Design standards

Section 2 Design standards

2.1 Regulations 35, 24 and 25

2.1 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 CO2 Emission Rate (TER) and Target Fabric Energy Efficiency (TFEE) rate

2.2 The Target CO2 Emission Rate (TER) and Target Fabric Energy Efficiency (TFEE) rate are the minimum energy performance requirements for a new dwelling approved by the Secretary of State in accordance with regulation 25. The TER is expressed as the mass of CO2 emitted in kilograms per square metre of floor area per year. The TFEE rate is expressed as the amount of energy demand in units of kilowatt-hours per square metre of floor area per year. The results are based on the provision and standardised use of specified fixed building services when assessed using approved calculation tools.

2.3 In line with the methodology approved by the Secretary of State in the Notice of Approval, the TER and TFEE rate for individual dwellings must be calculated using SAP 2012.

NOTE: A summary of the Part L 2013 notional dwelling is published at Table 4 in this approved document with the full detail in SAP 2012 Appendix R. If the actual dwelling is constructed entirely to the notional dwelling specifications it will meet the CO2 and fabric energy efficiency targets and the limiting values for individual fabric elements and buildings services. Developers are, however, free to vary the specification, provided the same overall level of CO2 emissions and fabric energy efficiency performance is achieved or bettered.

2.4 The TER is calculated in two stages:

a. First calculate the CO 2 emissions from a notional dwelling of the same size and shape as the actual dwelling and which is constructed according to the reference values set out in Appendix R of SAP 2012 (and summarised at Table 4). No values may be varied from these reference values when establishing the TER. The calculation tool will report the CO2 emissions (based on SAP 2012 CO2 emission factors) arising from:

i. The provision of space heating and hot water, CH

ii. The use of pumps and fans, CPF

iii. The use of internal lighting, CL

b. Second, calculate the TER using the following formula:
TER2013 = CH X FF + CPF + CL
Where FF is the fuel factor taken from Table 1 in accordance with the guidance in paragraph 2.5.

2.5 The fuel to be used when determining the fuel factor from Table 1 is one of the fuels used to provide heating and hot water to the actual dwelling, as follows:

a. If all the space heating and domestic hot water heating appliances are served by the same fuel, select that fuel.

b. If the dwelling has more than one appliance for space heating and/or domestic hot water and these are served by different fuels, select:

i. mains gas if used to fire any of the appliances; or

ii. otherwise the fuel used for the main space heating system.

c. Where the dwelling is served by a community heating scheme, select:

i. mains gas if used for any purpose in the community scheme; or

ii. otherwise the fuel that provides the most heat for the community scheme.

Table 1 Fuel factor

2.6 The TFEE rate is calculated by determining the fabric energy efficiency from a notional dwelling of the same size and shape as the actual dwelling and which is constructed according to the reference values as summarised in Table 4. This fabric energy efficiency is then multiplied by 1.15 to give the TFEE rate.

Buildings containing multiple dwellings

2.7 For a building that contains more than one dwelling (such as a terrace of houses or an apartment block), an average TER and/or TFEE rate can be calculated. The average TER and/or TFEE rate is the floor-area-weighted average of the TERs and/or TFEE rates for all the dwellings in the building, calculated according to the following formula:
{(TER1 X Floor area1) + (TER2 X Floor area2) + (TER3 X Floor area3) + ...} / (Floor area 1 + Floor area 2 + Floor area3 + ...)

The average TFEE rate is calculated according to an identical formula, replacing TER with TFEE rate.

An average TER and/or TFEE rate can be calculated across multiple dwellings in the same building but cannot be calculated across separate multiple buildings on the same site.

Criterion 1 - Achieving the TER and TFEE rate

2.8 Regulations 26 and 26A state that:

CO2 emission rates for new buildings

26. Where a building is erected, it shall not exceed the target CO2 emission 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.

Fabric energy efficiency rates

26A. Where a dwelling is erected, it shall not exceed the target fabric energy efficiency rate for the dwelling 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.

