Understanding damp & mould: What you need to know

Understanding Damp & Mould: What You Need to Know

Damp and mould are common issues faced by both landlords and tenants, no matter the age of the rental property. It's essential for both parties to understand the causes and take appropriate steps to prevent the problem from getting worse.


Condensation

Condensation in a property happens when warm, moisture-rich air—often generated by everyday activities like cooking or showering—comes into contact with cold surfaces such as external walls or windows. Without proper ventilation, this moist air remains trapped indoors and naturally moves toward the nearest cold surface, where it turns into water droplets.

Moisture is also naturally present in the air, and as temperatures drop, the air releases this moisture at what's known as the dew point. Condensation is most common during colder weather and tends to form on cold surfaces or in areas with limited airflow, such as behind furniture or inside cupboards. These conditions often lead to mould growth, particularly in corners of rooms, north-facing walls, or enclosed spaces where temperatures are lower and air movement is minimal.

Other types of damp

Mould growth is not always caused by condensation alone. Other types of damp can also contribute to the problem.

Rising damp can occur when the damp-proof course or membrane in a property’s walls or floors has been compromised. This is most common in ground floor flats and houses, often due to long-term deterioration of the damp-proof system.

Penetrating damp can result from rainwater entering through cracks in external brickwork or missing roof tiles. Blocked gutters can also cause water to overflow and soak external walls, while damaged external plumbing may allow water to seep into the building.

Unlike rising or penetrating damp, condensation can appear in various areas throughout a room. You may notice it affecting not just walls, but also furniture, soft furnishings, and even clothing.

Insufficient Insulation at Time of Construction

Properties built during certain periods often lack the higher insulation standards required in modern construction. As a result, these buildings are generally more prone to condensation issues than newer developments.
Problematic areas typically include hard-to-insulate sections such as spaces above or below balconies, undercrofts, and other architectural features. Proper insulation helps retain warmth, which in turn reduces the risk of condensation forming.

Cold Spots and Thermal Bridging
Construction elements like concrete beams naturally retain cold, and retrofitting them with sufficient insulation to meet current standards can be challenging. This often leads to cold spots or thermal bridging, where heat escapes and condensation can occur.
Additionally, during refurbishment projects, insulation is sometimes removed or inadequately replaced, increasing the likelihood of cold bridging and associated issues.

Poor Ventilation
Condensation can also be managed by ensuring adequate ventilation throughout the property. However, in tenanted homes, there is a common belief that ventilation leads to higher heating costs. This has resulted in more frequent condensation problems due to the blocking of trickle vents (small vents in window frames) or traditional wall vents, which are designed to maintain airflow in individual rooms.

How to Prevent Condensation in the Home

Condensation can generally be avoided by maintaining the right balance between heating and ventilation. Warm air holds more moisture, and without proper ventilation, this moisture can settle on cold surfaces and cause damp or mould. The key is to keep the property warm while allowing moist air to escape.

Minimising Moisture Production

• Cover pans when cooking to reduce steam.
• Dry clothes outside where possible. Avoid drying them on radiators.
• Wipe down condensation from windows and surfaces as soon as it appears.
• Keep trickle vents open (small vents in window frames), and open windows regularly, especially after cooking or showering, to allow moist air to escape.
• Use extractor fans in kitchens and bathrooms. To test if they’re working, hold a tissue up to the vent — it should stick.
• When running a bath, start with cold water before adding hot, to reduce steam.
• Close bathroom and kitchen doors when in use to prevent moisture spreading to other rooms.
• Place furniture such as wardrobes and drawers against internal walls where possible, allowing air to circulate behind them.

Heating Tips: Maintain a Consistent Temperature

• Set the heating thermostat to maintain a steady temperature rather than switching it on and off throughout the day.
• Use automatic heating schedules to ensure the home is heated for at least seven hours per day, even at a lower setting.
• Avoid manually adjusting the thermostat once set — allow the system to regulate itself.
• Ensure all radiators are turned on to prevent cold spots within the home.

Did You Know?

Typical daily moisture production in a home:

• Drying clothes indoors (without a vented dryer): up to 10 pints of moisture.
• Bathing: approximately 2 pints of moisture.
• Washing clothes: around 1 pint of moisture.

By following these simple practices, tenants can significantly reduce the risk of condensation, damp, and mould — creating a healthier and more comfortable living environment.

Tackling Mould in the Home

Mould can pose serious health risks and should be dealt with promptly and safely. Here’s how to remove it effectively and prevent it from returning:

Safe Removal of Mould

• Clean affected areas by wiping down walls, windows, and other surfaces with a fungicidal wash that carries a Health and Safety Executive (HSE) approval number.
• Always follow the manufacturer’s instructions carefully to ensure safe and effective use.
• Dry-clean clothing affected by mildew and shampoo carpets where mould is present.
• Take precautions when cleaning mould — disturbing spores can increase the risk of respiratory issues. Wear protective gloves and a mask if necessary.

Preventing Mould from Returning

• After cleaning, redecorate with a high-quality fungicidal paint, which helps to prevent future mould growth.
• Ensure external walls are properly insulated, as cold surfaces are more prone to condensation and mould development.

For Landlords: Long-Term Solutions

For more persistent or structural issues, consider the following more intrusive measures:

• Improve insulation:
  • External Wall Insulation (EWI)
  • Internal Wall Insulation (IWI)
  • Cavity wall insulation
  • Double glazing of windows
• Enhance ventilation:
  • Install extractor fans in kitchens and bathrooms
  • Ensure windows can be opened easily
  • Keep trickle vents open
  • Consider specialist solutions like Passyfier vents
• Upgrade heating systems:
  • Maintain constant temperature space heating to avoid cold spots and reduce condensation risk

By combining proper cleaning methods with long-term improvements to insulation, ventilation, and heating, both tenants and landlords can create a healthier, mould-free living environment.

To summarise…

What causes damp & mould?

• Everyday activities like cooking, showering, and drying clothes indoors
• Poor ventilation and lack of airflow
• Leaks from roofs, windows, or plumbing
• Cold surfaces causing condensation

• Open windows or use extractor fans
• Wipe down condensation on windows
• Avoid drying clothes indoors when possible
• Report leaks or persistent damp quickly