Cost model: Effect of Part L revisions on business parks and offices

<B><font size=”+1”>Revising the regulations</font></b>The revised Part L of the Building Regulations was published on 31 October. It aims to control carbon emissions created by building services. Of the UK’s carbon emissions, 46% relate to the occupation of buildings, and consequently Part L is one of the government’s principal tools in promoting its post-Kyoto environmental agenda.
The Kyoto protocol sets targets for a reduction in the production of six greenhouse gases to 12.5% below 1990 output, by 2008-12. In addition, the government has also set a target for the reduction of carbon dioxide production to 20% below 1990 levels by 2010. Much of the impact of the new Part L will be felt by housebuilders, as domestic housing produces almost 59% of the UK’s building-related carbon output, and it is the prime target of the new regulations. However, the regulations also set challenging targets for non-domestic buildings, which will affect designers, constructors and clients. A phased programme of revisions to Part L is also planned as part of a continuing process to increase the performance of buildings to meet the 2010 carbon production targets.
This article focuses on Approved Document L2, which sets out the compliance requirements for non-domestic buildings, and in particular deals with the provisions for new buildings. It includes a discussion of the broader issues raised by the implementation of the new standards, together with an examination of the three compliance methods. Cost models are included, providing an illustration of the potential financial impact of compliance with the new performance standards.
<B>Part L revisions explained</b>
The new Part L represents a significant change in emphasis on the conservation of fuel and power, from energy consumption to carbon production. The widening of the scope of the regulations means that they will affect a broader range of building components. In particular, they will encourage a greater consideration of the interrelationship between facade and building services performance and their effect on carbon production. The outcome of this should be buildings that are better detailed and constructed, and that achieve a balance between the performance of facade, services and other components. Furthermore, they should be cheaper to run and will, on completion, provide occupiers with more feedback on building performance and energy use.
The new Part L focuses on the following areas of performance improvement:

• The establishment of the interrelationship between envelope and building services performance
• Improved thermal performance of the envelope and resistance to solar overheating
• Improved airtightness of construction and reduced thermal bridging
• Increased efficiency of services installations
• Improved commissioning and handover procedures, including checking of as-built performance
• Requirements for improved energy metering.

<B>Assessment methods</b>
The application of specific elements of the regulations depends on the chosen compliance route. As with the 1995 regulations, there are three alternatives, but the emphasis is now on control of carbon production.
First, the “elemental method” considers individual aspects of building performance in isolation. The standards are clearly stated, which makes this the most straightforward route to demonstrate compliance. Details of the compliance criteria are discussed in detail below in the section summarising the requirements of Approved Document L2.
A potential disadvantage of the elemental approach is that there is only limited scope for the trade-off of performance between building elements. Consequently, the application of the method could result in design solutions that do not take full advantage of the relationship between envelope, solar gain control and building services. As a result, compliant schemes may be more expensive than others developed using the alternative methodologies.
Second, the “whole building method” aims to demonstrate that total carbon emissions related to the fabric and services of a building do not exceed a benchmark. In addition to meeting the benchmark, additional criteria need to be met to achieve compliance:

• Minimum fabric U-values that relate to roof, floor and wall construction only
• Airtightness standards
• Provision of energy metering
• Provision of reports on thermal insulation performance, and testing and commissioning
• Provision of the log book.

The whole building method is available for use on offices, schools and hospitals. As the relationships that the methodology seeks to evaluate are more complex than for the elemental method, computer-based evaluation tools are available. The approach is particularly suitable for projects where a high performance envelope is specified, as the co-ordinated assessment of envelope and building services performance will enable an optimum design to be considered. Furthermore, as no minimum fabric U-value is stated for windows or curtain walling, greater flexibility will be available to designers. For example, by using solar shading and high performance glass, the facade may provide sufficient performance to meet the requirements. This will help to avoid the need to specify solid panels or to adopt an expensive active facade solution to meet the required U-values.
Finally, there is the “carbon emissions calculation method”. This compares the annual carbon emissions of the proposed scheme with a notional, equivalent building that complies with the elemental method. It is the most complex approach, which can be applied to any building type, and offers the greatest flexibility to designers to trade off various elements of building performance, including alternative sources of energy such as combined heat and power. In common with the whole building method, in addition to meeting the benchmark, minimum design standards and information requirements are also necessary to achieve compliance.
The downside of the carbon emissions calculation method is the requirement for bespoke compliance calculations. Given the flexibility of the approach, in time it is likely to become the methodology of choice for complex or leading edge designs.
In conclusion, the three assessment methods vary in the extent to which they provide flexibility for designers to take into account the collective performance of the building. On projects with high-tech design solutions, the adoption of the more complex methods will result in a better fit between overall building performance (including aesthetics) and the requirements of the Building Regulations.
<B>Requirements of Approved Document L2</b>
The performance standards for the elemental method sum up the broad principles of the new regulatory framework. They affect design, construction and information requirements, and can be summarised as follows:

