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Condensation is water that has been released from the air. Air contains water vapour in varying quantities, how much it can hold depends on its temperature. Warm air holds more moisture than cold air. When moist air comes into contact with either colder air or a colder surface, the air is unable to retain the same amount of moisture and the water is released to form condensation in the air or on the surface.

Condensation is water that has been released from the air. Air contains water vapour in varying quantities, how much it can hold depends on its temperature. Warm air holds more moisture than cold air. When moist air comes into contact with either colder air or a colder surface, the air is unable to retain the same amount of moisture and the water is released to form condensation in the air or on the surface.

If this happens outside, near the ground, dew or frost will be formed. If a larger amount of air is involved, mist or fog will arise. If this happens to air that is rising in the atmosphere and expanding, clouds will form.

If it happens in the home, it’s called condensation.

Condensation is generally noticeable where it forms on non-absorbent surfaces, such as windows, mirrors or tiles, but it can form on any surface and it may not be noticed until mould growth or rotting of material occurs. The following sections explain further and give ideas on how to minimise it.

There is now a short Video in the Additional Resources section, ‘Controlling Condensation and Mould Growth’ (7mins)

Condensation is an underestimated cause of damage to our homes. It can significantly contribute to spoiled paintwork, wallpaper and flaking plasterwork. The condensed moisture can also react with the plaster ‘skim’ coat and cause ‘salting’.

Black mould growth is the most common effect of condensation, but mould can appear in other colours on carpets, clothing and wood. Sensitive people such as asthmatics, can be adversely affected by the airborne spores, meaning condensation can have an effect on health.

Condensation is an underestimated cause of damage to our homes. It can significantly contribute to spoiled paintwork, wallpaper and flaking plasterwork. The condensed moisture can also react with the plaster ‘skim’ coat and cause ‘salting’.

Black mould growth is the most common effect of condensation, but mould can appear in other colours on carpets, clothing and wood. Sensitive people such as asthmatics, can be adversely affected by the airborne spores, meaning condensation can have an effect on health.

This picture shows the effects of condensation in the corner of a room. The black mould concentrates on the coldest part of the wall – an outside corner.

The moisture in the air comes from a number of sources within the house.

1. Water vapour is produced in relatively large quantities from normal day to day activities – a 5 person household puts about 10 kg of water into the air every day (1 kg of water equates to about 1 litre)

The moisture in the air comes from a number of sources within the house.

1. Water vapour is produced in relatively large quantities from normal day to day activities – a 5 person household puts about 10 kg of water into the air every day (1 kg of water equates to about 1 litre)

• breathing (asleep) 0.3 kg
• breathing (awake) 0.85 kg
• cooking 3 kg
• personal washing 1.0 kg
• washing and drying clothes 5.5 kg

2. Heating – especially paraffin and flueless gas heaters. For every litre of paraffin burnt, over one litre of moisture vaporises into air. Every carbon fuel produces some amount of water from combustion.

3. Moisture can also be drawn from the structure of the building into the internal air, from below the floor or through the walls/ceilings.

4. Problems with the structure of the building can mean that its moisture content is unnecessarily high. This can either be due to the method of original construction or as a result of structure failures.

• Older houses may not have a damp proof course, (DPC), which prevent soil moisture from rising up into the living areas, lack of a DPC can occur in walls or under solid floors.
• Buildings may also lack or have insufficient air bricks to allow adequate underfloor ventilation.
• Structure failures can range from bridged DPC’s (either externally or within the cavity of the wall) to damaged roofing or gutters/down pipes.
• The wall cavity can be bridged by a build up of debris. Where the dampness is restricted to one area and no other reason can be identified, it is a relatively easy task to check/clean inside the cavity by removal of a brick at each corner and racking the cavity clean.

The effect of moisture generation is made worse by keeping the moist air in the house – it is theoretically possible to avoid condensation by adequate ventilation. Usually in certain areas of a house (such as bathrooms and kitchens) the warm air contains a lot of moisture, if that air then spreads to cooler parts of the house, it will condense on any colder surface.

The effect of moisture generation is made worse by keeping the moist air in the house – it is theoretically possible to avoid condensation by adequate ventilation. Usually in certain areas of a house (such as bathrooms and kitchens) the warm air contains a lot of moisture, if that air then spreads to cooler parts of the house, it will condense on any colder surface.

• Up until the middle/late part of the twentieth century, most houses had high natural ventilation as the level of home insulation was low. Natural ventilation was greatly reduced by the introduction of double glazing, draught excluders, fitted carpets (which prevent air movement up through suspended wooden floors) and the removal of open fire places with the introduction of central heating.
• Houses have become more effectively sealed, keeping any moisture produced within the house and providing better conditions for condensation to occur. Ventilation is only effective if consistent throughout the whole envelope of the house. Condensation is encouraged by poor air circulation where stagnant air pockets form (behind furniture and in cupboards) and the first evidence is often the appearance of mould growth.

