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How to Avoid Condensation on Windows

Example of Condensation on Windows

Main reasons for condensation appearing on windows

Condensation is formed when excess moisture in the air accumulates on cold surfaces, such as windows. The atmosphere contains numerous tiny water droplets that are invisible to the naked eye. When the humidity level rises, the number of water particles increases, leading to the formation of condensation on surfaces.

Just like with a glass of a cold drink that on a hot summer’s day might appear to be sweating. This is caused by the moisture still present in the warm air condensing on the cold surface of the glass. When the temperature drops, the tiny droplets of water present in the air get closer together, and merge, becoming bigger -- and visible. This phenomenon is called the ‘dew point’: a morning dew works exactly the same. 

Drops of water can be observed forming on a surface at the dew point. This phenomenon commonly occurs in various everyday situations such as condensation on a mirror after taking a shower, a steamed-up kitchen window when cooking, or moisture on windows when drying clothes indoors. Not only does condensation form on windows, but it can also form on any cold surface, particularly in areas where moisture can get trapped, such as windows with blinds or curtains, behind large furniture against a cold wall, or inside a fitted wardrobe on an external wall. 

Remember that windows should never have condensation between the panes. This indicates the seals are damaged and the window is not performing as designed. 

The accumulation of stagnant water can have a detrimental impact on any surface, regardless of whether it is waterproof or not. This is due to the potential development of limescale buildup and mould growth. While uPVC windows are intended to be resilient to water, excessive exposure to wet seals in combination with direct sunlight can result in the material drying and cracking due to constant expansion and contraction. Wooden frames are particularly susceptible to damage caused by sitting water. The continuous exposure to moisture can cause the paint or varnish to blister, fade and peel away, and any trim to become parched and cracked.

Mould is the biggest serious risk 

The primary concern that arises from the accumulation of stagnant water and moisture is the formation of fungal moulds. If not attended to, mould can inflict damage to both uPVC and wood surfaces and can cause them to lose their original colour. The most critical issue with condensation is that it can contribute to the growth of black mould.

Not only does black mould look unsightly when found in patches around windows, doors, and walls, but it can also pose significant health risks. The typical symptoms associated with black mould include a stuffy nose, wheezing, eye symptoms, rashes and itching, so similar to hay fever. Moreover, mould can contribute to the development of various serious medical conditions, such as asthma, allergic rhinitis, hypersensitivity pneumonitis, allergic alveolitis, chronic rhinosinusitis, and allergic fungal sinusitis. In some cases, severe black mould can cause acute idiopathic pulmonary haemorrhage, leading to memory loss and lethargy in infants.

Without question, mould is problematic and requires prompt attention. Any visible mould must be cleaned and removed, followed by preventive measures to eliminate condensation.

Measures to prevent condensation from forming on windows

Inadequate ventilation is the primary culprit behind condensation, and the solution is to enhance the airflow to balance the indoor and outdoor humidity levels. In the past, houses had poorly fitted windows and other opening and those gaps allowed air to circulate freely. However, with increasing emphasis on energy efficiency over the past few decades, many homes have become tightly sealed structures that trap moisture inside, resulting in poor air circulation.
To permanently eliminate condensation on windows, it is necessary to:

1) Enhance ventilation
2) Decrease moisture
3) Install double or triple glazed windows.

How to improve ventilation?

Several measures can be used to improve airflow.

1) Airflow system: New apartments are equipped with internal airflow systems that use ducts to extract and circulate air from inside to outside. Retrofitting these systems in older homes is costly and invasive.
2) Extractor fan: Having sufficient extraction in bathrooms and kitchens is crucial to eliminate excessive humidity. Some fans have humidity control that allows automatic operation when the humidity level surpasses a set level.
3) Air vents/bricks: Air bricks provide ventilation but decrease energy efficiency, while air vents in windows help to prevent condensation and can be mounted on most windows.
4) PIV Unit: Positive Input Ventilation (PIV) units can be installed in areas that generate excessive moisture, such as kitchens and damp basements. The PIV unit extracts humid air and draws in dry air from outside to maintain humidity balance.
5) Opening windows: Fresh air circulation through a space is essential to reduce moisture in the house. Traditional windows provided effective ventilation and can be left open for ventilation purposes. Modern windows have multi-point lock settings for secure ventilation. To correctly air rooms, it is recommended to open windows and doors to allow fresh air circulation and prevent stale air and odours. Traditional windows such as sash and bay windows are designed to provide effective ventilation. Newer windows have lock settings for secure ventilation. See the last section of this blog for tips on effective airing of rooms.

How to reduce moisture present in the air?

In addition to ventilation, it's crucial to reduce moisture in order to prevent condensation. Normal living activities produce a significant amount of water vapor in the home. For example, cooking can produce up to 3 liters of water vapour per day, while washing clothes can produce 0.5 liters per wash, and showers or baths can produce 1.5 liters per person. Dishwashing can also produce up to 1 liter of water vapor per day, while un-vented clothes drying can produce as much as 5 liters per load. Even breathing can contribute to humidity, with an active adult producing 0.2 liters of water vapor per hour. Houseplants and pets can also add to the humidity in the air and contribute to condensation. To minimize the impact of these factors on indoor humidity, it's important to address the following areas:

1) Cooking with boiling pans and kettles: cover pans, don't boil too hard and use extractor fans and open windows in the kitchen.
2) Taking showers and using hot taps: make sure the extractor fan is working and open the window during or after the shower/bath.
3) Using washing machines and tumble dryers: make sure the laundry areas are well ventilated, use low temperature washes and always vent tumble dryers outside.
4) Drying clothes on radiators or indoor airers: avoid doing this and if you need to, open windows and ideally use a dehumidifier in clothes drying spaces.
5) Keeping large houseplants indoors: place such plants in well ventilated areas, especially if they have rich foliage.
6) Storing wet logs for wood burners indoors: store logs away from living areas, and bring in as needed; don't use wet logs in wood burning stoves and fireplaces as they produce more smoke and less heat in addition to extra moisture.
7) Checking for unfound water leaks in cavities or under floors: this will benefit your home in any case, and help keep it in good structural condition.
8) Addressing rising damp in basements and ground-level buildings: just as checking for leaks, dealing with rising damp has more benefits than simply reducing condensation.

Double glazed windows to prevent condensation

Condensation on single glazed windows is a common issue because the glass is prone to cold and it causes the dew point in the air to increase. Double glazed windows can help reduce condensation as the air gap between the two panes of glass helps to keep the interior glass surface closer to room temperature. This temperature difference is sufficient to prevent water vapour from reaching the dew point and forming condensation on the glass. However, it's important to note that double glazing cannot entirely eliminate condensation. To completely get rid of condensation, it is necessary to adopt a combined approach of windows, ventilation and reduced moisture.

How to air rooms properly?

Regular airing reduces the risk of excessive indoor humidity and gets rid of harmful bacteria and viruses. Proper airing is important in the summer as well as in the winter period. Correct way to air your home depends mainly on the season and the prevailing temperatures.

Although we heat our rooms in the winter, we must not forget regular airing of the rooms. Before airing, turn off the heating and wait a few minutes. After this time, open the windows - during the cold months, close them after about 5 minutes. In the winter, the best thing to do is to keep airings short and intense. Let fresh air into the house twice a day - in the morning and in the evening. In addition, it is better to air individual rooms separately to avoid draughts.

In the summer, the situation is somewhat different: airing at inappropriate times can lead to excessive heating instead of cooling. For this reason, it is advisable to open the windows early in the morning or late in the evening. At such times, it is a good idea to create a draught to speed up the air exchange and make the rooms more comfortable.

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