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The Future for Part L 2010

24 January 2011

The Government’s CLG (Department for Communities and Local Government) has spoken and we have now received the consultation proposals for amending Part L of the Building Regulations for England and Wales in 2010. The CLG has a well-publicised timeline for improving the requirements of Part L in stages up to 2016.  New dwellings will require CO2 reductions of 25 per cent by 2010, 44 per cent by 2013 and 100 per cent (zero carbon) by 2016. For non-dwellings, CLG will insist on the same improvement levels as for dwellings in 2010 and 2013, but delay zero-carbon standards until 2019.

However, this does not mean that every component of a building will have to improve. The requirements for new buildings are based on the total energy performance of the whole building, which means that higher performance windows are likely to be required. This has already led forward thinking developers and architects to incorporate the substantial benefits of triple glazing into new, lower carbon properties – thus often offsetting the need to invest in costly renewable technologies.  As the regulations tighten, in new homes at least, the move to triple glazing, as in much of continental Europe, seems inevitable – still optimising both thermal insulation AND passive solar gain benefits.

For new homes, the Standard Assessment Procedure (SAP) fully takes into account the U-value, solar heat gain (g value) and daylight transmission characteristics of the windows. Therefore the positive, energy-gaining qualities of glass are embedded in the calculations. As a rough rule of thumb, an improvement in U-value is accompanied by a worsening of g value, and the two factors tend to balance. Lowering U values without considering the effect on passive solar gains can be counterproductive in terms of the total energy performance of buildings.
The ways in which windows are evaluated in the context of Part L fully consider the positive energy benefits of glazing. This means liberation from the traditional fixation with simple U-values and that the full benefits of larger areas of glazing are recognised.

For existing dwellings and domestic-style buildings, Window Energy Ratings (WERs) were a main way of demonstrating compliance in 2006, with an E rating being required in replacement windows and D in extensions. It is proposed that these levels will be increased in 2010 (a C rating for both), anticipating a move towards an A rating requirement in 2016. In 2010, there will be no standard for whole U-values for windows. Centre pane U-values, a poor indicator of total window energy efficiency, are likely to be an allowable demonstration of compliance only in exceptional circumstances, where choice of frame design is severely restricted.
Conservatories have also been introduced into Part L for the first time. In respect of glazing, the proposals are effectively to mandate low-E throughout vertical glazing and any glazed roofs. The proposal is to remove the current exemption from Part L, meaning that conservatories would be included in the list of building work but not notifiable to Building Control.

Although not covered by Part L, building lifecycle costs are also an important consideration and any reduction of natural light means money and energy must be spent on artificial lighting, heating and cooling; an unsatisfactory, environmentally-unfriendly and costly alternative to managing the sun’s free heat. The proposals for 2010, however, offer an increased focus on limiting overheating due to solar gains, particularly in non-domestic buildings.  These considerations have been endorsed in a recent independent study commissioned by Glass for Europe, the trade association for Europe’s manufacturers of flat glass, which reveals how high-performance solar control glazing can help contribute to carbon emissions savings.  Taking into account a ‘business as usual’ growth in the use of air conditioning systems to 2020, the possible annual CO2 savings through the introduction of solar control glazing are as much as 1,097,000 tonnes, a saving equivalent to 9.3 per cent of the UK’s CO2 emissions. The study clearly demonstrates that high performance solar control glazing will be an important aspect in the future of commercial buildings.

Part L 2010 in summary:

  • Significant reductions in target CO2 emissions for all new buildings
  • Tightening of elemental requirements for windows for replacements and extensions
  • Window Energy Ratings become main standard for dwellings
  • Conservatories introduced into Part L for the first time
  • Increased focus on risk of overheating in summer

With the major revision of Part L of the Building Regulations in England and Wales 2010, it is imperative that architects and specifiers are up-to-speed with how the proposed changes are likely to affect their designs. It is also important that the fenestration industry understands the implications for its products. The consultation ends on the 17th of September 2009 with implementation currently booked in for the 1st October 2010.

The consultation is now available for download at: In conjunction with Building Magazine we have produced a webinar on the changes to Part L with BRE and Ian Ritchie Architects. Please log onto for more information. If you have any glazing-related Part L 2010 questions please email