What is double glazing?
A double glazed window has two panes of glass separated by a gap filled with air or an inert gas, which acts as an insulator. Double glazing has become a standard feature in most UK homes because it retains internal heat, reduces noise and gives a stronger barrier against the weather, as well as security benefits.
Want the services and materials checked? Get a survey price for the home you are buying.
How long do double glazed windows last?
On average, double glazed windows last between 20 and 25 years. High-quality units can last up to 35 years if properly maintained.
The actual life expectancy depends on:
- the quality of installation;
- the type of materials used;
- the local climate;
- how well the windows and frames are maintained.
Life expectancy can be significantly reduced if the windows are not installed correctly or the frames are not adequately maintained.
What goes wrong with double glazed windows?
The common problems are failed seals, draughts, poor installation and cracked or broken glass, all of which reduce thermal efficiency and performance.
- Seal failure: damaged seals let the insulating gas escape, reducing efficiency.
- Draughts: these occur when frames have warped or seals have deteriorated.
- Poor installation: this can shorten the life of the window and compromise its performance.
- Cracked or broken glass: a problem, although usually easy to fix.
How do you make double glazing last longer?
Regular cleaning, checking the seals and frames, lubricating moving parts and repainting painted frames all extend the life of double glazed windows.
- Clean regularly with soft cloths and non-abrasive cleaning solutions. This prevents a build-up of dirt and grime that can damage the seals.
- Check the seals regularly for damage or wear and tear.
- Check the frames and seals after severe weather, and repair any damage quickly.
- Lubricate moving parts regularly so the windows operate smoothly.
- Repaint painted windows every few years to protect them from the elements.
How much does double glazing cost?
Standard double glazing in the UK typically costs between £400 and £600 per window (figures given when this guide was first written). Larger windows or those with special features can cost significantly more.
The cost depends on the size and type of window, the type of glazing and materials, and the complexity of the installation. Double glazing improves thermal efficiency and adds comfort through insulation against outside noise and harsh weather.
What to look for when viewing
- Condensation or misting between the panes.
- Draughts around the frames.
- Warped frames, or seals showing damage or wear.
- Cracked or broken glass.
- Windows that do not open and close smoothly.
- Peeling or neglected paint on painted frames.
- Mould or mildew around the windows.
What to do next
- Ask how old the double glazing is, bearing in mind a typical life of 20 to 25 years.
- Budget for replacing units with failed seals, using the per-window cost as a guide.
- After moving in, keep to a routine of cleaning, seal checks, lubrication and repainting.
What a survey can — and cannot — tell you
A building survey provides an informed assessment of the visible condition of a property. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.
For windows, a survey records visible defects that indicate failing double glazing, helping a buyer judge whether units are likely to need repair or replacement.
- Condensation between panes, indicating failed seals.
- The visible condition of frames and seals, including warping.
- Cracked or broken glass.
- Signs of mould growth around windows.
However, there are limitations to what a survey can determine without intrusive investigation.
- The quality of the original installation cannot always be judged from visible surfaces.
- Windows that are inaccessible or obstructed cannot be fully inspected.
Where higher-risk indicators are identified, further specialist or intrusive investigation may be recommended.
Frequently asked questions
How long does double glazing last?
Typically 20 to 25 years. High-quality units can last up to 35 years if properly maintained.
What does condensation between the panes mean?
It means the seal has failed and the insulating gas has escaped, which reduces the window's efficiency and can lead to mould and mildew.
Why do double glazed windows become draughty?
Draughts can occur when the window frames have warped or the seals have deteriorated.
How should double glazed windows be cleaned?
With soft cloths and non-abrasive cleaning solutions, regularly, to stop dirt and grime building up and damaging the seals.
How much does double glazing cost per window?
Standard double glazing typically cost between £400 and £600 per window when this guide was first written, with larger or specialist windows costing significantly more.
