Section 2: Design standards

  1. Regulations 35, 24 and 25
    1. Target CO 2 Emission Rate (TER)
    2. Criterion 1 – Achieving the TER
      1. Calculating the CO 2 emissions from the actual building
        1. CO2 emission rate calculations
          1. Achieving the TER
            1. Consideration of high-efficiency alternative systems
              1. Special considerations
                1. Industrial sites, workshops and non-residential agricultural buildings other than those with low energy demand
                2. Criterion 2 – Limits on design flexibility
                  1. Limiting fabric standards
                    1. Limiting services efficiencies
                    2. Criterion 3 – Limiting the effects of heat gains in summer
                      1. Limiting the effects of solar gains in summer

                      Regulations 35, 24 and 25

                      Table: Methodology of calculation of the energy performance of buildings2.1 Regulations 35, 24 and 25 state that: Interpretation 35(1). ‘Energy performance of a building’ means the calculated or measured amount of energy needed to meet the energy demand associated with a typical use of the building, which includes, inter alia, energy used for heating, cooling, ventilation, hot water and lighting. Methodology of calculation of the energy performance of buildings 24. (1) The Secretary of State shall approve–

                      (a) a methodology of calculation of the energy performance of buildings, including methods for calculating asset ratings and operational ratings of buildings; and

                      (b) ways in which the energy performance of buildings, as calculated in accordance with the methodology, shall be expressed.

                      (2) In this regulation– ‘asset rating’ means an energy performance indicator determined from the amount of energy estimated to meet the different needs associated with a standardised use of the building; and ‘operational rating’ means an energy performance indicator determined from the amount of energy consumed during the occupation of a building over a period of time and the energy demand associated with a typical use of the building over that period. Minimum energy performance requirements for  buildings 25. Minimum energy performance requirements shall be set by the Secretary of State calculated and expressed in accordance with the methodology approved pursuant to regulation 24, for–

                      a. new buildings (which shall include new dwellings), in the form of target CO2 emission rates; and

                      b. new dwellings, in the form of target fabric efficiency rates.

                      Target CO 2 Emission Rate (TER)

                      2.2 The Target CO2 Emission Rate (TER) is the minimum energy performance requirement for a new building based on the methodology approved by the Secretary of State in accordance with regulation 25. It is expressed in terms of the mass of CO2emitted per year per square metre of the total useful floor area of the building. 2.3 The TER must be calculated using one of the calculation tools included in the methodology approved by the Secretary of State for calculating the energy performance of buildings pursuant to regulation 24. Those tools include:

                      a. the Simplified Building Energy Model (SBEM) for those buildings whose design features are capable of being adequately modelled by SBEM; or

                      b. other software tools approved under the Notice of Approval.

                      2.4 From time to time further software may be approved. An up-to-date list can be found on the Department for Communities and Local Government webpages at www.gov.uk 2.5 As part of the submission to a BCB, the applicant must show that the software tool used is appropriate to the application. 2.6 The TER is established by using approved software to calculate the CO2 emission rate from a notional building of the same size and shape as the actual building, but with specified properties. These specified properties shall be as set out in the National Calculation Methodology (NCM) modelling guide, in the section headed 'Detailed definition of Notional Building for buildings other than dwellings'. The key components of the notional building specification can also be seen at Table 5. The TER is set equal to the CO2 emissions from this notional building, with no further adjustment being made. NOTE: The TER is based on a building of the same size and shape as the actual building, constructed to a concurrent specification. This concurrent specification for Part L 2013 is given in the NCM modelling guide. Developers are still given the freedom to vary the specification, provided the same overall level of CO2 emissions is achieved or bettered.

                      Criterion 1 – Achieving the TER

                      CO2 emission rates for new buildings2.7 Regulation 26 states that: CO2 emission rates for new buildings 26. Where a building is erected, it shall not exceed the target CO2emission rate for the building that has been approved pursuant to regulation 25 applying the methodology of calculation and expression of the energy performance of buildings approved pursuant to regulation 24.

