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CROSS Safety Report

Poor quality design leads to failure for a small design and build contract

Report ID: 1088 Published: 6 June 2022 Region: CROSS-UK


An example of a small design and build contract where poor design and management led to an inadequate structure being built.

Key Learning Outcomes

For clients and owners:

  • Require that all structural design is signed off by a suitably experienced chartered civil or structural engineer
  • Consider appointing an independent chartered building professional whose role is to monitor the design and build processes
  • Be wary of a quotation that is significantly lower than others

For contractors' site staff:

  • Request detailed drawings and specifications for any aspects of the build which are not clear

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 shares their concerns about a design and build project which they have appraised for the owner of a domestic property; the design and build contractor having produced a structurally unsound building.

The property was a Victorian two storey building split into ground and first floor flats. The project concerned a loft conversion to the first floor flat. The owner appointed an architect who provided a planning stage drawing for the scheme. The client then appointed a specialist loft conversion contractor to take the project to completion. The reporter, a consulting structural engineer, was contacted by the owner part way through the build process when cracking started to show in the existing structure. Upon investigation, the reporter found the following concerning issues:

  • Structural calculations which did not appear to allow for the full roof loading
  • A structural arrangement leaving the floor undersized and the roof partially unsupported
  • Loadings on existing masonry likely to cause settlement
  • New steel beams supporting the new floor, causing deflection and cracking in the ceiling below
  • Undersized and poorly constructed concrete padstones supporting new steelwork
  • Existing triangulated roof timbers cut, leaving a partially unstable roof
  • Inadequate structural support to the new stairs into the converted loft space

The reporter confirmed to the client that the design was structurally inadequate and that the building work undertaken was the cause of damage to the property. The client terminated the contractor’s involvement in the project. The reporter identified the following concerns as to how the project was progressed:

  • During the design period, there were no visits to site to assess the existing structure
  • Structural calculations completed using proprietary design software appear as though they were not compiled by a structural engineer
  • The lack of competent conceptual and detailed designs, led to a damaged building and extensive rebuilding being required
  • It was not known if the appointed building control approved inspector checked the structural design or any of the works

lack of competent conceptual and detailed designs, led to a damaged building and extensive rebuilding

The reporter concluded that:

  • Clients should seek chartered building professionals to put their names and reputations to projects in order that appropriate skill, judgement, and experience are applied
  • More detailed design should be undertaken for small projects before appointing contractors
  • Effective building control checking processes for both the design and site activities must be in place
  • Be wary of cheap quotations
  • Providing poorly developed services to clients should not be acceptable

Expert Panel Comments

Find out more about the Expert Panels

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.

Conversion and changes to domestic dwellings can be complex and demanding. Structural engineers are key to ensuring that these projects are progressed competently. Identifying potential conceptual structural schemes and developing detailed schemes that are appropriately elegant, effective, buildable and economic requires significant knowledge, skills and experience. Unfortunately, however, we see far too many reports which confirm that competent engineers have not been engaged on some projects. Clients should understand that structural engineering is a complex discipline that should only be entrusted to appropriately qualified and experienced structural engineers, either typically performing as a consultant, or as part of a design and build organisation, as in this case.

clients should understand that structural engineering is a complex discipline

Clients should check that the person undertaking the structural design is appropriately experienced and qualified before appointing. Using the services of a ‘designer’ who relies upon software to produce designs, but who is not competent to design structures, is a recipe for errors that may lead to financial loss, or worst still, lead to a structure liable to collapse.

Finally, owners considering a design and build procurement route may find it very beneficial to appoint an adviser who can use their experience to help the owner navigate the many processes and decisions required in a building project. The fees spent will generally represent good value in assuring safety and in reducing financial, time and other risks.

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