I'm confused about this myself!

That doc breaks the guidance into L1A, L1B etc but I can't see anywhere that summarises the emissions targets for the different categories. I'm also interested how they would differ in the 2013 and 2016 revisions, given that non-domestic isn't due to go zero carbon until 2019 and that the picture is far less clear still on refurbs.

Anyone know?

This whole topic is depressing news for the small joinery firm. It seems to have been steamrollered through by the double-glazing fraternity. It is all very good for new builds but, for many many people like myself, living in an older property, if these ridiculous Stasi-regulations come into place then it will be impossible for me to replace any of my windows and make them more energy efficient simply because they are all non-standard sizes and to fit a plastic window would be to adulterate an elegant period property.

This whole focus on windows is disproportionate and a waste of money. Take my house. I have solid walls. I lose more heat through those than I do through the windows. The rooms are small and so it is not viable to insulate internally. Adding external insulated render will make me look like a tea-cosy as there is not sufficient depth of window cills and door frames to cater for the 80mm thick render. So I would like to compromise, do my bit and fit new double-glazed windows. But now I won't be able to because there won't be a single supplier who can cost-effectively provide me with same.

To further point out why this is such a load of rubbish, my windows are relatively small - typically 0.5 sq m in size. If I went ahead under existing regulations and installed a set of timber windows that are double-glazed then my heat loss for 18 degrees inside and 0 outside is X watts. If, after these new regs come in, I can actually find someone to make them and that I can raise the money the size of the GDP of an African republic to pay for them, then the heat loss will be Y watts. Do you know what the difference is between X and Y ? 1000 watts? 500 watts? 100 watts? 10 watts ? No....3.6 watts. I rest my case.