                      Calculating the CO 2 emissions from the actual building

                      2.8 To demonstrate that the requirement in regulation 26 has been met, the actual Building CO2 Emission Rate (BER) must be no greater (no worse) than the TER calculated as set out in paragraphs 2.2 to 2.6. 2.9 The BER must be calculated using the same calculation tool as used for establishing the TER. 2.10 In order to determine the BER, the CO2 emission factors shall be as specified in Table 12 in The Government's Standard Assessment Procedure for energy rating of dwellings, SAP 2012. 2.11 When systems are capable of being fired by more than one fuel, then:

                      a. Where a biomass heating appliance is supplemented by an alternative appliance (e.g. gas), the CO2 emission factor for the overall heating system should be based on a weighted average for the two fuels based on the anticipated usage of those fuels. The BER submission should be accompanied by a report, signed by a suitably qualified person, detailing how the combined emission factor has been derived.

                      b. Where the same appliance is capable of burning both biomass fuel and fossil fuel, the CO2 emission factor for dual-fuel appliances should be used, except where the building is in a smoke control area, when the anthracite figure should be used.

                      c. In all other cases, the fuel with the highest CO2 emission factor should be used.

                      NOTE: This option is to cover dual-fuel systems where the choice of fuel actually used depends on prevailing market prices. 2.12 If thermal energy is supplied from a district or community heating or cooling system, emission factors should be determined by considering the particular details of the scheme. Calculations should take account of the annual average performance of the whole system (i.e. the distribution circuits and all the heat generating plant, including any Combined Heat and Power (CHP), and any waste heat recovery or heat dumping). The predicted effect of all buildings proposed to be newly connected to the system in the first 12 months of operation of the system can be considered in the calculation of the percentage of heat supplied so that the increased operation of any marginal plant (e.g. gas boilers) is properly accounted for. The electricity generated by any CHP or trigeneration scheme is always credited at an emission factor equal to the grid average. CO2 emissions associated with the thermal energy streams of a trigeneration scheme should be attributed in proportion to the output energy streams. The BER submission should be accompanied by a report, signed by a suitably qualified person, detailing how the emission factors have been derived. NOTE: This means that if a scheme burns F kWh of input fuel to produce E kWh of electricity and H kWh of useful heat (excluding heat rejected), the emission factor for the heat output should be taken as 1/H X (F X CO2F - E X CO2E) where CO2F is the emission factor for the input fuel, and CO2E the factor for grid electricity. See the NCM modelling guide at www.ncm.bre.co.uk.

                      CO2 emission rate calculations

                      2.13 Regulation 27 of the Building Regulations states: O2 emission rate calculations 27. (1) This regulation applies where a building is erected and regulation 26 (2) Not later than the day before the work starts, the person carrying out the work shall give the local authority a notice which specifies–

                      (a) the target CO2emission rate for the building calculated and expressed in accordance with the methodology approved pursuant to regulation 24,

                      (b) the CO2emission rate for the building as designed, calculated and expressed in accordance with the methodology approved pursuant to regulation 24, and

                      (c) a list of specifications to which the building is to be constructed.

                      (3) Not later than five days after the work has been completed, the person carrying out the work shall give the local authority–

                      (a) a notice which specifies–

                      (i) the target CO2emission rate for the building calculated and expressed in accordance with the methodology approved pursuant to regulation 24,

                      (ii) the CO2emission rate for the building as constructed, calculated and expressed in accordance with the methodology approved pursuant to regulation 24, and

                      (iii) whether the building has been constructed in accordance with the list of specifications referred to in paragraph (2)(c), and if not a list of any changes to those specifications; or

                      (b) a certificate of the sort referred to in paragraph (4) accompanied by the information referred to in sub- paragraph (a).

