I suppose if your frame isn’t thermally efficient enough to achieve an A rating, then a C or B rating is better than nothing. But in reality, there are plenty of suppliers out there now that are able to offer A rated windows. And the cost differences between C and A are minute, it wouldn’t make much sense to offer C if A rated windows cost only slightly more.
There’s one great big advantage about the changes to Part L in 2010. All those who are not selling energy rated windows are either going to get left so far behind the catch up will be too long, or companies will just go bust due to the inability to offer products that conform to the rules and are not competitive with other products on the market.
SIGN THE WINDOWS SCRAPPAGE SCHEME PETITION NOW!: http://www.petitions.number10.gov.uk/windowscrappage