Window condensation: Causes and cures explained

window condensation on glass with a unhappy smiley face drawn into it
Window condensation can be caused by poor ventilation (Image credit: Getty)

Window condensation can become a problem when temperatures outside drop — and it doesn't only affect older homes with single glazing. Water collecting on your frames can be unsightly but it can also cause damage over time.

Condensation can happen anywhere in a property but is often noticed on window glass with a "steamed up" appearance. It is most often caused by poor levels of household insulation as well as inadequate ventilation. Thankfully, for those looking to find out how to solve condensation, there are simple steps you can take to ensure  window condensation doesn't become a longer-term problem for you.

Here, we explain the causes so you can look to address them and prevent condensation forming on your windows. We also take a look at how to deal with and control a current condensation problem. 

What causes window condensation?

Window condensation is caused by water vapour in the air coming into contact with the cold, impermeable surface of the glass. When there is excess moisture in the air, on meeting a colder surface, the air will release water droplets on the window.

There are several factors that will make a window condensation problem worse, including: 

Thankfully, if you are wondering how to stop condensation, there is plenty you can do. These steps will also help rectify an existing problem.

What causes window condensation between double glazing?

Condensation in double glazing units is a common issue for many people. There are several reasons why it happens, but one of the main causes of condensation between double glazing is down to the seal that runs around the two panes of glass that make up the unit, deteriorating. When this happens, moisture is allowed to get into the air gap between the panes. 

Another cause of condensation in double glazed units is down to a faulty spacer bar. Many double glazed units now have a spacer bar between the two panes of glass. This spacer contains an absorbent material designed to deal with any moisture within the air gap. 

However, should the seal allow excess moisture or water into the unit, this spacer will become saturated and unable to suck up excess moisture — leading to condensation between units. 

Drips of water at the bottom of a plastic window frame with double glazed glass

Droplets of water can not only be a nuisance to clean up but can cause damage to the window over time (Image credit: Getty)

How does condensation damage windows? 

Window condensation is not just annoying, it can also cause serious damage to both your home (requiring window replacement in left unchecked for years), and your health. 

When it comes to property damage, window condensation could result in the following:

  • Window frame damage: If water is left to pool on wooden window frames, it will eventually lead to rot — which could be expensive to treat. 
  • Peeling paint: Window condensation can cause painted window frames to peel meaning they will need to be refinished. 
  • Damp: If a condensation problem is not dealt with, damp patches will also begin to form on walls and around the window — in fact condensation is one of the most common causes of damp
  • Mould: Untreated damp will eventually cause mould to form on window frames and the surrounding walls — this can not only cause damage to your home, but also to your health.
  • Wall and decoration damage: Damp and mould will eventually cause wallpaper to peel away and paint to flake. It could also result in crumbling plaster.
  • Damage to window treatments: Curtains and blinds can both be affected by damp and mould.

mould on window with condendation

If left untreated, window condensation can cause damp and mould. This can eventually lead to rot in the case of timber frames.  (Image credit: Getty)

How do you prevent window condensation?

Thankfully, if you have window condensation, or are wondering how to tackle condensation in conservatories, there are several steps you can take. 

  • Upgrade to double glazing: Single glazed windows are more likely to suffer from condensation than double glazed. This is because the glass doesn't warm up along with the room temperature, instead remaining as cold as the outside. With double glazing, however, the internal pane of glass will be far warmer.
  • Improve ventilation: Increasing home ventilation will make a huge difference to a window condensation problem. Even simply opening the windows or investing in trickle vents should considerably improve the issue. Wall vents or air bricks can also help. In bathrooms or kitchens, fit suitable extractor fans. 
  • Lower humidity levels: There are several ways you can lower humidity levels in your home. Aim to dry clothes outdoors, or open windows in the rooms where you have wet clothes hanging. Fit extractor fans and, in bathrooms, open windows or doors to allow humidity to disperse. 
  • Consider Positive Input Ventilation: Positive Input Ventilation units are easier to retrofit than mechanical ventilation with heat recovery (MVHR) and work by pumping and circulating fresh, filtered air into the house, while forcing stale or humid air out.  
  • Upgrade insulation: If your home is poorly insulated, it is likely to be cold and suffer from condensation. Improving your insulation levels will really help with this. 
  • Heat the room: Raising the temperature of a room – and keeping it steady rather than allowing it to fluctuate – just a little can help with a condensation problem. It will mean that the air holds on to the moisture better, rather than depositing on the windows. 
  • Consider a dehumidifier: Dehumidifiers can help with condensation by removing excess moisture from the air. 

steamy shower head

Bathrooms and kitchens produce lots of steam and moisture — so good ventilation is vital to avoid condensation issues.  (Image credit: Getty)

What is a window condensation absorber?

Window condensation absorbers are also known as moisture traps. They are small units filled with absorbent crystals that suck up moisture in the air. 

They can be quite effective depending on the severity of the condensation problem and are a cost-effective solution, although they might not add anything much to the attractiveness of your interior scheme. 

The Kontrol Streamline Moisture Trap from Amazon is a good option as it is slimline and unobtrusive. 

Should I buy a dehumidifier for condensation?

Dehumidifiers can help with a window condensation issue as they draw moisture out from the air. How effective a dehumidifier is relies on investing in one that is the right size for the room. Check out our guide on dehumidifier running costs to find out  more.

When choosing a dehumidifier be sure to consider where you will place it and also look for one that operates with low running noise — particularly if you want to use it overnight. 

Natasha Brinsmead

Natasha is Homebuilding & Renovating’s Associate Content 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. Over the years Natasha has renovated and carried out a side extension to a Victorian terrace. She is currently living in the rural Edwardian cottage she renovated and extended on a largely DIY basis, living on site for the duration of the project. She is now looking for her next project — something which is proving far harder than she thought it would be.