CO 2 emission rate and fabric energy efficiency rate calculations

2.10 Regulation 27 states that:

CO2 emission rate calculations

27. (1) This regulation applies where a building is erected and regulation 26 applies

(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 CO2 emission rate for the building calculated and expressed in accordance with the methodology approved pursuant to regulation 24,

(b) the CO2 emission 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 CO2 emission rate for the building calculated and expressed in accordance with the methodology approved pursuant to regulation 24,

(ii) the CO2 emission 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).

2.11 Regulation 27A of the Building Regulations states that:

Fabric energy efficiency rate calculations

27A. (1) This regulation applies where a dwelling is erected and regulation 26A applies.

(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 fabric energy efficiency rate for the dwelling calculated and expressed in accordance with the methodology approved pursuant to regulation 24;

(b) the fabric energy efficiency rate for the dwelling as designed, calculated and expressed in accordance with the methodology approved pursuant to regulation 24; and

(c) a list of specifications to which the dwelling 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 fabric energy efficiency rate for the dwelling calculated and expressed in accordance with the methodology approved pursuant to regulation 24;

(ii) the fabric energy efficiency rate for the dwelling as constructed, calculated and expressed in accordance with the methodology approved pursuant to regulation 24; and

(iii) whether the dwelling 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 26A 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 fabric energy efficiency rate.

NOTE: Where the BCB is an approved inspector see regulation 20 of the Building (Approved Inspectors etc.) Regulations 2010 (as amended).

CO2 emission and fabric energy efficiency rate calculations before work commences

2.12 Regulations 26 and 26A and 27 and 27A require that, before work starts, the builder must calculate the DER and the DFEE rate of the dwelling as designed, to demonstrate that the DER and the DFEE rate are not greater than the TER and the TFEE rate. The builder must give this design-based calculation to the BCB, along with a list of specifications used in calculating the DER and DFEE rate.

NOTE: This design-stage calculation and list of specifications will help the BCB to confirm that the dwelling as designed aligns with the claimed performance. As set out at Appendix C, it is expected that the builder will use software implementations of SAP 2012 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 dwelling as part of confirming compliance with regulations 26 and 26A. If a provisional energy rating is calculated and an interim recommendations report is therefore available, the developer should review the recommendations to see whether further measures may be incorporated in a cost-effective manner.

CO2 emission and fabric energy efficiency rate calculation when work is complete

2.13 When work is complete, the builder must notify the BCB of the TER and DER, the DFEE rate and TFEE rate, and whether the building was constructed in accordance with the list of specifications submitted to the BCB before work started. A list of any changes to the design-stage list of specifications must be given to the BCB. BCBs are authorised to accept a certificate of compliance to this effect signed by a suitably accredited energy assessor.

NOTE: It is useful to provide additional information to support the values used in the DER and DFEE rate 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. For example, for a boiler, details of the model reference and fuel type is sufficient evidence to allow the claimed performance to be checked against the Products Characteristics Database. Evidence that demonstrates that the dwelling as designed satisfies the requirements of criteria 2 and 3 is also useful.

Secondary heating

2.14 A secondary heating appliance may meet part of the demand for space heating. When calculating the DER, the fraction provided by the secondary heating system must be as defined by SAP 20 for the particular combination of main heating system and secondary heating appliance. Refer to the following when calculating the DER:

a. Where a secondary heating appliance is fitted, the efficiency of the actual appliance with its appropriate fuel must be used in the calculation of the DER.

b. Where a chimney or flue is provided but no appliance is installed, the presence of the following appliances must be assumed when calculating the DER:

i. if a gas point is located adjacent to the hearth, a decorative fuel-effect gas fire open to the chimney or flue with an efficiency of 20 per cent;

ii. if there is no gas point, an open fire in grate for burning multi-fuel with an efficiency of 37 per cent, unless the dwelling is in a smoke control area, when the fuel should be taken as smokeless solid mineral fuel.

c. Otherwise it must be assumed that the secondary heating system has the same efficieny as the main heating system and is served by the same fuel - i.e. the equivalent of having no secondary heating system.

Internal lighting

2.15 In all cases, when calculating the DER, allow for the proportion of low-energy lamps installed in the fixed lighting locations.

