Temporary works design can only be as good as the information it receives. A drawing request that says little more than “design a working platform” or “provide excavation support” leaves important assumptions unresolved. Before design starts, the project needs to define the loads, geometry, sequence, interfaces, constraints and intended use clearly enough for a suitable solution to be developed.
The design problem needs defining before it can be solved
HSE’s temporary works guidance says temporary structures must be designed, installed and maintained to withstand foreseeable loads and used only for the purposes for which they were designed, installed and maintained.
That legal requirement sounds straightforward, but it depends on the design team knowing what those foreseeable loads and intended uses actually are. If plant type, imposed loads, sequence, ground information or interface with permanent works is missing, the designer may be forced to make assumptions that do not reflect what happens on site.
A useful temporary works brief therefore does more than request a drawing. It defines the engineering problem and records the information that the designer is entitled to rely upon.
Start with purpose, geometry and loading
The brief should explain what the temporary works are intended to achieve and for how long. Dimensions, levels, clearances, access requirements and interfaces should be clear enough for the designer to understand the physical problem.
Loads need the same discipline. For a working platform, that might include the actual plant, outrigger or track configuration, operational positions and any delivery vehicles. For propping, the designer needs to understand what is being supported, the sequence of load transfer and when the temporary support can safely be removed.
“Suitable for a crane” is not a design load. “Support the wall” is not a construction sequence. The information should be specific enough that the final design can be checked against the intended operation.
Ground and existing structures can control the design
Temporary works frequently depend on conditions outside the element being designed. Excavation support relies on ground conditions and surcharge. A loading platform may depend on the capacity of the supporting structure. A scaffold can impose loads on façades, slabs or foundations.
Known ground information, buried services, existing structural details and restrictions on where loads can be applied should therefore be supplied where relevant. If reliable information is unavailable, that uncertainty should be made explicit rather than silently replaced with an optimistic assumption.
This is particularly important when permanent works are being used temporarily during construction. The fact that a slab, wall or frame will eventually be strong enough does not automatically mean it can accept the proposed construction load at that stage of the sequence.
The construction sequence belongs in the conversation
HSE notes that a Temporary Works Coordinator may need to advise on build sequence, systems of work and equipment so other activities do not damage or compromise temporary works. Sequence can be central to the design, not simply a site-management issue after the drawing is issued.
Consider a propping arrangement designed on the assumption that load is transferred gradually through a particular sequence. If site operations remove props early, change pour order or introduce extra loading before the structure gains strength, the design may no longer represent the actual condition.
The brief should therefore capture significant erection, loading, alteration and dismantling stages where they influence stability or design.
Changes need to come back through the process
Temporary works often encounter change: plant is substituted, levels alter, access routes move, excavation depth increases or another contractor needs to use the system differently. The safe response is not to assume that a small site change has a small engineering effect.
The TWC should have a process for referring relevant changes back to the designer and obtaining revised or confirmed information before the temporary works are used outside the original design basis. HSE describes the TWC approach as an effective way of coordinating suitable designs, checking and correct erection.
It is important to distinguish this industry management approach from statute. HSE states there is no single specific legal requirement prescribing exactly how temporary works must be organised. The underlying legal duties concern safe design, installation, maintenance and use.
What should you do now?
- Review the information your organisation normally sends with temporary works design requests.
- State the intended purpose, geometry, duration and relevant construction stages.
- Define real loads and plant configurations rather than generic descriptions.
- Provide available ground, structural and service information where it affects the design.
- Record significant assumptions and information gaps.
- Define how site changes are referred back for design review.
- Make sure the TWC has authority to stop use where the design basis has not been satisfied.
Our professional view
A temporary works register can tell you what designs exist, but it does not prove the designers were given the right problem to solve. A strong process starts earlier, with a brief that connects design calculations to the actual method, plant, sequence and site constraints.
For teams developing their understanding of the process, All Star Safety provides CITB Temporary Works General Awareness eLearning, while our consultancy service can assist with practical temporary works coordination and review.