What is condensation mould?
Condensation mould is mould that grows where excess humidity or moisture in a home condenses on cold surfaces. It is a common problem in homes across the UK.
It often appears as black or green specks on walls, ceilings and other surfaces, and it flourishes particularly near windows, in corners and behind furniture. It comes with a musty smell that is hard to ignore.
What causes condensation mould?
It is caused by moist, warm air coming into contact with a cold surface, such as a window or exterior wall, where the water vapour condenses into liquid droplets. Moisture alone does not cause it; the cold surface is the other half of the problem.
Most of the moisture comes from daily activities:
- Cooking.
- Bathing.
- Drying clothes indoors.
Conditions in the home then decide whether mould takes hold:
- Poor ventilation lets moisture-laden air linger indoors, creating ideal conditions for mould growth.
- Inadequate heating leaves surfaces colder, promoting condensation.
- Single-glazed windows and a lack of thermal insulation make some areas of the home particularly vulnerable.
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Is condensation mould dangerous to health?
Yes, with prolonged exposure. The bigger issue than appearance is the health risk, particularly where mycotoxins are present.
These effects can be worse for:
- People with pre-existing conditions.
- Children.
- The elderly.
- Those with weakened immune systems.
What to look for when viewing
- Black or green specks on walls, ceilings and other surfaces.
- Mould near windows, in corners and behind furniture.
- A musty smell.
- Single-glazed windows.
- Signs of poor ventilation in high-moisture rooms such as the kitchen and bathroom.
- Evidence of clothes being dried indoors.
- How the home is heated, and whether it appears to be insulated.
How can condensation mould be prevented?
Prevention means keeping surfaces warm and moist air moving out of the home.
- Heating: effective heating reduces the cold surfaces where condensation occurs. Consistent heating, especially in colder months, makes a significant difference.
- Thermal insulation: insulation helps maintain the internal temperature, reducing the risk of condensation.
- Double glazing: double-glazed windows give a less cold surface, reducing condensation on the glass.
- Ventilation: regularly airing the property, particularly high-moisture rooms such as the kitchen and bathroom, significantly reduces humidity indoors.
What a survey can — and cannot — tell you
A building survey provides an informed assessment of the visible condition of a property. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.
Where condensation mould is present, a survey can point to the conditions in the building that encourage it, such as single glazing or poor ventilation.
- Visible mould growth and where it occurs.
- The type of glazing.
- Ventilation provision in kitchens and bathrooms.
- The heating system, as seen at the time of inspection.
- Visible thermal insulation, for example in an accessible roof space.
However, there are limitations to what a survey can determine without intrusive investigation.
- Mould hidden behind furniture or fittings that cannot be moved.
- Whether mycotoxins are present, which a visual inspection cannot establish.
- How the occupants heat and ventilate the home day to day.
- Insulation concealed within walls.
Where higher-risk indicators are identified, further specialist or intrusive investigation may be recommended.
Frequently asked questions
What does condensation mould look like?
It often appears as black or green specks on walls, ceilings and surfaces, particularly near windows, in corners and behind furniture, with a musty smell.
Why does mould grow on windows and external walls?
Warm, moist air condenses into droplets when it meets a cold surface such as a window or exterior wall, creating the conditions for mould.
What are mycotoxins?
Toxic compounds produced by certain mould species, which can cause allergic reactions and respiratory issues.
Who is most at risk from mould?
People with pre-existing conditions, children, the elderly and those with weakened immune systems.
Does double glazing help prevent condensation mould?
It can. Double-glazed windows give a less cold surface than single glazing, reducing condensation on the glass.
