What trade professionals need to know about condensation between window panes

March 16, 2026

Condensation between window panes is never a surface issue. It is a product failure. When moisture appears between the panes of glass within a sealed unit, it points to a failed insulated glass unit and demands replacement.

For installers, this is a high-urgency callout. Homeowners often assume it is standard window condensation caused by high humidity levels inside of windows. In reality, moisture trapped between glass panes cannot be wiped away. It signals seal failure within the insulated glass unit itself.

Understanding the root cause allows you to diagnose confidently, explain the problem clearly and specify the correct remedy. At Dekko, we manufacture the complete finished window, fabricating the frames and inserting a high-performance insulated glass unit under strict quality control. That knowledge helps our trade partners resolve issues quickly and protect their reputation.

What does condensation between window panes mean?

Condensation between window panes occurs when moisture forms inside a sealed double glazing unit, between the panes of glass.

Unlike condensation on the inside of the window caused by warm air meeting a cold glass surface, or condensation on the outside of the window during temperature shifts, this type of double glazing condensation sits within the cavity and cannot be cleaned from either side. It is a clear indication that:

• The perimeter window seals have deteriorated
• The insulated glass unit has lost its hermetic seal
• Water vapour has entered the cavity
• The desiccant can no longer absorb the amount of moisture present

How does a double glazing unit fail?

A modern insulated glass unit is engineered to create a sealed cavity between two or more panes of glass. That cavity contains dry air or inert gas and a desiccant-filled spacer bar around the perimeter. The system relies on two critical sealants:

• A primary seal to prevent gas escape
• A secondary seal to provide structural integrity and weather resistance

Over time, exposure to UV radiation, temperature fluctuations, frame movement and environmental stress can degrade these window seals. Once compromised, moist air is drawn into the cavity.

When warm air carrying water vapour enters and meets colder internal surfaces, condensation forms between the glass panes.

The role of the desiccant in preventing moisture

Inside every insulated glass unit is a spacer bar containing desiccant. This material is designed to absorb any residual moisture trapped during manufacture. However, desiccant has a finite absorption capacity.

Once the amount of water entering the cavity exceeds what the desiccant can manage, visible condensation appears. At this point:

• The amount of moisture continues to increase
• The cavity environment is no longer dry
• Thermal performance begins to decline

Is condensation inside the unit different from other causes of condensation?

Yes. Distinguishing the causes of condensation is essential when advising customers. Surface condensation typically results from:

• High humidity levels indoors
• Poor air circulation
• Significant temperature differences between warm air and cold air
• Excessive amount of moisture from cooking, bathing or drying clothes

This form of window condensation appears on the inside of the window or on the outside of the window. It is influenced by humidity levels and ventilation.

Condensation between window panes is different. It forms within the sealed cavity and is unrelated to air circulation inside the property.

If the glass surface always looks misty and cannot be wiped away, the insulated glass unit has failed.

The impact on thermal performance and energy bills

When seal failure allows moist air into the cavity, the insulating properties of the double glazing deteriorate. A compromised insulated glass unit loses its gas fill, allows greater heat transfer, reduces thermal efficiency and contributes to rising energy bills.

The cavity is no longer functioning as an insulating barrier. Over time, this can result in cold spots around the pane of glass and increased heating demand.

Why replacement is the best solution

There is no reliable repair for condensation between window panes so the best solution is replacement. In many cases, the entire window frame remains serviceable. If the frame is structurally sound, replacing the insulated glass unit alone can resolve the issue efficiently.

However, where frames are ageing or poorly performing, replacing the entire window may be more appropriate.

At Dekko, we fabricate the complete finished window in-house, integrating premium insulated glass units into precision-manufactured frames. This approach ensures compatibility, consistent quality and dependable performance.

Our manufacturing process is built around supplying trade professionals with reliable products that reduce callbacks and protect margins. By fabricating the frame and inserting the insulated glass unit within our controlled facility, we maintain oversight at every stage.

For installers, this means confidence. When you specify Dekko windows, you are supplying a fully integrated system engineered for long-term durability.

Why specifying high-quality double-glazing matters

While no insulated glass unit lasts indefinitely, manufacturing quality significantly affects lifespan. Performance depends on materials, installation standards and environmental exposure. Specifying robust double glazing from a trusted manufacturer reduces the likelihood of early condensation between window panes and protects your reputation in the field.

Key takeaways

• Condensation between window panes is a clear sign of insulated glass unit seal failure
• It differs from standard window condensation caused by humidity levels
• Degraded window seals allow water vapour and moist air into the cavity
• Saturated desiccant cannot absorb further moisture
• Thermal performance declines, potentially increasing energy bills
• Replacement of the insulated glass unit is the only reliable solution
• Specifying high quality double glazing reduces premature failure
• Dekko manufactures complete window systems with integrated insulated glass units for dependable trade supply

Partner with Dekko for reliable insulated glass units

Dekko supplies trade customers with fully fabricated window systems incorporating high performance insulated glass units built to exacting standards to help you deliver dependable solutions to your customers. Contact our team today.

FAQs

Can condensation between window panes be repaired without replacing the unit?

No. Once seal failure has occurred and moisture has entered the cavity, the insulated glass unit must be replaced.

How long should double glazing last before seal failure occurs?

Well-manufactured double glazing can last 20 years or more, depending on installation quality and environmental conditions.

Is this caused by high humidity levels inside the home?

No. High humidity levels cause condensation on the inside of windows, not between sealed panes.