How to Fix Failed Seals on Insulated Glass Windows

Failed window seals are a common issue that homeowners face, but understanding your options can help you make informed decisions about repairs or replacements. When you notice condensation or fogginess between window panes that won’t wipe away, your insulated glass unit (IGU) seal has likely failed.

What Are Insulated Glass Windows?

Insulated glass windows, also known as thermal windows or double-glazed windows, feature two or three panes of glass separated by a sealed space. This space is typically filled with inert gases like argon or krypton, which provide superior insulation compared to regular air. These gases slow heat transfer, making your home more energy-efficient and reducing heating and cooling costs.

The glass panes are held together by specialized seals at the edges. While these seals are designed for long-term durability, they eventually wear down over time or can be damaged by external factors.

Recognizing Failed Window Seals

The most obvious sign of seal failure is fogginess or condensation trapped between the glass panes. This moisture appears on the interior surfaces of the glass and cannot be cleaned from either side of the window. Other indicators include:

Distorted or warped glass appearance
Visible mineral deposits between panes
Reduced energy efficiency in your home
Drafts around the window frame
Higher heating and cooling bills

Why Window Seals Fail

Understanding why seals fail can help you prevent future problems. Common causes include:

Age and Natural Degradation: Even under ideal conditions, the inert gas inside IGU windows escapes at approximately 1% per year. Over 15-20 years, this gradual loss significantly reduces the window’s insulating properties.

Temperature Fluctuations: Extreme temperature changes cause the glass to expand and contract, putting stress on the seal materials.

Poor Installation: Incorrectly installed windows are more prone to seal failure due to uneven pressure or gaps in the frame.

Physical Damage: Heat guns used during paint stripping, pressure washers, or direct impacts can compromise the seal integrity.

Sun Exposure: Prolonged UV exposure degrades the seal materials, particularly on south-facing windows.

Water Damage: Moisture accumulation around window frames can deteriorate the sealing materials over time.

Understanding IGU Seal Construction

The sealing system in thermal windows consists of two layers working together. The inner seal, typically made from polyisobutylene (PIB), creates an airtight barrier preventing gas escape. The outer seal functions as both an adhesive and a flexible barrier, holding the glass unit together while accommodating thermal expansion and contraction throughout the window’s lifespan.

This dual-seal system is engineered for durability, but when either seal fails, the entire IGU’s performance is compromised.

Repair Options for Failed Seals

While replacing the entire window is one solution, several repair options exist depending on the extent of damage and your budget:

IGU Replacement: The most effective solution involves replacing just the glass unit (IGU) rather than the entire window frame. This is more cost-effective than full window replacement and restores the window’s energy efficiency. A qualified glazier removes the failed IGU from the existing frame and installs a new sealed unit.

Defogging Services: Professional defogging involves drilling small holes in the glass, cleaning the interior surfaces, and sometimes introducing a desiccant or anti-fogging solution. While this eliminates the fog, it doesn’t restore the insulating gas or seal the unit properly, so energy efficiency remains compromised.

DIY Defogging Kits: These kits allow homeowners to drill, clean, and install vents in the glass. However, results are often temporary, and the process can damage the glass if not done carefully.

Is Repair Worth It?

Whether to repair or replace depends on several factors:

Consider IGU Replacement When:

Your windows are relatively new with quality frames
Only one or two windows are affected
The frames are in good structural condition
You want to restore full energy efficiency

Consider Full Window Replacement When:

Multiple windows have failed seals
Your windows are over 20 years old
Frames show signs of rot, warping, or damage
You want to upgrade to more energy-efficient windows
Modern features like low-E coatings would benefit your home

Cost Considerations for 2025

As of 2025, typical costs for addressing failed window seals in Ireland include:

IGU replacement: €200-€500 per window depending on size and glass type
Professional defogging: €80-€150 per window
Full window replacement: €400-€1,200 per window depending on size, style, and features

While defogging is the least expensive option, it provides only cosmetic improvement without restoring energy efficiency.

Energy Efficiency Impact

Failed seals significantly impact your home’s energy performance. When inert gases escape and moisture enters the IGU, the window’s R-value (insulation rating) drops dramatically. This means:

Increased heat loss during winter months
Greater heat gain during summer
Higher energy bills year-round
Reduced comfort in rooms with affected windows
Potential condensation issues on interior surfaces

Studies show that properly functioning thermal windows can reduce energy costs by 15-30% compared to single-pane windows or IGUs with failed seals.

Preventing Future Seal Failure

While seal failure is eventually inevitable, you can extend your windows’ lifespan:

Avoid using pressure washers directly on window seals
Keep window frames well-maintained and properly painted
Ensure adequate drainage around windows
Clean windows regularly with gentle cleaners
Inspect seals annually for early signs of deterioration
Maintain consistent indoor humidity levels (30-50%)
Install proper ventilation to reduce condensation

Choosing the Right Solution

Expert Windows specializes in helping Irish homeowners navigate window seal failures. Our team assesses your specific situation, considering factors like window age, overall condition, and your budget to recommend the most cost-effective solution.

Ready to restore your windows’ clarity and efficiency? Contact Expert Windows today for a free assessment. Our experienced professionals will evaluate your failed seals and provide honest recommendations—whether that’s IGU replacement, full window replacement, or another solution tailored to your needs and budget. Don’t let foggy windows compromise your home’s comfort and energy efficiency any longer.