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Building Regulations: Part L

[TECHNICAL & PRACTICE] The new energy-efficiency requirements of Part L of the Building Regulations come into force on 1 October. The AJ’s Regs columnist Geoff Wilkinson analyses the changes

It’s been a talking point for over a year, and now we’re just a few months away from the 25 percent improvement in energy efficiency required under the 2010 amendments to Part L. The changes take effect on 1 October 2010 for any project that hasn’t submitted a Building Regulations application before that date, and will apply retrospectively to any project that hasn’t commenced before 1 October 2011.

Building control bodies are reporting an increase in workload as clients seek to beat the October deadline

The capital cost of the new regulations varies depending on the type of project, but typical estimates are 4-8 per cent, which can make a critical difference to a scheme’s viability. As a result, building control bodies are reporting an increase in workload as clients seek to beat the October deadline.

The 2010 amendments to Part L are significant, but it should still be possible to gain compliance using traditional construction methods, and there is no specific requirement to incorporate renewables, so architects need not be too worried. The 2013 and 2016 Building Regulations, however, are another matter entirely, and the construction products industry must step up a gear to be able to cope. It will be necessary to run down existing stocks of 2006-compliant products and to begin introducing 2013 versions over the next few years, as the diagram illustrates.

The new Building Regulations seek to address this drag effect and what is referred to as the ‘performance gap’ - the difference between expected levels of performance and what is delivered on site (see diagram below). This concern was expressed in ‘Greener Homes for the Future?’, a report published in 2008 by the Environmental Audit Committee (EAC) that said: ‘We are very dismayed by the lack of urgency - especially considering how vital building control inspections will be to the entire zero-carbon homes policy - shown by the government in addressing the weaknesses in the current system.’

The first major change is to the Building Regulations themselves, in which a new requirement, 20D, has been introduced. As part of the application package (i.e. prior to works commencing), the architect must submit: the target CO2 emissions rate for the building (TER); the calculated CO2 emissions rate for the building as designed (DER); and a list of specifications to which the building will be constructed.

Ground-source heat pumps and biomass boilers are still the easiest ways to comply

The only method for complying with this requirement remains the National Calculation Method, which includes tools such as the Standard Assessment Procedure for the Energy Rating of Dwellings (SAP), the Simplified Building Energy Model (SBEM) and Dynamic Simulation Modelling (DSM). The National Calculation Method was recently revised in line with the 2010 changes, but it does not yet produce the specification list required to comply with the final part of
20D. This is to be addressed prior to 1 October, but architects wanting to design to 2010 requirements should discuss the level of detail required to be included in the submission with their building control body.

Now let’s consider each of the revised Approved Documents.

Approved Document L1A

For dwellings, the TER will be calculated in the same way as it was in Part L1A 2006. As a result, the majority of changes take place within the black-box technology of the SAP software itself, so it is difficult to explain concisely the effects of the changes. That said, ground-source heat pumps and biomass boilers are still the easiest ways to comply, and you will find boilers and electrical-resistance heating increasingly difficult to specify without improvements to the building elsewhere.

Building fabric has pretty much reached the limit of economic return, so the changes to minimum U-values are not significant as the table ‘Limiting fabric parameters 1’ shows. However, the eagle-eyed will notice that heat loss through party walls is now considered for the first time, with a limiting U-value of 0.2W/m2K. An unfilled and unsealed cavity wall would achieve a U-value of 0.5W/m2K, so it is clear that insulation to party walls must be specified before you start to look at the 25 per cent improvement required elsewhere (see ‘U-values for party walls’ table).



Air-pressure testing will be a big issue for contractors, with the testing requirement almost doubling. On top of this, testing is further encouraged with a confidence factor applied to any dwellings that are not pressure tested. This means, in effect, that the design air permeability on untested dwellings must be set below 8m3/hr/m2 @ 50 Pa in order to meet the actual allowable value of 10m3/hr/m2 @ 50 Pa on completion of the dwelling.

Approved Document L1B

The changes to Approved Document L1B are relatively simple and mostly concern alterations to minimum U-values, removal of automatic exemptions for historic buildings and a change in the definition of renovation. As a result, it will be necessary to consider upgrading insulation on almost any building project that affects the existing walls, windows, roofs or floors.

Approved Document L2A

The requirements for commercial buildings are significantly different from residential, because the TER is no longer based on a 2002 notional building. Instead designers will need to base the notional building on something of the same size and shape as the actual building constructed. This is illustrated in the diagram on the bottom left, which shows the difference between a 2006 notional building and the 2010 version. This is a tightening of the existing flexibility, although designers will still be able to vary the design provided that the same overall level of CO2 emissions is achieved. The net effect is that certain building types will require improvements that may be greater or less than the 25 percent overall improvement. The limiting U-values for commercial buildings are set out in the table ‘Limiting fabric parameters 2’.

Guidance on shell and core development has also been revised, and it will now be necessary to specify at the design stage how the shell and services will meet the requirements. It won’t be possible to simply design the shell to base levels and leave it to the fit-out contractor to install highly efficient services to compensate. On practical completion, it will be necessary to provide as-built calculations with the fit-out areas conditioned to the previously assumed temperatures. A predicted Energy Performance Certificate (EPC) rating is also required to show what level of performance is possible. However, there is no requirement for an EPC to be formally lodged.

A revised procedure is now in place to limit the effects of solar gain, whether or not a building has air conditioning at the time of design. Architects should be aware that even where a design achieves Part L approval in a naturally ventilated building, this does not automatically mean that internal environmental temperatures will be satisfactory.

The requirement for a building log book will be reinforced, despite low levels of current compliance

Guidance on avoiding thermal bridging at construction joints has been revised, and the option to adopt accredited construction details has been introduced. Approved Document L2A states that the design must be calculated in accordance with BR 497 (thermal performance of buildings) but, perhaps more importantly, developers must demonstrate how specific details will perform when assessed to BRE IP 1/06 (assessing the effects of thermal bridging at junctions and around openings in the external elements of buildings). In particular, builders will need to demonstrate factory-tested accreditation for the detail and that they operate quality-assured site inspection systems. If neither of these criteria is met, a 25 per cent penalty will be applied to the design assumptions in the Building Energy Rating (BER). If there is no accredited detail at all (and outside of repeat-build greenfield sites, this is likely to be the norm) a whopping 50 per cent penalty must be applied.

Finally, the requirement for a building log book will be reinforced, despite low levels of current compliance. We can expect building control bodies to come under pressure to ensure the enforcement of this requirement, so allowance should be made for this. The recommendation in Approved Document L2A is that CIBSE TM 31 (building log books) is followed and it also recommends that the input files used in calculations should be retained.

Approved Document L2B

The requirements for existing commercial buildings are essentially the same as those for residential, but with some amendments to the standards for controlled fittings, retained thermal elements and (as shown in the table below) new thermal elements.

Geoff Wilkinson is currently running a series of in-house training sessions for architects on the changes to Part L. More details can be found at www.thebuildinginspector.org

Readers' comments (1)

  • I, like many other architects I'm sure, am finalising a building regs submission on the understanding that applications submitted before Oct 1 2010, will be assessed under the current 2006 regs - as indicated in AJ 01.07.2010 article by Geoff Wilkinson.

    I have passed this deadline info onto my client, and today was informed by the relevant building control body that the works have to have started before 1st Oct 2010, otherwise the new regs shall apply - which I have not allowed for.

    Any others in the same boat?

    Unsuitable or offensive?

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