16-17 SB1009 Analysis 18/9/09 11:46 am Page 16
ANALYSIS
Definition of zero-carbon buildings
In July, the Government announced its intentions for the Zero Carbon Definition.
Dave Cheshire explains what it actually means in practice for housing development projects
DESIGNS ON THE
FUTURE
T
he consultation on the definition of zero which could cost around £2-3,000/tonne of
carbon proposed three steps towards CO
2
. Then it starts to get more expensive with
compliance. The first stage sets a mini- presence detectors on lighting costing around
mum level of energy efficiency, the second sets a £5-6,000/tonne. Costs could rise to £10-
minimum target contribution from low and 20,000/tonne of CO
2
for advanced insulation
zero carbon technologies called ‘carbon compli- standards. So, assuming energy efficiency com-
ance’ and a third stage uses on and off-site pliance is set at an appropriate level, then meet-
‘allowable solutions’. The last stage is there to ing the requirements through low and zero cost
make up the difference in CO
2
reductions measures could cost around £2-3,000/tonne.
between the first two stages and full zero carbon On-site renewable energy costs (‘carbon
and includes solutions such as exporting heat to compliance’) can vary widely depending on the
surrounding buildings or contributing towards technology applied. Typically, costs are around
community heat infrastructure and plant. £5-10,000/tonne CO
2,
which makes renewables
July’s written statement by John Healey MP less attractive when compared with the lower
confirmed the definition of zero carbon. This cost energy efficiency measures or allowable
included setting the minimum level of ‘carbon solutions. And on many sites there will be a
compliance’ for dwellings at 70% compared physical limit to just how much energy can be
with 2006 Part L – while the level for non- generated on-site. On a constrained inner-city
domestic buildings has yet to be set. It also
proposed a guideline maximum price that they
expect the industry to bear to implement
‘allowable solutions’. This has been set at £100
per tonne of CO
2
. Assuming this is the same for
non-domestic buildings and capitalising this
‘
The allowable solutions for
housing include both further
enhancements on-site and
off-site solutions to reduce the
figure over a 30-year period gives an equivalent
capital expenditure of £3,000/tonne CO
2
emit-
ted a year. So, how does this compare to energy
efficiency and on-site renewable technologies?
There are some potentially low-cost passive
’
overall carbon emissions
site, biomass and wind may be ruled out, and if zero-carbon community heating infrastruc-
the building is overshadowed, there would be ture). This is likely to be offered as a choice
energy efficiency measures that require funda- limited yield from solar technologies. Ground between implementing further measures on-site
mental architectural design changes. Optimising area may limit the contribution from ground or paying into a local community fund. In most
window sizes to balance daylight with heat source heat pumps. On a constrained site it situations, it is likely to be more cost effective to
gain/loss; providing rooflights and light wells; makes sense to move quickly to allowable pay into a local community fund.
changing the internal configuration of spaces to solutions, but on a site with potential for on-site For some projects it may be beneficial to
ensure areas that have high internal heat gains generation, it may well prove to be cost-effec- incorporate on-site technologies, for example, a
are positioned towards the north elevations. If tive to exceed the minimum levels of carbon CHP plant that can export heat to the local
these changes are implemented as part of the compliance. community. Contributions to off-site wind tur-
design concept, then they could have little or no The allowable solutions for housing include bines, for example, could be cheaper than the
cost implications. In fact, measures such as opti- both further enhancements on-site (for exam- £3,000/tonne of CO
2
maximum for allowable
mising window sizes may even reduce the ple, advanced building control systems which solutions and so could make it even more likely
glazed areas and so provide potential savings. reduce the level of energy use in the home) and that developers would only invest the minimum
Then there are low-cost active measures, such off-site solutions to reduce the overall carbon necessary to achieve energy efficiency and car-
as lighting controls and improved air tightness emissions (for example, investments in low and bon compliance.
16 October 2009 ❘ Sustainable Business
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36