                      (4) A local authority is authorised to accept, as evidence that the requirements of regulation 26 have been satisfied, a certificate to that effect by an energy assessor who is accredited to produce energy performance certificates for that category of building. (5) In this regulation, ‘specifications’ means specifications used for the calculation of the CO2 emission rate. NOTE: Where the BCB is an approved inspector see regulation 20 of the Building (Approved Inspectors etc.) Regulations 2010 (as amended). CO2 emission rate calculation before work commences 2.14 Regulations 26 and 27 require that, before the work starts, the builder must calculate the BER of the building as designed, to demonstrate that the BER is not greater than the TER. The builder must give this design-based calculation to the BCB, along with a list of specifications used in calculating the BER. NOTE: This design stage calculation and provision of a list of specifications will help the BCB to confirm that the building as designed aligns with the claimed performance. As set out at Appendix D it is expected that the builder will use compliance software to produce the list of specifications and highlight those features of the design that are critical to achieving compliance. These 'key features' can be used to prioritise the risk-based inspection of the building as part of confirming compliance with regulation 26. If a provisional energy rating is calculated and an interim recommendations report is therefore available, the developer should review the recommendations to see if further measures may be incorporated in a cost-effective manner. CO2 emission rate calculation after completion 2.15 After work has been completed, the builder must notify the BCB of the TER and BER and whether the building has been constructed in accordance with the list of specifications submitted to the BCB before work started. If not, a list of any changes to the design-stage list of specifications must be given to the BCB. BCBs are authorised to accept, as evidence, a certificate of compliance signed off by a suitably accredited energy assessor. NOTE: It is useful to provide additional information to support the values used in the BER calculation and the list of specifications. For example, U-values may have been determined from a specific calculation, in which case the details should be provided, or from an accredited source, in which case a reference to that source is sufficient. Evidence that demonstrates that the building as designed satisfies the requirements of Criteria 2 and 3 is also useful.

                      Achieving the TER

                      2.16 Certain management features offer improved energy efficiency in practice. Where these management features are provided in the actual building, the BER can be reduced by an amount equal to the product of the factor given in Table 1 and the CO2 emissions for the system(s) to which the feature is applied. NOTE: For example, if the CO2 emissions due to electrical energy consumption were 70 kgCO2/(m2.year) without power factor correction, the provision of correction equipment to achieve a power factor of 0.95 would enable the BER to be reduced by 70 X 0.025 = 1.75 kgCO2/(m².year). Table 1: Enhanced management and control features Table 1: Enhanced management and control features 2.17 Provided the building satisfies the limits on design flexibility as set out in Criterion 2, the compliance procedure allows the designer full flexibility to achieve the TER utilising fabric and system measures and the integration of low and zero carbon (LZC) technologies in whatever mix is appropriate to the scheme. The approved compliance tools include appropriate algorithms that enable the designer to assess the role LZC technologies (including local renewable and low-carbon schemes driven by the National Planning Policy Framework) can play in achieving the TER.  

                      Consideration of high-efficiency alternative systems

                      Consideration of high-efficiency alternative systems for new buildings 25A. (1) Before construction of a new building starts, the person who is to carry out the work must analyse and take into account the technical, environmental and economic feasibility of using high-efficiency alternative systems (such as the following systems) in the construction, if available—

                      (a) decentralised energy supply systems based on energy from renewable sources;

                      (b) cogeneration;

                      (c) district or block heating or cooling, particularly where it is based entirely or partially on energy from renewable sources; and

                      (d) heat pumps.

                      (2) The person carrying out the work must—

                      (a) not later than the beginning of the day before the day on which the work starts, give the local authority a notice which states that the analysis referred to in paragraph (1)—

                      (i) has been undertaken;

                      (ii) is documented; and

                      (iii) the documentation is available to the authority for verification purposes; and

                      (b) ensure that a copy of the analysis is available for inspection at all reasonable times upon request by an officer of the local authority.

                      (3) An authorised officer of the local authority may require production of the documentation in order to verify that this regulation has been complied with. (4) The analysis referred to in paragraph (1)—

                      (a) may be carried out for individual buildings or for groups of similar buildings or for common typologies of buildings in the same area; and

                      (b) in so far as it relates to collective heating and cooling systems, may be carried out for all buildings connected to the system in the same area.

