2.1 The same approved calculation tool must be used to calculate the target primary energy rate, the target emission rate, the building primary energy rate and the building emission rate.

2.2 The building primary energy rate and the building emission rate must be calculated at both of the following points using the same calculation tool.

a. Before work starts, using design values.

b. When work is complete, using figures for the building as constructed, and incorporating both of the following.

i. Any changes that have been made during construction to the list of specifications.

ii. The measured air permeability.

2.3 At both of these points the building primary energy rate and building emission rate must not exceed the target primary energy rate and the target emission rate, respectively. The specification of the actual building may vary from that of the notional building if the building meets the target primary energy rate, target emission rate and the guidance in this approved document.

Building control notification

2.4 The building control body must be notified, before the work starts, of all of the following.

a. The target primary energy rate and the building primary energy rate (calculated using design values).

b. The target emission rate and the building emission rate (calculated using design values).

c. A list of specifications used in the calculations.

Items (a) to (c) above may be reported using the design stage Building Regulations UK Part L compliance report (BRUKL report) which is produced as a standardised output from the approved software. For further details of the design stage BRUKL report, see Appendix C.

2.5 The building control body must be notified, once the work is complete, of all of the following.

a. The as-built target primary energy rate and as-built building primary energy rate.

b. The as-built target emission rate and the as-built building emission rate.

c. A list of specifications used in the as-built calculations, and whether the specifications have changed from those used in the design stage calculations.

Building control bodies are authorised to accept notification of (a) to (c) above as reported in the as-built BRUKL report, which is produced as a standardised output from the approved software.

For further details of the as-built BRUKL report, see Appendix C.

Heating in the building primary energy rate and the building emission rate calculations

2.6 When systems are capable of being fired by more than one fuel, the following applies, according to the fuel(s).

a. Biomass heating supplemented by an alternative appliance (e.g. gas) – the CO2 emission factor and primary energy factor should be based on a weighted average for the two fuels. The weighting should be based on the anticipated usage of those fuels. The building emission rate and building primary energy rate submission should be accompanied by a report, signed by a suitably qualified person, detailing how the combined emission factor has been derived.

b. Appliances capable of burning both biomass fuel and fossil fuel – the CO2 emission factor and primary energy 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.

2.7 If thermal energy is supplied from a district heat network or community heating system or community cooling system, CO2 emission factors and primary energy factors should be determined by considering the details of the scheme and following the guidance in items (a) to (g) below.

a. The CO2 emission factor and primary energy factor for the heat delivered to the building by the district heat network should be based on the ‘heat network’ specific factors from Table 32 in the National Calculation Methodology Modelling Guide.

b. Calculations should take account of the annual average performance of the whole system, including the distribution circuits, all heat generating plants, combined heat and power (CHP), and any waste heat recovery or heat dumping.

c. The calculation should include the predicted effect of all buildings or parts of buildings that will be connected to the system in the first 12 months of operation. A change in the number of buildings or spaces within buildings connected to the system might affect the percentage of heat supplied from the communal system. The increased operation of any marginal plant (e.g. gas boilers) can then be properly accounted for.

d. The electricity generated by any combined heat and power (CHP) or trigeneration scheme should always be credited using the appropriate CO2 emission and primary energy ‘heat network’ specific factors from Table 32 in the National Calculation Methodology Modelling Guide.

e. CO2 emissions and primary energy associated with the thermal energy streams of a trigeneration scheme should be attributed in proportion to the output energy streams.

f. When calculating the building primary energy rate and building emission rate for a building connected to a new district heat network, the calculation should include all heat sources to be used up to 31 December 2027. In this way, any planned transition of the heat network to an alternative means of heat generation will be properly accounted for. When there will be a change in heat source up to 31 December 2027, a submission to the building control body should
be made to show both of the following.

i. That planning permission, if required, has been granted for the change.

ii. That the heat network will connect to the new source, with confirmation in the form of a signed contract to connect and supply heat.

NOTE: An existing district heat network is defined in Appendix A. A new district heat network should be taken as meaning any other district heat network.

NOTE: When calculating the building primary energy rate and building emission rate for a building connected to an existing district heat network, the calculation should not include the effect of any change in heat sources after the buildings are connected.

g. The building primary energy rate and building emission rate submission should be accompanied by a report, signed by a suitably qualified person, detailing how the CO2 emission factors and primary energy factors have been derived.
The primary energy factor for the heat output should be taken as:

1/H x (F x PEF – E x PEE)

where:

H is the useful heat (excluding heat rejected) in kWh

F is the fuel input in kWh

PEF is the primary energy factor for the input fuel in kWhPE/kWh

E is the electricity production from the scheme in kWh

PEE is the primary energy factor for district heat CHP generated electricity in kWhPE/kWh.

