Double glazing works by trapping a layer of air or gas between two panes of glass, creating an insulating barrier that keeps heat in and cold out. When this seal fails, moisture enters the gap and the insulating properties are compromised.
Why Do Sealed Units Fail?
The average lifespan of a sealed unit is 15-25 years, though this varies based on quality, installation, and exposure. The main causes of failure include:
- Age and weathering - The seal naturally degrades over time, especially on south-facing windows exposed to more UV radiation
- Poor original installation - If drainage channels are blocked or the unit was fitted incorrectly, water can pool and accelerate seal failure
- Temperature fluctuations - Repeated expansion and contraction stresses the seal, particularly in conservatories
- Physical damage - Even minor impacts can compromise the edge seal without cracking the glass
Repair vs Replace: Making the Right Choice
Many homeowners assume failed double glazing means replacing the whole window. This is rarely necessary. If your frames are structurally sound and not warped or damaged, replacing just the sealed unit is the sensible choice.
However, if your frames are over 20 years old, showing signs of rot (timber) or becoming brittle (early UPVC), full replacement may be more economical long-term. We will explain your options clearly so you can make an informed decision.