                      (5) In this regulation—

                      (a) ‘cogeneration’ means simultaneous generation in one process of thermal energy and one or both of the following—

                      (i) electrical energy;

                      (ii) mechanical energy;

                      (b) ‘district or block heating or cooling’ means the distribution of thermal energy in the form of steam, hot water or chilled liquids, from a central source of production through a network of multiple buildings or sites, for the use of space or process heating or cooling;

                      (c) ‘energy from renewable sources’ means energy from renewable non-fossil sources, namely wind, solar, aerothermal, geothermal, hydrothermal and ocean energy, hydropower, biomass, landfill gas, sewage treatment plant gas and biogases; and

                      (d) ‘heat pump’ means a machine, a device or installation that transfers heat from natural surroundings such as air, water or ground to buildings or industrial applications by reversing the natural flow of heat such that it flows from a lower to a higher temperature. (For reversible heat pumps, it may also move heat from the building to the natural surroundings.)

                      NOTE: Where the BCB is an approved inspector see regulation 20 of the Building (Approved Inspectors etc.) Regulations 2010 (as amended). 2.18 Regulation 25A requires that, before the work starts, the person undertaking the work must carry out an analysis that considers and takes into account the technical, environmental and economic feasibility of using high-efficiency alternative systems in the building design. The following high-efficiency alternative systems may be considered if available, but other LZC systems may also be considered if available:

                      a. decentralised energy supply systems based on energy from renewable sources;

                      b. cogeneration;

                      c. district or block heating or cooling, particularly where it is based entirely or partially on energy from renewable sources;

                      d. heat pumps.

                      The analysis should state whether high-efficiency alternative systems have or have not been included in the building design. The requirement relates to considering, taking into account, documenting and making available for verification purposes the analysis of high-efficiency alternative systems. NOTE: The Building Regulations are technology neutral and do not require that high-efficiency alternative systems or other LZC systems are installed. 2.19 The analysis of the feasibility of using high-efficiency alternative systems may be carried out for individual buildings, groups of similar buildings or for common types of buildings in the same area. Where a number of buildings are connected to a community energy system, a single analysis may be carried out for all of the buildings connected to the system in the same area as the building to be constructed. 2.20 Before work starts, the person undertaking the work must give the BCB a notice which states that the analysis of the feasibility of using high-efficiency alternative systems has been undertaken and documented and is available for verification purposes. The documented results of the analysis must be retained for inspection by the BCB upon request. Although the analysis of high-efficiency alternative systems is not an explicit requirement of the CO2 emission rate calculation, a facility within calculation software output reporting (the design-stage Building Regulations UK Part L report) may be available to the builder to declare that the analysis has been carried out and documented and where it is available for verification purposes. 2.21 In order to facilitate incorporation of improvements in system efficiencies and the integration with LZC technologies, the designer should:

                      a. consider adopting heating and cooling systems that use low distribution temperatures; and

                      b. where multiple systems serve the same end use, organise the control strategies such that priority is given to the least carbon-intensive option; and

                      NOTE: For example, where a solar hot water system is available, the controls should be arranged so that the best use is made of the available solar energy.

                      c. consider making the building easily adaptable by facilitating the integration of additional LZC technologies at a later date. Providing appropriate facilities at the construction stage can make subsequent enhancements much easier and cheaper, e.g. providing capped off connections that can link into a planned community heating scheme.

                      2.22 Similarly, the designer should consider the potential impact of future climate change on the performance of the building. This might include giving consideration to how a cooling system might be provided at some future point.

                      Special considerations

                      2.23 Special considerations apply to certain classes of non-exempt building. These building types include:

                      a. non-exempt buildings with low energy demand; the guidance specific to such buildings is given in paragraphs 2.24 to 2.27;

                      b. modular and portable buildings with a planned service life of more than two years (at one or more sites); the guidance specific to such buildings is given in paragraphs 2.28 to 2.32;

                      c. shell and core developments; the guidance specific to such buildings is given in paragraphs 2.34 and 2.35.

