The thinking behind the new Building Regulations

AECOM, building regulations, Part L
Setting targets for new non-domestic buildings — David Ross.

How a building is used affects its pattern of energy consumption — which is acknowledged in the latest Building Regulations for new non-domestic buildings. David Ross explains.

A fundamental change in Part L 2010 for non-domestic buildings is in the target-setting process. The new process recognises that it is easier and more cost effective to make improvements in some building types than in others.

The aim for a 25% reduction in CO2 emissions from new non-domestic buildings is achieved on aggregate across the new-build stock rather than for each individual building. Some building types will be required to achieve a bigger improvement than 25%, whilst others will need to achieve less.

The reason behind this change is that for different building types there is significant variation in the breakdown of energy uses (heating, cooling, lighting, hot water etc.), so the relative cost effectiveness of reducing energy demand and CO2 emissions can also vary significantly.

For example, to achieve the same improvement in a building where demand is dominated by hot water, e.g. a hotel, is likely to be more difficult (and expensive) than one where lighting dominates, e.g. an office. It would be inequitable to require the same percentage improvement to all buildings.

The target-setting procedure has therefore been revised so that the targeted improvement for various types of building gives a similar level of net benefit in terms of £/tonne of CO2 saved. This is achieved by defining the notional building in terms of fabric and services standards that are deemed reasonable to achieve in 2010, and which, when aggregated across the new build stock, deliver the overall 25% improvement. By defining the notional building in this way, the need for improvement factors is eliminated and an equitable target set for different buildings.

Two other changes to the notional building are designed to make the target-setting procedure more robust.

The first is to recognise that different forms of building are serviced in different ways.

Most commercial and residential buildings are heated using centralised boiler systems, whereas warehouses and industrial spaces are usually heated by decentralised warm-air or radiant heaters. These different system types have different efficiencies, so the appropriate system type is installed in the notional building to reflect what is practically achievable in the actual building.

The other change is to vary the distribution of glazing in the notional building dependent on the building form.

The notional building will either have vertical glazing (lesser of 40% of facade area or 1.5 m high * facade width) or 12% rooflights, but not both, with the allocation being driven by the planning-use class. In contrast, the 2006 notional building always had 20% rooflights, irrespective of building use or form, which resulted in better daylight and higher solar gains than is achieved in most buildings and impacting on the target emission rate (TER) to be achieved.

Taken together, all the changes to the target-setting process are intended to equalise the costs and benefits of achieving the national CO2 reduction target across all building sectors and levels of servicing. Although the target setting process may sound complex, as far as designers and builders are concerned there is no change because all the target-setting rules are embedded in the compliance software, which will therefore generate the 2010 TER automatically.

One of the main criticisms of Part L 2006 was a perception that it was easier to get air-conditioned buildings to comply than naturally ventilated ones. The 2010 amendments outlined here should set a more equitable target for both.

The specification of ventilation and air-conditioning systems is also constrained by criterion 2 in Part L. This sets limits on design flexibility by specifying minimum efficiencies for plant items. Improved minimum efficiencies have been developed in close collaboration with industry, with the details being published via an updated and much expanded ‘Non-domestic building services compliance Guide’ (NDBSCG). ADL2A includes guidance that, where the efficiency claimed for the fixed building service is based on the test standard specified in the NDBSCG and on test data certified by a notified body, it would be reasonable for building-control bodies (BCBs) to accept the data at face value. In the absence of such quality-assured data, BCBs should satisfy themselves that the claimed performance is justified. This is a key element of the overall package of proposals to improve levels of compliance with Part L.

 

Another change that will have an impact on the design of air-conditioning systems is the setting of a solar-gain limit for all building types (which previously only applied to buildings that were not air conditioned). The intention is to reduce solar gains to reasonable limits, reducing the need for, or installed capacity of, mechanical cooling systems. This approach does not prevent highly glazed facades, but it does mean that where they are a feature of the design, good solar protection will also be needed.

David Ross is a regional director at AECOM and led the team that provided technical advice to CLG on the Part L and Part F amendment proposals.

 

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