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Blown Double Glazing: Repair or Replace?
Blown Double Glazing: Repair or Replace?
If your windows are looking misty, cloudy, or constantly wet on the inside, you are likely dealing with blown double glazing. This common issue means condensation is trapped between the glass panes, obstructing your view and drastically reducing the window’s insulating properties.
Replace the Glass Unit
Cost-Effective: Roughly £95–£400.
Best For: Restoring visibility and thermal performance quickly while keeping your existing frames (if they are in good condition).
Replace the Full Window
Comprehensive Fix: Roughly £200–£1,200+.
Best For: Frames that are old (15+ years), soft, rotted, or warped, or if you want to upgrade overall energy efficiency.
Table of Contents
1. Why Do Sealed Units Blow in the First Place?
A double-glazed window consists of two panes of glass separated by a spacer bar, with an insulating gas (usually argon) sealed tight in between. A unit “blows” when that perimeter seal fails. This can happen for several reasons:
- Age and Degradation: Over 15 to 20 years, the sealant simply breaks down due to constant expansion and contraction from the weather.
- Poor Installation: If a window isn’t fitted correctly, or the glass doesn’t have the right drainage blocks inside the frame, the unit can sit in pooled water, rotting the seal prematurely.
- Chemical Damage: Using harsh chemical cleaners on the glass and frames can slowly eat away at the sealant over time.
2. Option 1: Replacing the Sealed Glass Unit
If you are looking into repairing uPVC windows or timber frames that are still structurally sound, simply replacing the sealed glass unit is an excellent route to take.
By simply popping out the failed glass and slotting in a brand-new, argon-filled unit, you immediately restore the window’s thermal performance and clear visibility—all without the disruption of ripping out the frames.
When KJM Group replaces your blown sealed units, the old, failed glass doesn’t go to landfill. We ensure that all extracted glass is fully recycled, making this not only a cost-effective choice for your home but an environmentally friendly one, too.
The DIY Potential
For those highly comfortable with home maintenance, replacing a glass pane is a relatively simple task. It generally involves:
- Carefully removing the window beads around the frame edge.
- Taking accurate measurements of the existing glass unit (height, width, and depth).
- Ordering a bespoke replacement unit.
- Fitting the new glass with the correct packers and securing the beads.
If you aren’t confident in taking precise measurements or safely handling heavy glass, it is always best to call in the professionals.
3. Option 2: Replacing the Full Window
While replacing the glass is ideal for many, there are scenarios where a complete replacement of the frame and glass makes more financial and practical sense in the long run.
- Your frames are under 10–15 years old.
- Only one or two windows have failed.
- The frames open, close, and lock smoothly.
- You want the most cost-effective and eco-friendly fix.
- The frames are soft, rotted, or heavily warped.
- The windows are over 15–20 years old.
- You have multiple window failures across the house.
- You want to radically upgrade your home’s insulation and security.
4. Cost Breakdown: Glass Unit vs Full Frame
Budgeting for window fixes depends heavily on the size, style, and access requirements of your windows. Below is a rough estimate to guide your decision:
| Service | Estimated Cost (per window) |
|---|---|
| Replacing the Sealed Glass Unit Only | £50 – £400 |
| Replacing the Full Window (Frame & Glass) | £200 – £1,200+ |
5. Frequently Asked Questions
While some companies offer “de-fogging” services that drill holes to clear the moisture, we strongly advise against this. It does not restore the insulating gas between the panes or fix the broken seal. Replacing the sealed glass unit entirely is the only way to fully restore the window’s thermal efficiency.
High-quality double glazing typically lasts between 15 and 20 years. However, many units can last much longer depending on the quality of the initial installation, exposure to extreme weather, and routine maintenance.
While swapping a glass unit can be a DIY job for experienced individuals, ensuring the glass is packed correctly so the window operates smoothly can be tricky. Additionally, repairing structural damage to uPVC frames, hinges, or locks often requires a professional touch to ensure the window remains secure and watertight.
đź“š Knowledge Hub: Explore New Windows
If you’ve decided a full replacement is the best route, explore our range of energy-efficient profiles:
- uPVC Windows: Highly energy efficient, secure, and low maintenance.
- Aluminium Windows: Sleek, ultra-slim sightlines for a modern aesthetic.
- Timber Windows: Classic beauty and incredible natural insulation.
Need to Fix Those Misty Windows?
Whether you need to swap out a blown sealed unit or are ready for a complete window replacement, contact KJM Group for a free, no-pressure consultation in Hampshire and 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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