The new version of Part L kicks in next week, and its tough energy rules are going to make lighting a building altogether more problematic than ever before

If the 2006 version of Part L of the Building Regulations proved easier to comply with than many expected, the same is unlikely to be true of the 2010 update.
Due to come into force in a week’s time, the regulations covering energy use will look for a further 25% cut in carbon emissions across the board. Given the scale of the reduction, this target will require designers to use a wide range of measures to reduce energy use. But although a holistic approach will be needed, there is one area in particular that will come under scrutiny, and that’s lighting, especially in non-domestic properties.

According to Michael Pollock of IES, which specialises in environmental simulation modelling tools, lighting is going to play a large part in helping buildings to pass the 2010 changes, especially offices. “Designers will need to give detailed attention and careful consideration to lighting from an early stage. If it’s left to the last minute, they will have great difficulty in passing.”

There are a number of reasons why it makes sense to put lighting under greater scrutiny. In office buildings it can account for as much as half of the building’s regulated carbon emissions. And in air-conditioned facilities, any saving on the energy used to power lighting will also mean less energy is used to run the cooling systems that counteract the heat gains from the lighting.

The scale of the impact the 2010 changes will have is becoming clearer as the modelling software for assessing designs becomes available. Pollock has been using the national calculation methodology model to analyse the changes, and he says their effect on lighting will be significant. After modelling the sample building that was released with iSBEM (the software for showing compliance with the regulations) he says the target for lighting power is less than half what it was in 2006.

This fall is partly the result of changes in the method of calculation. One of the major changes in 2010 for non-domestic buildings is the aggregate approach now taken towards carbon emissions reductions. This means some buildings will be required to make a larger than 25% cut and others less, depending on how cost-effective and practical it is to achieve. A shallow plan, air-conditioned office is likely to have a tougher target than a deep plan one.

This in turn has led to a change in how the target emissions rate is calculated. Rather than using a notional building from 2002, the rate will now be worked out in relation to a 2010-compliant reference building that is the shape and size of the building being designed. This should make it easier for designers to determine where they need to focus their attentions. The downside, of course, is that the design criteria used to set the performance of the notional building, such as minimum efficiency for services plant, mean the baseline is much tougher.

For lighting, there are a number of changes. Significantly, where there was once a fixed value for the lighting power density - the efficiency of the system for a given lighting level - it is now based on a sliding scale. Large, open-plan spaces will have the most stringent targets while smaller, cellular spaces will be allowed higher densities, which in some cases are less onerous than those under the 2006 Regulations.

The lowest targets for open-plan spaces will be about 2.2W/m2 per 100lux, which, says David Kingstone, associate at Buro Happold, is going to be particularly challenging. This approach is much more realistic. “It was getting to the point previously where it was difficult to improve on targets, particularly in small cellular spaces such as toilets.”

The other big change is that it is assumed the notional building has daylight-linked dimming controls. Whereas it was once an easy win to specify controls to help meet the emissions target, this will no longer be possible. There is still scope to include others such as presence detectors, but Kingstone warns that the parasitic power consumption of such systems can approach their savings.

The changes made to limits on solar gains at the perimeter of the building also mean it is more difficult to take advantage of natural light. Previously the limit was based on overheating but now it is based on solar gain between April and September, which means designers will have to play the advantages of increased daylighting off against the rise in solar gain. This provides an argument for changing the specification of the glazing.“I suspect there will be a tight line between minimising your lighting load and making sure solar gain targets aren’t exceeded,” says Pollock. “It might be a case of looking at more expensive glazing products.”

Light shelves and light pipes should make meeting the criteria easier for deep-plan buildings, but the benefits will be reduced if more sophisticated modelling programs than iSBEM are used to show compliance.

Other designers disagree with Pollack over the effect of the new rules. Dominic Meyrick of Hoare Lea says: “The 2006 regulations were easy to comply with and I don’t think the update will pose too many problems for good quality designs.” For most of the sector, though, it could prove more challenging.