What Causes Seal Failure?

Seal failure occurs when the perimeter seal of an insulated glass unit (IGU) begins to deteriorate or lose its ability to protect the space between the panes of glass. When this happens, moisture, air, and contaminants can enter the insulated cavity, potentially affecting the appearance and performance of the window.

Seal failure is one of the most common issues affecting aging dual-pane and triple-pane windows.

What Is a Window Seal?

Dual-pane and triple-pane windows are constructed using multiple panes of glass separated by a spacer system.

Along the perimeter of the glass unit are specialized seals designed to:

• Hold the glass assembly together
• Protect the insulating air or gas space
• Prevent moisture intrusion
• Maintain thermal performance

These seals are critical components of the insulated glass unit.

What Is Seal Failure?

Seal failure occurs when the perimeter sealing system can no longer adequately protect the space between the glass panes.

Once the seal begins to fail, outside air and moisture may enter the insulated cavity.

This can lead to condensation, fogging, staining, and reduced energy efficiency.

Common Signs of Seal Failure

Some of the most common indicators of seal failure include:

• Fogging between glass panes
• Condensation trapped inside the insulated unit
• Cloudy or hazy appearance between panes
• Mineral deposits inside the unit
• Reduced clarity that cannot be cleaned from either side

If the condensation is located on the interior or exterior surface of the glass, seal failure may not be the cause.

True seal failure typically involves moisture trapped between the panes.

What Causes Seal Failure?

Age and Normal Wear

Like most building materials, window seals do not last forever.

Over time, exposure to weather, temperature changes, ultraviolet radiation, and environmental conditions can cause seals to deteriorate.

Many seal failures occur simply as a result of aging.

Thermal Expansion and Contraction

Windows expand and contract as temperatures change throughout the day and throughout the year.

This continual movement places stress on the seals surrounding the insulated glass unit.

Over many years, repeated expansion and contraction can contribute to seal deterioration.

Extreme Weather Conditions

Harsh environmental conditions can accelerate seal degradation.

Examples include:

• High temperatures
• Extreme cold
• Heavy UV exposure
• Severe weather events
• Large daily temperature swings

Windows exposed to these conditions may experience faster seal aging.

Poor Manufacturing or Installation

While modern insulated glass units are designed for long-term performance, manufacturing defects or installation issues can sometimes contribute to premature seal failure.

Examples may include:

• Improper seal application
• Defective spacer systems
• Improper glazing installation
• Frame-related stresses

Building Movement

Buildings naturally shift and settle over time.

Structural movement can place additional stress on windows and their sealing systems.

Excessive movement may contribute to seal deterioration in some circumstances.

Can Window Film Cause Seal Failure?

This is one of the most common questions asked by homeowners and property managers.

Architectural window film does not automatically cause seal failure.

However, because window film changes how solar energy interacts with glass, it can alter temperatures within the glazing system.

For this reason, film-to-glass compatibility should always be evaluated before installation.

When a compatible film is selected and properly installed, window film can provide significant benefits without creating unnecessary stress on the glazing system.

Independent testing backs this up. Standardized ASTM tests (E773 and E774) run on matched sets of insulated glass units — with and without film applied — found no meaningful difference in seal performance between the two groups. In other words, when properly researched and tested, adding film to a quality-manufactured, properly sealed IG unit doesn’t appear to cause seal failure on its own.

Can Seal Failure Be Repaired?

In most cases, the insulated glass unit itself must be repaired or replaced once seal failure has occurred.

The appropriate solution depends on the extent of the damage, the age of the window, and the window manufacturer's recommendations.

Property owners should consult a qualified glazing professional to evaluate available options.

How Does Seal Failure Affect Performance?

Seal failure can impact both appearance and performance.

Potential effects include:

• Reduced visibility through the glass
• Condensation between panes
• Reduced energy efficiency
• Loss of insulating gas fill
• Reduced thermal performance

The severity of these effects varies from one window system to another.

Can Seal Failure Be Prevented?

No insulated glass unit lasts forever, but proper window selection, professional installation, and routine maintenance can help maximize service life.

While no method can completely eliminate the possibility of seal failure, quality window systems typically provide many years of reliable performance.

Why Film-to-Glass Compatibility Matters

Because insulated glass units rely on perimeter seals to maintain performance, compatibility reviews are an important part of architectural window film selection.

Factors commonly evaluated include:

• Dual-pane or triple-pane construction
• Low-E coatings
• Glass thickness
• Window size
• Building orientation
• Film type

Proper compatibility evaluation helps identify products that may be suitable for the glazing system.

Key Takeaways

• Seal failure occurs when the perimeter seal of an insulated glass unit deteriorates.
• Common signs include fogging, condensation, and haze between glass panes.
• Age, weather, thermal movement, manufacturing defects, and building movement can all contribute to seal failure.
• Window film does not automatically cause seal failure.
• Film-to-glass compatibility should always be evaluated before installation.
• Seal failure typically requires repair or replacement of the insulated glass unit.