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In 1995, the Building Regulations Approved Document L 'Conservation of Fuel and Power' was just one document. Then, in 2004, it became L1 and L2, applicable to domestic and nondomestic buildings respectively. Now, as we wade through the treacle that is the 2006 edition, we have four documents: L1A, L1B, L2A and L2B, the numerical suffix applying to work in existing dwellings or non-domestic buildings, the letter applying to new build and refurbishment respectively. They come into force on 1 April 2006.

The combined total of pages is actually less than the original from 10 years ago, but when you add up all the bits that are missing, what the ODPM calls 'second-tier documents, ' there is a forest of paperwork to get to grips with.

Second-tier documents are those that play an integral part in making sense of the new Part L but already exist in some other form. For Approved Document L2B ('Work In Existing Buildings That Are Not Dwellings'), there are 19 references to other documents. These include the standard BRE 'Thermal Insulation Avoiding Risks', to the less well known 'Cost-Effective Carbon Efficiency Improvements' by the Carbon Savings Trust. Throughout the course of these Approved Documents, or ADLs (which we are advised to read with caution as they are still 'subject to amendment'), footnotes direct us to void or unpublished material.

The finished document is scheduled for mid-January 2006.

The new ADLs have been tightened up to help the government hit the Energy White Paper and 'Action Plan For Energy Efficiency' targets and aim to bring down carbon emissions - the principal measure adopted throughout - by some 25 per cent for new buildings (a report by the National Energy Services questions that assertion, and shows that the current ADL was better at doing this for some constructions).

In brief, the ADLs set performance targets for the whole building rather than for construction or elements. Thus the Target Carbon Emission Rating (TER) for a dwelling, say, or the average taken over a block of apartments, must be shown to be higher than the proposed carbon emission rate (DER). There is only one calculation available, as the Carbon Index Method, Target Method (ADL:2002) and Elemental Approach are out of the window.

In Part L1A, the TER is a minimum guidance value and is measured in kg/m 2/year (the mass of CO 2/floor area) and takes account of heating, lighting and ventilation. (Unfortunately, the most common calculation tool for dwelling - referring to those under 450m 2 - relies on the revised SAP guidance, which is yet to be published. ) The calculation is as follows:

TER = (C H x fuel factor + C L) x (1 - improvement factor) Where C H and C L are calculated from SAP:2005 (forthcoming), the fuel factor is read off from a table on page 4 and the improvement factor is a standard 20 per cent (why they couldn't write 20 per cent into the printed calculation is anyone's guess).

The DER is produced in the same way, although can be based on drawings (scheme proposals) or on finished buildings (similar to the distinction between a 'building approval' and 'building notice'). With calculations based on drawings, SAP software calculations are to be submitted to Building Control Bodies (BCB) for approval but they can refuse to accept them on the basis of the person submitting being adjudged to be insuffi ciently qualified to do so. This sounds remarkably like the BCB being unable to handle the software and needing to be confident in the accuracy of the submission. The associated guidance on self-certification (which is not a recipe for a free-for-all) means that 'energy consultants' will be offering their services to architects in the next few months.

The benefit (and risk) of the as-built DER method is that the results can be incorporated into the Energy Performance Certificates (the energy ratings for homes required by the Energy Performance in Buildings Directive [EPBD], that was scheduled for release in January 2006, but has been held back until April).

What is described as a 'limit on design flexibility' is imposed by the building fabric insulation standards. U-values have not increased, although they are now 'area weighted' to give a net average. Designers and contractors need to be aware of some guidance, such as that air permeability may need to be less than the standard of 10m 2 at 50Pa in order to fine tune the TER for compliance. Throughout, performance guidelines rather than definitive rules apply.

Other issues include: solar gain has to be factored in without acting to the detriment of lighting levels (because this might increase the use of electric lighting and hence CO 2 emissions); robust standard details (RSD) are still applicable although not yet updated; and where RSDs are not followed, there are more rigorous air-pressure tests required, in as much as the air pressure test must comply with permeability levels as well as complying with the figures that have been factored in to the TER.

The irony of hundreds of documents on energy efficiency that have not been combined in one place for ease of access has not been lost on those who understand that the document aims to save every sort of energy except the most important - human.

Key documents - The Code for Sustainable Buildings has yet to appear.

This document was intended to explain what makes a building sustainable and to do away with BREEAM ratings and EcoHomes schemes, etc in one unified standard.

? The EPBD, which results in a building Energy Rating that must be displayed to public view.

? The BRE has produced a National Calculation Method software package for buildings other than dwellings (ADL2A and B).

See: http: //www. ncm. bre. co. uk - SAP: 2006 is the essential component. This will include factors such as solar, non-repeating thermal bridges, and fixed electric lighting. It is not out yet.

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