Temporary works: the structures that hold everything else up

Temporary works are everything built on a site in order to build the permanent structure, and then removed: formwork and falsework, trench and excavation support, propping, needling, façade retention, temporary bracing, site access structures and the ground the cranes stand on. They are designed and installed under more time pressure than anything permanent, by people under pressure to get on, and they are load-bearing while they exist.

The uncomfortable pattern in temporary works incidents is that the engineering is rarely the thing that failed. A prop was removed early because the pour looked set. A design was produced for one ground condition and used in another. A change was made on site for good practical reasons and never fed back to the designer. The structure was adequate as designed and not as built.

Why it carries a formal process at all

Under CDM, the principal contractor plans, manages and monitors the construction phase, and designers — including those designing temporary works — carry duties to eliminate and reduce risk. Temporary works sit awkwardly in that framework because they are often designed by a subcontractor or a supplier rather than by the project's named designer, and because they change as the job progresses. That is precisely why the industry has settled on a defined procedure rather than leaving it to judgement.

The widely used approach appoints a Temporary Works Coordinator with explicit responsibility for the process on a project: maintaining the register, ensuring designs are produced and checked at a level appropriate to the risk, confirming that what is built matches the design, and controlling the permits to load and to strike. On larger or more complex projects the role may be supported by Temporary Works Supervisors on individual work faces. The detail of how this is structured varies between organisations and should follow current industry guidance and the project's own procedure.

The register is the spine

A temporary works register lists every temporary works item on the project, classifies it by risk, records who designed it, who checked it, at what category, and where the design and check certificates live. It sounds like administration and functions as the project's memory. Without it, the question 'who checked the propping on grid line 4?' is answered by asking around.

The register is also where scope creep becomes visible. Projects routinely accumulate temporary works nobody planned: an edge protection arrangement improvised around an awkward corner, a temporary ramp, a crane outrigger position moved onto made ground. Items that were never designed because they were never recognised as temporary works are a recurring theme in incident reports.

Design check categories, and why the right one matters

Temporary works designs are checked at a level proportionate to risk and complexity — ranging from a check by the designer's own colleague for simple, standard arrangements, through independent checks within the designing organisation, up to an independent check by a separate organisation for the most complex or high-consequence structures. Getting the category wrong in the low direction is the error that matters: a complex façade retention checked as though it were a standard trench box has been checked, and not adequately.

The category also has commercial consequences. An independent external check takes time and costs money, and discovering at the last minute that one is required is how programmes slip. Deciding the category early, at the point the item enters the register, keeps that out of the critical path.

Permits to load and permits to strike

Two moments carry most of the risk: putting load onto a temporary structure for the first time, and taking the structure away. Both are normally controlled by a permit signed by the coordinator, confirming that the structure has been inspected and matches the design, and in the case of striking, that the permanent works have achieved whatever condition the design assumed.

Striking too early is one of the most persistent causes of serious incidents in concrete frame construction. The pressure to recover formwork for the next pour is real and constant, and the judgement 'it looks set' is not the same as the evidence the design relied on. A permit system works because it moves that decision away from the person under the most pressure to make it quickly.

Change on site is normal — unrecorded change is the problem

No temporary works design survives first contact with real ground conditions, an unexpected service or a steel delivery that arrives in a different sequence. Sites adapt, and they should. What distinguishes a controlled project is that the adaptation goes back to the designer, gets assessed, and the register and certificates are updated before the structure is loaded.

The practical failure is usually one of distance. The person making the change is in a trench; the designer is in an office; the coordinator is on another part of the site. Where recording a change means filling in a form that will be typed up later, it does not reliably happen. Where it can be captured where the work is, with a photograph and a note attached to the register entry, it does.

What an investigation will look for

After an incident, the questions are predictable: was the item on the register, who designed it, at what check category and by whom, was there a permit to load, was the as-built condition inspected against the design, what changed and who approved it, and was the person who struck it authorised to do so. A project that can answer those from its own records is in a very different position from one reconstructing events from recollection.

The same records are, not coincidentally, the ones that make the job run better day to day. Knowing what is propped, by whom, since when, and when it can come out, is operationally useful before it is ever evidential. The projects that keep temporary works records well generally do so because the information is worth having, not because somebody might ask for it.

Specific design standards, check categories and procedural requirements change and vary by organisation and project. Work from current industry guidance and your own project procedure rather than from custom, and treat the register as the live document it is meant to be.

Competence, and the question that is hard to answer later

Temporary works roles carry competence expectations, and the ones that matter are specific rather than general. A designer competent in falsework for in-situ concrete is not automatically competent in façade retention or deep excavation support, and a coordinator who has run the process on housing sites is not automatically equipped for a complex refurbishment with unknown existing structure.

The appointment record should therefore say more than that somebody holds a qualification. What experience was relevant to this project's temporary works, who assessed it, and what the limits of the appointment are — particularly where a coordinator is handling items well outside their previous range — is what turns an appointment into a defensible decision.

This matters most on the projects least likely to do it. A large principal contractor has a procedure. A regional contractor running a single complex job is where an experienced site manager is quietly given the coordinator role on top of everything else, with no assessment of whether this project's temporary works are within their range, and no capacity to do it properly if they are.

Designing out the temporary works

The most effective temporary works control is having fewer of them. Sequencing that avoids needing a propping scheme, precast elements that arrive self-supporting, or a permanent works design that provides its own stability during construction all remove risk rather than managing it — which is the hierarchy CDM asks designers to work through.

That conversation has to happen early, while the permanent works design is still movable. Raised at construction stage it is simply a complaint about the design, and the temporary works get built because by then there is no alternative.