Mould Air Testing for UK Homes and Buildings

Typical reasons for an air test include a persistent musty smell with little or no visible growth, recurring mould that cleaning does not resolve, occupant symptoms with limited visual evidence, post-flood or post-leak verification, due diligence before purchase or letting of a property with damp history, disputed landlord–tenant complaints, and clearance testing after remediation.

Where visible growth is widespread and the moisture source is obvious, the priority is usually to address the moisture and remove the affected materials rather than to quantify what is already evident.

A typical visit lasts one to three hours. The technician calibrates the pump on site, then takes a paired outdoor reference sample upwind of the building. Indoor samples follow a defined hierarchy: the suspect room first, then adjacent rooms, then supply air from any central HVAC system if relevant.

Every cassette is labelled with location, start and end times, flow rate and total sampled volume. A short building walkthrough records visible growth, moisture meter readings, ventilation provision and any complaints — context that the laboratory and the interpretive report both depend on.

A raw spore count is meaningful only in context. Three comparisons make it diagnostic. Indoor versus outdoor totals show whether the building is amplifying spore concentrations or simply mirroring the outdoor load. Species composition matters: outdoor air is normally dominated by Cladosporium and Alternaria, so a strong indoor presence of Aspergillus, Penicillium, Stachybotrys or Chaetomium with little outdoor counterpart points to an indoor source. Room-to-room patterns help localise that source.

Stachybotrys and Chaetomium carry particular weight because both require sustained wetness — finding them indoors indicates ongoing or recent water damage that warrants focused investigation regardless of the headline count.

Air testing is a short snapshot. Spore release fluctuates with humidity, occupant activity and air movement. Standard non-viable cassettes count both living and dead spores; they cannot, on their own, tell you whether the source is currently active. Microscopy resolves spores to genus, not always to species — further methods such as viable culture or qPCR are added where finer resolution matters.

A spore count is not a medical diagnosis. It describes exposure, not causation. Where occupants are unwell, medical assessment remains with a clinician; the air-testing report provides exposure evidence that the clinician can weigh alongside symptoms.

You receive the laboratory's analytical report with raw counts and genera, alongside an interpretive report covering the indoor–outdoor comparison, comments on species of concern, the building observations made on site, and clear recommendations on whether further investigation, remediation or clearance re-testing is appropriate.

Reports are written in plain English and are routinely used to support repair requests, insurance claims, landlord–tenant correspondence and Awaab's Law responses.