Damp, condensation and mould

Damp in homes is common, has several distinct causes, and is frequently treated with the wrong remedy because the cause was not identified.

The three types

Condensation, by far the most common in modern homes.

Warm air holds moisture; when it meets a cold surface the moisture condenses.

The signs: water on windows in the morning, mould in corners and behind furniture on external walls, mould in bathrooms and on window frames, and a seasonal pattern that worsens in winter.

Penetrating damp, where water enters through the building fabric.

The signs: a defined patch rather than general dampness, worsening after rain, and a source that can generally be identified — a leaking gutter, a cracked render, a failed seal, a blocked drain, a slipped roof tile.

Rising damp, where moisture moves up through a wall from the ground.

The signs: a tide mark at low level with the damp stopping at a fairly consistent height, and salt deposits on the surface.

It is considerably rarer than the damp-proofing industry suggests, and a substantial share of diagnoses turn out to be condensation or penetrating damp on inspection.

Why the distinction matters

Because the remedies are entirely different.

Injecting a damp-proof course into a wall suffering condensation achieves nothing.

Applying anti-mould paint over penetrating damp conceals it while the water continues.

And increasing ventilation, which resolves condensation, does not address a leaking gutter.

Which is why an accurate diagnosis, ideally by an independent surveyor rather than by a company selling the treatment, is the first step for anything substantial.

Where the moisture comes from

For condensation specifically, the sources are domestic.

Breathing and perspiration produce a surprising quantity — several litres per household per day.

Cooking, particularly boiling.

Showering and bathing.

Drying laundry indoors, which is a very large single contributor.

Unflued heaters, which produce water vapour directly.

And a lack of ventilation to remove any of it, which modern airtight construction and draught-proofing have reduced substantially.

What resolves condensation

Ventilation, which is the primary answer.

Extractor fans in kitchen and bathroom, used during and after cooking and bathing, and vented outside rather than into a loft.

Trickle vents in windows, opened.

Opening windows briefly and widely rather than continuously and slightly, which changes the air without cooling the structure.

Heating, since warmer surfaces do not reach the temperature at which condensation forms.

Low continuous heat is generally more effective against condensation than intermittent high heat, though the cost implications depend on the building.

Reducing moisture production — lids on pans, drying laundry outside or in a ventilated room, and closing bathroom doors while showering.

Insulation, which raises surface temperatures and is the durable solution.

Cold bridges — lintels, corners, uninsulated sections — are where condensation appears first and where targeted insulation helps most.

Moving furniture away from external walls by a few centimetres, so air can circulate behind it.

Dealing with existing mould

Practical steps.

Clean small areas with a fungicidal wash or a dilute bleach solution, wearing gloves and eye protection and ventilating well.

Do not brush or vacuum dry mould, which disperses spores.

Discard porous items that are heavily affected.

And treat the cause, since cleaning alone means it returns within weeks.

Extensive mould, or mould in a rented property, warrants professional assessment, and tenants in many jurisdictions have rights regarding damp and disrepair that are worth knowing.

The health dimension

Worth stating clearly.

Damp and mould in homes are associated with respiratory symptoms, asthma exacerbation and allergic reactions, with the evidence strongest for respiratory effects.

The risk is higher for children, older people and anyone with an existing respiratory condition or a compromised immune system.

Which means damp is a health matter rather than a cosmetic one, and persistent problems should be pursued rather than tolerated.

General information only, not professional or medical advice. Persistent damp warrants professional assessment, and respiratory symptoms warrant consultation with a qualified clinician.