What are the Main Causes of Damp?

What are the Main Causes of Damp?

By Ruth MacEachern

Product Manager

Damp is a common but often misunderstood problem that affects homes throughout the UK. Beyond the unsightly patches it leaves on walls and ceilings, damp can lead to more serious issues such as mould growth, structural damage, and negative effects on health. For homeowners, understanding what causes damp and how to identify and prevent it from taking hold is crucial for maintaining a dry, healthy living environment.

The three types of damp

If you’ve noticed a damp patch forming on the walls or ceiling in your home, it is important to understand what type of damp it is so that you can take steps to resolve the problem.  There are three kinds of damp that you might encounter:

• Rising Damp
• Penetrating Damp
• Condensation Damp

Rising Damp

Rising damp occurs when moisture from the ground travels up through porous materials, such as bricks and mortar, by capillary action. This type of damp most commonly affects older buildings, especially those without an adequate damp-proof course (DPC) or where the DPC has become damaged over time.

How to Spot Rising Damp:

• Damp patches and staining low down on walls, usually less than a metre above ground level.
• Peeling or bubbling paint and wallpaper near skirting boards.
• Salty, powdery deposits on wall surfaces (these salts are brought up from the ground).

If you suspect rising damp, it’s recommended to seek professional advice, as treatment often involves repairing or installing a new damp-proof course.

Penetrating damp

Penetrating damp is caused by water entering the property from outside. This usually occurs because of defects in the building, such as cracked masonry, damaged roofs, blocked gutters, or leaking pipes. Unlike rising damp, penetrating damp can occur at any level of the building.

How to Identify Penetrating Damp:

• Damp patches that grow after heavy rainfall, often on ceilings or higher up on walls.
• Visible watermarks or mould growth, sometimes accompanied by a musty smell.
• Localised dampness, for example, near windows, doors, or chimney breasts.

Addressing penetrating damp typically requires fixing the underlying structural issues—repairing leaks, clearing gutters, or repointing brickwork.

Condensation Damp

Of the three types, condensation damp is by far the most widespread in homes across the UK. As our homes have become more insulated and airtight in the drive for energy efficiency, they can also trap more moisture inside, increasing the risk of condensation.

What is Condensation Damp?

Condensation occurs when warm, moist air interacts with cold surfaces, such as windows and external walls. The air cools rapidly and releases water vapour, which then collects as droplets on these surfaces. Over time, this moisture can soak into walls, create unsightly black mould, and even damage plasterwork and furniture.

How to Recognise Condensation Damp

• Water droplets on the inside of windows, especially in the morning.
• Black mould spots on walls, especially behind furniture or in corners.
• A musty odour in certain rooms, often bedrooms or bathrooms.
• Peeling wallpaper or blistering paint on external walls.

Condensation damp is more common in rooms subject to high humidity, such as kitchens and bathrooms, or in bedrooms where people breathe out moisture overnight.

Reducing humidity to prevent condensation damp

Addressing condensation is largely about managing moisture levels and improving ventilation. The most effective way to reduce humidity levels is by increasing the airflow in and out of your home through improved ventilation.

Natural ventilation such as leaving windows open can have a minor effect on humidity levels in your home, but in order to reduce condensation, mechanical ventilation is usually necessary and is specified in building regulations for rooms such as bathrooms and kitchens.

Bathrooms and kitchens are the main sources of humidity in most homes, so it is important to have effective extractor fans in these rooms helps to remove moisture-laden air directly at the source. While some extractor fans such as the EnviroVent Cyclone 8 feature an automatic humidity sensor that detects water in the air and adjusts power appropriately, other fans need to be manually turned on whenever you are doing something that creates steam such as boiling water or taking a shower. 

Condensation can form anywhere in your home, and if you have discovered patches of damp or black mould away from an obvious source of moisture, whole house ventilation may be more suitable. Positive Input Ventilation systems are an effective modern solution to persistent condensation. PIV units gently introduce filtered air into your home from outside (in the case of EnviroVent ATMOS, this is through a central unit mounted in the loft).  This incoming air displaces humid air, reducing condensation and mould. Over time, this helps create a healthier indoor climate and can also remove airborne allergens and pollutants.

Get help today

Damp patches can quickly become a real problem, affecting the fabric of your home and creating an environment where toxic moulds can grow.  Enter your postcode below to find a local ventilation specialist who can visit your home to identify the sources of condensation and damp and provide you with helpful advice and a free home survey.