CROSS Safety Report
Inadequate design for basement works
An inadequate structural design for alterations to a basement led to structural distress within a substantial five-storey townhouse.
Key Learning Outcomes
For property owners and clients:
- Understand the competencies required of engineers for the project in hand
- All structural design should be signed off by an appropriately experienced chartered civil or structural engineer
For civil and structural design engineers:
- Engineers should undertake full assessments of existing structures when considering alterations
- Designers have responsibilities under the Construction (Design and Management) Regulations 2015
- Consider basing the checking of designs upon drawings and specifications as well as the calculations
- Be aware that the adequacy of a structural design submitted to a building control body, lies with the originating designer - do not place reliance on the building control review
For building control bodies:
- Ensure that all structures are checked for compliance with Part A of the Building Regulations in England and Wales, and the equivalent in Scotland and Northern Ireland, by suitably qualified and experienced people
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A structural engineer reported they were commissioned to investigate cracking within a substantial five-storey Victorian house that had recently been altered. The alteration centred around the removal of a load-bearing wall at the basement level. The property had previously been altered on a number of occasions.
The client for the basement works had employed an engineer to prepare structural calculations for the works. The engineer prepared a design for a beam (with padstones) to span over the proposed opening to be created in the basement. However, the engineer failed to check the supporting walls, piers, and foundations.
The client employed a second engineer to check the first engineer's design. The second engineer approved the design without flagging up the original engineer's failure to check the walls, piers, and foundations. The building control body signed off the project without deploying a checking engineer to assess the structural design.
Furthermore, the client for the basement works did not serve notices or arrange awards to other owners within the building as required under the Party Wall Etc Act 1996, even though the client was advised to do so.
Sometime after completion of the works, the reporter was called in to investigate cracks that appeared in walls supported by the newly installed beam. The reporter found that walls, piers and foundations needed to be opened up and assessed for the revised structural configuration and that the client would be responsible for the repairs to the flats above.
Failings and missed opportunities
The reporter concluded that failure by both the first and second engineers to recognise that structural assessment of the supporting masonry and foundations was necessary, led to the inadequate structural alterations. In addition, the building control body not identifying the structural inadequacy and the client not complying with the party wall regulations meant that other opportunities to spot the inadequate design prior to construction were missed.
The reporter confirmed the following learning outcomes:
1) Engineers should encourage clients to fulfil their legal obligations (including compliance with the Party Wall Etc Act 1996) and explain the risks of not doing so.
2) Engineers should ensure that they carry out a full design. If their clients ask them to carry out only a partial design, they should explain the risks and be prepared to walk away if their client insists on a partial design.
3) Checking engineers need to not only check the calculations they receive but also flag up any omissions in the design.
Expert Panel Comments
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This is a very worrying report indeed. There were many opportunities for this serious situation to have been avoided. For two engineers to perform so poorly in undertaking their duties, for the building control process to have no apparent impact on the design proposal and for the client to ignore important advice concerning party walls, displays clear failings which should not go unnoticed.
A question of competency
The competence and suitability of both the design and checking engineers for the project appear very doubtful. Ideally, they could have acted as an ‘intelligent customer’ and advised the client of the scope of structural investigations and design that was necessary. Whilst it is possibly not known how close the building was to a serious collapse, it appears that critical structural work was undertaken with little regard to the stability of structural elements below, around and above the wall that was removed. Furthermore, it appears no attempt was made to understand the impact on the overall stability of this building or indeed the adjacent buildings. Clearly, a thorough structural investigation and assessment of the building (and probably adjacent buildings) should have been undertaken. The required assessment is made more necessary and complex if the property was of multi-occupancy. This would add uncertainty and difficulty in reviewing what changes have been made in the past and changes to load paths. Nevertheless, the investigations and assessments should have at least uncovered and considered the following:
- The structural arrangement of this and adjacent buildings
- Materials and construction techniques
- The strength of the materials
- Existing distress, misalignment, or degradation of building fabric
- What alterations and repairs have been previously undertaken
- The existing load path(s) to earth
- The existing and new loadings (both during construction and on completion)
- The nature of the existing foundations and basement construction
It would appear that both the design and checking ‘engineers’ were working outside their knowledge and experience; both should have identified that a thorough investigation and assessment were required. CIRIA report C740 Structural stability of buildings during refurbishment provides guidance for clients, designers, builders and others upon a range of refurbishment tasks, including removing walls. The advice also covers investigating and assessing existing structures.
the client was obligated to appoint competent persons
The client was obligated to appoint competent persons. Nevertheless, it may be the case that the designer was asked by the client to do a beam design only. If this were the case, the designer should have insisted that a proper assessment be undertaken or refused to undertake the commission. The checking engineer does not appear to have been competent to undertake the check. Their work should have included a review of the structural concept and design (as described on drawings and specifications) such that they could make their own independent calculations and exercise independent judgement as to the adequacy of the proposals. This would have exposed the lack of appropriate investigation. Works of this type should always be signed off by a chartered structural or civil engineer.
Under the Construction (Design and Management) Regulations 2015 (CDM 2015), the designer should also have considered how the works were proposed to be implemented. The designer should have indicated as part of the design, what method of working and temporary works were assumed to be necessary to implement the design. Clearly, to do this they should have understood the building they were working upon. The HSE provides clear CDM 2015 guidance for clients and designers for projects of this type.
the stability of several or indeed all buildings can be compromised
In this case, cracking occurred, but significant structural collapse could have occurred if the removed wall were a key structural element providing stability to other elements in this building or indeed adjacent buildings. The removal of walls in terraced-type buildings can leave properties depending upon the neighbouring building for stability. Where walls are removed in terraced properties eventually the stability of several or indeed all buildings can be compromised, unless the removal of walls is engineered properly. CROSS report Inadequate design submissions for alterations to an existing building dealt with a not dissimilar case including failure to consider the overall stability of a building. Similarly, the removal of walls within a basement can cause a loss of stability to adjacent retaining walls and the collapse of the building(s).
The checking of engineering designs submitted under building control processes can have many benefits including, not least, the prevention of unsafe structures being erected. Building control bodies have a responsibility to review all designs for compliance with Part A. It would be expected that the building control body dealing with this project should have identified that further assessment of the proposal was required.
the ethics of all involved appear open to question
Finally, but most importantly, the ethics of all involved appear open to question. The client decided it was necessary to appoint a checking engineer which is to their credit. However, they decided not to investigate party wall matters which would have likely opened up the lack of proper assessment. The designer appears not to have sufficient competence in that they did not understand their legal duties and unethical in that they did not have full regard for safety. The checking engineer and building control body also appear to have fallen short of their duty to ensure safety. Construction professionals should always be mindful of their professional duties under law, their terms of appointment and the code of conduct of their qualifying institution. The code of conduct alone will require them to be competent to perform the duties offered, apply appropriate skills, experience and knowledge, to act with impartiality and have full regard for safety.
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