Knocking out a loadbearing wall or underpinning a subsided corner of a Victorian terrace sounds straightforward enough until something moves that shouldn’t, and then you’re in serious trouble. Temporary works propping on UK domestic building sites is one of those areas where corners get cut all the time, usually because the job looks simple, the client wants it done fast, and everyone assumes it’ll be fine. I’ve seen lintels crack because props weren’t spread right, and I’ve spoken to subbies who had building control turn up mid-job and pull the brakes entirely because there was no temporary works plan in place. It’s not worth it.
This guide is written for small contractors and one-man-bands who are taking on domestic beam installations, wall removals, and underpinning. We’re going to cover the kit, the process, the coordinator role, and the bits people routinely get wrong.
What is temporary works in a domestic context?
Temporary works is the term for any structure or system put in place to support or stabilise a building or excavation while permanent work is carried out. On a domestic job, that usually means acrow props and needles supporting the floors and masonry above a wall you’re removing, or strutting used during underpinning to keep walls stable while you dig down in bays.
The critical thing to understand is that temporary works are structural. They carry real loads. A poorly specified prop arrangement can allow settlement, cracking, or in the worst cases, partial collapse. The Health and Safety Executive is clear that duty holders are responsible for ensuring temporary works are designed and managed competently, regardless of the size of the site or the simplicity of the job in question.
Needling and propping: what the job actually involves
When you’re removing a loadbearing wall, the sequence matters as much as the kit. You’re transferring load from the wall above through a temporary system until the new beam or lintel is bedded in and cured. Get the sequence wrong and you load up the temporary arrangement unevenly, which causes differential settlement in the floor above.
Needling involves drilling or cutting holes through the wall above the opening, sliding steel or timber needles through, and then hanging acrow props off those needles on both sides. The needles carry the load from the structure above directly down to the props, which sit on spreader plates or boards on the floor. The spreader plates are not optional. A prop foot landing on an unsupported floorboard can punch straight through or cause localised settlement in the floor below. I always use a minimum of a scaffold board under each foot, and on timber suspended floors I’d rather get a padstone down to the joist beneath than just trust the boarding.
The props themselves need to be rated for the load. Standard acrow props are available in different sizes and load ratings. For a typical two-storey domestic job with a 3-metre beam, you’re routinely looking at loads that require you to double-prop or close-space props at no more than 600 to 900mm centres. A single prop each side for a long span is not engineering, it’s optimism.
What is a temporary works coordinator and when is one legally required?
A Temporary Works Coordinator (TWC) is the person responsible for overseeing the design, checking, installation, monitoring and removal of temporary works on a project. On larger sites this is often a structural engineer or senior site manager with formal TWC training. On a domestic job, it’s far more likely to sit with the contractor, and that’s where things get murky.
Under BS 5975:2019 (the British Standard for temporary works procedures), a TWC should be appointed on any project involving temporary works. There is no minimum size threshold in the standard. The TWC doesn’t have to be an external professional on a simple domestic job, but they do need to be competent. That means they understand the loads, the kit, the checks, and the sequence. They also need to be independent from the commercial pressure to crack on.
For underpinning specifically, or any situation where the structural arrangement is more complex (say, a prop arrangement spanning across a stepped floor, or temporary works interfacing with an excavation), you really should have a structural engineer signing off the scheme. LABC (Local Authority Building Control) can and do request to see temporary works drawings on notifiable projects, and if you can’t produce them, the job stops. I’d rather spend a few hundred pounds on an engineer’s temporary works note than lose a week of site time.
Underpinning: temporary works in a different beast
Underpinning uses a different form of temporary support called raking shores or horizontal struts, depending on the geometry. The principle of working in bays is critical: you never underpin adjacent bays simultaneously, because removing soil support across a continuous length of wall invites movement. The standard approach is to work in alternating bays of around 900mm to 1,200mm, completing and backfilling each bay before opening the next.
Before any dig begins, the wall above needs to be monitored. That can be as simple as a tell-tale crack monitor glued across any existing cracks, which gives you a visible record of movement. If cracks are widening during the works, you stop, re-prop, and get an engineer to look. Anyone who tells you otherwise is taking a risk that isn’t theirs alone to carry.
Steps small contractors commonly miss
The first is load path tracing. Before you set a prop, you need to know what’s above the wall you’re removing. Is there a loadbearing wall above it on the first floor? Is there a chimney breast that transfers load through the structure? If you don’t trace the load path from roof level down, you might correctly prop for the first-floor load and completely ignore the second-floor contribution. I’ve seen this catch people out on 1930s semis where the first floor wall lined up directly above the ground floor wall being removed.
The second is propping the floor above before you start cutting. On a two-storey job, if you start cutting without propping the ceiling joists, those joists start to sag the moment the wall comes out from under them. The sequence is: prop from below, needle through the wall above the opening, hang props on the needles, then cut. Not cut first and hope.
The third is leaving the props in place long enough. For a standard padstone-and-steel-beam installation, you want the mortar or grout under that padstone to have achieved adequate strength before you strike the props. That typically means at least 48 to 72 hours, sometimes more in cold weather. Striking props after 24 hours to get the ceiling made good is a false economy.
If you’re working on an extension where drainage and structural elements overlap, it’s worth reading up on getting your drainage layout right before you pour the slab, because conflicts between services and prop positions are more common than people think. And if the project involves internal partition changes as part of the same job, understanding the structural differences between stud walls and blockwork partitions will help you assess what else in the building might be carrying load.
Documentation and sign-off
BS 5975 requires a checking process before temporary works are loaded. That means someone (ideally not the person who designed the scheme) walks the installation and confirms props are plumb, spreader plates are down, needles are bearing correctly, and nothing has been improvised. This check should be recorded. A photo on your phone with a timestamp is better than nothing. A written check sheet is better still.
When the temporary works are struck, that should also be recorded. Building control inspectors increasingly ask for evidence that temporary works were properly managed, especially on projects involving structural alterations. For anything requiring a practical completion certificate, having a clear record of how the temporary phase was handled protects you as the contractor.
Get the propping right, document it, and don’t rush the strike. That’s the job.
Frequently Asked Questions
Do I need a structural engineer for temporary works on a domestic wall removal?
Not always, but you do need a competent person to design and oversee the temporary arrangement. For straightforward single-storey domestic beam installations, an experienced contractor with a clear understanding of load paths may manage this. For anything involving complex load paths, underpinning, or multi-storey structures, a structural engineer’s sign-off is strongly advisable and may be required by building control.
What is a temporary works coordinator and do I need one on a small job?
A Temporary Works Coordinator is the person responsible for overseeing the entire temporary works process, from design through to striking. BS 5975:2019 recommends appointing one on any project involving temporary works, regardless of size. On small domestic jobs, this role often sits with the main contractor, but that person must be genuinely competent, not just the most available person on site.
How many acrow props do I need when removing a loadbearing wall?
It depends on the span and the loads above, but as a rough guide you should not have props spaced more than 600 to 900mm apart for a loaded double-storey wall. Always use spreader plates or scaffold boards under prop feet. A single prop each side on a long span is rarely adequate and should be confirmed against the actual load calculations.
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