Double glazing is one of the most effective features for improving insulation, reducing noise and maintaining comfort in London homes. However, when a double glazing unit fails, property owners often assume the entire window must be replaced. In reality, many issues can be resolved with cost-effective repairs that restore performance without the expense of a full window replacement.
This in-depth guide explains the common causes of double glazing unit failure, the signs you shouldn’t ignore, and how professional glazing specialists determine whether repair or replacement is the best solution. By understanding your options, you can protect your property, save money and keep your glazing performing at its best.
What Is a Failed Double Glazed Unit?
A double glazed unit, often referred to as an IGU or insulated glass unit, consists of two panes of glass sealed together with a spacer bar and insulating gas. When this sealed unit fails, the airtight barrier breaks down.
The most common signs of a failed unit include:
• Condensation or mist between the panes
• Fogging that does not wipe off
• Water droplets inside the glass cavity
• Cold drafts coming through the window
• Visible gaps or broken seals around the edges
Once the seal is compromised, the insulating gas escapes and moisture enters the space between the panes, reducing the thermal efficiency of the window.
Why Do Double Glazing Units Fail?
Double glazing can fail for various reasons, many of which are accelerated by London’s climate and building conditions.
Heat expansion and contraction cause pressure on the seal, especially in south-facing windows. Over time, this repeated stress leads to weakening and eventual failure.
Building movement in older London homes and flats can also strain window frames, bending or loosening the edges of the glass.
Poor installation is another major factor. If the unit was not fitted correctly or the sealant was applied unevenly, the window becomes vulnerable to early failure.
Finally, general wear and tear plays a huge role. Double glazing typically lasts 10 to 20 years, and many period or older properties across London now have units reaching the end of their lifespan.
Repair vs Replacement: Knowing Which Option Is Right
When homeowners see condensation or fogging inside their double glazing, they often assume a full window replacement is necessary. However, this is not always the case.
In many situations, replacing only the sealed unit is all that is needed. This solution is cost-effective and preserves the existing window frame, hardware, and structure.
When a Repair Is Possible
A repair is usually suitable when:
• The window frame is in good condition
• Only the sealed unit has failed
• Glass is cracked but the frame is intact
• A misted unit needs replacing
• No structural damage exists around the window
Replacing the sealed unit restores insulation, clarity and performance without removing the frame. This keeps costs lower and reduces disruption inside the property.
When Full Replacement Is Necessary
Although repairs are often the best choice, a full window replacement is required if:
• The frame is damaged, rotten or warped
• Moisture has affected the surrounding structure
• The window no longer opens or closes correctly
• The design is outdated and no longer meets energy standards
• There are multiple failures across the window system
Modern double glazing options offer higher energy efficiency, better noise reduction and improved security, making replacement a worthwhile investment when needed.
Why Emergency Glaziers Are Helpful for Double Glazing Issues
Double glazing problems can quickly escalate, especially when cracks spread or moisture builds up inside the unit. Emergency glaziers in London provide fast assessment and immediate solutions to prevent further damage.
A specialist will:
• Inspect the unit and frame
• Determine whether repair or replacement is best
• Install temporary solutions if glass has cracked
• Secure the property if the pane has shattered
• Measure for accurate double glazing replacements
Fast professional attention is particularly important for ground-floor windows, shopfronts and flats facing busy streets, where security and insulation are critical.
London-Specific Challenges
London’s diverse building styles create unique challenges for glazing repairs.
Sash windows found in Georgian and Victorian homes often require custom-sized units. Modern flats may need specialist safety glass. Some conservation areas require specific glazing styles or thicknesses.
Experienced glaziers understand these requirements and ensure replacements match both safety standards and architectural expectations.
Preventative Maintenance for Double Glazed Windows
Property owners can extend the lifespan of their double glazing with simple maintenance checks.
Regularly inspect seals for gaps or cracks, especially around the edges of the frame. Keep the frame clean and dry to prevent moisture damage. Lubricate hinges and handles to maintain smooth operation.
If condensation appears on the inside of the room-facing pane, improve ventilation to reduce humidity levels.
For older London homes, consider upgrading to more modern units with higher energy ratings when the time comes, as these new units offer better performance and longevity.
Case Example: A London Flat with Misted Double Glazing
A homeowner in North London noticed fogging in the living room windows that continued to worsen over several months. Believing the entire window needed replacing, they contacted a glazing specialist for advice.
Upon inspection, the glazier confirmed the frames were in excellent condition and only the sealed units had failed. The specialist replaced the units within a day, restoring clarity and warmth without a full window installation. The homeowner saved significant costs and avoided the disruption of having frames removed.
This example demonstrates how many glazing failures can be solved quickly and affordably with the right professional guidance.
Quick Takeaways
• Misted or fogged windows are signs of a failed double glazing sealed unit
• Repairing the unit is often cheaper and less disruptive than full replacement
• Cracks, leaks and drafts should be addressed quickly to prevent worse damage
• Emergency glaziers can stabilise and secure cracked double glazing immediately
• London’s older homes experience unique glazing challenges due to building movement
• Good maintenance extends the lifespan of your double glazing
• Professional assessment is essential to choose the most cost-effective solution
Contact Our Team Today
If you notice misting, cracks or drafts in your double glazing, early action can save you time and money. Contact Enter Glazing for reliable double glazing repair London services and expert advice on repair vs replacement. Our team provides fast, efficient solutions to restore comfort and security to your home.