CROSS Safety Report
Dangerous building work on domestic project
Temporary propping fails during works to a semi-detached property putting the whole building at risk of collapse.
Key Learning Outcomes
For clients and owners:
- Check that your proposed builder has completed similar projects safely
For structural designers:
- Structural designers should seek to ensure they are commissioned to input on matters concerning structural stability throughout all project stages
- Structural designers must have in mind the construction processes required to build their designs and as far as reasonably possible, eliminate foreseeable risk
For the construction team:
- Temporary works must be designed and constructed with the same degree of competence and quality as required for permanent works
- Propping work must be undertaken by competent people – collapses can cause fatalities
- Responsibility for and scope of inspections for temporary works must be clearly assigned and documented on-site. Inspections should be undertaken by competent staff.
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The site of a building scheme was reported to a local authority by a concerned neighbour. A reporter working for the local authority and responsible for dealing with dangerous buildings visited the site and found that the whole rear elevation had been rendered unstable by the works in progress. The site was a semi-detached property with works being undertaken at ground, first and second floor levels. The works included the making of a large opening in the rear elevation of the property. A steel beam to support the masonry above was due to be inserted to span this large opening.
The reporter found that inadequate temporary propping to the large opening in the rear elevation had allowed the rear wall to distort. There was lateral movement of the external leaf with partial collapse of the masonry. The cavity had opened up from 50mm to 125mm.
There were at least two inadequacies evident with the temporary propping causing the instability:
- The masonry wall was supported from one side only using props and cantilever brackets; the brackets had deflected through overloading. The reporter would have expected to see props on both sides of the wall with needles through the wall.
- The props sat onto a timber floor which was considered unlikely to be sufficient to sustain the temporary loadings. The reporter would have expected to see the propping taken to the site concrete.
In addition, there appeared to be a time delay between cutting the opening in the masonry and readying for the insertion of the steel beam.
The instability was such that structural failure of the whole of the rear wall supporting the roof was possible.
Effective propping of the rear elevation was immediately erected and the elevation rebuilt as required.
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Expert Panel Comments
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Unfortunately, this is a far too common issue with private clients splitting the design and construction so that the structural designer is not involved in the construction process. The structural designer may well highlight that temporary propping is required, but the nature of it will be chosen by the contractor to suit the method of working. The delivery and handling of materials, including steelwork, may also influence how the contractor decides to provide temporary supports. Changes to the approved design also occur and are probably never referred back to the structural designer.
In short, there is ample opportunity for the structural designer’s instructions and expectations in terms of temporary supports not to be realised. The obligation is on clients, designers and contractors to put instruction, process and responsibility in place to ensure this does not happen. This is an area that does need to be highlighted as although the projects are of relatively small value and duration, they can result in significant damage and possibly fatalities if things go wrong.
Be sure your contractor is competent
Clients need to be satisfied that the contractor they intend to appoint can do the job safely and without risks to health.
Clients need to be satisfied that the contractor they intend to appoint can do the job safely and without risks to health
This means making enquiries about the competence of the contractor – do they have the right combination of skills, experience and knowledge? The degree of competence required will depend on the work. Similarly, the level of enquiries required will be determined by the level of risks and the complexity of the job. On domestic scale projects, clients can engage with their designers for support in selecting a contractor. The Health and Safety Executive provides helpful guidance (Domestic client – Project owner – HSE Regulations - Construction) for domestic clients including the application of the Construction (Design and Management) Regulations 2015 (CDM 2015).
Temporary works design
It is critically important to understand that temporary works designers have the same designers’ duties as permanent works designers, as confirmed within the Construction (Design and Management) Regulations 2015. The regulations also require the Principal Designer to take reasonable steps to ensure cooperation between all designers, including to confirm that permanent and temporary works designs are compatible. The Principal Designer’s role continues into the construction phase when design work is carried out.
The propping and needling that would be expected for a project of this type should have been designed by a competent person. Part 10 of the IStructE / TWf Temporary Works Toolkit 'Propping and needling' is a very useful reference in this regard; considerations for both permanent work designers and temporary works designers are explained.