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Part-L Like It's 2010

24 January 2011

With changes to Part L in England and Wales on the horizon, now is the time for housebuilders to get to grips with the forthcoming Building Regulations and how glazing and windows fit in.


The Government’s CLG (Department for Communities and Local Government) has a well-publicised timeline for tightening the minimum requirements of Part L in stages up to 2016. In 2006, immediately after the last change to Part L, the following targets for energy and carbon improvement were set out for dwellings: 2010 – 25 per cent, 2013 – 44 per cent, 2016 – 100 per cent. The requirements for new buildings continue to be based on the total energy performance of the whole building. In the case of replacement windows, CLG has indicated that substantial improvements for 2010 are expected.

But what will these changes mean for specifying glazing and windows? For new housing, Building Regulations are based on the total energy/carbon performance of the whole building, expressed as the CO2 Dwelling Emission Rate (DER). Part L 2010 will not require any specific performance of windows, just as the current 2006 Part L does not.

For new buildings, 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 reduction in g-value, and the two factors tend to balance. This means that the total energy performance of a building is largely independent of window U-value. Similarly useful solar gains through a window counterbalance  heat losses, so the energy performance of a building is largely independent of its window area. 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 U-values and that the full benefits of larger areas of glazing are recognised.

House builders that specify windows incorporating our energy efficient glazing range, Pilkington energiKare™ family, will find that the glazing will already meet the upcoming changes to building regulations in 2010. From new homes to older traditional buildings, the Pilkington energiKare™ family will provide better energy ratings in a wider range of properties. Pilkington energiKare™ is different to standard double glazing as it works in two ways. It reduces the amount of net heat lost by up to 90 percent and it also allows more heat (energy) from the sun in through the window. Pilkington energiKare™ family products are made up of Pilkington K Glass™, the UK’s best selling low e glass and Pilkington Optiwhite™, a special ‘extra clear’ glass which allows more solar heat in through the windows, making a home feel warmer without the need to turn up the heating.