Ant Wilson outlines the proposed changes to Part L, and how their implementation could see a significant improvement in the energy performance of our commercial buildings.
The Office of the Deputy Prime Minister (ODPM) has published proposals for more demanding energy performance standards for all types of buildings, which will come into effect at the end of 2005. The Energy White Paper and The Action Plan, published in April this year, identified revisions to Part L as an important element in the government’s response to reduce greenhouse gas emissions that are the cause of global warming. In the 2002 review, the Approved Documents were split into two, one covering dwellings, the other for non-domestic buildings, referred to as ‘buildings other than dwellings’. This process has been taken a stage further for the 2005 proposals. Now the construction of new buildings is separated from building work in existing buildings. Thus it is proposed that there will be four Approved Documents, ADL1A, ADL1B, ADL2A and ADL2B.
The energy efficiency (or more precisely, the carbon emissions) of all new buildings should be improved by around 25% compared to the 2004 standard. More work in existing buildings will now be subject to the Building Regulations. The intention is that by capturing this additional work, it becomes possible to incorporate energy efficiency improvements at the most cost-effective point, ie as part of building work which is already planned. Through this approach, there should be a progressive improvement in the energy standards of the existing stock. The draft Approved Documents do not go into technical detail. This will be provided through a second tier of technical publications prepared in conjunction with industry, and will also draw on established publications produced by professional bodies and trade organisations.
New Buildings summary
A major change at this revision is to adopt a carbon performance standard as the primary measure of compliance. The carbon performance is to be determined by a whole-building energy calculation method. For dwellings, this will be a revised version of the Standard Assessment Procedure (SAP), but a variety of tools are likely to be used for non-domestic buildings. This approach would fulfil one of the requirements of the Energy Performance of Buildings Directive (EPBD), which is being implemented in England and Wales in parallel.
It might seem that this energy calculation approach will make compliance checking more complex than before, especially since many Building Control bodies may not have staff with expertise in detailed energy calculations. It is proposed that we utilise the concept of an 'expert or accredited person', as detailed in the EPBD. Where such a person has signed off the energy calculation it is proposed that it would be reasonable for the Building Control Officer (BCO) to accept the calculated energy performance without the need for further checking. It is proposed that the energy calculation tools produce a schedule of the key elements of the design that are responsible for delivering the required performance, allowing BCO's to focus their sample checking on the key elements of the building. There are a number of other supporting measures that must be checked to ensure overall compliance. These include:
In most cases, it is proposed that the BCO's role in checking compliance is to receive reports or schedules from accredited experts and then to check that the overall performance meets the required level. To facilitate this last step, a draft pro forma check list has been produced detailing what checks need to be made, what evidence should be produced by whom to demonstrate compliance. This will make more information available without being too technically demanding. This will improve the overall levels of compliance.
Proposals for new non-domestic buildings
The energy performance of new buildings will need to be about 25% better than the current standard. This overall improvement is made of two elements:
One of the most significant changes is that the new performance standard is based on a target CO2 emission rate for heating, cooling, ventilation and lighting. This would have to be estimated using an appropriate whole-building calculation method. This whole-building approach would give developers and builders a great deal of flexibility. Some might prefer to concentrate on improving the envelope performance by including more insulation in the walls, floor and roof, and specifying better performance windows. Others might wish to concentrate on the building services plant, or on renewable energy systems.
What constitutes reasonable target emissions would depend on the size, shape and use of the building. Since the size and shape of the building is often dictated by site constraints and the patterns of occupation will vary according to the intended use, a bespoke target would have to be calculated for each building. The proposed target carbon emission rate is therefore set using the same calculation procedure as is used to estimate the performance of the actual building. A notional building of the same size and shape as the actual building is defined, but the envelope and hvac and lighting systems are to specific elemental standards (set out in ADL2 [2002]). The actual design then has to beat the performance of the notional building by a defined percentage margin.
Defined standards must also be achieved. As well as meeting the carbon target, the building has to meet a number of other standards.
Poorest acceptable standards will be set for the various elements of the envelope and the hvac and lighting systems. This is to make sure that the carbon target is not achieved through a relatively inefficient basic building that is compensated by a large amount of renewable energy systems. The reason for this is that renewable energy systems may be removed or fall into disrepair such that the total energy demand then has to be met from conventional sources.
