The new Approved Document Part L2A:2006 (ADL2A) covers new buildings other than dwellings. If you are constructing a building comprising many dwellings, Part L1A applies but L2A will apply to the heated communal areas or shops under dwellings. Residential homes however, do not qualify as 'domestic', hence L2 will apply.
The five central criteria for ADL2A compliance are:
The CO 2 emissions from the as-built building must be less than the Target Emission Rate (TER). The ODPM creates a needless complication in describing this lesser figure in Approved Document Part L1 as the DER (Domestic Emission Rate), meaning L2 has to be known as the BER (Building Emission Rate). It follows a similar calculation path to L1 (see AJ 27.10.05), based on:
TER= C notional x (1 - improvement factor) x (1 - LZC benchmark) where LZC means a low- and zero-carbon emission energy source which is read off from Table 1; the improvement factor is similarly read off and relates to the required energy efficiency in buildings of a given type. Note that there is an extraneous and wilfully confusing letter 'l' in the calculation on page 4. This is an error.
U-value standards, air-permeability rates, controlled services etc have been given substantial limiting - or minimum - values that need to be met. U-values remain and are spelled out for areaweighted averages as well as for an individual element. For curtain walling, for example, it recommends the limiting U-value be applied to glazed areas and opaque panels separately. For CO 2 emissions, if you can make the case that the design will have high internal gains, then U-value limiting figures can be relaxed.
As well as meeting the criteria laid out in 21 clauses in L2A, you must also meet the design limits set out in L1 (here described confusingly as L1(a)(i) and L1 (b)).
These design-limit conditions are:
Minimising solar gain while making sure to limit the amount of compensating electric lighting. For all the talk of improving conditions, it is still deemed acceptable to subject staff to over 20 hours at over 28ºC. Even though this is per annum, in this country theoretically this could occur in one week. The impact of CO 2 emissions from air conditioning is factored into the equations and is intended to be a strong incentive towards natural ventilation.
The fact that air conditioning was invented to keep people cool is lost somewhat in this approach.
The emissions rates of the built structures must meet, or exceed, the pre-built calculation assumptions. These results must be verifiable. Be aware that even though Part L2 cites various documents, it often increases (improves) the criteria beyond those permitted in those documents. Ductwork leakage testing is a case in point (page 14).
A logbook, including operational data and maintenance instructions, must be handed over. Usefully, it suggests that an electronic copy would aid the updating of this information due to any subsequent alterations improving the condition of the building.