CLG drop quite a few hints in the zero carbon consultation that they’re prepared to set the carbon compliance requirement at 70%. In other words, new schemes would have to achieve a reduction of 70% in regulated emissions relative to 2006 regulations. But if you look a little closer, it soon becomes clear that this figure isn’t what it seems.
Because we’re talking about a reduction in regulated emissions we ignore cooking and appliances, which in a very efficient home can be a very significant chunk. For example, I’ve been assuming that unregulated emissions might add on another 40%, but CLG reckons the figure is as high as 50 – 70% (see page 38 of the consultation doc). So total actual emissions would be 150 – 170% of regulated emissions.
Returning to CLG’s preferred reduction for carbon compliance (70% of regulated emissions), it’s clear that 70% doesn’t mean 70%, it’s actually much less. Here’s an illustration. If you look at the likely reductions in allowed emissions over the coming years as a percentage of regulated emissions, the picture looks like this:
Ok, that 70% appears to take a pretty big chunk out of the carbon. But if you look at the same upcoming regulations in terms of total emissions, the graph looks like this. I’ve assumed that unregulated emissions add 60% (averaging CLG’s 50% and 70%).
Suddenly our carbon compliance levels in 2016 are actually saving less than half of the total emissions. Keep in mind that at one point, the CLG was calling for a 100% reduction in total emissions from efficiency and onsite energy. They’re now taking a GIANT step back and only calling for a 44% reduction. Although it’s not immediately obvious from the consultation text, that is some serious backpedaling.
carbon limited 
maybe the thought is that for as long as unregulated emissions are well, unregulated, they should be left alone from the Building Regs perspective.
I would certainly advocate in an ideal world that decarbonising the electricity system should be dealt with via national energy policy. However, perhaps there should be recognition built in to the system to allow those future biomass chp district networks to be measured as contributing to the full emissions of a dwelling.
A wider question is how do you predict or quantify unregulated emissions, without stepping full into nanny-state ism? I know BREDEM 12 does it, but I would be really (relatively) interested to see the research that informs the calculation.
Having said that, pretending they don’t exist and ending up with the situation above is clearly unacceptable too.