A structural engineer can design the steel beam that will permanently support a new opening. But before that beam is installed, the wall above still needs support.
That gap between the existing structure and the finished structure is where temporary works become critical.
Temporary works can include props supporting floors and walls, shoring around excavations, temporary bracing, needling, working platforms and other engineered arrangements used to keep a structure stable while permanent construction is taking place.
For extensions, basement excavations, load-bearing wall removals and major renovations, the permanent structural calculations are only part of the engineering problem.
The building also needs to remain stable during the work.
What Are Temporary Works?
The Health and Safety Executive describes temporary works as engineered solutions used to support or protect a structure during construction, support an excavation, support plant or equipment, or provide access.
Examples include propping for walls and floors, excavation shoring, falsework, scaffolding and working platforms.
The HSE guidance on temporary works states that temporary structures must be designed, installed and maintained so they can withstand the foreseeable loads imposed on them.
The word “temporary” therefore does not mean unimportant.
A prop may only remain in place for a few days, but during those days it may be part of the only load path preventing an existing wall or floor from becoming unstable.
Permanent Works and Temporary Works Are Different
Permanent works are the parts of the completed building that remain after construction.
These include foundations, structural walls, steel beams, columns, floors and roof structures.
Temporary works support the construction process.
For example, imagine a homeowner wants to remove a load-bearing rear wall and replace it with a steel frame.
The final structural design may include a beam and columns capable of supporting the building above.
But the existing wall cannot simply be demolished before that new frame is capable of carrying the load.
The floor, wall or roof above may need temporary support while the existing masonry is removed, bearings are formed and the permanent steelwork is installed.
The engineer and contractor therefore need to think about two structural conditions:
How will the building stand when the project is complete?
And:
How will it remain stable while the project is being built?
When Are Temporary Works Needed?
Not every alteration requires an elaborate temporary-works scheme.
The need depends on the structure and construction sequence.
Temporary support is commonly relevant where permanent load paths are being interrupted or where excavation temporarily removes support from existing construction.
Examples can include:
- removing load-bearing walls;
- forming large structural openings;
- installing steel beams or frames;
- removing chimney breasts or structural masonry;
- underpinning foundations;
- excavating basements;
- constructing retaining walls;
- altering roofs;
- supporting façades;
- and working close to existing foundations.
HSE’s structural stability guidance states that temporary bracing or propping may be necessary where a structure is weak, where loads change during the work, where permanent structural elements are removed or where the load path changes.
A suitably qualified and experienced engineer should determine where temporary support is required.
Why a Permanent Steel Beam Calculation Is Not Enough
A calculation showing that the finished beam can support the permanent building does not automatically explain how the contractor should reach that finished condition safely.
Construction changes the structure step by step.
Before an opening is formed, the masonry may be carrying loads.
During demolition, some of that masonry disappears.
Before the new beam is fully installed and bearing correctly, the original load path may no longer exist.
If the work involves columns or a steel box frame, new concentrated loads may also need to reach foundations that are being constructed or modified during the same sequence.
Temporary works therefore need to reflect the construction stages, not only the final structural model.
This is one reason AC Design Solution’s structural drawings and calculations focus on buildable structural solutions rather than beam sizing in isolation.
What Is Temporary Propping?
Temporary propping provides short-term structural support while part of the permanent structure is removed, altered or constructed.
Props can transfer loads from floors, walls, roofs or beams to a suitable supporting level while the permanent work is carried out.
But simply placing props beneath a floor is not a complete temporary-works design.
The designer and contractor need to understand what is being supported, how much load may reach the temporary support and where that load goes next.
A prop carrying load at first-floor level ultimately needs something capable of supporting its reaction below.
That might require consideration of the floor construction, foundations or additional levels of support.
The important principle is the same as permanent structural engineering:
the load needs a continuous and reliable path to a suitable support.
Why Prop Positions Matter
Props need to support the structure that actually requires temporary support.
If a load-bearing wall supports floor joists, roof members or masonry above, the temporary arrangement needs to reflect how those loads are currently transferred.
The position of joists, beams, walls and other structural elements therefore matters.
In an older building, these may not always match assumptions made from a simple floor plan.
Previous alterations can also change the original load path.
That is why major structural alterations can require inspection, measurement or targeted opening-up before the final construction sequence is confirmed.
Where the existing structure itself is uncertain, AC Design Solution’s Structural Survey London service can help establish structural conditions before major alteration work proceeds.
The Floor Beneath the Props Matters Too
One of the most important principles in temporary propping is that the support is only as useful as the structure beneath it.
A prop creates a concentrated reaction.
If that reaction is placed onto a floor that cannot safely distribute the load, the temporary support can create a new problem elsewhere in the building.
The arrangement therefore needs to consider not just the prop itself but also the supporting floor or ground beneath it.
On multi-storey alterations, temporary loads may need to be considered through more than one level.
This is why temporary works should not be reduced to a generic instruction to “use Acrow props”.
Proprietary props are useful construction equipment, but their safe arrangement depends on the actual structure, loading, spacing, restraint and support conditions.
