Home Improvement

How To Fix & Prevent Condensation In Double Glazing

Written by  Harry Taylor
Last updated: August 8, 2023

If you notice condensation between the sheets of a double-glazing unit, you need to find a solution immediately because:

  • Heating bills could blow up because that window or door has lost some, if not all, of its insulating capabilities
  • The condition will only get worse because the frame and surrounding brickwork are vulnerable to water damage
  • Moulds will flourish and they can damage property and cause breathing difficulties

Therefore, when it comes to double glazing, it is crucial to fix condensation issues as quickly as possible. Even better, knowing how to prevent the problem from happening again is vital. So, keep reading if you want to know about the whys, the fixes and the preventive measures of condensation in double glazing. 

However, before getting to the good bits, let’s explore condensation and double glazing as separate terms.   

What is Condensation?

Condensation is the process by which vapour turns into liquid. It happens when moist air loses heat upon contact with a colder surface, like window panes. The moisture-retaining ability of air depends on temperature. The warmer air is, the more moisture it can retain, and vice versa.

Therefore when moist air comes in contact with a colder surface (in this situation, the double glazing), it doesn’t just lose warmth. It also loses its moisture-retaining ability. Therefore it becomes oversaturated, allowing vapour to escape as condensates.

However, the temperature of the moist air has to drop to its dew point for condensation to happen. Therefore, condensation depends on the following:

  • Humidity (the amount of vapour in the air), and 
  • The difference between ambient temperature (temperature of the moist air) and the temperature of the cold surface, the double glazing

What is double glazing?

You probably already know that two sheets of glass are involved, so let’s start from there. These two sheets have a cavity between them. This cavity is filled with inert gas and sealed on all sides so that nothing (neither dirt, moisture, air etc.) can enter. All of these combined give double glazing its thermal insulating capabilities.

The cavity between the glass sheets must remain sealed. Nothing must get in or out. Therefore, the seal is not the only protection in place. A barrier of desiccant is also added to keep water from getting through. Then two more barriers (sealant and glazing beads) are added during installation. 

The last two are added to make the window structurally secure. But they also protect that all-important cavity, even though that’s not their primary purpose. So, despite all of these layers of protection-

How does condensation get into double glazing?

The answer is simple. The layers of protection have failed or are failing. These include the glazing beads and sealant added during installation, the desiccant and finally, the seal that had the primary role of keeping the cavity impenetrable.

This is why water, in the form of vapour and liquid, got inside the double glazing. However, it is also possible that the seals are not at fault. Moisture could also get in through a crack in the glass sheets.

Whatever the cause, the problem may have started long before it came to your attention. Plus, it will only get worse if you don’t find a solution as soon as possible. As water sits inside (or even on) the glazing, it gets more time to damage the window and surrounding brickwork. 

However, you can’t find a solution without knowing the cause. So here are the two main reasons condensation gets in double glazing. Do note that we are talking about when the condensates actually appear in the cavity between the glass sheets, not on the glazing.

The double glazing is damaged

This could mean damage to the glass sheets or the seals protecting the cavity between them. The latter is more likely, often caused by poor drainage and direct sunlight.

Poor drainage allows water to sit on the windowsill long enough to penetrate the barriers and enter the double glazing. On the other hand, direct sunlight and extreme temperature fluctuations cause the window frames to expand and contract. This weakens the frame and seals over time.

The double glazing is old

Sometimes the answer is this simple. Age catches up with everything. Double glazing can last for 20 to 35 years. So you probably don’t have to worry about this for a while. Still, condensation can get in if the double glazing is old and failing.

How to fix condensation in double glazing

Now that we have discussed the problem and its likely causes, here are the solutions.

Reseal the glazing

This is obvious, right? Resealing should plug the leaks and stop condensation from happening inside the double glazing. However, there is an issue with this approach. There is no guarantee that a fix will work or last. 

You also need to be aware that this could void the warranty. So, if the warranty is still active, contact the manufacturer or sellers before doing anything. They may cover the cost or send someone to handle the repair.

