Temporary works and propping: keeping a building up during alterations
Whenever a builder removes a wall, cuts in a beam or digs beside a foundation, something has to carry the load in the meantime. That temporary support is a design job in its own right.
What are temporary works?
Temporary works are the props, needles, shoring and other supports that hold a building stable while permanent structural work is carried out. When an existing wall is removed, a beam is installed or ground is excavated near a foundation, the loads normally carried by that part of the building need somewhere to go. Temporary works give them a safe route to the ground until the new structure takes over.
On small domestic jobs, propping is often treated as something the builder sorts out on the day. For a simple opening and an experienced builder, that can be fine. But the loads are real, and collapses during alterations do happen. Where the load is large, the sequence is unusual or the building has been altered before, temporary works deserve the same thought as the permanent design.
Temporary works also protect the people on site. A prop that slips or a needle that rolls can drop masonry onto someone working below, so stability during the job matters as much as the finished result. A clear, written arrangement means everyone knows what is holding the building up at each stage.
Common types of temporary support in house alterations
Most domestic temporary works use a small set of familiar components:
The components are simple. What makes the difference is choosing the right number, spacing and positions, and checking that everything beneath them can take the load they deliver.
- Adjustable steel props under timber or steel spreaders, carrying floors and ceilings
- Needles: short steel or timber beams passed through holes in a wall and propped on both sides, so the masonry above is held while the wall below is removed
- Sole plates or boards under prop bases to spread load onto the floor or ground
- Raking shores to restrain a wall against sideways movement
- Trench sheets and struts to support the sides of an excavation
Following the load down to the ground
The most common mistake is to think only about the top of the prop. A prop standing on a suspended timber floor, a cellar ceiling or a thin screed can punch straight through. Each prop's load has to be carried down through every floor below until it reaches something solid. That may mean propping at every level, or lifting floorboards so props can stand on the oversite concrete or the ground.
Older London houses add their own complications. Joists may span in an unexpected direction, walls that look solid may be thin partitions, and earlier alterations can leave loads in odd places. In a terraced house, a wall being removed might also carry part of the roof, a chimney stack or the floor of the room above. A short inspection before work starts sorts out which is which.
Props also need to be plumb, braced where they are tall, and placed so they do not obstruct the new beam going in. It sounds obvious, but a common problem on site is props positioned exactly where the steel needs to land, which leads to improvised moves halfway through the job.
Sequence matters as much as strength
Good temporary works design sets out the order of operations, not just the equipment. A typical sequence for opening up a load-bearing wall looks like this:
Taking props out too early, or failing to pack the new beam tight to the masonry above, lets the wall above drop slightly. That shows up as cracking in the rooms upstairs. Our guide to steel beams and padstones covers the permanent side of the job.
- Install props and needles, and tighten them so they take load before anything is cut
- Remove the masonry in stages, watching for movement or cracking
- Build the padstones and allow mortar or concrete to gain strength
- Lift the steel into place and pack it tight to the masonry above
- Remove temporary supports only once the permanent structure is carrying the load
Who is responsible for temporary works?
The contractor is generally responsible for temporary works and site safety under the Construction (Design and Management) Regulations 2015. On larger projects, a named temporary works coordinator manages the design, checking and sign-off of each item. On a small house job the same principles apply on a smaller scale: someone competent should decide what support is needed, and it should be checked before it is loaded.
The engineer designing the permanent works usually provides propping guidance as part of the design, such as where props should go and the order of work. Where the job is more demanding, a separate temporary works design gives the builder a scheme to install and check against, rather than leaving it to judgement on the day.
When you need a formal propping scheme
A designed scheme is worth having where any of the following apply:
Our temporary works design and propping scheme covers prop and needle sizing, the installation and removal sequence and drawings for the contractor, from £500 + VAT. For bigger or more sensitive jobs, a demolition and construction method statement sets out how the whole sequence will be carried out safely, including protection of neighbouring buildings. All our designs and calculations go through a three-step quality control process, with final sign-off by our Head of Engineering.
- Removing a wall that carries more than one floor, or a roof and chimney stack
- Openings in party walls, or work close to a neighbour's structure
- Removing a ground floor wall where there is a cellar or suspended floor beneath
- Basement excavation or underpinning beside existing foundations
- Partial demolition, where the remaining walls lose their usual restraint
- Any building already showing cracking, bowing or signs of movement
Neighbours, party walls and monitoring
Temporary works often affect next door. Needles through a party wall, props bearing against a shared wall or an excavation beside a neighbour's foundation can all fall under the Party Wall etc. Act 1996, with notices served well before work starts. Our guide to the Party Wall Act and structural works sets out the notice periods.
On sensitive jobs, such as a basement conversion or work to a building that is already cracked, simple monitoring helps. Targets or tell-tales fixed to walls before work starts let the team spot movement early, adjust the propping and keep a clear record for the neighbours.
Frequently asked questions
Can my builder decide on propping without an engineer?
For a simple opening in a wall carrying a single floor, an experienced builder often can, guided by the engineer's propping notes. Where the wall carries several floors, a roof or a chimney, or the floor below is suspended, a designed scheme is safer. The question is not who installs the props, but whether anyone has checked the load path all the way to the ground.
How long do props need to stay in?
Until the permanent structure is carrying the load. For a new steel beam, that means the padstones have gained enough strength and the beam has been packed tight to the masonry above. Mortar and concrete need time to cure, so props commonly stay in for at least a few days. The engineer or the propping scheme should say when they can safely come out.
Do props need Building Control approval?
Building Control is concerned mainly with the permanent work, so temporary propping is not normally part of the approval. Inspectors will still expect the work to be done safely and may comment on inadequate propping during a visit. Legal responsibility for temporary works sits with the contractor under health and safety law, which is why a clear scheme helps everyone.
What should I do if the wall above cracks while it is propped?
Stop work and have it looked at. Fine hairline cracks are common when masonry is disturbed and are usually cosmetic. Wider or growing cracks, doors sticking upstairs or visible dropping suggest the props are not carrying the load properly. Adding support and checking the arrangement is far easier at this stage than repairing damage once the work is finished.
Can props stand on a timber floor?
Only if the floor has been checked for the load and each prop sits on a spreader across several joists. Even then, the load usually has to be propped down through the floor below as well. On a ground floor with a void beneath, it is often better to lift boards and stand the props on the oversite concrete or another solid base.