and tested.
The Missing Link: Design Must Include Constructability
The intent of the Temporary Works Designer role is not simply to respond to a brief, but to consider the full scope of the problem.
This includes:
Where these factors are not considered, the design becomes theoretical rather than practical. The most effective temporary works designs are those informed by site experience; where designers understand not only structural behaviour, but also the realities of construction environments, access limitations, and testing constraints.
The intent of the Temporary Works Designer role is not simply to respond to a brief, but to consider the full scope of the problem.
This includes:
- How the system will be installed
- How loads will be applied and verified
- How operatives will access critical components
- How the sequence of works affects stability
- How testing and inspection will be carried out
Where these factors are not considered, the design becomes theoretical rather than practical. The most effective temporary works designs are those informed by site experience; where designers understand not only structural behaviour, but also the realities of construction environments, access limitations, and testing constraints.
What This Means (Practical Interpretation)
For contractors and principal designers, a compliant design is not necessarily a deliverable design.
There is a need to move beyond accepting designs at face value and instead challenge whether the solution can be safely installed, loaded, and verified on site.
For Temporary Works Designers, this means engaging more deeply with the construction methodology, rather than relying solely on the issued brief.
For contractors and principal designers, a compliant design is not necessarily a deliverable design.
There is a need to move beyond accepting designs at face value and instead challenge whether the solution can be safely installed, loaded, and verified on site.
For Temporary Works Designers, this means engaging more deeply with the construction methodology, rather than relying solely on the issued brief.
Key Risks
The misunderstanding of the designer role creates several recurring risks:
The misunderstanding of the designer role creates several recurring risks:
- Designs that are technically compliant but not buildable
- Late-stage redesign and programme delay
- Unsafe improvisation on site
- Disputes over responsibility between designer and contractor
- Inability to demonstrate compliance within the Golden Thread
Market Impact
As regulatory scrutiny increases under the Building Safety Act, the expectation for demonstrable, auditable design decisions is growing.
Designs that fail at the execution stage expose not only delivery teams, but also designers, to increased professional liability.
The industry is gradually shifting toward more integrated delivery models, where design, installation, and verification are considered together rather than in isolation.
As regulatory scrutiny increases under the Building Safety Act, the expectation for demonstrable, auditable design decisions is growing.
Designs that fail at the execution stage expose not only delivery teams, but also designers, to increased professional liability.
The industry is gradually shifting toward more integrated delivery models, where design, installation, and verification are considered together rather than in isolation.
Contractor Implications
Contractors should not assume that a completed design is ready for execution.
There is a need to actively review designs against site constraints, including access, equipment, and sequencing. Early involvement of installation and testing specialists can identify issues before they become critical.
From a commercial perspective, clarifying assumptions and constraints at the design stage reduces the risk of variation claims, delays, and rework.
Contractors should not assume that a completed design is ready for execution.
There is a need to actively review designs against site constraints, including access, equipment, and sequencing. Early involvement of installation and testing specialists can identify issues before they become critical.
From a commercial perspective, clarifying assumptions and constraints at the design stage reduces the risk of variation claims, delays, and rework.
Evidence-Based Summary
The misunderstanding of the Temporary Works Designer role is not driven by a single factor but by a combination of clearly defined responsibilities and limited engagement with site execution.
The misunderstanding of the Temporary Works Designer role is not driven by a single factor but by a combination of clearly defined responsibilities and limited engagement with site execution.
While designers may produce technically compliant outputs based on the brief, evidence from site operations shows that critical factors such as access, sequencing, and installation constraints are often not fully considered.
In practical terms, this means that designs can be complete in theory but unworkable in reality, creating risk, delay, and the need for redesign during construction.
Image © London Construction Magazine Limited
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Expert Verification & Authorship: Mihai Chelmus
Founder, London Construction Magazine | Construction Testing & Investigation Specialist |
