Differential Settlement on Reclaimed Land in Lekki, Lagos
During a routine site visit to a three-storey mixed-use building in Lekki, Lagos, the architect observes 3–5 mm diagonal cracks above ground-floor window openings on the north elevation, two internal doors that no longer close, and a 25 mm fall across the ground-floor slab toward the rear. The building sits on reclaimed sand fill. A 2019 geotechnical report specified a raft foundation with 600 mm hardcore and a suspended slab. The contractor's as-built drawings show strip footings at 1.2 m depth, and the architect was not copied on the foundation inspection. The client has a buyer for the building and asks the architect to sign the completion certificate 'so we can close the sale'; the local building control authority has not yet issued a certificate of occupancy. The architect's file contains no structural engineer's foundation inspection report.
1. Diagnose the likely technical cause of the movement and state the architect's immediate actions.
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The pattern is consistent with differential settlement: diagonal cracking at openings, doors out of plumb, and a slab fall all point to movement rather than shrinkage alone. The critical discrepancy is the foundation. A raft on 600 mm hardcore was specified for reclaimed sand fill; as-built strip footings at 1.2 m are a material departure, and the architect has no foundation inspection report. Immediate actions: do not sign any completion certificate; advise the client in writing that there is a suspected structural safety issue and that the building should not be sold as defect-free; engage a structural engineer and geotechnical engineer; install crack tell-tales and take a level survey; restrict use of affected areas if the engineer advises; notify the local building control authority; and retrieve the contractor's inspection records, concrete test results, and reinforcement details. The architect should also check whether her own site supervision failed to detect the foundation change.
2. Evaluate the client's request to sign the completion certificate so the sale can close.
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The request should be refused. A completion certificate certifies that the works have reached the contractual standard, not that the building is fit for sale or free from structural risk. The architect has actual knowledge of movement and a likely foundation non-compliance; signing would be a misrepresentation and could expose her to professional negligence, contractual liability, and disciplinary action under the ARCON code. The certificate of occupancy is a separate regulatory approval and cannot be replaced by the architect's signature. The architect should issue a written schedule of defects and non-conformances, explain the need for investigation before any sale, and advise the client to disclose the issue to the buyer. If the client pressures her, she should document the refusal and seek legal advice. Public safety and honesty take precedence over the client's commercial timetable.
3. Outline the regulatory and remedial path, including the investigations and approvals required.
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Notify the Lagos State Building Control Agency or relevant local authority immediately and provide the as-built foundation information. The structural and geotechnical engineers should carry out trial pits, boreholes, plate-load or penetrometer tests, a level survey, and crack monitoring over at least three months to establish whether settlement is ongoing. Remedial options depend on the findings: local underpinning, mini-piles, compaction or resin grouting, ground improvement, or a new raft or ground beam system. The engineer should design the remedy, obtain building control approval, and supervise the works. The architect should issue the necessary instructions and variations, record costs, and notify insurers. After remediation, re-inspection and monitoring must show stabilisation before any completion certificate or occupancy approval is considered. The contractual position with the contractor should be reserved pending the investigation.