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Blown Double Glazing: Repair or Replace?
Blown Double Glazing: Repair or Replace?
Got misty windows? Discover whether you should replace your blown double glazing units or upgrade the entire frame. Find exact cost estimates and eco-friendly solutions below.
Replace the Glass Unit
Cost-Effective: Roughly £95–£400.
Best For: Restoring clear visibility and thermal performance quickly. Furthermore, this option is perfect for keeping your existing frames intact if they remain structurally sound.
Replace the Full Window
Comprehensive Fix: Roughly £400–£1,200+.
Best For: Frames that are older than 15 years, visibly rotted, or physically warped. Ultimately, this is the superior route if you want a major kerb appeal upgrade.
Table of Contents
1. Why Do Sealed Units Blow in the First Place?
A standard double-glazed window fundamentally consists of two panes of glass separated by a spacer bar. Additionally, an insulating gas (usually argon) is securely sealed tight in between. A unit technically “blows” when that crucial perimeter seal inevitably fails. Naturally, this frustrating breakdown happens for several key reasons:
- Age and Degradation: Over a period of 15 to 20 years, the heavy-duty sealant simply breaks down. Ultimately, this degradation is primarily caused by constant expansion and contraction from harsh UK weather cycles.
- Poor Installation: If a new window isn’t fitted correctly originally, it lacks the proper drainage blocks inside the frame. Consequently, the glass unit can sit submerged in pooled rainwater, severely rotting the seal prematurely.
- Chemical Damage: Regularly using harsh, abrasive chemical cleaners on the glass and plastic frames can slowly eat away at the sealant. Therefore, we highly recommend sticking to mild, warm soapy water.
2. Interactive: Repair vs Replace Analyser
Are you currently deciding what to do with your misty windows? Simply use our interactive analyser below. Subsequently, we will point you toward the most financially sensible strategy.
3. Option 1: Replacing the Sealed Glass Unit
If you are looking into repairing standard uPVC windows or timber frames that remain structurally sound, simply replacing the sealed glass unit is a spectacular route to take.
By merely popping out the failed, misty glass and slotting in a brand-new, highly efficient argon-filled unit, you immediately restore the window’s performance. Furthermore, you achieve this excellent result without the immense mess and disruption of ripping out the surrounding frames.
When KJM Group professionally replaces your blown sealed units, the old glass strictly avoids going to landfill. Instead, we carefully ensure that all extracted glass is fully recycled. Ultimately, this makes our service not only a cost-effective choice for your wallet, but an incredibly environmentally friendly one, too.
The DIY Potential
For those individuals who are highly comfortable with complex home maintenance, replacing a glass pane is a manageable task. Generally, it involves the following steps:
- Carefully removing the tight window beads around the frame edge.
- Taking perfectly accurate measurements of the existing glass unit (height, width, and overall depth).
- Ordering a bespoke, exact-match replacement unit.
- Fitting the new, heavy glass with the correct toe-and-heel packers and securing the beads tightly.
However, if you aren’t completely confident in taking precise millimetre measurements or safely handling heavy glass, it is undeniably best to call in the professionals.
4. Option 2: Replacing the Full Window
While replacing the glass alone is frequently ideal, there are certain scenarios where a complete replacement of the frame makes vastly more financial and practical sense in the long run.
- Your current frames are comfortably under 10–15 years old.
- Only one or two isolated windows have actually failed.
- The frames still open, close, and lock incredibly smoothly.
- You strictly want the most cost-effective and eco-friendly fix available.
- The frames are visibly soft, severely rotted, or heavily warped.
- The plastic windows are well over 15–20 years old.
- You have multiple, widespread window failures across the house.
- You are deciding whether to replace all windows at once or one by one to secure a massive energy efficiency upgrade.
5. Cost Breakdown: Glass Unit vs Full Frame
Budgeting accurately for window fixes depends heavily on the specific size, style, and access requirements of your property. Therefore, below is a rough financial estimate to securely guide your ultimate decision:
| Service Required | Estimated Cost (per window) |
|---|---|
| Replacing the Sealed Glass Unit Only | £95 – £400 |
| Replacing the Full Window (Frame & Glass) | £400 – £1,200+ |
6. Frequently Asked Questions
While some smaller companies offer “de-fogging” services that actively drill holes to clear the moisture, we strongly advise against this practice. Specifically, it completely fails to restore the insulating argon gas between the panes. Therefore, replacing the sealed glass unit entirely is the absolute only way to fully restore the window’s vital thermal efficiency. For further authoritative advice on managing indoor moisture, read the official FENSA guide to condensation in double glazing FENSA.
High-quality double glazing typically lasts anywhere between 15 and 20 years. However, many premium units can certainly last much longer. Naturally, this lifespan depends heavily on the quality of the initial installation, the frame’s exposure to extreme weather, and routine homeowner maintenance.
While swapping a basic glass unit can be a DIY job for highly experienced individuals, ensuring the heavy glass is “toe and heeled” (packed) correctly is remarkably tricky. Furthermore, repairing structural damage to uPVC frames, dropping hinges, or complex locks absolutely requires a professional touch. Consequently, expert help guarantees your home remains secure and fully watertight.
📚 The Transparency Hub
We believe an educated customer makes the best decisions. Explore our transparent buying guides below:
Need to Fix Those Misty Windows?
Whether you urgently need to swap out a blown sealed unit or are finally ready for a complete window replacement, contact KJM Group today. We provide a completely free, absolutely zero-pressure consultation across Hampshire and the surrounding areas.
Get a Free Quotation
Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.
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