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'L' is for low (heat losses)

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Part L has at last been revealed - it requires robust detailing, better practices on site and more rigorous certification

Even the Department of the Environment, Transport and the Regions (DETR) has realized that the rolling revision of most of the Building Regulations Approved Documents (Parts A, B, E, F, H, J, L and M are all up for grabs) has been a source of concern for the building industry; specifiers, suppliers and contractors alike.

Everybody knows that something is afoot, but nobody has been willing or able to commit to anything definitive until the ubiquitous consultation and appraisal processes have ended.

For Part L, 'Conservation of Fuel and Power', that time is now (though minister for housing, planning and construction Nick Raynsford warns that the draft 'cannot be finalized' until responses to the current consultation on Part E, Resistance to the passage of sound have been received).

Remarkably (or should that be unsurprisingly) there were only 370 responses to the consultation. To allay the fears that the industry is unprepared for massively changed legislation, the DETR has decided to issue a 'draft interim' document.

When questioned by the AJ, a spokesman from the DETR said that there were no plans for the department to provide any guidance, training, seminars or conferences on the subject, adding 'that will have to be done by the industry itself '. This may be an attempt to provide an opportunity for self-improvement through CPD, and a financial boost for 'training consultants', but it has the potential to create some misunderstanding.

The DETR has sent out guidance but, in typically unhelpful fashion, this lists the variations to the consultation document, not variations to the current Part L. In order to fathom out the changes, one has to read the consultation document, cross reference these proposals with the amendments to the consultation, and then compare and contrast with the original (current) Approved Document. This article looks at the requirements for air tightness and reduced thermal bridging specifically, although other key changes are shown in the box article (opposite page).

Anyone wishing to access the consultation document (the consultation process has now ended), and to explore the amendments should visit www. construction. detr. gov. uk/ consult/eep/index. htm The new guidelines recommend that the building fabric should be constructed to avoid significant thermal bridges or gaps in the insulation layers within the various elements of the fabric, at the joints between elements and at the edges of elements such as those around window and door openings. Reasonable provision should be made to reduce air infiltration (unwanted leakage) through extraneous air paths in the building fabric, notwithstanding the requirements of Parts F and J (ventilation for health and for combustion purposes respectively).

The requirements may also be met by demonstrating compliance with a forthcoming Building Research Establishment (BRE) paper, Assessing the Effects of Thermal Bridging at Junctions and Around Openings.

However, this paper is not yet available, and sources in the BRE suggest that it will not be published until after June.

The draft interim document makes reference to certain approved 'robust construction details'which are intended to indicate the deemed-to-satisfy requirements for limiting thermal bridging. Although these details have not yet been approved, they are intended for publication as the same time as the launch of Part L in August.

The AJ understands that building inspectors will pay particular attention to reducing the bridging and air infiltration effects between elements and around openings, taking these as-yet unknown details as benchmarks.

For building elements that contain unavoidable repetitive thermal bridges, which mean that the insulation is not continuous - for example, wall ties in cavities, timber joists in flat roofs, or even mortar joints in insulating blockwork - the effects of these thermal bridges must be taken into account when assessing the Uvalue performance. The calculation method for this is known as the combined method. The inverse of half the sum of both the upper and lower level resistance figures is the ascribed Uvalue, and this must be multiplied by factors relating to the method and accuracy of fitting insulation and a factor relating to the location and type of mechanical fixing. These compensatory factors are tabled in the document. In this way, thermally weak elements, which should be kept to a minimum, can be accounted for in the overall energy rating efficiency of the building.

To show that the calculation, specification and actual installation of the insulation complies with the Building Regulations in buildings other than dwellings, applicants should submit to the building control department a report to that effect, signed by a competent person. This report must document the use of appropriate fixing techniques and design details with a supporting regime of site practice and inspection. Alternatively, it could be a report - again signed by a competent person - giving the results of infra-red thermography inspections that show that the insulation is reasonably continuous over the whole visible envelope.

In order to demonstrate the integrity of the air leakage provisions, a report should be submitted that records the results of an air leakage test. This should indicate an air permeability rate of 10m 2/hr/m 2at 50Pa.

