Why Does My Double Glazing Get Condensation On the Inside?

water condensation

Is there condensation on the inside of your windows? Have you noticed that your windows are wet on the inside in the morning?

This can be a worrying find (understandably) but the good news is that the phenomenon actually indicates that your windows are working as they should. In fact, you’re as likely to get condensation on new windows as old windows, and new windows may even increase condensation, since they should reduce draughts in the home.

That said, condensation on the inside of windows is something we should try to reduce, since it can damage window frames. It’s also indicative of a bigger problem – excessive moisture in the home.

Why do you get condensation on the inside of a window?

One of the main advantages of double glazing is its ability to prevent heat from moving from one side of the glass to the other.  It does this by sandwiching a vacuum (or a layer of inert gas) between two sheets of glass.  When heat energy builds on one side, it has trouble passing through this inner layer, and so instead is mostly conducted back into the room.

This will prevent heat escaping, and reduce your energy bills,  but in doing so it’ll create a considerable difference in heat from one side of the glass to the other.  It’s this difference that creates the conditions for condensation.

Cold air contains less energy than warm air, and it’s less capable of keeping water vapour in its gaseous form.  This means that the air inside your home will be damper than the air outside.  When this air hits a cold surface, like a window, it will lose the energy necessary to hold onto the airborne water, and so that water will be deposited.  Over time, this effect causes the build-up of water condensing on the glass.

Chances are, you will notice this happening primarily in  three rooms of the house:

  • The kitchen.
  • The bathroom.
  • The bedroom.

Cooking, showering and bathing all create substantial moisture which unless you keep the rooms very well ventilated, will settle on the windows. This probably isn’t surprising. What is puzzling is why we get condensation on bedroom windows, since we’re probably not cooking or showering in there.

The most likely reason is that during our waking hours we typically move around the house but at night we’re confined to one small space for 8 hours or more, often with the door closed. This causes all the water we lose over those 8 hours to build up. We also tend to keep bedrooms a little cooler than the rest of the house, which mean the surface of the windows will be colder, and water will be more likely to condense when it hits it.

What’s bad about condensation?

Condensation can reduce the lifespan of a window, as it’ll encourage the growth of mould which can damage the frame.  It can also be taken as evidence that the humidity inside your home is excessive – which can be a health concern.

How do you stop condensation on windows?

To prevent condensation settling on windows we need to take steps to reduce the amount of condensation in the home generally.  Ideally, we want humidity levels to be at around 50%.  In order to achieve this, we might try the following:


Aim to open windows for about 20 minutes daily (yes, even in winter!) This will allow the damp air to escape and (unless it’s especially humid outside) dry air to replace it.

Installing trickle vents can help reduce condensation too.

Use extractor fans

If you’re cooking or showering, an extractor fan will remove damp air before it can settle on surfaces and cause problems.

Dry laundry outside

Drying laundry inside significantly increases the amount of water vapour in the air.  The water has to go somewhere, after all.

If drying laundry outside isn’t an option, ensure the space around your laundry is as ventilated as possible.

Manage other humidity sources

When you’re taking steps to guard against excess humidity, you’ll want to consider the things that can contribute to it.  One of the most obvious causes are the living beings which inhabit a house – each of which, be they humans, dogs, cats or guinea pigs, will emit water vapour over the course of the day.  Paradoxically, you might also encounter an uptick in humidity when you return from a spell away – as an empty house will be unheated, and therefore prone to absorbing moisture, which will be released when the heat rises again.

Invest in a dehumidifer

If the steps above don’t remedy the problem, or at least don’t sufficiently reduce condensation in the home, you may want to invest in a dehumidifier, which  will extract moisture from the air.

Do double glazed windows stop condensation?

While condensation can be worse on single glazed windows (due to the internal surface of the window being much colder than the internal surface of a double glazed window) replacing single glazed windows with double glazing is not enough to eliminate the problem. The reason being is that although the inside of your new windows will be warmer, they will simultaneously eliminate draughts. This will reduce ventilation, and contribute to the build-up of moisture.

Acute causes of condensation

If your condensation has appeared almost overnight, then you might be wondering what could possibly have caused it.  There are several potential short-term contributing factors.


When the weather outside gets cold, the chances of condensation occurring increase substantially.  At the start of winter, it’s therefore worth taking preventative steps before the condensation has a chance to develop.

New windows

Newer double-glazed windows are able to do their job much more effectively than old ones, so don’t be surprised to see more condensation after getting new windows installed.

Underfloor heating

Radiators help warm air to rise and circulate, so if you’ve swapped out your radiators for underfloor heating, you might see an uptick in condensation on your windows.

What about condensation between the panes?

So far, we’ve been talking about condensation on the inside of the glass – but what happens when vapour gets in between the window panes?  This means that the window has sprung a leak, which has allowed the water vapour to get in.  The inert gases inside a modern double-glazed window contribute enormously to its ability to retain heat, so if yours is showing this symptom, it’s probably time to replace your windows.

For more information, take a look at our blog post on why condensation forms between window panes.

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.

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