You are correct in that simply providing the frames excludes the supplying from requiring CE marking. If you manufacture or process glass, produce insulated glass units (IGUs) or fully glazed windows – you have to make a declaration of performance and CE mark your products to show they comply with the relevant standards. However, looking at the British Woodworking Federation website, it seems that one off bespoke designs are exempt:

“There will be only a few occasions where CE marking will not be required and these will be limited to building work which is exempt from complying with the Building Regulations and then for products which are ‘bespoke’, a unique design of window or doorset, and which are supplied for inclusion in only one building project.” (http://www.bwf.org.uk/choose-wood/ce-marking-windows-and-external-doorsets-what-should-i-specify)

However, I would recommend contacting the Glass and Glazing Federation to confirm that this is indeed the case. More information can be found here: http://www.ggf.org.uk/ce-marking-faqs

Andrew Hobbs (Build It’s Digital Assistant Editor)