Window condensation. Photo by Designs in Detail.
If you’re waking up to misty windows and water droplets on your window sills, you're not alone. Window condensation is a common household nuisance that can lead to more serious problems if left unchecked.
This guide explains the root causes and how to combat the problem. By understanding the science behind condensation and implementing the guidance outlined here, you'll be well equipped to solve the problem once and for all.
Black mould growth on window frame caused by condensation.
Window condensation is a widespread issue in wet temperate climates during winter, such as in the UK, where cold outdoor temperatures and high humidity combine to create ideal conditions. If not addressed, it can damage windows and cause damp and mould problems.
Window condensation happens when warm, humid air comes into contact with a cooler surface, in this case a windowpane. As the air cools, it loses its ability to hold moisture and condenses into water droplets.
The temperature where water vapour turns into liquid is called the 'dew point'. When your window gets colder than the dew point, you get condensation. The dew point is influenced by two main factors: temperature and humidity.
Condensation is caused by the interplay between humidity and temperature. Relative Humidity (RH) measures how much moisture is in the air compared to how much it can hold. At 50% RH, the air is at half of its moisture capacity; at 100% RH, it is fully saturated and cannot hold any more moisture.
Warm air can hold more moisture than cold air. For instance, air at 21°C can hold about twice as much moisture as air at 10°C. Consequently, warm, humid air raises the dew point, meaning surfaces don't need to be as cold for condensation to occur. This principle is similar to what happens when you boil water in a pan – the hot steam will condense on even warm surfaces nearby, demonstrating how moisture in warm air can quickly turn to liquid when it encounters a cooler surface.
In terms of window condensation, consider a room with a temperature of 20°C and 60% RH. In this scenario, the dew point is around 12°C – high enough for condensation to occur on most surfaces, even energy-efficient glazing on a very cold day. To avoid the problem, we need to maintain a minimum room temperature of about 18°C and keep RH between 40-55%. At these levels, condensation will only form on surfaces below 7°C, which is much easier to manage.
Condensation cycle during a winter's day: 1. Intermittent heating and poor ventilation and insulation creates condensation during the evening; 2. Consistent, low-level heating and good ventilation and insulation regulates the indoor temperature, avoiding the conditions that create condensation.
To maintain ideal room temperature and RH levels which prevent window condensation from happening, we need to:
Below are some practical solutions for each of these areas.
Dehumidifiers are effective at reducing condensation, but it’s better to address the source of the problem rather than just managing it.
Insulating your home will help regulate indoor temperatures and prevent condensation. Image by Ciarcelluti Mathers Architecture.
Yes, by implementing the solutions outlined above, you can eliminate window condensation altogether. However, it's almost impossible to stop if you have single-glazed windows due to their poor insulation properties.
Using a home hygrometer to monitor indoor humidity and temperature will help you maintain the right conditions to avoid condensation.
Home hygrometer.
By following these guidelines, you'll be well on your way to having condensation-free windows. Remember, tackling condensation requires tackling ventilation, insulation, and heating simultaneously for the best results.