NOTE: Low-energy lighting provision is therefore tradable. The minimum amount that would be reasonable provision in the actual dwelling is given in the Domestic Building Services Compliance Guide.

Buildings containing multiple dwellings

2.16 A building that contains more than one dwelling (such as a terrace of houses or an apartment block) complies with regulation 26 if:

a. either every individual dwelling has a DER that is no greater than the individual dwelling's corresponding TER;

b. or the average DER for the whole building is no greater than the average TER.
The average DER is the floor-area-weighted average of the individual DERs for all the dwellings in the building, and is calculated in the same way as the average TER (see paragraph 2.7).

An average DER cannot be calculated across separate multiple buildings on a site.

NOTE: When an average DER is calculated, it is still necessary to provide information for each individual dwelling, as required by regulation 27.

2.17 A building that contains more than one dwelling (such as a terrace of houses or an apartment block) complies with regulation 26A if:

a. either every individual dwelling has a DFEE rate that is no greater than the individual dwelling's corresponding TFEE rate;

b. or the average DFEE rate for the whole building is no greater than the average TFEE rate;
The average DFEE rate is the floor-area-weighted average of the individual DFEE rates for all the dwellings in the building, and is calculated in the same way as the average TFEE rate (see paragraph 2.7).

An average DFEE rate cannot be calculated across separate multiple buildings on a site.

NOTE: When an average DFEE rate is calculated, it is still necessary to provide information for each individual dwelling, as required by regulation 27A.

Achieving the TER and TFEE rate

2.18 Provided the dwelling satisfies the limits on design flexibility set out in Criterion 2, the designer can achieve the TER by using fabric energy efficiency, system measures and integrating low and zero carbon technologies in whatever mix is appropriate.

2.19 Similarly, provided the dwelling satisfies the limits on design flexibility set out in Criterion 2, the designer can achieve the TFEE rate by using fabric energy efficiency measures in whatever mix is appropriate.

2.20 The approved compliance tools include algorithms that enable the designer to assess the role that low and zero carbon technologies (including local renewable and low carbon energy sources driven by the National Planning Policy Framework) can play in achieving the TER.

2.21 Where a dwelling is connected to a community energy system, the annual percentage heat supplied from each heat source should be the same for each newly connected dwelling. The submission should demonstrate that the capacity of the community scheme is sufficient to provide the percentage that is assumed. The predicted effect of all dwellings 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.

2.22 In order to facilitate incorporation of improvements in system efficiencies and the integration with low and zero carbon technologies, the designer should:

a. consider heating system designs 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, use controls that make best use of the available solar energy.

c. consider making the dwelling easily adaptable by facilitating the integration of additional low and zero carbon 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.

Consideration of high-efficiency alternative systems

2.23 Regulation 25A states that:

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 (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).
2.24 Regulation 25A requires that, before 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 dwelling The following high- efficiency alternative systems may be considered if available, but other low and zero carbon 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 low and zero carbon systems are installed.

2.25 The analysis of the feasibility of using high-efficiency alternative systems may be carried out for individual dwellings, groups of similar dwellings or for common types of dwelling in the same Where a number of dwellings are connected to a community energy system, a single analysis may be carried out for all the dwellings connected to the system in the same area as the building to be constructed.

2.26 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 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 BRUKL 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.

Special considerations

2.27 The following paragraphs describe some 'special areas' that fall outside the normal five criteria, and give guidance on how to demonstrate reasonable provision for the conservation of fuel and power.

Common areas in buildings with multiple dwellings

2.28 The common areas of buildings containing more than one dwelling are not classified as dwellings and therefore fall outside the scope of the five criteria outlined above.
For such areas, reasonable provision is:

a. if they are heated, to follow the guidance in Approved Document L2A; or

b. if they are unheated, to provide individual fabric elements that meet the fabric standards set out in paragraphs 2.33 to 2.35.