Ventilation systems should be capable of achieving the same specific fan power at part load as that achieved at the design flow. As part of this, it is proposed that all fans with a rated power greater than 1100 W should be equipped with an efficient form of flow control.
If any zone of the building does not have any mechanical cooling system, it should be designed such that the space will not overheat. This is to minimise the likelihood of a subsequent air conditioning retro-fit.
As well as assessing the basic design, compliance with the proposed new Part L requires a number of checks to be made on the quality of the completed building.
An air pressure test will become a legal requirement for all non-domestic buildings with a floor area greater than 500 m2. For buildings between 50 m2 and 500 m2, if no test is undertaken then the assumption that air change rates are 15 m3/hm2 @ 50 Pa has to be used in the calculation of the predicted carbon emissions from the actual building. Because an air tightness test is a very good proxy for many aspects of construction quality as well as air tightness, it is therefore proposed that such a test should become mandatory for all buildings.
It is also proposed that ventilation ductwork for systems with a capacity of greater than 1 m3/s should be the subject of leakage testing.
An important part of the implementation of the EPBD, which must come into effect starting in January 2006, is the energy certification of buildings. The proposed new Part L2A will require the production of an 'Asset rating' for the building as part of fulfiling the energy certification requirements. This 'Asset rating' is a measure of the predicted energy performance of the building, and is based on exactly the same calculations as will be used to demonstrate compliance with Part L. This means that there is no additional effort required to produce an energy certificate for a new building.
Existing Buildings summary
In existing buildings, the proposed changes will capture more work and make them subject to the Regulations. For the first time, this will include the notion of consequential improvement, ie requiring the whole building to be improved once work of sufficient scale is envisaged. As well as controlled services and fittings, the concept of a controlled element is introduced, thereby picking up work on walls, floors and roofs.
In existing buildings, performance standards are still set primarily on an elemental basis. In applying the standards, one of the difficulties for Building Control officers is that what is reasonable is often context dependent. To help understand the context, it is proposed that the new Approved Documents will draw on the list of cost-effective energy efficiency improvements that has to be prepared by 'an expert or accredited person' as part of the energy certificate required by the EPBD. This will link into the Energy Statement that it is proposed should be produced as part of a submission to Building Control. Again, as part of bringing consistency to the compliance system, a draft pro forma energy statement has been prepared.
Proposals for work in existing non-domestic Buildings
More work in existing buildings will now be subject to the Building Regulations. The intention is that by capturing this additional work, it becomes possible to incorporate energy efficiency improvements at the most cost-effective point, ie as part of building work which is already planned. Through this approach, there should be a progressive improvement in the energy performance of the existing stock.
Because the work done in existing buildings is different in scale and nature from constructing new buildings, the requirements and the associated guidance covering existing buildings has been published separately in Approved Document: ADL2B. This Approved Document defines the type of work that is now subject to building control, and sets out the standards that are considered reasonable.
In some existing buildings, it is not practical or cost-effective to achieve the standard of energy efficiency that is appropriate for new buildings. Equally, it is not sensible to discourage people from improving properties because the cost of achieving the standards is too high. The approach therefore concentrates on achieving worthwhile improvements at reasonable marginal cost.
The most important proposal relates to the requirement to improve the whole building once building work of a sufficient scale is scheduled. Previously, only those elements of the building that were being altered or replaced were subject to control. Under the proposals, it will now be necessary to upgrade the whole building, always provided that the marginal costs of so doing are not excessive. For example, if the building was undergoing a refurbishment, the Regulations call for the whole building to be considered and general improvements made where appropriate; this is in addition to requiring the specific refurbishment work to meet a defined energy performance standard. Unless the owner wishes to go further, this more general improvement work should only include those measures that achieve a payback of less than seven years. A marginal cost cap of 10% limits the number of such measures that must be included.