                      Non-exempt buildings with low energy demand 2.24 For the purposes of this approved document, non-exempt buildings with low energy demand are taken to be those buildings or parts thereof where:

                      a. fixed building services for heating and/or cooling are either not provided, or are provided only to heat or cool a localised area rather than the entire enclosed volume of the space concerned (e.g. localised radiant heaters at a workstation in a generally unheated space); or

                      b. fixed building services are used to heat space in the building to temperatures substantially less than those normally provided for human comfort (e.g. to protect a warehouse from condensation or frost).

                      2.25 In the situations described in paragraph 2.24 it is not reasonable to expect the entire building envelope to be insulated to the standard expected for more typical buildings. In such situations, no TER/BER calculation is required, but reasonable provision would be for every fixed building service that is installed to meet the energy efficiency standards set out in the 2013 edition of the DCLG Non-Domestic Building Services Compliance Guide. In addition, the building envelope should be insulated to a degree that is reasonable in the particular case. If some general heating is provided (case b above), then it would be reasonable that no part of the opaque fabric had a U-value worse than 0.7 W/(m².K). 2.26 If a part of a building with low energy demand is partitioned off and is heated normally (e.g. an office area in an unheated warehouse), the separately heated area should be treated as a separate 'building' and the normal procedures for demonstrating compliance (including a TER/BER calculation) should be followed to demonstrate the heated area complies with the energy efficiency requirements. 2.27 If a building with low energy demand subsequently changes such that the space is generally conditioned, then this is likely to involve the initial provision or an increase in the installed capacity of a fixed building service. Such activities are covered by regulation 28. The guidance in Approved Document L2B would require the building envelope to be upgraded and a consequential improvement to be made, a process that is likely to be much more expensive than incorporating suitable levels of insulation at the new-build stage. Alternatively, if the building shell was designed as a building with low energy demand and the first occupier of the building wanted to install (e.g.) heating, this would be first fit-out work, and a full TER/BER submission would then be required (see Appendix B paragraph 1b). Modular and portable buildings with a planned service life of more than two years 2.28 Special considerations apply to modular and portable buildings. The following paragraphs detail what is considered as reasonable provision for a variety of different circumstances. NOTE: The placing of an existing module to a new site is considered to be the construction of a new building as far as the Building Regulations are concerned. In that context, it is not always appropriate to expect such a relocated unit to meet the new-build standards set out in this approved document, especially as the embodied energy in an existing module is retained, a benefit that compensates for small differences in operating energy demand. Further, portable buildings are often 'distress purchases', and the constraints imposed by the time in which a working building must be delivered mean that additional considerations apply. At given location 2.29 Portable buildings with a planned service life of more than two years at a given location are often new or re-sale units. In such cases, compliance with the energy efficiency requirements should be demonstrated by showing that satisfactory performance has been achieved against each of the five compliance criteria set out in this approved document. However, if more than 70 per cent of the external envelope of the building is to be created from sub-assemblies manufactured prior to the date this approved document comes into force, the TER should be adjusted by the relevant factor from Table 2. One way of demonstrating the date of manufacture of each sub-assembly is by relating the serial number to the manufacturer's records. If the units are to be refurbished as part of the process, then the guidance in Approved Document L2B should be followed in terms of the standards to be achieved, for example for replacement windows and new lighting. At more than one location 2.30 Portable buildings with a planned service life of more than two years but with an intended time of use in a given location of less than two years are often 'distress purchases' (e.g. following a fire), and the buildings must be up and operational in a matter of days. In such cases, different arrangements for demonstrating compliance with regulation 26 apply, as set out in the following paragraphs. An example of the evidence that the planned time of use in the given location is less than two years would be the hire agreement for the unit. 2.31 In the case of a modular or portable building intended to be sited in a given location for less than two years, a TER/BER calculation should be carried out when the module is first constructed and can be based on a standard generic configuration. This calculation can then be provided as evidence of satisfying the requirements of regulation 26 whenever the building is moved to a new location, always provided its intended time of use in that new location is less than two years. In addition to the details of the calculation, the supplier should provide written confirmation that:

                      a. the modules as actually provided meet or exceed the elemental energy standards of the generic module on which the calculation was based; and

                      b. the activities assumed in the generic module are reasonably representative of the planned use of the actual module.