The resealing process is simple. It involves extracting the moisture inside the double glazing before sealing it back. For the extraction, the repairer will drill holes into the glass and inject liquid that will expel the liquor. Aside from resealing, they may add extra measures like a one-way vent and antifogging.

Replace affect panes

Once again, resealing is not a foolproof solution. Sometimes, replacement is better. Other times, it may be the only option. Fortunately, your warranty could cover this. Even if it doesn’t, the repair will be affordable because you only replaced the affected panes.

Replace the entire double-glazing window unit

This is a nuclear and costly solution, but it is still an option. Plus, you only need this if the entire unit is compromised. On the other hand, replacing the window offers assurance that the other two solutions don’t.

How to prevent condensation in double glazing

Double glazing is durable and condensation resistant. Therefore, it is easy to prevent condensation. You need to control the humidity in your house and offer double-glazing units a bit of protection. Here are some ways to do these.

Aerate the house for 15 to 20 minutes daily

Moisture builds up from daily activities like cooking, bathing, washing and breathing. So, open the windows, doors and vents for 15-20 minutes daily to allow damp air to escape and fresh air to come in. Do this in the morning or afternoon.

When cooking or engaged in an activity that releases much moisture, open the windows and close the entrances to other rooms. This will stop damp air from building up indoors. 

Get an extractor fan

Install an extractor fan in the dampest parts of your house, such as kitchens and bathrooms. It will help to reduce dampness, thus reducing condensation issues. 

Get a dehumidifier

A dehumidifier is a great way to control humidity inside a room. If you get one, use it to maintain a humidity level of 30% to 50%. That is the recommended range. It is suitable for you and the double glazing. 

Avoid drying wet clothes indoors

Drying clothes indoors will only increase the moisture levels inside your house. As you already know, this will add to the condensation problems. So, it is better to dry your clothes outdoors.

If that’s not an option, open the windows and close the doors leading to other rooms when drying clothes indoors.

Keep room temp relatively constant

Remember that temperature fluctuations can damage window frames by making them expand and contract.

Protect your double-glazing units from direct sunlight

Direct sunlight can also cause window frames to expand, which means they have to contract to their original shape and size later. You already know how this can affect double glazing.

Shade your windows with canopies, trees, hedges etc. It will protect them from direct sunlight and thus prevent condensation in the double glazing.

Don’t let condensate sit on the double glazing

You can’t totally prevent condensation. Despite your best efforts and the resistance of double glazing, condensation will happen. But this is not necessarily bad news.

Condensation is actually a sign that the double glazing is doing an excellent job of stopping heat, cold, air and moisture from entering your house. However, this is only true if the condensation occurs on the double glazing, not inside.

Still, this doesn’t mean that you should let it happen. Remember that water will eventually cause damage if it sits on the window long enough. Double glazing is not brittle but the impact will eventually build up over time.

So, when you notice condensation on the double glazing (on either side), don’t wait for it to dry up by itself. Wipe the glass with a cloth. You can also use a hair dryer, although you should only do this on low heat and at a distance.

Improve drainage conditions of the window

This will stop water from building up on the windowsill. It will also reduce the risk of leaks. Build the window sill with a slight slope and keep it clear so that water always has a clear path. 


Even though you now know how to fix condensation in double glazing, we should warn you that preventing this problem is easier and better than curing it. Resealing can fail, a replacement can be costly and condensation is inevitable. After all, you can’t control everything. There will always be high humidity and temperature differences.

That is why condensation is common in cold seasons. As the outdoors gets colder, close our windows and crank up heating systems. This increases humidity and reduces ventilation. It also increases temperature differences between indoors and outdoors (i.e. both sides of a window).

Therefore, condensation will happen. The important question is, where does it happen? If it happens on (either side of) the glass, there is no cause for alarm. Condensation on the indoor side means that the room is humid. Condensation on the outdoor side of the double glazing means that the outdoors is colder than the indoors. In either situation, the double glazing is not the problem.

However, that changes when condensation starts to get inside the double glazing. 

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