Temporary Works Design: The Part of the Job Where Half the Building Is Missing

Ask most people when a building is at its most vulnerable and they will picture a storm, or the day the roof goes on. The honest answer is usually a Tuesday afternoon halfway through the job, when the old structure has been cut away and the new one is not in yet. Temporary works design is what holds a building up during that gap, and it is one of the least discussed parts of construction until something moves.

It is also one of the easiest things to get wrong quietly, because temporary works are, by definition, meant to disappear. Nobody photographs the props for the brochure.

So what counts as temporary works?

Anything installed to support, protect or provide access during construction that will not form part of the finished building.

On a domestic job that might be two props and a needle beam while a lintel goes in. On a commercial refurbishment it might be a full propping grid across three floors, or a façade retention scheme holding a listed frontage upright while everything behind it is demolished.

Same principle, wildly different scale. The common thread is that the structure is being asked to carry its loads through a route it was never designed for.

Why the temporary condition is often the worst one

A finished building has a settled load path. Weight goes down through walls and columns, into foundations, into the ground. Everything has a job and has had it since the day it was built.

Take a section of wall out and that path has to be rerouted, usually through something slender, usually bearing onto a floor that was never intended to take a concentrated point load.

Three things make this harder than it looks.

The first is that the loads change as work progresses. What the props carry on Monday is not what they carry on Thursday once the floor above has been broken out.

The second is that older buildings rarely tell you what they are doing. Original drawings often do not exist. Walls have been altered by three previous owners, none of whom left a record. What looks like a partition may be quietly carrying a purlin.

The third is that temporary works get moved. Someone needs to get a wheelbarrow through, so a prop shifts half a metre. On a designed scheme that half metre has been checked. On an improvised one, nobody knows.

Who actually designs it

This is where it gets murky on site, and where responsibility often ends up sitting with whoever is standing closest.

A temporary works engineer designs the propping, needling or retention scheme as a structure in its own right — with its own load cases, its own connections and its own failure modes. That is a different exercise from designing the permanent structure, and it is not something that should be inferred from the permanent drawings.

On larger projects the process is formalised. A Temporary Works Coordinator is appointed under BS 5975, a register is kept, designs are checked to a category appropriate to their risk, and nothing gets loaded until it has been formally signed off. That framework exists precisely because temporary works failures tend to be sudden rather than gradual.

On smaller jobs that structure often is not there. The result is a scheme designed by experience and instinct rather than calculation. Most of the time experience is right. The problem is that the failure mode when it is wrong is not a crack you notice next month.

Where we see it go wrong

• Props landing on unsuitable ground. A prop is only as good as what it bears onto. Suspended floors, recently backfilled trenches and paving over soft ground are all common and all worth checking.
• Nobody has checked the floor below. Propping transfers load downwards. On a multi-storey job the props often need to continue floor by floor to something that can genuinely take it.
• The sequence is not designed. A scheme can be perfectly adequate in its final arrangement and dangerous halfway through installation. Order of operations is part of the design, not a site decision.
• Removal is treated as an afterthought. Striking props too early, or in the wrong order, has caused more problems than installing them ever has.
• Nothing is written down. If there is no drawing, there is nothing to check against when a prop gets moved.

Façade retention deserves its own mention

Retaining a frontage while the building behind it comes down is one of the more demanding things in this field, and it is increasingly common in conservation areas and on listed buildings.

The retained façade is usually old, often in indifferent condition, and has spent its life being braced by floors and cross walls that are about to be removed. Wind load becomes the governing case almost immediately, on an element with very little capacity to resist it on its own.

These schemes need designing properly, monitoring while they stand, and dismantling in a controlled sequence. They are not a scaled-up version of domestic propping.

When to bring an engineer in

Earlier than most people do.

The useful moment is while the demolition or alteration sequence is still being planned, because the temporary works often influence it. Occasionally the cheapest answer is to change the order of work rather than design a more elaborate support.

If you are already on site with the ceiling down and a prop under something you are not confident about, that is also a legitimate reason to call. We would rather look at it that day than read about it later.

Frequently asked questions

Is temporary works design a legal requirement?

There is no single law that says “you must have a temporary works design.” But the Construction (Design and Management) Regulations place duties on designers and contractors to manage risk, and BS 5975 sets out the recognised procedural framework. In practice, on anything beyond the very simplest job, an undesigned scheme is difficult to defend.

Can my structural engineer do this as part of the main design?

They can, but it should be an explicit part of the appointment rather than an assumption. Permanent works drawings do not automatically cover the temporary condition, and plenty of disputes start with both parties assuming the other had it covered.

Do I need it for a single lintel replacement?

Often a straightforward needle and prop arrangement is well established practice. It still needs someone competent deciding prop positions and checking what they bear onto — particularly on a suspended floor or where the wall above carries more than it appears to.

What is a Temporary Works Coordinator?

A named individual responsible for managing the temporary works process on a project under BS 5975 — maintaining the register, ensuring designs are checked, and controlling loading and removal. Larger projects appoint one as standard.

Planning something where the structure comes out before it goes back in?

If your project involves removing structure before the permanent works are complete, temporary works design is the part worth sorting out before the programme is fixed rather than after the props are already in. We provide it as a standalone service alongside permanent structural design, from our offices in Peterborough and Borehamwood, covering the East of England, Hertfordshire and Greater London, and we are fully insured to £5 million professional indemnity.

Send us the drawings and the demolition sequence and we will tell you what the temporary condition actually needs.