                      2.32 It is recognised that in situations where the planned time of use in a given location is less than two years, the only practical heating technology is electric resistance heating. In such cases, reasonable provision would be to provide energy efficiency measures that are 15 per cent better than if using conventional fossil fuel heating. This can be demonstrated by assuming that the heating in the generic configuration used for the TER/BER calculation is provided by a gas boiler with an efficiency of 77 per cent. Post initial construction, any work on the module should meet the standards set out in Approved Document L2B. If a TER/BER calculation is not available for a module constructed prior to 6 April 2014, reasonable provision would be to demonstrate that the BER is not greater than the Part L 2013 TER adjusted by the relevant factor from Table 2. Table 2 TER multiplying factor for modular and portable buildings Table 2 TER multiplying factor for modular and portable buildings Swimming pool basins 2.33 In terms of Criterion 1, the building should be assessed as if the pool basin were not there, although the pool hall should be included. The area covered by the pool should be replaced with the equivalent area of floor with the same U-value as the pool surround. Shell and core developments 2.34 If a building is offered to the market for sale or let as a shell for specific fit-out work by the incoming occupier, the developer should demonstrate via the design-stage TER/BER submission how the building shell as offered could meet the energy efficiency requirements. For those parts of the building where certain systems are not installed at the point the building is to be offered to the market, the model that is used to derive the BER should assume efficiencies for those services that will be installed as part of the first fit-out work. The specification provided to the BCB (see paragraph 2.14) should identify which services have not been provided in the base build, and the efficiency values assumed for each such system. This should enable the BCB to ensure that the necessary infrastructure needed to deliver the assumed fit-out specification is provided as part of the base build. At practical completion of the base building, the as-built TER/BER calculation should be based only on the building and systems as actually constructed; the fit-out areas should be assumed to be conditioned to temperatures appropriate to their designated use, but no associated energy demand included. NOTE: As part of the design-stage calculation, a predicted energy performance certificate (EPC) rating for the fit-out areas should be available to inform prospective occupiers of the energy performance that is achievable. However, a formal EPC lodged on the EPC register is not required at this stage. 2.35 When an incoming occupier does first fit-out work on all or part of the building through the provision or extension of any of the fixed services for heating, hot water, air-conditioning or mechanical ventilation, then TER/BER submission should be made to the BCB after completion to demonstrate compliance for the part of the building covered by the fit-out work. This submission should be based on the building shell as constructed and the fixed building services as actually installed. If the fit-out work does not include the provision or extension of any of the fixed services for heating, hot water, air-conditioning or mechanical ventilation, then reasonable provision would be to demonstrate that any lighting systems that are installed are at least as efficient as those assumed in the shell developer's initial submission. NOTE: Since the fit-out is specific to the needs of the particular occupier and is, by definition, uniquely controlled by him for his benefit, this is creating a new 'part designed or altered for separate use', and under regulation 29 a new energy performance certificate is required for that part of the physical building covered by the fit-out.

                      Industrial sites, workshops and non-residential agricultural buildings other than those with low energy demand

                      2.36 Special considerations may apply in such cases, e.g. where a CO2 target is established through other regulatory frameworks such as the Carbon Reduction Commitment, or where it is impractical for the generic National Calculation Methodology to adequately account for the particular industrial processes or agricultural use without leading to the possibility of negative impacts on cost-effectiveness and/or increased technical risk. In such cases, reasonable provision would be to provide fixed building services that satisfy the standards set out in Approved Document L2B.