Consideration is also being given to broadening the concept of a material change of use. Broadly speaking, the Regulations currently only impose standards where the newly converted building includes sleeping accommodation, or is to be used as a public building. It is proposed that other changes of use could be included (eg warehouse to office). Whatever the definition of a material change of use finally encompasses, the proposals suggest that the standard of the newly created building should be as high as practicable.It will be appreciated that the cost of achieving a given improvement in energy efficiency is context dependent. For example, it is easier and cheaper to improve the U-value of an unfilled cavity wall than it is to achieve a similar improvement on a solid wall. Consequently, the level of improvement that might be reasonable in one building may not be reasonable in another. This consideration of context provides an important link with the requirements of the EPBD. This directive requires that whenever a building is made available for sale or let, an energy performance certificate should be made available to the prospective purchaser or tenant. This certificate is required to include a list of cost-effective improvements that could be made to the building. The list of cost-effective improvements will provide the context that will enable Building Control inspectors to determine what is reasonable in the particular case.
At the last review, the concept of a replacement controlled service or fitting was widened. Essentially this means that now when building services components or windows are replaced, they have to meet a defined performance standard. With this review, the proposal is to extend this concept to include controlled elements, and to enhance the scope by not only including 'the provision or extension' of these controlled items, but their 'alteration or renovation' as well. This means that when any part of the building envelope or the building services systems is subject to substantial repair or replacement, then improvement should be made.
ADL2B sets out minimum performance standards that are considered reasonable when replacing a controlled element, service or fitting. In most cases, these standards are equivalent to those that would be typical of new construction, although poorer standards might be acceptable where there are specific problems (eg where internal areas or head room might be significantly reduced, or where achieving level floors would be difficult).
In terms of building services plant and equipment, better efficiencies are now considered reasonable than those set out in ADL2 (2002). In particular, attention is given to the efficiency of systems at part load, since in many buildings, the majority of systems spend little time at design condition. For boilers and chillers this is addressed through setting seasonal efficiency standards, where the seasonal efficiency is a weighted average of the system at various load conditions. For mechanical ventilation plant the requirement is expressed in terms of achieving the same specific fan power at part load as is required at design duty. New guidance is introduced to reduce leakage from ventilation ductwork.
In line with the general philosophy adopted for this review, the draft Approved Documents do not go into technical detail. It is proposed that this will be provided through a second tier of technical publications prepared in conjunction with industry, and will also draw on established publications produced by CIBSE, HVCA and Action Energy.
Improving levels of compliance
One of the key issues being considered as part of this review of Part L is to improve the degree of compliance with the standards set out in the requirements and associated guidance. The opportunity has been taken to firm up on some aspects of performance. For example, it is proposed that air pressure testing of all non-domestic buildings become a legal requirement rather than merely guidance.
At first sight, it may seem that having to use a whole-building energy calculation tool will make the process of demonstrating compliance with Part L much more complex than previously. In reality, this approach should make demonstrating and checking compliance easier than before, since most of the rules are built into the software and therefore are not open to individual interpretation. This would create a much more consistent compliance regime. It has been proposed that compliance calculations prepared by an expert and or accredited assessor should be accepted by Building Control. In order to further streamline demonstrating and checking compliance, a draft checklist has been prepared that details what information is needed to be provided and who might be best equipped to provide it.
The proposals also recognise that small builders in particular may not have ready access to the skills needed to use whole-building models as a design tool. Consequently, the proposals recognise the concept of model designs. These are 'recipes' of measures, which if adopted, would deliver a building that meets the performance standard. These 'recipes' are not included in the Approved Documents; instead, it is anticipated that different trade organisations and other bodies will produce solutions that are optimised for their particular technologies. However, even with this approach, a specific energy calculation will be required to confirm the standard has been achieved and to provide the basis of the energy performance certificate.
Summary
The proposals represent a further development of the thinking that was introduced at the last review of Part L. If the UK is to achieve its climate change targets, then the energy efficiency of the existing stock must be raised. The proposals include a number of new mechanisms for requiring improved standards, and through its tier of supporting documents, the Approved Document should provide much better guidance on how these standards can be implemented.
Through the provision of information signed-off by expert or accredited persons and the use of pro forma checklists, the aim is to reduce the burden of technical complexity on Building Control and to improve the levels of compliance with Part L.
Clearly the proposed revisions to Part L will need to be understood and implemented by building services engineers, and input by readers of BSj to the ODPM consultation document would be helpful. Visit: www.odpm.gov.uk/br/consult
Source
Building Sustainable Design
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