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Part L Uncovered

24 January 2011

The consultation of Part L of the Building Regulations in England and Wales 2010 was the subject of the summer for the construction industry. Now published, the Government’s CLG (Department for Communities and Local Government) 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.

For new dwellings, the CO2 emissions associated with the energy consumption of the whole dwelling remains as the sole criterion for demonstrating compliance to Part L 2010, in that the predicted rate of emissions from the dwelling (the Dwelling Emissions Rate) must not be greater than the Target Emissions Rate. So, what are the implications of Part L 2010 for glazing? As the Standard Assessment Procedure (SAP) software fully takes into account solar gains, ‘hard coat’ low emissivity (low-e) glass such as Pilkington K Glass™ with its high g-value will generally result in a dwelling having a similar emissions rate to one with ‘soft coat’ low-e glass. Adding low iron glass, such as Pilkington Optiwhite™, increases the g-value of the glazing and improves the Dwelling Emission Rate. The limiting U-value of 2.2 means low-e double-glazing stays as the minimum requirement for Part L 2010. Although not a requirement, triple-glazing may become increasingly more common in new dwellings as demonstrated by its prevalence in low energy houses.  The glass industry has responded by launching triple glazing units, such as Pilkington energiKare™ Triple, specifically tailored for the UK market and with a U-value of as low as 0.7.

In existing dwellings, certain ‘controlled fittings’ remain within the scope of Part L 2010. These include replacement windows for existing dwellings and windows for extensions. The requirements apply to whole windows, roof windows, rooflights and doors (including the frame). Applications where only the glass is being replaced in the existing frame are outside of the scope of Part L 2010.  The standard for controlled fittings for windows is a Window Energy Rating (WER) of minimum band C.  It is important to note, based on the proposals, whole U-values are no longer to be used for demonstrating compliance for windows. WERs are to be the only compliance route for all but a few installations. Centre pane U-values of 1.2 W/m2K are permitted as an alternative, but only in ‘exceptional circumstances’, for example, as a ‘one-off’ to match the existing retained windows. 

WERs were launched in 2004 by the British Fenestration Rating Council (BFRC), an independent government-supported body established to develop and administer a system of WERs in the UK. Full details of the organisation, and how a window company can have its products rated, are given on the website  A window’s rating is determined by a formula which takes into account its g-value, U-value and air infiltration. The resulting value is attributed to a band on an A-G scale. This makes the system of rating windows consistent with other products which have energy performance labels (such as washing machines, light bulbs and fridges), with which the public is very familiar and can therefore relate to when it comes to understanding the energy-efficiency of windows, allowing them to make an informed choice of what is best for them.

We are sure that it is partly in recognition of the progress our industry has made in the development of energy-efficient products that WERs will become in effect the sole measure for replacement windows and windows for extensions in Part L 2010. The proposals recognise the importance of taking into account the solar gain provided by the glazing in a dwelling. As a minimum, a rating of band C is required, this acknowledges the positive contribution energy-efficient windows can make in delivering CO2 and energy savings in homes. Energy-efficient windows, such as those containing Pilkington energiKareTM with its high g-value, will continue to meet and exceed the requirements of these regulations.

Conservatories are another area in which there are significant changes outlined in the Part L 2010 consultation.  Based on the proposals to remove the current exemption of conservatories, conservatories with a floor area less than 30m2 are introduced into Part L for the first time. Conservatories would be included in the list of building work but not notifiable to Building Control. A new definition of a conservatory is given - as before, it needs to be thermally-separated with independently-controlled heating (if applicable) and the separation between dwelling and conservatory must be to a comparable standard as to the rest of the external envelope. However, the transparent and/or translucent material in the external envelope must be more than 150 per cent of the floor area. There must also be reasonable provision for ventilation.

In Part L 2010 glazed elements are required to meet the same standards as for controlled fittings, i.e. for vertical and roof glazed elements, WERs of minimum band C are required.  In the industry response to the consultation, concern was expressed that WERs may not be the most appropriate criterion for assessing compliance.  WERs were developed for the assessment of vertical replacement windows in dwellings and take into account the positive benefit of solar gain for such applications.  However, in conservatories, large amounts of solar gain are not necessarily welcome, particularly if they lead to the installation of portable air-conditioners.  In conservatories, the objective in respect of solar gain must therefore be to limit its ingress, particularly through roofs.  In the industry response to Part L, we have proposed that a criterion based on maximum U-value and g-value should be introduced.  We have suggested that maximum U-value and g-values should be considered for vertical glazed elements and for roof glazing.  It remains to be seen if these suggestions will be introduced in the final Approved Documents.