Conservatories and porches

2.29 Where conservatories and porches are installed at the same time as the construction of a new dwelling, and adequate thermal separation (see Tables 2 and 4) is provided between the dwelling and the conservatory or porch, and the dwelling's heating system is not extended into the conservatory or porch, follow the guidance in Approved Document L1B. Where conservatories and porches are installed at the same time as the construction of a new dwelling, and no, or inadequate, thermal separation is included between the dwelling and the conservatory or porch, or the dwelling's heating system is extended into the conservatory or porch, follow the guidance in this approved document including TER/DER and TFEE/DFEE rate calculations.

Swimming pool basins

2.30 In terms of Criterion 1, the dwelling 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.

Criterion 2 - Limits on design flexibility

2.31 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.

2.32 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 the minimum energy efficiency standards specified in the following paragraphs.

NOTE: Note that, in order to satisfy the TER and the TFEE rate, the building specification needs to be considerably better than the stated limiting values in many aspects of the design.

NOTE: Achieving the TFEE rate could be dependent on very good performance of one specific feature of the fabric design with poorer fabric performance elsewhere. If this key element of fabric design was to fail, or perform less well than expected, this would have a significant impact on performance. Continuing to have limiting fabric standards in Criterion 2 reduces such an impact.

Limiting fabric standards

2.33 Table 2 sets out the limiting standards for the properties of the fabric elements of the building. Each stated value represents the area-weighted average for all elements of that type. In general, to achieve the TER and the TFEE rate, a significantly better fabric performance than that set out in Table 2 is likely to be required.

2.34 U-values shall be calculated using the methods and conventions set out in BR 443 Conventions for U-value calculations, and should be based on the whole element or unit (e.g. in the case of a window, the combined performance of the glazing and the frame).
In the case of windows, the U-value can be taken as that for:

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

b. the standard 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 window configurations, which can be used if there are no test data or calculated values.

2.35 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 2 Limiting fabric parameters

Note: Approved Document C gives limiting values for individual elements to minimise the risk of condensation.

Limiting system efficiencies

2.36 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 Domestic Building Services Compliance Guide. If a 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.

2.37 The efficiency claimed for the fixed building service should be based on the appropriate test standard set out in the 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.

Limiting the effects of solar gains in summer

2.39 Solar gains are beneficial in winter to offset demand for heating, but can contribute to overheating in the summer. The effects of solar gain in summer can be limited by an appropriate combination of window size and orientation, solar protection through shading and other solar control measures, ventilation (day and night) and high thermal capacity. If ventilation is provided using a balanced mechanical system, consider providing a summer bypass function to use during warm weather (or allow the dwelling to operate via natural ventilation) so that the ventilation is more effective in reducing overheating.

2.40 SAP 2012 Appendix P contains a procedure enabling designers to check whether solar gains are excessive. Reasonable provision is achieved if the SAP assessment indicates that the dwelling does not have a high risk of high internal temperatures. This assessment should be done regardless of whether or not the dwelling has mechanical cooling. If the dwelling has mechanical cooling, the assessment should be based on the design without the cooling system operating, but with an appropriate assumption about effective air-change rate through openable windows.

NOTE: Designers may want to exceed the requirements in the current Building Regulations to consider the impacts of future global warming on the risks of higher internal temperatures occurring more often. CIBSE TM 36 Climate change and the indoor environment gives guidance on this issue.

2.41 When seeking to limit solar gains, consideration should be given to the provision of adequate levels of daylight. BS 8206-2 Code of practice for daylighting gives guidance on maintaining adequate levels of daylight.

NOTE: The Building Regulations do not specify minimum daylight requirements. Reducing the window area has conflicting impacts on the predicted CO2 emissions: reduced solar gain but increased use of electric lighting. As a general guide, if the area of glazing is much less than 20 per cent of the total floor area, some parts of the dwelling may experience poor levels of daylight, resulting in increased use of electric lighting.

Heat losses and gains from circulation pipes

2.42 Reasonable provision should be made to limit heat losses from pipes as set out in the Domestic Building Services Compliance Guide. This includes insulating primary circulation pipes for domestic hot water services throughout their length.

NOTE: In the case of apartment blocks, insulating primary circulation pipes for space heating as well as for domestic hot water services within communal spaces can help to limit potentially unwanted heat gains and overheating of the space.