For specific guidance, Approved Document L2 offers three methods for demonstrating that reasonable provision has been made for limiting heat loss through the building fabric:
The elemental method has the advantage that it does not require complex calculations. Each aspect of the building is considered individually, and a minimum level of performance must be achieved in each of the elements. Some flexibility is provided by allowing trade-off between different elements of the construction, and between insulation standards and heating system performance.
The whole-building method considers the performance of the whole building. It is applicable to office buildings, but similar alternative methods are available for schools (see DfEE Building Bulletin 87 ) and hospitals (see NHS Estates Guides ).
The carbon emissions calculation method considers the performance of the whole building and can be applied to any building type. To comply, the annual carbon emissions from the proposed building should be no greater than those from an equivalent notional building that satisfies the criteria of
the elemental method. The carbon emissions from both the proposed building and the notional building must be estimated by means of an appropriate calculation tool.
Although there is no obligation to adopt any particular method or solution for satisfying the requirements, the Approved Document provides a check-list, in the form of a 'Summary Guide', that helps the designer choose the most suitable of the above three methods. This summary guide is shown in flow chart form in Figs 3.1a, 3.1b and 3.1c.
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