The approach of cold and wet weather during winter in the UK is a leading cause of condensation and dampness, which if left untreated, can lead to mould. Damp and mould can rot timber frames and furniture and can spread across curtains and upholstery.

It’s an urban myth that installing new double glazing will eliminate condensation problems in the home. Unless a few rules are followed condensation and associated mould growth can still become a serious problem.

What is condensation?

There is always some moisture in the air, even if you cannot see it. If the air gets colder it cannot hold all the moisture and tiny drops of water appear. This is condensation.

Condensation occurs mainly during cold weather, whether it is raining or dry. It appears in places where there is little movement of air so tends to occur in corners, on or near windows, in or behind wardrobes and cupboards and it is more likely on north-facing walls.

What do we need to consider?

When undertaking home improvements, it is important to consider the likelihood of condensation and ventilation needs when initial surveys are being done and ensure adequate ventilation is specified.

With the increased trend for installation of additional loft and cavity wall insulation and new windows and doors our properties are becoming more airtight and circulation of air that would have occurred naturally is being restricted. In many cases, additional mechanical ventilation is required.

Will the inclusion of trickle vents provide an adequate solution?

If the property has no mechanical extraction in the kitchen and bathroom then trickle vents (small openings in a window) alone might not be enough. Additional mechanical ventilation is likely to be required.

What other things do we need to consider?

It is also important to consider the ventilation needs of any heating system, be it gas, oil or solid fuel. Reduced airflow can cause problems with how combustion appliances work and may lead to a build up of carbon monoxide in the property.

Handover documentation

Ongoing advice to occupiers should be provided to help them manage any condensation issues that they may experience. This advice should include the following four simple steps:

1.  Produce less moisture

Some ordinary daily activities produce a lot of moisture very quickly so:

• When cooking reduce the amount of moisture, by covering pans and do not leave kettles boiling.
• Paraffin and portable flue-less bottled-gas heaters put a lot of moisture into the air – one gallon of gas or paraffin produces about a gallon of water. If there is a problem with condensation, try to find alternative means of heating.
• When having showers or baths close the bathroom door and ensure any extractor fan is on or open the window slightly to allow damp air to escape.
• Dry clothes outdoors whenever possible. If drying indoors put it in a room with the door closed and the window open. If using a tumble dryer make sure it is vented to the outside (unless it is the self-condensing type).

2.   Ventilate to remove the moisture

It is possible to ventilate a property without making draughts. Some ventilation is needed to get rid of moisture that is being produced all the time.

• Keep a small window ajar or trickle vents open all the time if possible, especially when someone is in the room.
• Much more ventilation is needed in the kitchen and bathroom so opening the windows will help. Better still have an extractor fan installed that vents to the outside.
• Close the kitchen and bathroom doors when these rooms are in use even if an extractor fan is fitted.
• Allow space for the air to circulate in and around furniture. Leave space between the backs of wardrobes and the wall. Where possible, position wardrobes and furniture against internal walls, rather than against outside walls.
• Curtains or blinds make the surface of the window cooler and increase condensation. Open trickle vents to help reduce the problem.
• Dehumidifiers will help dry out dampness in newly built houses and can also help reduce condensation but they are of limited use in cold damp rooms.

3.  Insulate and draught proof

Insulation in the loft, cavity wall insulation and draught proofing of windows and outside doors will help keep the property warm and can lower fuel bills and when the whole home is warmer condensation is less likely. When putting in draught proofing:

• Do not block permanent
• Do not completely block chimneys (leave a hole about two bricks in size and fit a louvered grille over it).
• Do not draught-proof rooms where there is a fuel-burning heater (e.g. gas fire) or
• Do not draught-proof windows in the bathroom or

4.  Heat your home a little more

In cold weather, the best way to keep rooms warm enough to avoid condensation is to keep low background heating on all day, even when there is no one at home. This is particularly important in flats and bungalows and other dwellings where the bedrooms are not above a warm living room.

Central heating should be set to provide background warmth in all rooms, including unused rooms.

Alternatively, the use of suitable thermostatically-controlled heating (do not use paraffin or flue-less bottled gas heaters for this purpose) will help control heating and costs.

Remember to provide background ventilation at the same time.

Further Information

Further information on the requirements for ventilation and air supply is detailed in Approved Document F – Ventilation and Approved Document J – Combustion Appliances and Fuel Storage Systems of the Building Regulations.