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What is condensation?

All air contains varying amounts of water vapour. The warmer the air temperature, the greater the amount of water vapour the air can hold

Condensation occurs because the moisture in the warm air can no longer be held as vapour and returns it to its liquid form. This occurs when warm moist air comes into contact with either cooler air, or more importantly, a cooler surface.

The point at where condensation becomes obvious/visible as moisture is known as the dew point. The dew point describes the temperature when air containing a given quality of water vapour will condense onto a surface. This happens mostly when hot moist air meets a COLD surface.

Where does condensation occur?

Examples of condensation in a property on impermeable surfaces

Common examples of the occurrence of condensation in properties include:

  • External windows particularly those that are single glazed or windows with no ventilation or wooden frames
  • External walls with poor insulation (creating cold walls)
  • Accommodation with inadequate heating
  • Rooms with lots of moisture - areas such as bathrooms and kitchens
  • Hard furniture such as wardrobes, tables, chest of drawers

Whilst condensation might be most obvious on these surfaces as they are impermeable, condensation will also form on permeable surfaces which absorb moister.

Condensation on impermeable surface

Condensation on impermeable surface

Examples of condensation in a property on permeable surfaces

Permeable surfaces that are affected by condensation include:

  • Wallpaper
  • Plasterboard such as ceilings
  • Fabrics - clothes, curtains, bed linen

It only normally becomes obvious of condensation on permeable surfaces with the growth of mould.

Examples of condensation in a property on permeable surfaces

Examples of condensation in a property on permeable surfaces

Mould growth caused by condensation

Mould growth is a typical sign of chronic condensation and occurs as spores, present in the air all the time. Mould is a significant health risk to asthmatics, those with other respiratory conditions, skin conditions and other allergies, and the vulnerable (those that are very young, old or with chronic health issues).

The humidity levels associated with condensation also enable house dust mites to flourish. The droppings from these microscopic creatures and mould spores can cause allergic reactions which are also linked to the onset of asthma.

Where does condensation come from?

Obviously, it’s important to understand where the source of moisture is coming from, once you know this it is possible to minimise the level of condensation and subsequently the amount of mould.

Water vapour in the air is generated by a range of human-related activities. A typical daily moisture level produced in a three bedroomed family house is approximately 10 litres of water. A large quantity of moisture can come from a range of sources which include:

  • A family asleep - 1.5 - 2 kg
  • A families typical daytime activities - 2.5 - 3.5kg
  • Cooking - 2.0 - 3.0kg
  • Washing and bathing - 1.0 - 1.5kg
  • Washing clothes - 0.4 - 0.6kg
  • Drying clothes - 3.0 - 5.0kg

Heating appliances can also produce significant quantities of moisture. In the case of solid and gas fired heat source, most of this moisture is removed via flues. However, some appliances, such as portable gas bottle heaters, produce large quantities of moister which are not removed from the living space, while electrical radiant fires produce no moisture at all.

In addition to these sources of moisture from humans, any incidents of rising damp or damp penetration will contribute further to the quantity of moister in the house.

Condensation does not always occur where the source of moisture is created. For example, though substantial amounts of moisture vapour can be created in kitchens, the additional heat produced in this space will rise the surface temperature of the structure and elements, this reducing the likelihood of condensation occurring directly.

In poorly insulated houses where the surface temperature of the structure external walls, ground floors and upper storey ceilings are low, then condensation can occur at any or all these points.

The restriction of airflow can cause condensation as the level of moisture in the area increases and has no way of escaping. Areas where there is restricted air circulation behind cupboards and wardrobes are also more likely to suffer condensation.



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