Building Regulations and Window Energy Ratings
1) Check for existing WERs on file
A window installer or sealed unit manufacturer can commission a simulation for a WER using their chosen window frame specification with details of components from their chosen IG supplier. Alternatively, a fabricator can commission a WER which can be registered for use by installers. Therefore, before commissioning a WER, window installers or sealed unit manufacturers should consider this and contact their chosen fabricator to see what WERs they have on file that may be of use.
Building Regulations and WERs Page 7