CROSS Safety Report
Temporary works design for basements
This report is over 2 years old
A reporter had an inquiry from a contractor who, after appointment, discovered that there was a serious lack of temporary works design information provided.
Key Learning Outcomes
For civil and structural design engineers:
Health and safety risk assessments should be included in the pre-tender information in accordance with CDM Regulations 2015
It is good practice to outline one method of safe construction and sequence on the drawings and highlight any temporary works that may be required, particularly for basements
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A reporter had an inquiry from a contractor who, after appointment, discovered that there was a serious lack of temporary works design information (surveys/loads/wall thicknesses, sequencing, in principle method statement regarding the party walls). The contractor had phoned twelve consulting engineers who had all turned down the opportunity to carry out the temporary works design due to lack of information, as did the reporter.
The main consulting engineer insisted that the above information had to be determined by the contractor's own engineer. The reporter considers that few contractors would spot this before they take on the job. They then have committed to a programme of works and struggle to find another consulting engineer to take on the work.
The reporter is also aware of instances where the main consulting engineers did not supply the contractor with a pre-tender health and safety risk assessment. When asked for one they simply stated that the drawings were the risk assessment, however the unknowns/ risks were not stated on the drawings. These are, says the reporter, collapses waiting to happen.
When asked for one they simply stated that the drawings were the risk assessment, however the unknowns/ risks were not stated on the drawings.
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These comments are in relation to the matter of what represents an "unknown". I'd say that it is possible to know "unknowns" in as much as I can know that I don't know the water level and flow rate (ie if the sand and gravel will wash into an underpin bay.) I can know that I don't know the structure on the other side of the wall. The job of an Engineer is to define the problem and solve it. That includes defining the information that is needed to solve the problem. If the "unknowns" are not presented at Tender Stage then the Engineer has not carried out the activities for which they are responsible. Also as I understand it,within CDM, designers have a responsibility to design out risks within reasonable cost ranges. Don't design a three metre deep trench fill foundation if mini piles remove the safety risks at minimal increase in cost. I also believed that designers are required to provide Tender Stage Health and Safety risk assessments that describe the risks, how they have been designed out, plus any residual risks and hazards remaining (eg beams designed as cantilevers that need loads applying on the main span before the cantilever end.) For example the lack of knowledge of a structure to be underpinned and lack of knowledge of the structure directly adjacent to the underpinning (that could fall in the excavation and kill someone) are unknowns that the designer is aware of. The potential problems associated with those unknowns could be designed out in the design stage by a considered and responsible designer. Or they could highlight the unknowns to the tenderers. Failure to determine the risks (design parameters) and failure therefore to try to design out the risks at design stage could cause a designer to fail to exercise their duties under the CDM regs? It also knowingly puts the winning Tenderer in the position to have to pass around a "hot potato" to temporary works designers when contractual and time pressures are being forced on them.
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On a large project the consulting engineer would normally be engaged by a client, either individually or as part of a design team and would be contracted to design only the permanent works; his responsibilities would include ensuring that his design can be constructed safely by a competent contractor. The consulting engineer would normally indicate in outline one method of safe construction but would expect the contractor to take on the detailed temporary works design.
Temporary works design
The design of the builders’ actual temporary works will be dependent on the builders’ particular method of construction and will include consideration of available skills, resources, programme of works, available space on site, and so forth. The expectation is that the main contractor is responsible for the detailed design of temporary works which may involve developing alternative methods which can often give them commercial advantage and offer best value to the client.
On small projects such as residential extensions the client generally engages a builder, and it is the builder who engages a consulting engineer. The scope of works for the consulting engineer in this instance is therefore determined by the builder and will usually include for both permanent and temporary works design.
Complying with CDM 2015
The transfer of relevant information between the various parties and the identification of residual, significant risk is a fundamental part of the CDM Regulations 2015. As this report suggests, it is debatable as to how well this is sometimes achieved, particularly with domestic projects and even projects where a CDM coordinator has been appointed (pre CDM2015).
The transfer of relevant information between the various parties and the identification of residual, significant risk is a fundamental part of the CDM Regulations 2015.
A key change in the revision of the CDM Regulations in 2015 has been the introduction of the principal designer. In the same way that a principal contractor must plan, manage, and monitor the construction phase the principal designer has the same duty during the pre-construction phase, and this includes domestic projects.
The principal designer should be appointed early and have the skills, knowledge and experience to understand the work being undertaken during the pre-construction phase. They should consider the adequacy of information provided by designers and challenge this if it is considered to be unsatisfactory. For example, has the main consulting engineer provided enough information for a temporary works designer to do their job properly?