What Are Needles in Temporary Works?
Needling is one method used to provide temporary support to masonry or other construction while work is undertaken beneath or through it.
A needle is a temporary structural member arranged to transfer load to supporting props or another temporary system.
The Institution of Structural Engineers’ Temporary Works Toolkit on propping and needling discusses their use in demolition, refurbishment and work close to existing structures.
The appropriate arrangement is project-specific.
The position of openings, floor construction, wall thickness, available working space and loads all influence how support can be provided.
Construction Sequence Is Part of Structural Safety
Structural alteration drawings show what is being removed and what will replace it.
For complex work, the order in which those changes happen can be just as important.
Consider a large opening through an existing masonry wall.
A simplified sequence might involve establishing temporary support, carefully forming the required pockets or bearings, installing the permanent structural member, completing the permanent supports and connections, allowing relevant materials to achieve the required condition, and only then removing temporary support in a controlled manner.
The actual sequence will depend on the design.
For underpinning, the sequence can be even more important because excavation itself changes the support conditions beneath the existing building.
The work may need to progress in controlled stages so that adjacent sections continue to support the structure while individual sections are excavated and reconstructed.
The sequence should therefore come from the project-specific engineering and construction methodology rather than from a generic online detail.
Real Project: Hazlebury Road, Fulham
AC Design Solution’s Hazlebury Road basement extension provides a practical example of temporary works forming part of a wider structural strategy.
The Victorian terraced property at 37 Hazlebury Road, Fulham required excavation and underpinning to create usable basement accommodation, together with a rear extension and roof alterations.
The structural work included underpinning existing foundations, temporary works during excavation, reinforced-concrete retaining structures and steelwork for new structural openings.
AC Design Solution designed a phased underpinning sequence so the basement could be lowered while maintaining the stability of the existing structure.
Temporary propping was used as part of the excavation process, while the permanent basement solution included a new reinforced-concrete slab and retaining construction.
This is a useful example because the temporary support cannot sensibly be separated from the permanent engineering.
The sequence of excavation, temporary support, underpinning and permanent construction all had to work together.
Temporary Works for Load-Bearing Wall Removal
Removing a load-bearing wall is one of the most common situations where homeowners encounter temporary support.
The existing wall may be supporting floor joists, another wall, roof construction or a combination of loads.
Once that wall is removed, the permanent beam or frame takes over its structural role.
But there is a transition period when the existing support is being removed and the new support is not yet fully established.
Temporary works bridge that transition.
AC Design Solution’s wider structural engineering services consider the load path, permanent support and structural alterations required for the completed project.
The contractor then needs a safe construction methodology consistent with the structural design and any temporary-works requirements.
Temporary Works During Basement Excavation
Basement construction can involve more complex temporary conditions because the project is changing the support beneath an existing building while also retaining surrounding ground.
Excavation can alter how loads are transferred.
It can also expose or affect neighbouring foundations.
Temporary works may therefore include propping, excavation support, staged underpinning or other engineered systems depending on the project.
The sequence is particularly important.
Excavating too much of an existing foundation at one time can remove support that the building still relies upon.
A phased underpinning design controls this by dividing the work into sections and specifying an appropriate sequence.
Hazlebury Road demonstrates this approach in practice.
Temporary Works and Existing Buildings
Alteration work carries a particular challenge: the engineer is dealing with a structure that has already been built, used and potentially altered several times.
Original drawings may be unavailable.
Floor joists may run in an unexpected direction.
Previous owners may have removed walls.
Old beams may be hidden behind finishes.
Masonry may differ from what was assumed.
The design process therefore needs reliable information about the existing building.
Where critical information is hidden, targeted opening-up can sometimes be necessary before steelwork or temporary support is finalised.
The objective is to avoid basing the construction sequence on a structural arrangement that does not actually exist.
Who Is Responsible for Temporary Works?
Responsibility depends on the project and contractual arrangements.
Temporary works should not be assumed to belong automatically to one particular consultant simply because permanent structural calculations have been produced.
The scope of appointment should establish who is responsible for designing, coordinating, checking and implementing the temporary works required for construction.
HSE explains in its temporary works FAQs that BS 5975 provides an industry consensus view of good practice for temporary-works procedures.
HSE also makes an important distinction: there is not a universal legal requirement to use the specific job title Temporary Works Coordinator on every project.
However, temporary works still need to be properly managed so that they do not create unacceptable risk.
On more complex projects, clearly defined temporary-works responsibilities and coordination become particularly important.
Does Every Temporary Support Need a Bespoke Calculation?
Not necessarily.
HSE notes that some straightforward situations can use recognised standard solutions, provided the person organising the work verifies that the assumptions behind the standard solution are valid for the actual site.
The key point is the word verified.
A standard arrangement should not be copied into a project where the loads, ground conditions, geometry or supporting structure fall outside the assumptions on which that arrangement is based.
As the structural complexity increases, project-specific design becomes more important.