• Significant improvements in building fabric performance. These changes involve increases in standard U-values and greater restrictions on the application of trade-offs between elements. The main changes to U-values are summarised below (see box, below right). Improving the performance of the building fabric is the primary aim of the regulations, as it will be subject to less change over time than the building services installation, which will be periodically replaced. The regulations also require improved construction detailing to avoid thermal bridging and other defects.
• Reduced air leakage. Improved construction detailing to achieve improved airtightness is required under the new regulations. On buildings of more than 1000 m2, physical tests in accordance with the CIBSE TM 23 methodology will be required. A target leakage rate of 10 m3/hr/m2 of external surface area at an applied pressure of 50 Pa will be required – however, a slightly lesser requirement for the retesting of failed buildings will be in force until October 2003.
• Improved resistance to solar overheating. The regulations will limit the extent of windows or will require the greater use of solar control devices such as high-performance glass and solar shading.
• Heating system efficiency. The setting of maximum carbon intensity targets for heating systems will encourage the use of more efficient boilers. Enhanced controls are also required. Limited trade-offs will permit the specification of building fabric with higher U-values, when used on projects with energy efficient boilers.
• Hot water efficiency. Design principles for efficient hot water systems are included. For example, the use of local electric water heating is discouraged in circumstances where hot water consumption is low.
• Improved insulation of building services. Improved insulation of pipes, ducts and vessels used for space heating and cooling and hot water supply is required. Installation in accordance with BS 5422, 2001 will achieve compliance.
• Improved lighting efficiency. The new regulations take a global view and focus on the overall performance of luminaires, lamps and control gear. A target value for overall lighting efficiency is set out in the regulations. Improved controls, either through enhanced local control or automation, are also required.
• Efficiency of air-conditioning and mechanical ventilation. An important theme of the regulations is the achievement of an appropriate balance between building fabric and air-conditioning performance, ensuring that the architecture does not result in an excessive cooling requirement. The regulations set benchmark targets for carbon performance or fan efficiency and require plant to be efficient and appropriately sized for the calculated loads.
• Insulation continuity. In order to demonstrate the thermal performance of the envelope, reports based on inspection or infrared thermography are required on all buildings.
• Commissioning. Reports proving that appropriate testing and commissioning has been completed before handover will be required on all projects.
• Building logbook. An additional element of the operations and maintenance documentation will be required, detailing the building, the main plant, controls strategies, testing and commissioning records, energy metering and the calculation of carbon emissions.
• Energy metering is required to account for 90% of consumed energy.
• This metering could potentially be provided as part of a BMS system.
• The interrelated nature of these changes means that the design of building envelopes and building services will need to be better co-ordinated. Furthermore, the sizing of plant will need to be more closely matched to realistic loads. The need to demonstrate performance upon completion of the building to obtain approval will focus minds during both design and construction to ensure that compliance targets are achievable, and that detailing and workmanship are right first time.
• <B><font size=”+1”>Implications for designers and constructors</font></b>What are the wider implications of the changes to Part L?
• Learning curve. The regulations and their compliance methods are unfamiliar and involve a higher level of integrated design than has previously been the case. It will take time for designers to become familiar with the regulations, to be able to identify readily optimum solutions for different buildings. In the interim, problems that may be faced will include: Speed of design and compliance. The new Part L requirements may slow the design and compliance process as a greater understanding of the requirements is developed. Additional time will also need to be allowed for the compliance requirements of the whole building and carbon methods.
• Selecting the optimum compliance route for the building type.
• Different methods have varying pros and cons.
• Avoiding over-complicated and expensive compliance solutions. Consideration of the interaction between building components, alternative design options and the effective use of performance trade-offs will encourage the selection of the optimum solutions.
• Programming of testing and commissioning. The inclusion of testing and commissioning standards in the new regulations means that greater control of the handover process will be required to ensure that the installation is compliant at practical completion. This may mean that more time may need to be allocated to testing and commissioning in the construction programme.
• Requirement for the collective consideration of design. A closer working relationship between different building disciplines would be required to fully explout the opportunities for trade-offs under some compliance methods. This may slow down the overall design process and will require careful management to avoid the risk of non-compliance (such as updating specifications).
