Sustainable Housing – defining zero carbon

In the last budget on 23rd March, the UK government, quite discretely, changed the definition of zero carbon.  The 2011 budget changed the requirements from having to balance all the regulated loads plus an allowance for cooking and appliances, to simply balancing the emissions from the regulated loads only.  In essence this is just the heating, hot water and lighting loads.   There appears to be a split in opinion on this issue, with some for the change arguing that it is a more realistic target for the construction industry to meet, while the other camp argue that the new definition isn’t really zero carbon.

I have been involved in a project that has just completed the construction of a Code 6 vicarage.  Level 6 of the code for sustainable homes requires the building to meet “zero carbon”.  The new definition is effectively the requirement for Code 5 in the 2009 version of the Code for sustainable homes on the dwelling emission front.  With the old definition, there was no way out of producing a small power station for a house.  In the vicarage the south facing roof was covered in around 8 kWp of photovoltaic panels. The cost of these panels still significant, even with the feed-in-tariffs it is going to put a lot of people off the thought of installing them, and even thinking about going for Code 6.

2016 is still the target date for all new homes to be zero carbon, and built to Code 6 standards.  The pressure to meet this target is probably behind the change in the definition of zero carbon.  With this new definition, it is feasible to build a dwelling with minimal generating capacity, and so reducing the cost.  I’m sure the Passivhaus approach will come more into the frame – a more fabric first approach.  Reducing heat loss (or gain for summer months) simply makes sense.

Even with the definition of zero carbon changing, making it cheaper to build to Code 6, it will still be difficult.  Whether using the Passivhaus approach or not, the correct site is even more important than ever.  The Code for Sustainable Homes includes other issues, not just energy, that needs to be taken into account.  Things like ecology, cycle storage, water use and the lifetime homes standards have rarely stopped a house from being built in the past, but this may happen once Code 6 becomes the mandatory standard.