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Many of us are familiar with condensation on the inside of our windows. It’s a common problem in Britain, even for those of us living with new windows or in new homes. Why does condensation form? Shouldn’t we have solved that particular issue by now, given all the headaches it can cause?

The factors involved in condensation go beyond the technology of the window units alone. The moisture comes from all kinds of normal daily activities, with a number of environmental and lifestyle factors making it more or less likely to occur. While modern double and triple glazing can certainly help with the issue, they won’t solve it alone.

Writing in condensation on a window

What causes condensation on different surfaces?

Condensation is the result of water vapour in the air cooling into water droplets when it hits a cold surface. It normally forms on the coldest surface in the room, which is often a window but could be anything in theory.

Water vapour is produced in any number of ways, from breathing to taking a shower (we’ll look at more causes in the next section). It’s simply not feasible to prevent water vapour from being produced at all. Upon its release, water vapour is absorbed into the air, but the air can only hold so much before it gets saturated.

As soon as saturated air hits a surface that’s cold enough, some of the air that it’s holding will condense. The colder the surface, the more vapour will condense and the more condensation will appear. Windows often hold condensation as they tend to be the coldest surface in a room (glass doesn’t retain heat very well). While double and triple glazing will stay warmer than single glazing, they’ll still be colder than most other surfaces.

How is water vapour produced in the home?

There are a long list of activities that can produce water vapour, many of which are unavoidable in the course of normal life. We’ve already mentioned the simple act of breathing (have you ever noticed a window or mirror steam up when you stand near it?) but there are many others:

  • Cooking (especially if you’re boiling water)
  • Washing up or opening a dishwasher
  • Taking a bath or shower
  • Washing and drying laundry
  • Heating your home (most heaters produce some excess vapour)

Even growing indoor plants releases more water vapour than you might think, so it’s truly impossible to stop it occuring. That said, you can conduct many of these activities in such a way that less vapour is produced. We’ll look at some of those methods below.

What factors make condensation more or less likely?

Along with the sheer volume of water vapour in the air, there are other factors that can make condensation more or less likely to occur on your windows. The main considerations are the temperature difference between the inside and outside of the house, the temperature of the inner side of the glass compared to the rest of the room and your ventilation.

The temperature differential is most noticeable when the outside temperature is very low and you’re heating the inside of your house. This is because your windows – which will always be a source of heat loss no matter how good they are – will be colder the colder it is outside. If you have single glazing this effect will be especially pronounced, as there’s no insulating layer to prevent heat from escaping as there is with double and triple glazing.

The insulating layer means that the inner layer of glass can stay much closer to the temperature of the room. Even if some condensation still forms, the amount of moisture will be lower the if the window is warmer. This is also why condensation is most likely in unheated rooms of the house – although the temperature difference isn’t actually as high as in a warm room, the inner surface of the glass will be colder, which means that any water vapour finding its way into the room from warmer parts of the house is much more likely to condense.

Finally, ventilation is a big factor. Good ventilation allows moist air to escape outside, keeping the air inside the house drier. A lack of ventilation is the reason that newer windows can still run into condensation problems. Because they have better seals to cut off drafts, it’s harder for water vapour to escape, which means that more stays inside the house where it can condense.

Poorer ventilation means that windows are more energy efficient, but also that you’ll have to be more proactive about removing water vapour from the air yourself. We’ll look at ways to do this later on.

raindrops on a window

Does double glazing help?

As you’ll have picked up by now, double glazing is undoubtedly beneficial when it comes to condensation because the inside temperature of the glass stays higher. We’ve seen that double glazing isn’t enough to eliminate the problem entirely, but less moisture on the glass means that the area around the windows will stay much drier than it would with single glazing.

This, combined with the energy efficiency benefits that double glazing gives in colder weather makes it a no-brainer. It’s also advisable to look for double glazed windows with insulating seals made of plastic rather than aluminium and a layer of argon gas rather than air, as these factors will reduce heat loss between the two panes even further.

One other subject to touch on before we move on is the particular case of double glazing that has been created by adding a second pane to single glazed windows. It’s possible that you’ll see condensation forming on the inside of the cavity, which needn’t concern you as long as it’s only a small amount. This just means that a little moisture was in the air that was trapped inside the glass when the second pane was added. If you see moisture inside purpose-made double glazed windows, however, it’s a sign that your seal is broken and needs repairing.

How to reduce condensation on your windows

You can’t stop water vapour from occurring inside your house, but there are a number of ways to stop it from causing problems. The key is in good ventilation and minimising the amount of water vapour that can move from room to room.

In the rooms where you’re likely to have a lot of water vapour, like the kitchen and any bathrooms, you’ll need to be proactive. If you can, leave windows open when you’re showering or boiling water, but at the very least make sure your extractor fans are working properly. It’s also wise to boil only as much water as you need and to shower for the minimal amount of time.

As well as ventilating these rooms, it’s a good idea to minimise amount of water vapour that can escape into your other rooms. Keep the doors shut when the rooms are in use, and invest in good draft excluders to prevent the movement of moist air into a drier part of the house.

If you’re aware of condensation becoming an issue, don’t be afraid to leave a few windows open in the worst affected parts of the house. It might seem counterintuitive to open a window when you want to keep the house warm, but doing so will let moist air escape and allow dry air to come into the house. Even if this dry air is initially colder than the warm, moist air, it’s actually much easier to heat, which means your heating system won’t have to work so hard in the long run.

For information on how to stop condensation in conservatories specifically, be sure to consult our guide.