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CROSS Safety Report

Unsafe instructions from a building inspector

Report ID: 1086 Published: 10 March 2022 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.


On the site for an extension to a domestic property, a building inspector instructed a contractor to excavate a deep trench. The trench was in front of the neighbour's adjacent boundary retaining wall and left a deep vertical face under the house being extended.

Key Learning Outcomes

For policy makers:

  • Set high competency standards for building control professionals

For owners and clients:

For construction professionals:

  • Comply with the CDM Regulations by ensuring hazards (such as undermining existing structures) have been communicated to the principal contractor
  • Time and money spent on desktop and soil investigations is well spent

For contractors and builders:

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.


The project was a small two-storey domestic extension to the side of a house. The design for the foundations was shown on the architectural drawings and the plans approved by the local authority. The building contractor excavated trenches for the footings and asked the local authority building inspector to view.

The building inspector, who was an experienced chartered engineer, was not confident that the exposed formation material was natural and instructed the contractor to excavate deeper. A further instruction to go yet deeper followed. The contractor ended up creating deep trenches in front of the adjacent neighbour's 1.2m high boundary retaining wall, and with up to 1.8m vertical faces to the raft foundation of the house being extended. The building inspector then informed the house owner that the foundations would need to be re-designed and recommended no further work until this happened. The excavations were then left exposed.

The householder approached the reporter asking for a re-design.

Based upon the appearance of the retaining wall, the reporter considered it reasonably likely that the retaining wall relied on the ground in front of the wall to provide resistance to sliding and/or overturning. Due to the open trench, the reporter would not have been surprised if the wall had collapsed. The building inspector however made no effort to determine if the retaining wall foundations relied on passive resistance in front of the wall. Similarly, there was no direction on how to prevent the soil left standing under the existing foundations from collapse, leaving voids under the building. The reporter considered it was unwise to delay the backfilling any longer and therefore asked the builder to complete the trench fill.

The building inspector instructed the contractor to delay, and also to enter the deep (unsupported) trench and carry out a 'peg test'. The reporter considered it unsafe to expect an operative to enter the trench to carry out a test without consideration of a safe method of work.

The reporter considered it unsafe to expect an operative to enter the trench

The building inspector apparently told the householder that he was a chartered engineer with vast experience. The reporter considered that the inspector focused on the requirement to inspect the formation without an appreciation of the potential failures of other elements outside that focus. In the opinion of the reporter, the inspector failed to recognise that his instructions could cause collapse.

The reporter concludes that it is was very difficult for the contractor to refuse what appeared to be an instruction from a professional in authority. Furthermore, the reporter believes that a building control inspector who is also a chartered engineer must display a higher duty of care than that which he observed.

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 report sadly reflects what CROSS hears too often - concerns about the lack of competency of some people involved in construction processes. In this case, to receive a report that a chartered engineer performing as a building inspector did not recognise obvious personal safety and building instability risks is grossly concerning. The reported actions of the contractor blindly following ‘instructions’ from the building inspector compound the concerns. The contractor's first duty is to protect life and not to please a building inspector.

a chartered engineer performing as a building inspector did not recognise obvious personal safety and building instability risks is grossly concerning

Health and Safety legislation places duties on individuals as well as companies to ensure that they don’t put people at risk of harm. In the most serious of cases, and where a death results, this can amount to gross negligence manslaughter. There have been cases where, following collapse, individuals have been prosecuted. Some years ago, there was a case where a designer (an experienced engineer) agreed to a contractor excavating a trench alongside a wall to a depth 900mm deeper than the base of the wall. The wall slid into the excavation killing two workers. The charge of manslaughter by gross negligence was laid against the individual who was an employee.

charge of manslaughter by gross negligence was laid against the individual

In the circumstances described by the reporter, had an operative entered the trench and been killed by a collapse, any party that ignored a clear and obvious risk of death would likely be investigated and possibly face charges relating to manslaughter. Penalties can include prison sentences, let alone knowing that your negligence has led to a fatality. 

It appears that there was a lack of understanding of the role performed by building control. A building inspector cannot instruct anything. They are not a party to any normal building contract and have no authority to instruct. They can as part of their duties request that something is done to facilitate their inspections, and it is down to the contractor to enable this in a safe way. They can also state that something is non-compliant with the building regulations, but again it is down to the contractors or designers to correct this in a suitable way. Contractors should refuse to do anything they feel is unsafe, but ensure they enable building control inspections.

Unsupported excavations

This report raises at least two very significant risks to life; the collapse of unsupported excavations onto anyone in the excavation and the collapse of existing structures adjacent to the excavations. Many garden or boundary walls, let alone retaining walls, have very shallow foundations which are easily undermined by even small trenches. The picture painted of a 1.8m vertical excavated face to the exposed edge of a concrete raft supporting a house defies belief. For excavations 1.8m deep, appropriate support to the excavated faces was required. The Health and Safety Executive (HSE) provide extensive guidance upon excavations including Excavations What you need to know’.

Adequacy of investigations and design

The designer of the extension should have been thinking about the foundations of the existing building and had the designer uncovered the fact that the building was founded on a raft, that may have started a deeper examination of what foundations are likely to be required for the extension. Indeed, a structural engineer would likely have been called in to assess foundation requirements. Proper site and soil investigations would probably have led to the project progressing without the severe safety risks that unfolded. Money and time spent on investigations, even for smaller projects, is invariably money and time well spent.

In that the neighbour’s retaining wall was apparently undermined, agreement under the Party Wall Act 1996 may have been required. Again, this was a missed opportunity to start the project well; a building professional dealing with party wall matters may have highlighted acceptable excavation depths to avoid undermining the retaining wall.

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