Temporary works design and the designer's duties

Temporary works design duties sit with a designer, and the Construction (Design and Management) Regulations 2015 do not distinguish between designing a building and designing the propping that holds it up while you build it. Anyone who prepares or modifies a temporary works design is a designer under Regulation 9, with the full duty to take account of the general principles of prevention, eliminate foreseeable risks where possible and control what remains. That duty attaches to the person doing the design, not to whoever signed the contract.

Most disputes on site come from assuming someone else was the designer.

What counts as temporary works

BS 5975 describes temporary works as the parts of the works that allow or enable construction of, protect, support or provide access to the permanent works, and that may or may not remain in place at completion. That definition is broader than most people's working assumption.

It takes in falsework and formwork, propping and needling, facade retention, shoring to a party wall, trench support, sheet piling and cofferdams, crane bases and outrigger spreads, piling and crane working platforms, dewatering, hoardings, edge protection, access scaffolding, and the temporary bracing a steel frame needs before the floors go in.

Two categories get missed with some regularity. Working platforms for piling rigs, which are a structural design requiring a platform certificate and ground data, and temporary stability of a partially built structure, which is a condition the permanent works designer has to think about even though it never exists in the finished building.

So the first job on any scheme is a list. Everything on that list needs an owner, a design, a check and a release.

Duties under the construction design regulations

Five duty holders matter here.

The client has to make suitable arrangements for managing the project, which includes allowing adequate time and resource for temporary works design. The principal designer plans, manages and monitors the pre-construction phase and coordinates design work, and compiles the health and safety file. A designer, including a temporary works designer, carries the Regulation 9 duties. The principal contractor plans, manages and monitors the construction phase. And a contractor who carries out design, which many do for their own temporary works, picks up designer duties as well as contractor duties.

The point practitioners miss is that designer duties cannot be contracted away. A subcontractor who adapts a standard propping arrangement to fit an opening has modified a design and has become a designer for that element.

Regulation 9 also requires the designer to provide sufficient information about the design to those who need it. For temporary works that means the loads the arrangement applies to the permanent structure, the sequence it assumes, the tolerances it depends on, and the conditions under which it must not be used.

Appointing a coordinator and defining the register

BS 5975 sets out a management structure rather than a design method, and the structure is what prevents the failures.

A designated individual within the organisation appoints a temporary works coordinator for the project. The coordinator maintains the temporary works register, issues design briefs, obtains designs and independent checks, and issues permits to load and permits to strike. On larger or dispersed sites, temporary works supervisors report to the coordinator for defined areas.

The register is the document that matters. One row per temporary works item, recording the design brief, the designer, the check category, the checker, the date of the design certificate, the permit to load, the permit to strike and the removal date.

Check categories scale with complexity. A straightforward arrangement from a standard solution can be checked within the design team. A comparatively simple design needs a checker not involved in it. A complex or unusual design needs a checker independent of the design team, and the most complex designs need an independent organisation. Deciding the category is itself a decision that should be recorded, because the common failure is a Category 2 design given a Category 1 check because the programme was tight.

Interfaces with permanent works design

The riskiest interfaces are the ones where neither designer thinks the condition is theirs.

Three recur. Propping loads applied to a permanent slab that was never designed for a point load from a raking prop. Temporary stability of a structure part-built, where the permanent design relies on diaphragm action from floors that are not yet cast. And demolition sequence, where the permanent works designer of a retained element has assumed a restraint that the demolition contractor intends to remove first.

The fix is procedural rather than technical. The permanent works designer should state, in writing, the erection or demolition sequence assumed and any temporary restraint the permanent design depends on. The temporary works designer should state the loads and tolerances imposed on the permanent structure. Both statements belong in the design brief, and the coordinator should refuse to issue a permit to load without them.

Where an existing building is being altered, a structural survey of what is actually there, rather than what the historic drawings show, is the input both designers need. Opening up is nearly always worth the disruption.

Where planning conditions reference temporary works

Planning conditions do not design temporary works, but several of them constrain the design, and the constraint is discovered late if nobody reads them at tender stage.

A construction management plan that fixes plant positions before the temporary works are designed can make the design impossible, which then needs a variation and a fresh approval. Write the plan with the temporary works coordinator in the room.

Tree protection is the sharpest example of this, because a root protection area excludes the ground a crane or a scaffold wanted, and our note on temporary works and tree protection on tight sites sets out the usual resolutions. Crane oversail is the other one, and the right to swing a jib over a neighbour is a property matter rather than a planning one, covered in our piece on crane oversailing and third party land.

On basements, movement trigger values set by a basement impact assessment become the performance requirement the temporary works design has to meet, so the propping scheme and the monitoring regime should be designed together.

Insurance and design liability

Temporary works design is professional design, and it needs professional indemnity cover sized to the consequence rather than to the fee.

Three gaps appear repeatedly. A contractor designing its own temporary works under a contract with no contractor-designed portion, so the design liability sits nowhere clear. A standard proprietary solution adapted on site, where the manufacturer's liability covers the standard arrangement and not the adaptation. And a collateral warranty chain that covers the permanent works designer but not the temporary works designer, which matters when the failure happens during construction.

Record the design responsibility matrix at the start, item by item, against the register. It takes an hour and it is the document the loss adjuster asks for.

Records and handover

Keep the design certificate, the independent check certificate, the permit to load and the permit to strike for every register item. Those four documents are the audit trail, and an incomplete set is what an investigation finds first.

Then hand over what survives. Temporary works that remain in place at completion, such as permanent ground anchors, retained sheet piles or a piling platform left under a car park, have to be recorded in the health and safety file so that whoever alters the building in 30 years knows they are there. Items removed should be recorded as removed, with the date.

One honest uncertainty. The boundary between a design modification and a minor site adjustment is not sharply drawn anywhere, and reasonable engineers disagree about it. The safer habit is to treat any change to a load path, a prop position or a sequence as a modification requiring the designer's confirmation, and to accept that this generates paperwork nobody enjoys.

Enter your postcode on PlanScope to see which construction and structural documents a scheme is likely to need alongside the application.

This is general guidance, not legal advice; check the position with your local planning authority, your principal designer or a qualified structural engineer before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.