• Changed design practices. In particular, the approach taken to determine plant capacity for meeting realistic loads should be reviewed. Research published by Stanhope has demonstrated consistent under-utilisation of specified cooling and small-power capacity in office developments. Rules of thumb and the use of safety factors will need reassessing to eliminate the risk of over-specifying plant capacity.
• <B>Design changes in response to Part L</b>
• Areas in which designs will be reviewed as a result of the new standards include:
• Enhanced envelope performance: fabric insulation and air barriers, building orientation, proportion of glazing, specification of window/curtain walling performance, use of solar shading.
• Enhanced services performance: reduced plant size due to improved envelope performance, higher efficiency heating and cooling plant, heat recovery plant, variable speed drives to fans and pumps, increased cross-sectional areas of ductwork and plant, services insulation; luminaire and lighting control specification, BMS specification including energy meters.
• <B>Procurement issues</b>
• Contract documentation should be reviewed to ensure that workmanship and handover provisions meet the new standards.
• Contractor design issues, such as: Greater co-ordination of the design and installation of specialist subcontractors’ work to ensure that compliance targets are met.
• The allocation of the responsibility on design-and-build projects for checking that the employers’ requirements are Part L-compliant.
• <B>Capital allowances implications</b>
• Plant and machinery allowances. Reduced expenditure on mechanical plant may result in a reduced percentage of the total building expenditure qualifying for capital allowances. Areas of increased expenditure under the regulations, such as fabric insulation, generally do not qualify.
• Entitlement to enhanced capital allowances. Many of the changes to building services specifications will result in the use of equipment that qualifies for enhanced capital allowances. Under the ECA scheme, 100% first year allowances can be claimed on seven categories of energy saving plant and machinery including variable speed drives, high efficiency boilers, lighting and pipe insulation. The enhanced allowances, in effect, save 30% of the qualifying costs. Unfortunately, they are not available to property investment companies or other businesses that lease plant and machinery.
• Potential for claiming capital allowances for active facades. The definition of plant and machinery for capital allowance purposes is a complex issue, and the boundaries between what is and is not allowable are often blurred. Elements of active facades including moving louvres, interstitial blinds and the plenums and ventilation cavities featured in triple wall facade systems could all potentially be considered as qualifying items. As a result, the scope for claiming capital allowances could be extended, although it is unlikely that any item that could be characterised as a wall or window would be accepted without challenge from the Inland Revenue.
• <B><font size=”+1”>Cost models</font></b>The cost models on pages 59-62 provide an assessment of the cost implications of the new regulations, and indicate that they will have a significant effect on the costs of simple buildings where the costs of the envelope makes up a high proportion of the overall cost.
• Most of the additional cost of compliance is associated with enhancements to the thermal performance of the envelope. Buildings with a high ratio of wall and roof area to floor area will incur particularly high costs associated with improved fabric insulation. Some of the costs of improved insulation will be offset by savings resulting from smaller plant being required (shown in the table as negative figures).
• The cost models illustrate the effects of the new Part L on two common building types: out-of-town business park buildings and city-centre office blocks. The models have been developed using thermal modelling provided by engineer Oscar Faber and Partners.
• Each model provides an indicative comparison of the costs and specification of a scheme that would meet the current (1995) regulations, with two alternatives that would both comply with the new Part L document.
• The business park scheme is a 3600 m2 two-storey naturally ventilated brick office building, with double-glazed, opening windows. The two options would both comply with the elemental method, and feature enhanced fabric insulation, coated glazing with reduced U-values and internal blinds.
• The cost model indicates that compliance with the new Part L could add up to 4.4% to the costs of a simple scheme. Most of these costs, on both options, are associated with improved insulation standards.
• The city-centre scheme is a glass clad, 33,000 m2 office, typical of the City of London. The two options illustrate different designs that can be adopted with different compliance routes. Option one, featuring a triple wall facade with a U-value of 1.1, would comply with the elemental method, whereas option two, which uses a more economic curtain wall, complies with the whole building method.
• This cost model illustrates a potentially significant cost implication associated with the selection of the compliance strategy on highly glazed, highly serviced buildings. The model does not, however, consider broader performance issues that might determine the specification of different facade options. The thermal performance of buildings is sensitive to many variables, including plan and orientation. While the generic models illustrate the potential cost impact of the new Part L, assessments on a building-by-building basis are necessary to identify project specific design and cost implications.
• The costs of the models are current in fourth quarter of 2001, based on locations in the South-east (for the business park) and central London (for the office). Costs of site preparation, external works and services, professional fees, VAT and inflation are excluded.