Make sure your home has the right windows to make it as energy efficient as possible

MT960219Windows are rated according to their U-value, or the heat loss through the glass and frame. The lower the U-value, the more efficient the windows. Quality double glazing could have a U-value of around 1.5 and triple glazing around 1, but at a far greater expense (at least £75 per m extra). 

This rating doesn’t take into account two other main factors which determine the performance of a window – how well it absorbs warmth from the sun (solar gain), and heat lost through draughts. However, the British Fenestration Rating Council (BFRC) rates windows from different manufacturers using all three measures. So far so good, but there’s a catch: you’re not getting a true indication of all the options, as some smaller manufacturers haven’t signed up to the scheme.

Then you have to decide whether wood is more sustainable than cheaper uPVC, which is the subject of passionate debate in the windows industry. The former is renewable and regarded as a more eco-friendly resource, while the latter is made from oil. On the other hand, wood requires more maintenance, and painting and preservatives can pollute. WWF has tried to nail the issue in a report which says, sustainably speaking, wooden windows pip uPVC to the post.

If your windows are salvageable but your budget is restricted, why not consider secondary glazing. For heat retention, a 10-16mm gap between the existing window and the new glass is suggested.

If your windows are in decent condition, it could be more eco friendly to stick with what you’ve got rather than rip them out and add to the waste stream.


  • Double glazing could reduce your home’s heat loss.

  • If budget restricts, you don’t have to do the whole lot in one go.


  • Very expensive, so perhaps better to spend money on other eco benefits elsewhere.

  • It can be difficult finding an installer who specialises in highly efficient wooden windows.

  • You might need to do a little internet research for this, and use a local builder to do the fitting.

Useful Contacts

The British Fenestration Rating Council: www.
Green Building Store:

Words: Dominic Murphy  Image: Jefferson Smith

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