What Causes Condensation

What Causes Condensation in Homes?

Condensation is one of the most common forms of damp found in UK homes, yet it’s also one of the most misunderstood. Many homeowners first notice it as water droplets on windows or black mould forming in corners, bathrooms, or behind furniture. Understanding what causes condensation is the first step towards preventing it and protecting your property and health.

What Is Condensation?

Condensation occurs when warm, moisture-laden air comes into contact with a colder surface, such as windows, external walls, or uninsulated ceilings. The air cools rapidly, releasing excess moisture as water droplets.

Unlike rising damp or penetrating damp, condensation is driven primarily by internal humidity and temperature differences, not water entering the building fabric from outside.

The Main Causes of Condensation

1. Everyday Household Activities

Normal daily activities generate a surprising amount of moisture, including:

• Cooking and boiling kettles

• Showering and bathing

• Drying clothes indoors

• Breathing and perspiration

• Using tumble dryers without proper ventilation

In a typical household, these activities can produce several litres of water vapour every day.

2. Poor Ventilation

Ventilation allows moist air to escape and be replaced with drier external air. Condensation is far more likely when:

• Extractor fans are missing or ineffective

• Air bricks are blocked

• Trickle vents on windows are closed

• Bathrooms and kitchens lack proper airflow

Without adequate ventilation, moisture becomes trapped indoors and settles on the coldest surfaces.

3. Cold Internal Surfaces

Condensation forms most readily on cold surfaces, such as:

• Single-glazed or poorly insulated windows

• External walls with little or no insulation

• Cold corners, particularly in north-facing rooms

• Areas behind wardrobes, sofas, or cupboards

These cold spots encourage warm air to cool quickly, triggering moisture release.

4. Inconsistent or Inadequate Heating

Homes that are heated irregularly or only in short bursts often suffer from condensation. This is because:

• Cold walls remain below dew point temperature

• Warm air holds more moisture, which condenses rapidly when heating is turned off

• Bedrooms and spare rooms are often left unheated

Maintaining a consistent, low-level background heat can significantly reduce condensation risk.

5. Modern Airtight Homes

While modern homes are more energy-efficient, they are also more airtight, which can unintentionally trap moisture. Improvements such as:

• Double or triple glazing

• Draught-proofing

• Sealed floors and walls

must be balanced with suitable ventilation systems to prevent excess humidity buildup.

Signs Condensation Is the Problem

Condensation-related damp often shows itself as:

• Water droplets on windows, especially in the morning

• Black mould on walls, ceilings, or window frames

• Peeling wallpaper or blistering paint

• Musty smells in bedrooms or bathrooms

These symptoms are usually worse in winter, when temperature differences between indoors and outdoors are greatest.

Why Condensation Shouldn’t Be Ignored

Left untreated, condensation can lead to:

• Persistent mould growth (a health risk, especially for asthma sufferers)

• Damage to plaster, decorations, and furnishings

• Rotting window frames and skirting boards

• Reduced indoor air quality

While condensation is often seen as a “minor” damp issue, long-term exposure can cause significant problems.

How to Reduce Condensation

Although every property is different, common solutions include:

• Improving ventilation (extractor fans, air vents, or positive input ventilation systems)

• Maintaining steady heating levels

• Insulating cold surfaces

• Reducing internal moisture where possible

In some cases, professional assessment is recommended to ensure the issue isn’t being confused with another form of damp.

Need Expert Advice on Condensation?

If you’re experiencing persistent condensation or mould and want a clear diagnosis, a professional damp survey can identify the cause and recommend the most effective long-term solution.

Understanding what causes condensation is key to preventing it — and to keeping your home dry, healthy, and comfortable year-round.