13-12-01 About 27 % of the national UK emission of CO2 is caused by the energy consumption of houses. Another 19 % is derived from non-domestics buildings and associated building services. This 46 % of the national total is an area where government legislation could have a meaningful impact on these emissions, hence the proposed moves to improve the current energy efficiency standards of Part L.
From the designer's perspective, CO2 emissions can be radically curtailed by the efficient design and insulation of buildings, in conjunction with energy saving devices and facilities management.

The proposal set out in the initial Part L consultation paper was to introduce the new standards in 2 stages, each 12 months apart. However, during the consultation period the response from the industry was to 'leapfrog' stage 1 and move directly to the stage 2 proposals, which has now been reflected in the new standards.
Amendments to the Approved Document Part L (ADL will become enforceable in March 2002. The new document will be divided into two parts, Part 'L1' for Dwellings and Part 'L2' for Non Domestic buildings. However, the energy performance standards required for all categories will be very similar. From a purely thermal perspective, the new Part L will amplify the need for higher levels of insulation and emphasise the importance of robust performance in real buildings, as opposed to theoretical calculations.

Compliance can be achieved by one of 3 methods;
-- The Elemental Method: each element of the building fabric must achieve a maximum U value with a minimum boiler efficiency.
-- The Target U Value Method: This allows more design flexibility, allowing an area of the building that is less well insulated to be offset against another where the insulation is better. Boiler efficiency and solar gain may also be taken into account.
-- The Carbon Index Method: this also offers design flexibility while achieving similar performance to that obtained by the Elemental Method. The building's performance is related to CO2 release, with values ranging between 1-10. Similar to the current SAP method of compliance, requirements will be met where the Carbon Index (CI) for the dwelling is not less than 8.0.

Due to the tighter controls on the wall fabric from 0.45 to 0.35W/ m2K (0.30 in Scotland), a common misconception is that the resulting increase in insulation thickness will require cavities to be greater than 100 mm wide. This is not the case. Traditional masonry cavity wall constructions will meet requirements for all block types, which is similar to today's average cavity size.
Rockwool is in the process of producing a new Part L Solutions Guide for designers and specifiers. This guide will illustrate cost effective constructions to meet or exceed the new regulations using conventional building techniques.