Case Study: Eight Months of Mould Blamed on a Tenant — Independent Survey Found Two Building Defects
A case study from a Leicester Edwardian terrace in Clarendon Park — details anonymised, property representative of a common type of enquiry from private tenants.
The tenant had been reporting black mould in the main bedroom and bathroom for eight months. The landlord had arranged for the property to be inspected twice — once by a maintenance contractor who applied anti-mould paint, and once by a damp proofing company who attributed the problem to "tenant lifestyle" and recommended the tenant improve ventilation habits. The mould returned within weeks both times. The tenant contacted me for an independent assessment to support a formal complaint.
This case illustrates why the distinction between building defects and lifestyle condensation matters — and why it requires proper investigation to establish, not assumption.
The Property
A mid-terrace Edwardian property, approximately 1905. Two bedrooms, one bathroom with extractor fan. Rented to a single professional tenant. Central heating throughout. The main bedroom — rear first floor — had heavy black mould in two corners and on the ceiling above the window. The bathroom had extensive mould on the ceiling despite the extractor fan being present.
What Previous Inspections Found
The maintenance contractor’s visit noted visible mould, applied an anti-mould wash and redecorated. No investigation of cause. The damp proofing company visit noted no structural issues and attributed the problem to condensation from inadequate ventilation by the tenant.
The tenant disputed this — she worked from home and habitually opened windows, ran the bathroom fan during and after showers, and had not been drying clothes indoors. She had kept records of these practices.
What My Survey Found
Bathroom: the extractor fan was present but had failed. It made noise when switched on but the internal impeller was seized — it was moving no air whatsoever. I tested it with a tissue held against the grille: zero airflow. The landlord’s maintenance contractor had presumably not checked whether it was actually functional. A non-working extractor fan is a building defect, not a lifestyle issue.
Main bedroom — thermal imaging: the rear corner showed two distinct cold zones. The first, in the upper corner, was consistent with cold bridging at the ceiling/wall junction — the ceiling joist pocket in the external wall creating a thermal bridge. The second, more significant anomaly, was a broad cold zone at mid-height on the rear wall corresponding precisely with the position of the rainwater downpipe on the rear elevation outside.
External inspection: the cast iron downpipe at the rear had a joint that had separated approximately halfway up. During rain, water was discharging from the joint directly onto the brick wall behind. The ivy growth on the rear wall had partially concealed this — it was only visible from a specific angle from the yard below. The wall behind the downpipe joint was visibly stained dark with algae.
Calcium carbide test on the rear wall at the downpipe position confirmed elevated actual moisture content — significantly above what condensation alone would produce.
The Finding
Two separate problems, both building defects:
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Failed extractor fan — the bathroom mould was primarily caused by inadequate extraction. The fan had failed mechanically and was not removing moisture from the room. This is the landlord’s responsibility to maintain.
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Leaking downpipe joint — penetrating damp was entering through the separated downpipe joint, saturating the wall behind. The mould in the bedroom corner near the downpipe was partly condensation (cold bridge) and partly from the consistently wet wall from the leak.
The tenant’s ventilation habits were not the cause of either problem. The written report set out the findings clearly with photographic and thermal imaging evidence.
The Outcome
The report was submitted with the formal complaint to the landlord. The landlord arranged repair of the downpipe joint (£85) and replacement of the extractor fan (£145 including installation). Both were completed within two weeks.
The tenant’s complaint was upheld. The landlord subsequently carried out internal redecoration of the affected areas.
What This Case Illustrates
"Lifestyle condensation" is a real phenomenon — tenants who never open windows, dry clothes on radiators in closed rooms, and run no extraction do generate condensation. But it is an easy default attribution that avoids the need for proper investigation.
An independent survey with thermal imaging and mechanical testing of extraction equipment established objectively that the cause here was building defects, not tenant behaviour. Without that evidence, the dispute would have continued indefinitely.
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✉️ richard.bull@dampdetectives.co.uk
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Richard Bull MISSE, ACIEH — Independent & Unbiased — Tenant and Landlord Survey Reports Available