During winter, condensation on windows is a common occurrence, especially for windows which are single glazed.
Condensation is not just unsightly, but can cause damp, mould and mildew, all of which can contribute to respiratory ailments (asthma, bronchitis) and other health problems (eczema etc).
Pooling water around a window can promote paint decay and wood rot, potentially requiring costly repair as well as the daily inconvenience of having to mop up the excess water.
Consequently, homes become less comfortable and more time consuming to maintain.
This article discusses condensation, its causes, prevention and management.
What is Condensation?
Condensation is the process where water vapour (moisture held in the air) turns back into a liquid.
It happens when warm moist air cools down, forming a mist or water droplets on the window surface.
Why Do I Get Condensation On My Windows?
Condensation usually forms on cold surfaces. During winter, windows, especially if single glazed, are often the coldest surface in the house.
Causes Of Condensation
A root cause of condensation is high humidity – i.e. the amount of water vapour in the air.
The warmer the air, the more capacity it has to hold water.
This water vapour, when cooled through contact with a cold surface, forms condensation.
Sources of Humidity
Humidity (water vapour) build-up occurs through activities related to everyday living:
- Cooking
- Showering
- Drying Clothes
- Respiration & Transpiration
High humidity not only makes the air smell damp and musty but, also allows cooking smells to linger, penetrating clothes and soft furnishings.
Humidity levels are often greater in smaller, high occupancy dwellings and can be a significant (yet poorly understood) problem in the rental sector.
Measuring Humidity
Relative Humidity (RH) is the most common measure of humidity and indicates how close the air is to being saturated with water vapour at a given temperature. Relative humidity is expressed as a percentage, with 100% being fully saturated.
The ideal relative humidity is below 60% – humidity levels above 60% hold too much water, leading to poor indoor air quality and can promote mould growth (mould struggles to grow below 60% humidity).
The first step to improving household air quality is periodic monitoring of humidity levels – for this we recommend the excellent Govee Hygrometer.
How to Stop Condensation on Windows
Condensation can be managed through a combination of passive and active measures to reduce humidity and cold surfaces inside the home.
Measures To Reduce Humidity
- Opening windows and trickle vents allows moist air to escape the property. However, this can involve a significant loss of heat which, in the age of high energy prices, is often undesirable. Consequently, homes can remain poorly ventilated.
- Extractor fans in the bathroom and kitchen are effective in removing moist air although again, this does incur some heat loss.
- Use a dehumidifier this works by drawing moisture out of the air, which is collected into a tank for periodic emptying. Newer dehumidifiers now come with built-in humidity sensors and can be fitted for continuous drainage which, once setup, needs very little intervention.
(We do not recommend the use of desiccant dehumidifiers, as they tend to be less effective) - Avoid drying clothes indoors, especially on radiators.
- Wipe down wet surfaces and windows. A Karcher Window Vac is a good time saver.
Measures To Reduce Cold Surfaces
- Insulating windows (secondary glazing) can significantly reduce condensation formation, especially on single glazed windows. This is achieved as the interior glazing temperature is now much higher.
- Adequate heating is important to enable evaporation and keep surfaces warm (minimum of 16 degrees Celsius).
- Insulate walls, floors and ceilings to reduce cold surfaces which can allow the formation of condensation.
The one thing we absolutely recommend, regardless of property or window type, is the purchase of a good quality dehumidifier. These are highly effective and cheap to run. The Meaco Arete series of dehumidifiers are an excellent option.
Special Considerations – Rental Properties
For landlords and rental properties, it is highly recommended that dehumidifiers are set up for continuous drainage and left on an automated timer or humidity setting. By ensuring continuous operation (minimal intervention required), this will combat potential issues related to damp and mould, especially in high occupancy dwellings. Feel free to contact us for further advice.
How WindowSkins Can Reduce Condensation
WindowSkins works by creating an airtight seal against the window frame, thereby trapping an insulating layer of air and blocking draught, much like double glazing.
When fitted, the surface temperature of the WindowSkin is much warmer – above the dew point1 – thereby reducing the ability of condensation to form on the WindowSkin (the room side you can touch).
Additionally, by creating a barrier against the existing glass, moist air cannot freely enter and come into contact with the cold glass in between – thereby starving the cold surface of warm moist air.
Overall, we cite a 95% reduction2 in condensation, increasing to nearer 100% for opening windows.
1. Assumes an average humidity level of 60%
2. Equivalent to a light misting on very cold days
In practical terms, our guidance means better internal air quality, less dampness, near elimination of mould, fresher smelling clothes (and furnishings), as well as waking up to much clearer windows without the need to mop up each morning.
Additional benefits such as cold, draught and noise reduction are a welcome bonus – all whilst preserving the windows original character and avoiding potentially costly repairs related to water damage.