Last Updated on April 17, 2025

Condensation Between Window Panes: What Causes It & How To Fix It

Condensation between window panes is one of the most common and frustrating issues faced by UK homeowners and landlords. It’s not just a cosmetic nuisance. It’s a tell-tale sign of something more serious: a failed double glazing unit. 

Left unresolved, it can lead to mould, reduced energy efficiency, and increased heating bills.

In this expert guide, we’ll break down exactly what causes condensation between double glazing panes, how to fix it, and most importantly, how to prevent it from returning.

What Causes Condensation Between Window Panes?

If you’ve spotted mist, moisture, or a foggy haze trapped inside your double glazing, it’s a clear indicator of something more serious than a bit of surface condensation. 

This type of condensation occurs within the sealed unit, between the two panes of glass, and typically signals a failure in the window’s structural integrity. 

Below, we’ll explore the most common reasons this happens and why it’s not just a cosmetic concern, but a sign that your window is no longer performing as it should.

Ageing Seals and Natural Wear

Over time, the rubber seals around the edge of double glazed units begin to deteriorate. Exposure to UV light, changes in temperature, and general wear and tear cause the seals to break down, allowing moisture to enter the space between the panes.

Poor Window Installation

Incorrectly installed windows may look fine initially, but poor alignment, over-tightened frames, or inadequate sealing can cause the unit to fail prematurely. This leads to air and moisture entering the sealed space, causing condensation.

Drastic Temperature Fluctuations

UK homes often experience sharp contrasts between indoor heating and outdoor cold, especially in winter. This pressure differential can strain the seals, particularly in south-facing rooms or conservatories, where thermal expansion is frequent.

Frame Damage or Drainage Blockages

Damaged window frames, especially timber or low-quality uPVC, can hold moisture that eventually finds its way into the sealed unit. Inadequate drainage around the window can also lead to water pooling and seeping into vulnerable areas.

Manufacturing Defects

Although less common, poor manufacturing practices or substandard materials can lead to early failure of the insulating glass unit (IGU). This is especially likely with very cheap or imported windows lacking quality certification.

How to Fix Condensation Between Window Panes

Unfortunately, once condensation forms inside a sealed unit, it can’t be wiped away. Your options are:

1. Replace the Sealed Unit

This is often the most cost-effective route, especially if the window frame is still in good condition. The failed unit is removed and a new double glazed panel is inserted.

Pros:

• Less expensive than full window replacement
  
• Minimal disruption
  
• Improves thermal performance
  

Cons:

• Doesn’t address issues with the window frame
  
• Might not match older frames or aesthetics perfectly
  

2. Replace the Entire Window

If your window frames are damaged, dated, or causing seal issues, replacing the whole window may be the smarter long-term investment.

Full window replacement improves:

• Energy efficiency (better U-values, modern materials)
  
• Noise insulation
  
• Aesthetics and kerb appeal
  
• Long-term durability

Can Condensation Between Panes Be Prevented?

Yes, and it starts with quality windows and professional installation.

Here’s how to prevent future seal failures:

Choose High-Quality Double or Triple Glazing

Look for windows with:

• Low-E glass
  
• Warm edge spacer bars
  
• Argon gas filling
  
• BFRC-rated energy efficiency
  

Ensure Professional Installation

An incorrectly installed window is far more likely to fail within a few years. Make sure your installer is FENSA or CERTASS certified.

Maintain Adequate Ventilation

While seal failure causes internal condensation, poor indoor ventilation can make things worse. Ensure:

• Trickled vents are clear
  
• Kitchens and bathrooms are well-ventilated
  
• Humidity levels are monitored in colder months
  

Regularly Inspect and Maintain Frames

Rotting or warping uPVC and timber frames can allow water ingress, damaging the sealed units. A quick visual check every season can go a long way.

When Should You Consider Full Window Replacement?

Here are some red flags that it might be time to replace the entire window:

• Repeated condensation between panes in multiple windows
  
• Visible frame damage or rot
  
• Draughts or cold spots near the window
  
• Stiff or broken locking mechanisms
  
• Dated appearance impacting property value

If any of the above sound familiar, now might be the right time to consider upgrading. Wondering what a new window installation will set you back? Our guide on new window costs has all the details you need.

Benefits of Replacing Failed Windows

Whether you opt to replace just the sealed unit or the entire window, the benefits are immediate and measurable:

• Lower energy bills
  
• Improved thermal insulation
  
• Better soundproofing
  
• Enhanced security
  
• Improved appearance and property value

Get a Free Window Replacement Quote Today

We’ve helped homeowners and landlords across the UK upgrade to better-performing, longer-lasting windows that look great and perform even better. Whether you need one unit replaced or a full property upgrade, we’ll guide you through your options and provide a no-obligation quote.

Request your free window replacement quote now — quick, easy, and 100% tailored to your property.

Final Thoughts

Condensation between window panes won’t go away on its own—and it’s a clear sign that your home is losing efficiency and comfort. Fixing the issue quickly not only improves your living environment but could also save you money long-term.