                      Criterion 2 – Limits on design flexibility

                      Table 3 Limiting fabric parameters2.37 While the approach to complying with Criterion 1 allows design flexibility, paragraph L1(a)(i) of Schedule 1 to the Building Regulations requires that reasonable provision be made to limit heat gains and losses through the fabric of the building, and paragraphs L1(b)(i) and (ii) require that energy-efficient fixed building services with effective controls be provided. 2.38 One way of showing that the Part L requirement is satisfied is to demonstrate that the fabric elements and the fixed building services all meet minimum energy efficiency standards as specified in the following paragraphs. NOTE: In order to satisfy the TER, the building specification needs to be considerably better than the stated limiting values in many aspects of the design. Table 5 provides a summary specification of the notional building and is a better indication of the standards required to meet the TER.

                      Limiting fabric standards

                      2.39 Table 3 sets out the limiting standards for the properties of the fabric elements of the building. The stated value represents the area-weighted average value for all elements of that type. In general, achievement of the TER is likely to need better fabric performance than set out in Table 3. 2.40 U-values should be calculated using the methods and conventions set out in BR 443 Conventions for U-value calculations, and should be based on the whole unit (e.g. in the case of a window, the combined performance of the glazing and the frame). The U-value of glazing can be calculated for:

                      a. the smaller of the two standard windows defined in BS EN 14351-1; or

                      b. the standard window configuration set out in BR 443; or

                      c. the specific size and configuration of the actual window.

                      The U-value of the door can be calculated for:

                      a. the standard size as laid out in BS EN 14351-1; or

                      b. the specific size and configuration of the actual door.

                      NOTE: For domestic-type construction, SAP 2012 Table 6e gives values for different configurations that can be used in the absence of test data or calculated values. 2.41 The U-values for roof windows and roof-lights given in this approved document are based on the U-value having been assessed with the roof window or roof-light in the vertical position. If a particular unit has been assessed in a plane other than the vertical, the standards given in this approved document should be modified by making an adjustment that is dependent on the slope of the unit, following the guidance given in BR 443. Table 3 Limiting fabric parameters Table 3 Limiting fabric parameters NOTE: Approved Document C gives limiting values for individual elements to minimise the risk of condensation.

                      Limiting services efficiencies

                      2.42 This section sets out the design limits for fixed building services to meet the requirements of Part L1(b). Controls 2.43 Systems should be provided with appropriate controls to enable the achievement of reasonable standards of energy efficiency in use. In normal circumstances, the following features would be appropriate for heating, ventilation and air-conditioning system controls:

                      a. The systems should be subdivided into separate control zones to correspond to each area of the building that has a significantly different solar exposure, or pattern or type of use; and

                      b. Each separate control zone should be capable of independent timing and temperature control and, where appropriate, ventilation and air recirculation rate; and

                      c. The provision of the service should respond to the requirements of the space it serves. If both heating and cooling are provided, they should be controlled so as not to operate simultaneously; and

                      d. Central plant should operate only as and when the zone systems require it. The default condition should be off.

                      2.44 In addition to these general control provisions, the systems should meet specific control and efficiency standards as set out in the paragraphs below. System efficiencies 2.45 Each fixed building service should be at least as efficient as the minimum acceptable value for the particular type of service as set out in the Non-Domestic Building Services Compliance Guide. If the type of service is not covered by the Guide, then reasonable provision is to demonstrate that the proposed service is not less efficient than a comparable service that is covered by the Guide. NOTE: To not inhibit innovation. 2.46 The efficiency claimed for the fixed building service should be based on the appropriate test standard set out in the Non-Domestic Building Services Compliance Guide and the test data should be certified by a notified body. It is reasonable for BCBs to accept such data at face value. In the absence of quality-assured data, the BCB should satisfy itself that the claimed performance is justified. Energy meters 2.47 Reasonable provision for energy meters would be to install energy metering systems that enable:

                      a. at least 90 per cent of the estimated annual energy consumption of each fuel to be assigned to the various end-use categories (heating, lighting etc.). Detailed guidance on how this can be achieved is given in CIBSE TM 39 Building Energy Metering; and

                      b. the output of any renewable system to be separately monitored; and

                      c. in buildings with a total useful floor area greater than 1000 m², automatic meter reading and data collection facilities.

