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Approved Document L: Conservation of fuel and power

by Austin Williams
NBS Content Development Manager

New measures to make buildings more energy efficient, were announced by ODPM and Defra on 13 September 2005. These much awaited changes are having a significant effect on design and construction practices and are intended to improve energy efficiency standards by 40%.

Approved Document L: Conservation of fuel and power, which came into force on 6th April 2006, sets out to save one million tonnes of carbon per year. The document has been published in four parts:

• L1A: Conservation of fuel and power in new dwellings,
• L1B: Conservation of fuel and power in existing dwellings,
• L2A: Conservation of fuel and power in new buildings other than dwellings, and
• L2B: Conservation of fuel and power in existing buildings other than dwellings.

At only 20-25 pages each, these documents are considerably shorter than previous versions and are intended to be more accessible than Approved Document L: 2002 (ADL 2002). However, there are a series of 'second tier documents', referenced throughout these new ADLs, that need to be borne in mind to navigate the user successfully through the process. Many of these will play an integral part in making sense of the new Part L.

For Approved Document L2B: Conservation of fuel and power in existing buildings other than dwellings, for example, there are 19 references to other documents, ranging from  the BRE document 'Thermal insulation avoiding risks', to the less well-known 'Cost Effective Carbon Efficiency Improvements' written by the Carbon Savings Trust. A key document is the updated Standard Assessment Procedure - which is essential for completing fuel calculations, and includes factors such as solar, non-repeating thermal bridges, and fixed electric lighting. It is available through the BRE website (www.bre.co.uk/sap2005).

The new ADLs have been tightened up to help government hit their Energy White Paper and 'Action Plan For Energy Efficiency' targets and aim to bring down carbon emissions – the principle measure adopted throughout – by some 25% for new buildings.

In brief, the ADLs set performance targets for the whole building rather than for construction or elements. Thus, in Part L1A, 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 Dwelling Carbon Emission Rate (DER). This is the only calculation method allowable from April – that is for schemes that are being assessed by the Building Control Body from April and therefore may apply to schemes in preparation now. For such schemes, the current Carbon Index Method, Target Method (ADL: 2002) and Elemental Approach are no longer permissible.

In Part L1A, for example, the TER is a minimum guidance value and is measured in kg/m²/year (the mass of CO2/floor area over time) and takes account of heating, lighting and ventilation. The actual designed and constructed building's emission rates must be less than this figure. For dwellings over 450m², reference is made to the calculation tool, the Simplified Building Energy Model, which is, as yet, unpublished. For more common dwelling sizes - referring to those under 450m² – the calculation relies on SAP guidance. The calculation is as follows:

TER = (C_H x fuel factor + C_L) x (1 – improvement factor)

Where C_H and C_L are the CO₂ emissions arising from the hot water and heating systems (including pumps, fans, etc) and from the internal fixed lighting respectively. These figures are calculated from SAP: 2005. The fuel factor is read off from a table on page 4 (ADL1A: 2006) and the improvement factor is a standard 20%.

For terraced housing, or apartments within buildings, the TER may be calculated on the basis of:

(TER₁ x Floor Area₁) + (TER₂ x Floor Area₂) + etc
Floor Area₁ + Floor Area₂ + etc

The DER is produced using the same process, although it can also be based on drawings (scheme proposals) or on finished buildings (similar to 'building approval' and 'building notice'). With calculations based on drawings, SAP software calculations must be submitted to Building Control bodies (BCB) for approval but they can refuse to accept it on the basis of the person submitting adjudged to be insufficiently qualified to do so.

The benefit (and risk) of the as-built DER method, is that the results can be incorporated into the Energy Performance Certificates (which are the energy ratings for homes, required by the Energy Performance in Buildings Directive [EPBD] which is due to be released in April 2006). In Part L2A and Part L2B, the 'DER' becomes the 'BER' (Building Emissions Rate).

What the ADLs describe as a 'limit on design flexibility' in housing is imposed by the need for an improvement in the insulation standards of the building fabric. Effectively, the ODPM was concerned that poor building fabric insulation standards might be offset by low energy, low emission technology within the building in order to reach the emissions targets. To encourage an improvement in the building fabric, the presence of U-values means that the external envelope and building elements must have minimum insulation levels.

In the new Part L1A, U-values have not increased since those set in the 2002 regulations, although they are now 'area weighted' to give a net average. Designers and contractors need to be aware that some guidance, such as the air permeability standard of 10m³/hm² at 50Pa may need to be exceeded in order to fine tune the TER for compliance. Throughout, performance guidelines rather than definitive rules apply.

Other issues for L1A include:

• Solar gain has to be factored in without acting to the detriment of lighting levels (because if cutting out sunlight encouraged users to leave lights on this might increase the use of electric lighting and hence CO₂ emissions).
• A minimum recommended use of fluorescent lights and low energy light fittings are suggested and prioritised over halogen lamps.
• 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.

Air pressure testing compliance will follow the recommendations of the Air Tightness Testing and Measurement Association's “Air Permeability Measurement” (publication date to be confirmed). Those not using RSD must test 2 units of dwelling type per development, or 5 percent of each dwelling type overall. A dispensation for small developers is that if a pressure test has been carried out on a dwelling in the last 12 months, dwellings constructed by the same developer on the 'same building type' will be deemed to satisfy. If relying on calculations, the dispensation allows for an air permeability value of 15m³/hm² at 50Pa to be factored into the TER to provide a suitable contingency.

Key documents for ADL1A:

• The Code for Sustainable Buildings. This document, due for publication in April 2006, intends 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 requires that a building Energy Rating be displayed to public view.
• The BRE have produced a National Calculation Method software package for buildings other than dwellings (ADL: 2A and ADL: 2B). See: www.ncm.bre.co.uk
• SAP: 2005 is currently available from www.bre.co.uk/sap2005.
• Using Robust Standard Details (RSD) should eliminate the need for air pressure testing although a checklist detailing compliance must be included in submissions to the Building Control Body. New RSDs are forthcoming.
• The Air Tightness Testing and Measurement Association's (ATTMA) “Air Permeability Measurement” gives guidance on air pressure testing. Publication date to be confirmed.
• A checklist at the back of Approved Document Part L1A provides a step-by-step guide to ensure that all eventualities are covered.

Written March 2006

 

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