If you’re considering investing in double glazing—or already have it—a common and crucial question is: How long does double glazing last? It’s a significant home improvement, and knowing the expected lifespan is key to budgeting and future planning. The good news is that modern double-glazed windows are a long-term investment, offering decades of efficiency and comfort.
Double Glazed Windows should last Decades, not years.
On average, a high-quality, professionally installed double-glazed unit (the sealed glass panel) and its accompanying frame will last between 20 and 35 years. Some units can even exceed this range, reaching 40 years or more with proper maintenance.
However, this isn’t a single, fixed number. The lifespan is influenced by several factors.
Key Factors Affecting Longevity of double glazing
The durability of your double glazing is a function of the following elements:
1. Quality of Installation
This is perhaps the most critical factor. A poorly fitted window can put undue stress on the seals and frames, leading to premature failure.
Professional fitting ensures the frame is plumb and square, and the unit is seated correctly, maintaining the integrity of the seal.
A correct fit prevents water ingress around the frame, which can cause frame damage and eventual unit failure.
2. The Sealed Unit (The Glass Itself)
The core of double glazing is the sealed unit – two panes of glass separated by a spacer bar and filled with an inert gas (usually Argon). The seal around the edge is what holds the gas in and keeps moisture out.
Seal Failure: The most common issue is the failure of this perimeter seal. When the seal breaks down, moisture-laden air enters the cavity, causing condensation, or a “foggy” appearance, between the panes. Once this happens, the unit’s insulating properties are severely reduced.
Spacer Bar Material: Older units used aluminum spacer bars, which can conduct cold and slightly decrease efficiency. Modern units often use ‘warm edge’ spacers, which are less conductive and better at protecting the seal.
3. Frame Material
The material of the window frame significantly impacts its maintenance needs and overall lifespan.
| Frame Material | Typical Lifespan | Key Maintenance Needs |
| uPVC (Unplasticised Polyvinyl Chloride) | 20-35 years | Requires minimal cleaning; no painting needed. |
| Aluminium | 30-40+ years | Highly durable; minimal maintenance. |
| Timber (Wood) | 30-60+ years | Requires regular painting/staining and maintenance against rot/warping. |
uPVC windows are the most common choice due to its balance of cost, longevity, and low maintenance.
4. Weather and Exposure
Windows facing harsh elements – such as constant direct sunlight, driving rain, or sea spray – will naturally degrade faster than sheltered windows. UV rays are particularly harsh on uPVC frames and the unit seals.
When Does Double Glazing Need Replacing?
While a replacement is usually necessary around the 20-35 year mark, there are definitive signs that your double glazing is past its prime and needs attention:
Foggy Windows: You see persistent condensation, mist, or moisture inside the two panes of glass that you can’t wipe away. This is the clearest sign of seal failure.
Drafts or Leaks: You feel cold air coming in or notice water dripping from the frame even when the window is closed. This could indicate a problem with the frame seals or hinges.
Difficulty Opening/Closing: The frame has warped, or the mechanism is sticking, making operation difficult.
Noise Intrusion: If external noise levels suddenly increase, the seal may have failed, or the window is no longer insulating correctly.
Deterioration of Frame: Cracking, significant yellowing (on uPVC), or extensive rot (on timber) means the frame itself is failing.
Pro Tip: If the glass unit has failed (foggy appearance) but the frame is still in excellent condition, you only need to replace the sealed unit, not the entire window. This can save you a significant amount of money.
Maximising the Lifespan of Your Double Glazing
You can help your windows reach the higher end of their expected lifespan with simple maintenance:
Clean Weep Holes: These small holes at the bottom of the frame allow trapped water to drain out. Keep them free of dirt and debris to prevent water build-up.
Lubricate Moving Parts: Apply a silicone spray or light oil to hinges and locking mechanisms annually to keep them moving smoothly.
Regular Cleaning: Clean the glass and frames with mild soapy water. Avoid harsh, abrasive chemicals that can damage the seals or the frame finish.
Inspect Seals: Periodically check the mastic seal (silicone) around the outside of the frame for cracking or shrinking and re-seal if necessary.
The Verdict
A good set of double-glazed windows is an asset that will provide thermal and acoustic benefits for decades. By opting for a quality product and a certified windows installer, and dedicating a little time to basic maintenance, you can confidently expect your double glazing to last for 25 years or more.