In short, low-e glass is effectively the minimum standard for conservatories, meaning that ordinary (i.e. non low-e) double-glazing will no longer be permissible. If a requirement for a maximum g-value is subsequently introduced, summer overheating in conservatories can be limited by the addition of solar control (and self-cleaning) glass such as Pilkington Activ™ Blue and Pilkington Activ™ Neutral.

For new non-dwellings there are no specific elemental requirements for windows, other than a limiting value of 2.2 W/m2K for windows as well as roof windows, rooflights, curtain walling, pedestrian doors. The limiting value does mean that low-e glass is a minimum requirement, but there are no such limits for ground floor display windows and similar glazing.

For existing non-dwellings, the standard for replacement windows, roof windows or rooflights is that the U-value for the whole unit must not exceed 1.5 W/m2K.  For doors with a glazed area greater than 50 per cent, a U-value of 1.8 W/m2K or better is required.  Specifically for curtain walling as a controlled fitting in non-dwellings, the proposed standard for overall U-value is based on the percentage area of glazed and opaque elements.

In the consultation there is a greater focus on ensuring a building has appropriate passive solar control, thus limiting the effects of solar gains in summer. The requirement applies to all non-dwellings and aims to reduce the need for air-conditioning or reduce the installed capacity of an air-conditioning system. Reasonable provision for air conditioning can be considered if the total solar gains during the summer period are no greater than for the given reference cases. This recognition complements an independent study, ‘Impact of Solar Control Glazing on energy and CO2 savings in Europe’, which quantifies the potential CO2 savings in the year 2020 through the installation of solar control glass in what are traditionally air-conditioned buildings.  It gives figures separately for each EU country, including the UK.  The study details the amount of CO2 emissions that would be saved in buildings equipped with both air conditioning and solar control glass and compares the figures to those with just air conditioning. It examines what would happen if air conditioning were to grow between now and 2020 at the current rate, and also at a higher rate, mirroring the use of air conditioning in the USA.

The study shows that installing solar control glass instead of air conditioning under the current growth scenario produces annual savings of around 1.1 million tonnes of CO2 by 2020.  Under the ‘USA’ scenario, the annual savings are 6.9 million tonnes. The significance of these savings can be seen in the context of the UK National Energy Efficiency Action Plan, which sets a target for the country’s CO2 savings for the year 2020 as 94.2 million tonnes; 74.1 million tonnes of which must come from non-transport sectors.  Therefore, the contribution of solar control glass to the UK’s non-transport CO2 reduction targets is between 1.5 and 9.3 per cent.  This greater emphasis on limiting solar gains in the summer through passive control measures, particularly in commercial buildings, will require an increased use of high performance solar control glass, such as Pilkington Suncool™ and Pilkington Eclipse Advantage™ - good news for the glazing industry.
The one aspect of the consultation that has polarised views across the whole construction sector is that of Consequential Improvements (CI), particularly as they were not actually included in the consultation documents.  CI is where a refurbishment or extension of an existing building triggers an additional upgrade in energy performance of the existing building. If, for example, the proposals had been in line with the draft revision of the Energy Performance of Buildings Directive (EPBD), they would have only required CI in cases where a major renovation is taking place. The concern of some industries, including our own, would be if CI were to be required when a householder undertakes any form of home improvement, irrespective of the size and value of the contract. It could be counterproductive and likely to result in the modest home improvements not carried out. An example could be where a homeowner is contemplating replacing their inefficient single glazed windows with new modern energy-efficient ones, but may decide not to proceed with the work if faced with additional costs linked to CI. This would therefore be counterproductive in terms of energy-efficiency. 
The subject of historic and traditional buildings is another issue which also generates great debate when Part L is revised. According to the consultation, the current exemption for listed buildings and buildings in conservation areas is removed. Specific guidance is provided as to where special considerations apply and how to arrive at an appropriate balance between heritage and energy conservation. An appropriate balance may be possible to achieve using products that can replace energy inefficient single glazing in older traditional buildings whilst retaining the original frames. Utilising advanced Pilkington Spacia™ vacuum glazing technology, Pilkington energiKare™ Legacy has the same thickness as single glazing but with four times better thermal insulation.

In terms of timings, the consultation period for Part L 2010 ended on 17th September 2009.  The new Approved Documents for Part L will then be issued in April 2010 and implemented on 1st October 2010.  The huge level of interest in the consultation means that the discussion will continue until and beyond this time. This was reflected in the Part L 2010 webinar, organised by Pilkington in conjunction with Building magazine. Taking place only a few days after the consultation commenced, it attracted almost 500 live participants and generated 45 questions during the event. The webinar is still available to view at

For more information on Part L 2010, or our range of products, please contact our Technical Advice Centre on 01744 692000.