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Can I Reseal Double Glazed Windows?


Resealing double glazed windows requires an extremely careful approach, and amateur attempts to replace double glazing window seals can do more harm than good. Double Glazing is a solid investment for householders who want to cut heating costs by improving their home’s insulation and energy efficiency. However, the importance of window seals is often overlooked, although they’re crucial to enable double glazing to do its job properly.

Failed window seals cause multiple problems so it’s a concern that needs addressing promptly. But what does resealing double glazed windows involve? And is it something you can do yourself?

This blog post explores the topic of double-glazed window seals, from how they work and why they fail, to DIY repairs vs professional window resealing or window replacement.


How Are Double-Glazed Windows Sealed?

The performance of a double-glazed window will be significantly compromised if moisture or air penetrates the gas-filled space between the dual panes of glass. To prevent this, an airtight seal is fitted between the window frame and the double-glazed unit. 

Like double glazing window frames, window seals are often made from uPVC (unplasticised polyvinyl chloride). Other sealing materials include rubber, silicon, and EPDM (ethylene propylene diene monomer). 

Whatever the material, double glazing window seals make sure your windows keep your home warm in cold weather, cool in summer, and absorb external noise.Double glazing seals – especially uPVC seals – can last a long time without any sign of weathering, but sometimes things may go wrong.


Why Do Window Seals Fail?

Shrinkage is a common problem that causes seals on double-glazed windows to fail.

Heat from the sun expands the glass in windows. As the window gets cooler at night, the glass shrinks. This repeated pressure on the seals may eventually cause them to fail. 

The problem – known as solar pumping – is more common in south- and west-facing windows, which get more sunlight.

Other reasons window seals fail include:

  • Wear and tear. Window seals are exposed to varying weather conditions – heat, cold, rain, and wind – that can cause them to wear down in time.
  • House settling. It’s normal for a property to sink into the ground over time but it can put pressure on windows and their seals.
  • Physical damage. Damage resulting from physical force such as slamming a window shut can damage window seals.
  • Poor installation. A badly-fitted window puts additional pressure on window sealing.
  • Strong sunlight. Direct sunlight can cause small cracks and fissures in the seals.


What Problems Do Faulty Window Seals Cause?

When a window seal has worn out, double glazing can become completely ineffective. This can cause a range of problems, including condensation, draughts, water leakage, exterior noise intrusion, and increased heating costs.

These issues can affect your health, create uncomfortable living conditions, and damage property.



Condensation is a common problem when double glazing window seals stop working properly. Excess moisture builds up between the two panes of glass and on the outside and inside of your windows. 

Condensation on the interior of your window can result in growth of toxic mould on the window frame and sill and surrounding walls. Spores released by this mould can cause respiratory problems and trigger allergic reactions.


Failed sealing between the window frame and the glass or between the frame and the wall allows a cold breeze into your home. It also means warm air inside your home has an escape route.

Water Leakage

If a window’s weather seals have failed, rainwater can leak through the frame. This can lead to water damage in your home, electrical hazards, and the appearance of rot and mould.

Noise Pollution

When functioning optimally, double glazing reduces noise pollution. However, just as cold air can get into your home through broken window seals, so can sounds from outside.

Higher Energy Bills

Many of the issues caused by faulty double glazing seals result in increased heating costs.

When window seals fail, they no longer provide the same level of insulation. As a result, your home’s heating system has to work harder to maintain a comfortable temperature, and this means higher energy bills. 


Signs Your Double-Glazed Windows Need Resealing

Seals on double-glazed windows typically last 10 to 15 years. It’s a good idea to inspect them at least once a year. Spotting the signs of window seal failure in the early stages enables you to address the issue before things get worse. Here’s what you need to look for.

Misted Glass

A broken window seal often causes condensation between the two panes of glass in double glazing. 

This results in a foggy or cloudy appearance. You may notice this issue more often during winter when the outside temperature falls. 

Identifying and fixing this problem before it gets worse can prevent permanent damage to your window.

Cold Spots

If you notice some areas of your home feel colder than others, it could be down to gaps around a window that allow draughts into your home while the warm air inside leaks out.

You can check for window draughts by lighting a candle near the frame on a windy day. If the flame flickers a lot, it’s because of a draught.

Less Energy Efficiency

Faulty seals reduce the insulating properties and energy efficiency of your windows. An indication of this is your heating costs increasing because you’re having to turn up the heating to keep your home warm.

Damp Patches

Damp patches or water stains on areas of a wall around a window could be the result of failing window seals. You may also notice wallpaper peeling or mould forming on the wall.

Window Frame Damage

Warping or cracking of a window frame could be a sign of moisture damage due to defective sealing.

Difficulty Opening or Closing the Window

Broken, warped or otherwise damaged window seals can make it difficult to open or close a window.

Seal Deterioration

The seals around windows can degrade over time. Look for signs of wear and tear like cracked, peeling, or flattened seals.


Window Spacer Bar Problems

Besides defective seals around the window, there could also be an issue inside your double glazing – a faulty spacer bar.

The spacer bar is an integral and critical component of a double-glazed unit. It creates the gap that provides thermal insulation between the two sheets of glass.

Spacers are built into a frame smaller than the width of the glass. Sealant is then applied to ensure optimal insulation. 

Furthermore, spacer bars contain a silicon material that acts as a desiccant. This keeps air in the gap dry. Small holes in the surface of the spacer facilitate the attraction and absorption of any moisture.


Spacer Sealant Failure

Some types of spacers can be prone to sealant failure. Like the rest of the window, spacer bars expand and contract as temperatures change. This puts added pressure on its seal, which can open up over time. 

If this happens, the desiccant in the spacer will try to absorb all of the moist air that’s sucked into the unit. Eventually, the spacer bar can become saturated and unable to absorb any more moisture.

This results in vapour condensing and running down the cooler of the two panes of glass. And the situation can get worse. When warmed by the sun, chemicals in the desiccant can react with the condensation and become baked into the glass permanently.


Can You Reseal Double Glazing Windows Yourself?

If your double glazing needs resealing, you may be wondering whether you can save money by doing the job yourself.

Before going ahead, you need to ask yourself a couple of questions:

  • Do I have the right tools and materials, and do I know how to use them properly?
  • Do I understand the structural design of double glazing and how the various components work together? 

If you’re still confident about resealing the windows yourself, you’ll find that DIY options are essentially limited to reinforcing the sealing externally. Even this requires an extremely careful approach, and amateur attempts to replace double glazing window seals can do more harm than good.

For instance, overfilling gaps around the edges of your windows with silicon or expanding foam can dislodge the window frame and cause major problems.

And tackling the problem of condensation – drying the window out with a hairdryer, for example – may clear your windows temporarily but does nothing to address the underlying issue.

Resealing double glazing is invariably a job best left to a professional window installer. Besides resealing the window, they’ll also rectify the unsightly condensation build-up between the two panes of glass.

However, even professional window resealing is unlikely to be as effective as a window replacement.


Double-Glazed Unit Replacement

If your double glazing window seals have failed, the most effective, long-term solution is to replace the entire double-glazing unit.

Swapping out only the sealed glazing unit while retaining the original window frame can save hundreds of pounds compared with replacing the entire window. A professional can typically replace the window unit in under an hour, at a cost of £50 to £150, depending on the size of the window.

Once your new window unit with its airtight seals is installed, you’ll be able to continue to enjoy the benefits of double glazing as your heating bills come down. And you won’t have to worry about condensation issues, mould growth, cold draughts, or rainwater leakage.

Contact Greencastle today for more information.

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