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CROSS Safety Report

Unauthorised structural alterations to accommodate drainpipes

Report ID: 902 Published: 1 July 2020 Region: CROSS-UK

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A reporter became aware of cases where main structural steel sections were ‘butchered’ on site to accommodate drainpipes.

The alterations were not approved by the designer and were picked up during a routine inspection by building control.

Key Learning Outcomes

For clients and construction professionals:

  • Any alterations to structural elements should be approved by the designer prior to works being carried out on site

  • On building information modelling (BIM) projects it is beneficial for the entire design team, including third-party designers, to have BIM capabilities. This will allow for better collaboration and communication across the project.

  • Independent supervision on site by the design team or a third-party inspector can reduce the risk of any unauthorised changes from occurring, especially in Risk Category 3 buildings

Full Report

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The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.


On a recent project under construction, a reporter became aware of cases where main structural steel sections were ‘butchered’ to accommodate plastic foul drainage runs. Flanges and webs were compromised significantly.

Clash Detection via BIM

This was, continues the reporter, a BIM project and the clashes should have been picked up with clash detection review. However, much of the detailing was passed down the supply chain to sub- contractors who had no BIM capability.

This meant that the coordination of some key elements was not properly carried out in advance of construction. Furthermore, the building was a Risk Category 3 building which should have had extended supervision in accordance with Table B4 of BS EN 1990.

Quality control on site

This issue once again calls into question quality control on site. It demonstrates a complete lack of understanding by those undertaking the works of the potential consequences of their actions. The defects were picked up by a routine inspection by building control, but it raises further questions on what else has been modified that has been covered up.

It is clear that strict protocols are required before such modifications are carried out and that there must be sign off by the engineer before works are permitted. The lack of control on site which allows such things to prevail is evidence of questionable competency by those managing the construction process.

Expert Panel Comments

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Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

This illustrates several concerns. The fact that inappropriate and potentially catastrophic changes were made to the structure illustrates the need for adequate construction supervision and independent supervision e.g. by the design team. This is discussed further in report 905.

The fact that inappropriate and potentially catastrophic changes were made to the structure illustrates the need for adequate construction supervision and independent supervision

Coordination issues on site

However, one must call into question why the changes were deemed necessary in the first place. Often such unauthorised alterations are made as a consequence of an uncoordinated design, where there has been inadequate interdisciplinary coordination. In this case perhaps between the structural engineer and the building drainage designer.

Clients and project managers need to give the design team the time and tools they need to ensure adequate coordination of the design, to ensure the coordinated design is constructible and without clashes.

BIM collaboration

Such attention to detail usually results in significant overall cost savings for all parties. BIM should have identified the clashes and the reporter makes the valid point that sub-contractors must be party to the whole system for it to work properly.

This report also shows the valuable role that building control can play, because this type of situation is all too common. It also shows either a blatant disregard for safety, or a lack of knowledge on the part of the contractor – both situations are not acceptable in our industry.

It also ties into report 894 and report 905 of Newsletter 59 (and many other CROSS reports): what has been designed is not necessarily what has been built. A safe construction procedure should recognise that changes are inevitable but must always be controlled and sanctioned by the designer.

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