A multi-level propping arrangement, basement excavation or temporary support for significant structural masonry should not be treated in the same way as a simple proprietary access system.
Temporary Works and CDM 2015
Temporary works are also relevant to the wider management of construction risk.
Under the Construction (Design and Management) Regulations 2015, designers have duties to eliminate foreseeable health and safety risks where reasonably practicable and to reduce or control risks that cannot be eliminated.
HSE’s guidance for designers under CDM 2015 also requires designers to provide appropriate information and coordinate with other designers and contractors.
For structural alterations, this means buildability and temporary stability should not be ignored simply because the permanent structure works mathematically.
Where a design creates a significant temporary condition, that condition needs to be recognised and communicated appropriately.
Temporary Works and Building Regulations
Building Regulations and temporary works overlap in their concern for structural safety, but they should not be treated as exactly the same process.
In England, Approved Document A provides statutory guidance relating to the structural requirements of buildings, including loading, ground movement and structural stability.
The permanent structural design needs to satisfy the applicable Building Regulations.
Temporary works, meanwhile, are concerned with the stability and safety of the structure during construction.
Building Control approval of a permanent beam calculation should therefore not be interpreted as a complete temporary-works method for removing the wall beneath it.
The construction-stage stability still needs to be managed appropriately.
Should the Builder Decide the Propping Arrangement?
Contractors have an essential role because they understand how the work will actually be carried out on site.
But complex temporary support should not be improvised without the necessary engineering input.
HSE states that bracing and propping should be designed by experienced temporary-works designers where required and installed, checked, inspected, maintained and dismantled in accordance with the design.
The best result comes from coordination.
The permanent structural engineer needs to make the design intent and relevant structural risks clear.
The temporary-works designer needs to understand the actual construction stages.
The contractor needs to follow an appropriate methodology and identify site conditions that differ from the design assumptions.
Changes on site should be reviewed rather than simply worked around.
Why Temporary Works Should Be Considered Before Construction Starts
Waiting until demolition day to decide how a building will be supported can create avoidable risk and delay.
Early consideration of temporary works can identify whether there is enough physical space for props, whether floors beneath can support temporary reactions, whether access is available for steel installation and whether the permanent structure can be installed in the proposed sequence.
It can also influence the permanent design.
A theoretically efficient beam may be difficult to install into an existing building.
A slightly different structural arrangement may sometimes provide a safer or more practical construction sequence.
Buildability should therefore form part of structural design rather than being treated as the contractor’s problem after the drawings are complete.
Frequently Asked Questions
What are temporary works in construction?
Temporary works are engineered arrangements used to support or protect structures, excavations, plant or access during construction. Examples include propping, shoring, falsework, temporary bracing and excavation support.
Do I need temporary props to remove a load-bearing wall?
Temporary support is commonly required where removing the wall would interrupt the existing load path before the permanent beam or frame is installed. The appropriate arrangement depends on what the wall supports and the construction sequence.
Can a builder decide how many Acrow props to use?
A generic number of props should not be assumed to suit every project. The required arrangement depends on the loads, spacing, existing structure, support beneath the props and the proposed sequence of work. Complex temporary works require suitable design and management.
Are temporary works the structural engineer’s responsibility?
Not automatically. Responsibility depends on the professional appointments and construction arrangements. The project should clearly establish who is responsible for temporary-works design, coordination, checking and implementation.
What is a Temporary Works Coordinator?
A Temporary Works Coordinator is a role commonly used to help manage temporary works. HSE explains that there is no universal legal requirement to use that specific job title, although temporary works must still be properly managed. BS 5975 provides recognised industry good-practice procedures.
Do temporary works need Building Control approval?
The permanent building work needs to comply with the applicable Building Regulations. Temporary works are also subject to construction safety requirements, but Building Control review of the permanent design should not be treated as approval of every temporary support arrangement.
Why does construction sequence matter when installing steel beams?
Before the new steel becomes part of the permanent load path, the existing structure may need temporary support. The sequence determines when loads move from the existing wall to temporary support and ultimately to the permanent steelwork.
Are temporary works needed for basement underpinning?
They can be a major part of basement construction. Excavation and underpinning alter the existing support conditions, so temporary propping, excavation support and carefully planned sequencing may be required depending on the structural design.
Structural Design Has to Work During Construction Too
A successful structural alteration is not only one that is safe when the last beam is installed and the project is complete.
It also needs a credible route from the existing building to that finished condition.
Temporary works provide that route.
For a straightforward opening, this may involve relatively simple temporary support. For a basement excavation or major structural alteration, it can require a coordinated sequence of propping, excavation, underpinning and permanent construction.
Hazlebury Road demonstrates why this matters. The basement could not simply be excavated and the permanent reinforced-concrete structure added afterwards. Temporary stability and phased construction were part of the engineering problem from the beginning.
AC Design Solution provides structural engineering services and structural drawings and calculations for residential and commercial alterations, with technical information coordinated alongside Building Regulation Drawings where required.
For project-specific structural advice, contact AC Design Solution.