Methods of air testing were given in brief in AJ 30.11.00.

The owner or occupier of the building should be provided with details of the installed building services plant and controls, their method of operation, state of maintenance, and details forecasting annual energy consumption for the building.

This information will probably need to be included within the health and safety file, although it seems that, as yet, there is no party designated with the responsibility for carrying out this work. The details could reasonably be expected to include:

a schedule of the floor areas of each of the building zones, categorised by environmental servicing type (eg air-conditioning, natural ventilation);

the purpose of the individual building services systems;

the location of relevant plant and equipment;

the installed capacities (input power and output rating) of services plant;

descriptions of the operational and control strategies of the energy consuming services in the building;

operating and maintenance instructions that include provisions enabling the specified performance to be sustained during occupation;

a schedule of the building's energy supply meters and sub-meters, indicating for each meter the fuel type, its location, identification and description. The schedule should indicate how the normalised energy performance of the building (or each separate tenancy in the building where appropriate) can be calculated from the individual metered energy readings to facilitate comparison with published benchmarks; and for systems serving an office floor area greater than 200m 2, a design assessment of the building services system's carbon emissions and the comparable performance benchmark.

Key changes in proposed Building Regulations The new Approved Document lists a series of additional requirements for fuel and energy conservation, some of which are outlined below:

Part L1 will relate to dwellings and a separate document, Part L2 will relate to buildings other than dwelling houses.

The three ways of demonstrating reasonable provision for limiting heat loss through the building fabric include the elemental, the target U-value and carbon index methods.The elemental method cannot be used with a direct electric heating system.

Carbon index calculations are documented in Appendix M of the draft interim report and will be incorporated into SAP 2001, which will be published later this year.Once again, this is not yet available.

Effectively, the carbon emission factors take account of all CO 2emission sources, as part of the government's commitment to reduce CO 2emissions under the Kyoto protocol.The results will need to be monitored and documented.

Window, door and rooflight replacements, and the replacement of boilers and services installations will need to comply with Part L, although maintenance items are exempted. In domestic dwellings, rooflights are exempted.The regulations now apply to existing dwellings rather than simply to 'material alterations and change of use'.

The flexibility to trade off U-values against boiler efficiency has been removed, although 'reasonable provision' for boiler efficiency can be demonstrated by using a boiler with seasonal efficiency of a domestic boiler in the UK (SEDBUK) of 78 per cent for mains natural gas,80 per cent for LPG and 85 per cent for oil. Target U-value and carbon index methods are available for those who want flexibility.

In order to limit the heat loss through glazed elements in non-domestic buildings, new target glazed areas have been set (rooflights cannot normally be traded off against windows and doors).Although there is scope for compensating calculations, compliance will be guaranteed if the area of windows or doors in offices makes up a maximum of 40 per cent of internal wall area of exposed walls and a maximum of 20 per cent of rooflights.

Electric lighting systems in offices, industrial and storage buildings, should be provided with 'reasonably efficient' lamp/luminaire combinations.Compliance criteria will be satisfied with lighting with an initial efficacy, averaged over the whole building, of not less than 40 luminaire-lumens/circuit watt. This should not be too onerous, although calculations will need to be provided to show compliance.


Documents referenced in the interim draft Approved Document Testing of building for air leakage , TM23:2000, CIBSE A professional's guide to testing housing for energy efficiency , General Information Report 64, Energy Efficiency Best Practice Programme, 2000 A practical guide to infra-red thermography for building surveys , by JM Hart, BRE report 176, BRE,1991 Thermal insulation: avoiding risks , BRE report 262, (new edition in preparation) Daylight and window design , LG10, CIBSE,1999 Thermal performance of buildings - Transmission heat loss coefficient calculation method , BS EN ISO 13789:1999 The need for old buildings to breathe , SPAB Information Sheet 4, 1986 DETR circular No 07/2000,13 October 2000, giving administrative guidance on producing and displaying SAP ratings.

Details for limiting the adverse effects of thermal bridging an air leakage, currently being prepared by the DETR and BRE BRE IP document, assessing the effects of thermal bridging at junctions and around openings, is yet to be published

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