CROSS Safety Report
Dangerous alteration work results in two terraced houses being demolished
Overview
Two mid terrace properties forming four flats had been underpinned and excavated to form a new basement whilst simultaneously removing internal and rear walls. This left the building in a dangerous condition and subject to a demolition order from the local council.
Key Learning Outcomes
For clients:
- Building owners should always ensure that professional advice is taken, ideally from a suitably qualified and experienced engineer
- The ability of a contractor to undertake the works should be confirmed prior to the award of contract
For contractors:
- The proper management of temporary works is essential in maintaining the stability of structures during extensive renovation
Full Report
Find out more about the Full Report
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.
A reporter’s firm was called by a demolition contractor to review a structure prior to demolition following a dangerous structures notice and demolition order from the local council. It was found that there were two mid terrace properties forming four flats in a very poor state and at imminent risk of collapse due to works that had been undertaken.
The whole building had been underpinned and excavated to form a new basement. This had been done while simultaneously removing internal and rear walls. When reviewing the work on site (from a safe distance due to a prohibition order preventing entry), the reporter observed that inadequate temporary works had been put in place.
The structure was at high risk of collapse at any moment and the work was so poor that the building and its neighbour had to be demolished to make the area safe
The reporter was informed that no engineer had been involved in the design and that the contractor had just built what they considered to be necessary. Architectural drawings had been submitted to the local authority, but the works on site did not match what had been proposed.
The lack of engineering input meant that the job had progressed without anyone understanding how to stabilise the building during the works, and without anyone knowing how to progress the works safely for both those involved in the construction and the public. The structure was at high risk of collapse at any moment and the work was so poor that the building and its neighbour had to be demolished to make the area safe.
Figure 1 shows the extent of works partially completed to the rear and internally when the reporter visited the properties.
After the local authority and the Health and Safety Executive (HSE) became involved, the contractor disappeared and has not been able to be traced.
This issue stems, says the reporter, from there being no suitably qualified persons to undertake the structural design of the permanent and temporary works, and the appointment of a contractor who was not competent.
The reporter concludes that this highlights the need for clients to ensure that there is a competent design team and competent site team who understand the risks associated with the complex task of adding a basement to an existing terrace property.
Along with an understanding of the temporary works that are required on site, the reporter feels that basement works such as this, should need full building control approval and planning permission prior to work being started. This would ensure that works are appropriately designed and will not cause undue risks.
Figure 2 shows the extent of the works partially completed to the front of the property when the reporter visited the properties.
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Feedback
The Association of Specialist Underpinning Contractors (ASUC) provides free guidance on Safe and Efficient Basement Construction Directly Below or Near to Existing Structures
I have experienced a similar issue with a basement that stemmed from a lack of clarity as to who was responsible for temporary works and where they were required. The engineer had provided a design that worked in its finished state, but which needed significant temporary works for it to be constructed.
The contractor (wrongly) assumed that the drawings showed all they needed to know and set about constructing the scheme based on the drawings, not being aware that temporary works were required.
This was a case of each party being unaware of temporary works requirements and more specifically assuming the other party would take responsibility for them. The engineer assumed that a competent contractor would know to install the temporary works to maintain the building stability whilst they were installing the basement. The contractor assumed that the engineer had taken the temporary state into account and as nothing was shown on the drawings, no temporary works would be required.
This serves as a reminder to all designers that significant temporary works, particularly those that would be essential to the construction of their design, must be indicated as being required on their design/construction information.
Expert Panel Comments
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We have seen reports of similar instances before and sadly this is not an uncommon situation. CROSS Safety Reports 123, 423, 1044 and 1062 are all examples of similar issues.
The sentiments expressed in the reporter’s last paragraph are correct.
Very often, a builder (who may or may not have suitable experience) will be engaged by the householder without reference to professional advice. The proper management of temporary works is essential in maintaining the stability of structures during such extensive renovation, yet many small and medium sized enterprises do not have sufficient knowledge, nor do they engage either temporary works designers, or structural engineers to design the permanent works.
As they do not understand the work they are undertaking, they are unable to control risks.
With the current financial difficulties to the forefront in clients' minds, it is likely that they will be tempted by inappropriate advice from unqualified enterprises
Building owners should always ensure that professional advice is taken, that the ability of a contractor to undertake the works is confirmed prior to the award of contract, and that building control inspectors are provided with all necessary details and inspect the works at appropriate stages.
With the current financial difficulties to the forefront in clients' minds, it is likely that they will be tempted by inappropriate advice from unqualified enterprises in an effort to save money. Whilst it may be difficult, this temptation should be resisted.