As the temperature outside drops, how to stop condensation from affecting your windows becomes a much bigger priority.
But just what is condensation? Basically, air contains moisture, but the temperature of the air determines how much moisture it can hold, and warm air contains more moisture than cold air.
When warm, moist air comes into contact with either a surface or air that is colder than it is, the warm air is unable to retain the same amount of moisture as it did and the water is released either into the cold air or onto the colder surface, causing condensation to form, quickly followed by mould.
What are the Main Causes of Condensation in the Home?
Day-to-day activities such as cooking, washing and drying clothes, heating and even breathing produce water vapour. Air can only hold so much moisture in the form of an invisible vapour, no matter what temperature it is.
When the air contains more moisture than it can hold, it reaches ‘saturation point’ and when this is reached, the moisture turns back into water and condensation occurs. The temperature reached at saturation point is called the ‘dew point’.
When this happens, the air has a relative humidity of 100%. The air in the majority of homes tends to have 50-70% relative humidity. Problems occur when structural defects in a building mean the moisture content has become too high; when old houses have no damp-proof course (DPC) and when there is inadequate ventilation in the home.
Period homes often have no damp proof course, which means moisture from the soil beneath the house rises up into ground floor rooms, whilst other homes suffer from bridged DPCs or damaged guttering.
What Problems can Condensation Cause?
The issues that condensation can cause are often the sign that it needs addressing in your home, and their effects can vary depending on the fabric of your home.
Problems caused by condensation include:
- Timber window frames decaying
- Water droplets on windows, obscuring the glass
- Damp walls where paint and wallpaper may peel
- Black mould on walls, window sills, soft furnishings and more
- Risk of rotting and structural decay
- Potential health issues, especially to the young, elderly and those who suffer from respiratory issues
How do you Stop Condensation?
There are three basic ways to control the problem of condensation:
Control the relative humidity in your home through the use of extractor fans in kitchens and bathrooms. Shutting the doors to these rooms whilst the extractor fans work also helps.
Ensure there is adequate ventilation. Trickle vents in windows work well, but a more sophisticated option is a mechanical extract ventilation unit (MEV) or MVHR system. These replace the air in your home by taking the stale, damp air outside, then bring fresh air back in via a separate grille, passing it back over the heat exchanger to be warmed. It is also possible to buy central extract systems which connect all of the wet areas in your home to a central fan before discharging the stale, moist air outside.
Another ventilation option is a positive input ventilation (PIV) system that works by gently supplying fresh, filtered air into the property from a unit installed in the loft area and a distribution diffuser mounted in the ceiling. The continual supply and slight positive pressure results in the air being continually diluted, displaced and replaced to create a healthier indoor air quality.
Adding insulation so that internal walls are kept at a temperature above the dew point of the air inside is another way to prevent condensation on walls. Internal wall insulation is best when it is not an option to external insulation to your property. However, wall insulation is also linked to increasing issues with condensation in other areas. Where it may raise the temperature of the wall where the insulation is fitted, areas that remain cold, such as where the internal meets the external wall can be more susceptible to condensation.
How Can I Reduce the Effects of Condensation?
There are also behavioural changes you can make that reduce the effects of condensation without making significant changes to your home.
- Using the cooker hood for ventilation when cooking in the kitchen
- Using lids for pans
- Limit significant temperature changes caused by turning your heating on and off - try to keep a consistent temperature
- Dry clothes in well ventilated spaces (outside if possible)
- Don't hang wet clothes on radiators to dry
- Ensure extractor fans are on when using a bathroom or open a window
- Leave a gap between furniture and walls to allow air to circulate from the base of walls
Will a Dehumidifier Stop Condensation?
Dehumidifiers can be effective in reducing condensation; however, it's worth understanding how they work to get the most out of them. Dehumidifiers draw air across a cold surface (as an air conditioning unit does) which causes moisture to condense out of the air, which is then returned to the room.
The water that is condensed out is caught in a container and in some of the cheaper dehumidifiers that container is not sealed. This then allows the water to be warmed back to room temperature, when it can evaporate back into the house, making the whole process pointless. Ideally the condensate is ducted to the outside world, if not then caught in a properly sealed container, which has to be regularly emptied.
Natasha is Homebuilding & Renovating’s Associate Editor and has been a member of the team for over two decades. An experienced journalist and renovation expert, she has written for a number of homes titles. She has renovated a terrace and is at the end of the DIY renovation and extension of her Edwardian cottage. She is now looking for her next project.
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