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Condensation and mould: evidence, not blame
Mould in a rented or leasehold London flat almost always ends in the same argument: the landlord or freeholder says condensation, the occupier says the building. Both can be partly right, and neither position is worth much without measurements. We measure, and the report says which factors are actually driving it.
What a report has to establish to be worth anything
- Whether the affected surfaces are cold enough to condense at normal indoor humidity
- Whether the mould pattern follows the structure or the room
- Whether the ventilation provided actually moves the air it was specified to move
- Whether extract discharges to outside air or into a void
- What the internal conditions are over time, rather than at one moment on one afternoon
The distinction the whole dispute turns on
Condensation is a symptom, not a cause. Moisture condenses where a surface is below the dew point of the air, so the question is always why that surface is cold and why that air is moist. If the surface is cold because of a cold bridge at a slab, a reveal or a panel joint, that is a building defect. If the air is moist because extract ventilation moves a fraction of its rated flow, or discharges into a roof void, that is also a building defect.
Mould that runs in a band along a slab or a reveal is following the structure. Mould spread evenly through a room, worst behind furniture and in cupboards, is following the air. The two have different causes and different remedies, and telling them apart is a matter of recording where the mould actually is relative to the building rather than noting that mould exists.
What we measure
Surface temperatures at the affected areas and at unaffected comparison points, so a cold bridge shows up as a measured difference rather than an assertion. Air temperature and relative humidity, and therefore the dew point the surfaces are being asked to stay above. Calibrated moisture readings, recorded by location.
Ventilation performance, measured. An extract fan is rated for a flow rate and very often does not achieve it, because of crushed ducting, long runs, blocked terminals or a unit that was never suitable. Measuring the actual flow against the requirement is the single most useful thing a report of this kind can contain, and it is frequently the thing that is missing.
Who this is written for
Housing disrepair claims, where the report has to survive scrutiny from the other side. Landlords and managing agents who want to know their actual position before committing to work or defending a claim. Leaseholders whose freeholder has attributed a building performance problem to how they live. Buyers who have found mould and want to know what it will cost to resolve.
ATi carries out no remedial work of any kind. There is nothing in any conclusion for us, which is precisely why a report of this sort is worth commissioning from a practice like this rather than from a contractor who would carry out the remedy.
Get it measured rather than argued about
Surface temperatures, humidity, calibrated moisture readings and measured ventilation performance, in a written report within 24 hours of the visit.
Book a surveyOr call 020 3355 4944.
Questions
Our landlord says the mould is our lifestyle. Is that a defence?
Only up to a point, and it is testable. A dwelling is expected to cope with the moisture that normal occupation generates, and the provision for that is ventilation. If the extract moves materially less air than it should, or discharges into a void, or does not exist, the building is failing whatever the occupancy. Equally, if surfaces are measurably colder than they should be because of a cold bridge, condensation will occur at humidity levels no household could avoid. Measurement settles it; assertion does not.
What makes a report usable in a disrepair claim?
Independence, measurement and specificity. It needs readings recorded against locations rather than general statements, the mould pattern mapped against the structure, ventilation performance tested rather than described, comparison points so a cold bridge is demonstrated rather than claimed, and photographs. And it needs to come from somebody with no financial interest in what the remedy turns out to be, which is why we carry out no remedial work.
Can you assess a flat in one visit?
In most cases yes, and where conditions vary a great deal we will say so. A single visit captures surface temperatures, humidity, dew point, moisture readings, the mould distribution and the measured ventilation performance, which resolves the large majority of these questions. Where a property is behaving very differently at different times, monitoring over a period adds real value and we will recommend it rather than pretending one afternoon settled it.