CODE FOR SUSTAINABLE HOMES ‘ZERO CARBON’ BIAS
H
omes are getting smaller. The average new home in England is now 76m2
compared1 to the average for all homes of 85m2 .
In order to protect what’s left of Britain’s countryside, planners now prefer high- density urban housing to suburban sprawl and developers are happy to oblige, as it enables them to sell more homes on the same-sized plots. As well as losing out on living space,
those living in ‘hobbit homes’ will also find it more expensive to upgrade their property to ‘zero carbon’ status than those living in more spacious abodes. Because of the way ‘zero carbon’ is calculated in the Code, smaller dwellings have a harder renewable energy target than bigger dwellings. It means that, to build or upgrade to ‘zero carbon’, as defined under the Code, is disproportionately more expensive for smaller houses. The standard for low-carbon dwellings
in England and Wales is the Code for Sustainable Homes2
aspects, of which energy and CO2
. This area covers nine
emissions are the most heavily-weighted. To be classed as ‘zero carbon’, for stamp duty purposes a dwelling must achieve a CodeLevel 6, which includes a mandatory CO2
emissions requirement. This corresponds to net zero emissions
when energy for internal uses – like appliances and cooking – is offset by renewable energy generation. This requirement is assessed using the Standard Assessment Procedure (SAP), the same as for Part L compliance. An additional calculation (SAP Appendix L2 and L3) is used to find the predicted energy use for appliances and cooking, which is not included in normal Part L compliance calculations. Appliance energy use is based on floor area and occupancy; cooking energy use is based solely on occupancy. The occupancy assumptions in SAP are
based on floor area, but are highly non- linear, as shown in Figure 1. For example, 60 m2 occupancy
gives an
The larger house uses six times more energy for internal appliances in total, but only a third as much if measured per floor area
www.cibsejournal.com
June 2013 CIBSE Journal 27
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