Modern life styles mean that many houses remain unoccupied and unheated throughout the greater part of the day, allowing the fabric of the building to cool down. The moisture producing activities are then concentrated into a relatively short periods (morning and evening) when the structure is relatively cold while the building is still warming up.

A combination of heating and ventilation is the main form of control. A change of air is recommended in all rooms in the house, at the very least, once a day. Firstly, however, you should ensure that the amount of moisture in the air is not excessive.

Look at the life style of the occupants within the building:

Look at the life style of the occupants within the building:

• After a bath or shower, try to ventilate the room to the outside, not to the rest of the house – just opening a window (and closing the door) will help.
• Dry clothes out of doors or in a cool area of the premises – this latter suggestion may sound strange, it will take longer but less moisture will be held in the air at any one time.
• While drying clothes indoors, ventilate the room.
• When people come in with wet coats, hang them outside the living area to dry. A good reason for a porch.
• Try to increase the change of air in the premises – increase ventilation. Add forced ventilation/extraction to areas which produce a lot of moisture (kitchen, bathroom).
• Consider using a dehumidifier – domestic types are now available and can remove a surprising amount of water from the air.
• Keep furniture a little further away from the walls so the air has a free flow around the room.
• Do not fill cupboards to bursting point, again, allow the air to flow.

Check the structure of the building:

• no rising damp
• suitable damp proof course, not bridged or damaged
• cavities clear of debris
• all airbricks are clear, consider fitting additional airbricks to ventilate under suspended floors (modern practice is to fit a duct across the cavity so that the cavity itself is not vented).
• roof, guttering and downpipes all sound and unblocked
• no damp coming up through solid floors
• no leaking water pipes or tanks within the house

Check the structure of the building:

• no rising damp
• suitable damp proof course, not bridged or damaged
• cavities clear of debris
• all airbricks are clear, consider fitting additional airbricks to ventilate under suspended floors (modern practice is to fit a duct across the cavity so that the cavity itself is not vented).
• roof, guttering and downpipes all sound and unblocked
• no damp coming up through solid floors
• no leaking water pipes or tanks within the house

• Consider changing the heating fuel, electric is the driest, paraffin probably the wettest.
• Get the heating thermostatically controlled wherever possible.
• Install extractor fans in the kitchen and bathroom. They are available with humidistat control.
• Ventilate tumble driers externally.
• Install trickle vents in windows. The vents come in two halves for inside and outside of the window. Several holes are drilled through the top of the widow head to allow air passage into and out of the room.
  
  • Consider changing the heating fuel, electric is the driest, paraffin probably the wettest.
  • Get the heating thermostatically controlled wherever possible.
  • Install extractor fans in the kitchen and bathroom. They are available with humidistat control.
  • Ventilate tumble driers externally.
  • Install trickle vents in windows. The vents come in two halves for inside and outside of the window. Several holes are drilled through the top of the widow head to allow air passage into and out of the room. Flaps are fitted so the vents can be closed and insect grills keep out the creepy crawlies.
  • Install cavity wall insulation, if permissible through building regulations in your home.
  • Make sure the insulation in the loft is not blocking the ventilation provided by the gap between the facia boards and the house wall, or any purpose made vents.
  • Ceilings under the roof should not suffer too much from condensation providing adequate roof insulation is fitted. If there is no or little roof insulation, additional insulation should be installed. Additional insulation will not only reduce condensation, but also reduce energy loss and so save money.

If condensation persists after you have sorted out the basic structure of the building and the occupants life style, there are still some other changes to try.

If condensation persists after you have sorted out the basic structure of the building and the occupants life style, there are still some other changes to try.

• In Britain, condensation will almost always occur with single glazed windows. The inside surfaces of these windows can be almost the same as the outside temperature, overnight in winter their temperature can drop below freezing; often the inside window sill will be awash first thing in the morning. Try simple secondary glazing, or new double glazing. Although secondary or double-glazing is unlikely to eliminate all condensation, they should reduce it to an acceptable amount.
• Some decorative materials always have cold surfaces, (i.e. ceramic tiles, mirrors etc.) and are well known for the formation of condensation. There is not much you can do where this occurs other than keeping the room (and so the tiles) evenly heated throughout the day or improve ventilation.
• Where the wall is papered the situation may be made worse if there are many layers of paper, (this can acts like blotting paper) so strip off all the layers and re-paper the wall. Anti mould paste is available.
• Painted walls can also have a cold surface. Some products contain anti-mould additives that can help.
• Solid floors (i.e. a slab of concrete) are often cold because of their large thermal mass (they take a long time to warm up). Even vinyl floor tiles tend to be cold, however there are a number of ‘warm’ flooring available such as cork or cushion tiles. Thin wood flooring can be fitted on most existing solid floors.
• Salt Neutralisers can be found to eliminate salt in walls before redecoration.
• Apply Anti-Mould Cleaner to kill the spores before attempting any redecoration: decorating over the top of mould will not work – the mould simply re-grows through the paint or paper.