What Landlords Need to Look For When Diagnosing Damp

Whilst cleaning mould, repainting a wall or replacing damaged plaster may improve appearance for a while, the problem will return if the moisture source remains. Remember: you cannot diagnose damp from the stain alone. Mouldy patches on walls, salt deposits or damp corners only tells you where moisture has become visible. It does not tell you where the water came from, how long it has been there or which building defect is the cause.

Remember: dampness can only be solved once building defects, inadequate ventilation or heating has been rectified. You should never rely on surface treatment alone.

Identifying Patterns of Dampness

A practical damp inspection begins by analysing the pattern and position of moisture. Is the problem low on the walls, localised around a window or door, spreading across a cold corner or linked to recent rain?

Whether a problem presents as penetrating damp, rising damp or condensation depends on how moisture moves through or into the building. Solving it depends on identifying where that moisture is coming from.

Low-level damp staining with salt marks may point to rising damp, caused by a combination of ground moisture, bridging at the damp-proof course level or a missing/faulty damp-proof course. 

A patch that worsens after rain often suggests penetrating damp; external water ingress through masonry defects, failed pointing, cracked render, leaking gutters or roof defects. 

Black mould in corners, behind wardrobes or around window reveals may be due to condensation on cold surfaces with weak air movement.

Check Exteriors First

The Risks of Misdiagnosing Rising Damp

Rising damp is often misdiagnosed, but this doesn’t mean that ground moisture is never a cause of dampness. It just means that extra care should be taken to first rule out bridging via high external ground levels, penetrating, rising damp and condensation before concluding that a damp-proof course has failed.

For landlords, that is a useful safeguard against unnecessary remedial work. A low-level tide mark may suggest moisture from the ground, but it is not enough on its own to justify an injected damp-proof course or full replastering specification.

Why Condensation Occurs

Condensation is common, but it still requires careful diagnosis. Very simply, condensation forms when warm moist air meets a cold surface. The task for you as a landlord is to find out why that surface is cold and why moisture is not clearing. Common causes include inadequate extract ventilation, intermittent heating, thermal bridges around windows and doors, blocked background ventilation and furniture packed tightly against colder external walls.

In practice, appropriate actions involve assessing the ventilation and central heating situation and condition of insulation, as well as taking into account the moisture production inside the room itself.

Salt Contamination

Process. Process. Process.

A sound damp inspection follows a sound process. 

Record the symptoms. Inspect externally first. Compare the defect pattern with weather exposure, plumbing routes and room use. Check ventilation and surface temperatures where condensation is suspected. Review whether any previous repairs may have trapped moisture or left contaminated plaster behind. 

If the cause is still unclear, consult a suitably qualified surveyor rather than defaulting to a standard treatment package.