An introduction to window energy ratings (WER)

Three are three simple points to remember when considering energy rated windows:


  1. Windows can carry an energy rating similar to that given to electrical goods.
  2. Any window with a ‘C’ rating or higher is deemed to be energy efficient.
  3. A window with an ‘A’ rating should allow more free heat in from the sun than it loses from your home, over the course of a year.

For more information visit the British Fenestration Rating Council or consult their consumer faq.

Bulding Regulations

In general, compliance with building regulations can be demonstrated by installing:

  • Windows with an overall U value of 1.8W/m2K (or lower).
  • Windows with a WER rating of D (or above)
  • Glass centre pane U value of 1.2W/m2K (or lower).

Less efficient windows are permissible in some circumstances. When considering an extension to an existing dwelling, the energy efficiency of the extension may need to exceed current minimums in order to bring the overall energy efficiency of the extended building in line with current Building Regulations – please consult with your local Building Control and/or a qualified architect.

Need more information?
You can view energy ratings and efficiency documents on the downloads page