This case study is an anonymised composite based on publicly reported PI claim patterns. It is not actual Apex client data and does not constitute legal or insurance advice. Names, locations and identifying details have been changed. Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority, FRN 724952.
A specialist temporary works and geotechnical engineering consultancy with nine engineers, fee income around £1.9m. The practice undertakes a mix of temporary works design and independent third-party check (“Cat 3 check” in BS 5975 terminology) work for construction contractors and main contractors across the south-east.
The instruction was a Category 3 independent check on a temporary works design for a propped excavation supporting a basement construction in central London — a relatively complex temporary works scheme involving a contiguous bored pile wall, two levels of horizontal propping, and significant adjacent property considerations on a tight urban site.
The Category 3 check, under BS 5975, is an independent check undertaken by an organisation separate from the original designer, to confirm the design is fit for purpose. The check engages a careful review of the principal calculation pathways, the load combinations, the structural arrangement and the practical buildability and risk-management considerations.
The firm’s check was undertaken by a senior engineer with substantial temporary works experience. The check was thorough on the principal calculation pathways and on the lateral stability of the propping arrangement. The omission lay in the engagement with the construction sequence as a separate consideration distinct from the static design. The original designer’s calculations addressed the steady-state propped condition; the check, by following the original designer’s analytical structure, did not adequately engage with the load conditions during the propping installation sequence itself, where the wall was temporarily relying on a single level of propping while the second level was being installed.
The construction proceeded. During the propping installation, at the point at which the first level of propping had been installed and the second level was being prepared, ground conditions disclosed during excavation produced higher lateral loads than the steady-state design had assumed at that elevation, and the construction sequence at that specific moment produced an under-propped condition. The wall moved laterally by approximately 70mm before stabilising — well above the design movement allowance, sufficient to trigger reportable settlement on the adjacent property and the appointment of a structural survey to assess the implications for the adjacent building.
Remedial measures were taken on site and the project was subsequently completed. The cost of the additional propping installed at short notice to stabilise the wall, the remediation works to the adjacent property, the consequent programme delay and the additional party-wall engagement costs aggregated to approximately £620,000.
The main contractor claimed against the original temporary works designer; the original designer claimed against the firm for breach of its independent check obligations. The firm’s defence engaged the proper scope of the Category 3 check — whether it extends to a separate engagement with the construction sequence beyond the static design that the original designer had prepared. The expert evidence on both sides agreed that a thorough Category 3 check should engage with the construction sequence as part of the practical buildability consideration; the firm’s check had been thin on this point.
The pleaded loss against the firm was approximately £380,000 as the firm’s contribution to the overall £620,000 quantum.
The defence resolved at mediation at approximately £225,000 inclusive of the original designer’s contribution to costs.
Section 5 notification was made on receipt of the original designer’s pre-action correspondence. The wording responded subject to the firm’s £20,000 excess. The £3m limit was sufficient.
A coverage question arose on the independent check role itself. The wording responded to the firm’s professional services including “design verification and independent check services”. The independent check role is professional advice within the scope of the wording, not a separate type of activity outside cover. The wording responded cleanly.
A second question arose on the subrogated waiver between the firm and the original designer’s professional indemnity insurer. The original designer’s settlement with the main contractor had been funded by their PI insurer, which now pursued the firm directly. The subrogated framework was familiar but added complexity to the negotiation — managed through coordinated counsel and a single mediation.
The matter resolved at mediation at approximately £225,000 inclusive of the original designer’s contribution to costs. The £20,000 excess applied.
The settlement was paid. The firm undertook a structured review of its independent check protocol. The principal change was the introduction of an explicit construction sequence review as a documented stage within every Cat 3 check, with a specific checklist and reasoning record. The firm’s PI premium rose by approximately 30% at renewal.
Independent check claims are a specialised but increasingly common category as temporary works complexity and party-wall sensitivity grow. First, the BS 5975 Category 3 check requires explicit engagement with the construction sequence as a distinct consideration; relying on the original designer’s analytical structure can lead the checker to miss the dynamic loading conditions during installation. Second, the firm’s check protocol should be documented explicitly and the file should evidence the reasoning record on each checked element, not just the conclusion. Third, subrogated claims following another professional’s settlement with their client are common in this space; the firm’s defence will encounter coverage counsel from the subrogating insurer who knows the area well, and the broker’s role is to ensure the firm’s defence counsel is equally specialist. Fourth, the firm’s PI wording’s treatment of independent check, peer review and verification roles should be specifically confirmed at renewal; some wordings treat these roles narrowly. Fifth, the renewal narrative on the firm’s Cat 3 check methodology and its documented checklist is the substance of an underwriter’s view of the specialist temporary works check market.
For specialist temporary works and check engineers, the broker’s role on a claim of this character is principally in the defence coordination and the renewal narrative. We work with practices on the panel-counsel selection (the difference between general PI counsel and specialist temporary works counsel is real and consequential) and on the renewal pack — including the documented Cat 3 check methodology and the construction-sequence-review protocol — that earns the underwriter’s confidence in a specialist practice.
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