                      2.48 The metering provisions should be designed such as to facilitate the benchmarking of energy performance as set out in CIBSE TM 46 Energy Benchmarks. Centralised switching of appliances 2.49 Consideration should be given to the provision of centralised switches to allow the facilities manager to switch off appliances when they are not needed (e.g. overnight and at weekends). Where appropriate, these should be automated (with manual override) so that energy savings are maximised. NOTE: A centralised switch would be more reliable than depending on each individual occupant to switch off their (e.g.) computer.

                      Criterion 3 – Limiting the effects of heat gains in summer

                      2.50 This section sets out the approach to limiting heat gains as required by paragraph L1(a)(i) of Schedule 1 to the Building Regulations.

                      Limiting the effects of solar gains in summer

                      2.51 The following guidance applies to all buildings, irrespective of whether they are air-conditioned or not. The intention is to limit solar gains during the summer period to either:

                      a. reduce the need for air-conditioning; or

                      b. reduce the installed capacity of any air-conditioning system that is installed.

                      2.52 If the criterion set out below is satisfied in the context of a naturally ventilated building, this is NOT evidence that the internal environment of the building will be satisfactory, since many factors that are not covered by the compliance assessment procedure will have a bearing on the incidence of overheating (incidental gains, thermal capacity, ventilation provisions etc.). NOTE: Therefore the developer should work with the design team to specify what constitutes an acceptable indoor environment in the particular case, and carry out the necessary design assessments to develop solutions that meet the agreed brief. Some ways of assessing overheating risk are given in CIBSE TM 37 Design for improved solar shading control and, for education buildings, in Building Bulletin 101 Ventilation of school buildings. 2.53 For the purposes of Part L, reasonable provision for limiting solar gain through the building fabric would be demonstrated by showing that, for each space in the building that is either occupied or mechanically cooled, the solar gains through the glazing aggregated over the period from April to September inclusive are no greater than would occur through one of the following reference glazing systems with a defined total solar energy transmittance (g-value) calculated according to BS EN 410:

                      a. For every space that is defined in the National Calculation Methodology (NCM) database as being side lit, the reference case is an east-facing façade with full-width glazing to a height of 1.0 m having a framing factor of 10 per cent and a normal solar energy transmittance (g-value) of 0.68.

                      b. For every space that is defined in the NCM database as being top lit, and whose average zone height is not greater than 6 m, the reference case is a horizontal roof of the same total area that is 10 per cent glazed as viewed from the inside out and having roof-lights that have a framing factor of 25 per cent and a normal solar energy transmittance (g-value) of 0.68.

                      c. For every space that is defined in the NCM database as being top lit and whose average zone height is greater than 6 m, the reference case is a horizontal roof of the same total area that is 20 per cent glazed as viewed from the inside out and having roof-lights that have a framing factor of 15 per cent and a normal solar energy transmittance (g-value) of 0.46;

                      NOTE: In double-height industrial-type spaces, dirt on the roof-lights and internal absorption within the roof-light reduce solar gains. These effects, combined with temperature stratification, will reduce the impact of solar gains in the occupied space and so increased roof-light area may be justified. In such situations, the developer should pay particular attention to the design assessments referred to in paragraph 2.53b.

                      d. For the purpose of this specific guidance, an occupied space means a space that is intended to be occupied by the same person for a substantial part of the day. This excludes circulation spaces and other areas of transient occupancy, such as toilets, as well as spaces that are not intended for occupation (e.g. display windows).

                        • Table 1 Enhanced management and control features Table 1 Enhanced management and control features
                        • Table 2 TER multiplying factor for modular and portable buildings Table 2 TER multiplying factor for modular and portable buildings
                        • Table 3 Limiting fabric parameters Table 3 Limiting fabric parameters
                        • Table 4 Ductwork pressure classes Table 4 Ductwork pressure classes
                        • Table 5 Summary of concurrent notional building specification Table 5 Summary of concurrent notional building specification
                        • Planning Use Classes Planning Use Classes
                        • Parameter Parameter