Combat condensation

Condensation can be miserable and unhealthy for homeowners, and so prevention is key for any new build residential project. Martin Panes of Altaterra explores solutions, including roof windows.

Water vapour is always present in the air – as a gas. If warm air is humid, – containing moisture it is likely to condense on windows, and when window glazing is cold (as in autumn and winter months) it is even more likely.

Actions such as frequent boiling of water, cooking and showering, are major contributors to this air humidity. New builds sometimes experience early condensation issues – due to plastering or wet trades – but these tend to dry out during the first few years.

Most house owners will be aware if a room has a condensation problem; the atmosphere will feel damp, mildew can appear on the internal walls, and paint on exterior walls may also begin to bubble. If ignored, wood items in the room can begin to rot over time.

The importance of ventilation

Internal air humidity becomes too high when there is insufficient, or no, ventilation. The air condenses, allowing the moisture to collect on the walls, in corners and around doors, and in particular windows. Over time, mould and fungi can develop in these places.

Any family home could experience condensation. On average, four people in a typical home produce between 10 and 15 litres of water vapour a day. Therefore, housebuilders must plan good ventilation into their build to enable fresh air to circulate and used air to be expelled. This cooler, fresh air will contain more oxygen, allowing it to absorb moisture generated in the building. This will then be removed by the ventilation system to keep the room moisture-free.

Roof windows

A roof window will greatly reduce the risk of condensation in any room, but particularly in kitchens and bathrooms. For a condensation-free building, triple glazing is encouraged; three pane windows have a better U-value to reduce heat loss, and make it easier to keep the room warm.

An improved insulation level in the design – such as using argon or krypton gas between panes – will keep the room warmer and cut the risk of condensation. Correct installation and use of flashing is essential, as a poorly-installed window will lead to cold spots around the window, and a build-up of condensation or leakage around the frame. PVC frames are designed to offer greater resistance to mould than their timber counterparts.


Whether a room has a roof window or not, different ventilation approaches can help combat condensation. Air valves and ventilation systems allow air to be extracted into ducts, and can be adjusted according to the building’s specific ventilation requirements. It is worth noting that an extraction system in the kitchen or bathroom will make a noticeable difference. They can cost around £400 to install, but help to remove moisture-rich air created as a result of cooking or showering, and replace it with fresh air.

Window vents can be added above windows to allow air to move through the room and prevent moisture condensing on the window panes, and air bricks can be installed in rooms that are poorly ventilated.

In loft or attic conversions, as well as openable roof windows, roof ventilation tiles or soffits can be installed to encourage air movement through the room and voids. Attic conversions are often at a high risk of developing mould, because they can be hard to insulate and ventilate. In such projects, any incorrectly installed plasterboard should be addressed, and radiators relocated or additional heating added.

Everyday steps to beating condensation

Improving ventilation and reducing the level of humidity in the home are the routes to beat condensation. Owners should be encouraged to dry clothes outdoors, or use a vented tumble dryer wherever possible.

Opening windows for at least 10 minutes a day will allow warm moisture laden air to escape, and cool dry air to enter the room. When a room is under-heated, there will be excessive saturation of water vapour as the air can hold less moisture. The use of a thermostat will ensure the room and building are at a constant warm temperature.

Martin Panes is housebuilder manager at Altaterra