The CO2 emission factor for the heat output should be taken as:

1/H x (F x CO2F – E x CO2E )

where:

H is the useful heat (excluding heat rejected) in kWh

F is the fuel input in kWh

CO2F is the emission factor for the input fuel in kgCO2/kWh

E is the electricity production from the scheme in kWh

CO2E is the emission factor for district heat CHP generated electricity in kgCO2/kWh.

NOTE: See the National Calculation Methodology Modelling Guide for further information.

NOTE: The same CO2 emission factors and primary energy factors used to calculate the building emission rate and building primary energy rate for buildings connected to a district heat network or community heating system should be used to check against the minimum performance standards described in Section 6 of this approved document.

Management and control features in the building primary energy rate and the building emission rate calculations

2.8 Where enhanced management and control features are provided in the building, the building primary energy rate and building emission rate can be reduced. This is done by applying the appropriate factor given in Table 2.1 to both of the following, for the system(s) to which the feature is being applied.

a. The CO2 emissions.

b. The primary energy.

NOTE: For example, if the CO2 emissions due to electrical energy consumption were 70kgCO2/(m2·year) without power factor correction, the provision of correction equipment to achieve a power factor of 0.95 would enable the building emission rate to be reduced by 70 0.025 = 1.75kgCO2/(m2·year).

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Table 2.1 Enhanced management and control features

Achieving the target primary energy rate and target emission rate

2.9 Provided the building satisfies the minimum standards for fabric elements set out in Section 4, the designer can achieve the target primary energy rate and target emission rate by using any combination of the following.

a. Fabric energy efficiency.

b. Efficient building services.

c. Low and zero carbon technologies integrated in an appropriate mix.

NOTE: The target primary energy rate and target emission rate are not likely to be met by using the minimum standards for fabric set out in Section 4 alone.

Special considerations when calculating building primary energy rate and building emission rate

2.10 Special considerations may apply to certain classes of building. These building types include all of the following.

a. Modular and portable buildings with a planned service life of more than two years (at one or more sites), follow paragraphs 2.11 to 2.19.

b. Swimming pools, follow paragraph 2.20.

c. Shell and core developments, follow paragraphs 2.21 to 2.25.

d. Industrial sites, workshops and non-residential agricultural buildings, follow paragraph 2.26.

e. Buildings with low energy demand, follow paragraphs 2.27 to 2.32.

NOTE: Industrial sites, workshops and non-residential agricultural buildings with low energy demand and buildings with a planned service life of less than two years are exempt from the energy efficiency requirements. See paragraph 0.11.

Modular and portable buildings with a planned service life of more than two years

2.11 Placing an existing module on a new site is considered by the Building Regulations to be the construction of a new building.

2.12 Special considerations apply to modular and portable buildings with a planned service life of more than two years.

a. For modular and portable buildings at a single location, follow paragraphs 2.13 to 2.15.

b. For modular and portable buildings intended for use at more than one location, for example under hire agreements, follow paragraphs 2.16 to 2.19.

At a single location

2.13 Modular and portable buildings with a planned service life of more than two years at a single location should be shown to comply with the energy efficiency requirements.

2.14 If more than 70% of the external envelope of this type of building will be created from subassemblies manufactured before the date when this approved document came into force, the target primary energy rate and target emission rate should be multiplied by the relevant factors from Table 2.2.

NOTE: One way of demonstrating the date of manufacture of each sub-assembly is by relating the serial number to the manufacturer’s records.

2.15 After initial manufacture, any work on a module should meet the standards in this document, treating it as work on an existing building. Fabric elements that will be refurbished or replaced in modular sub-assemblies should meet the minimum standards given in Section 4. Fixed building services elements that will be replaced in modular sub-assemblies should meet the minimum standards in Sections 5 and 6.

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Table 2.2 Target primary energy rate and target emission rate multiplying factors for modular and portable buildings with a service life of more than two years at a single location

At more than one location

2.16 Modular and portable buildings with a planned service life of more than two years but with an intended time of use in a single location of less than two years should be shown to comply with the energy efficiency requirements. An example of this type of building would be a modular or portable building intended for short term hire to multiple locations.

NOTE: An example of evidence that the planned time of use in the given location is less than two years is the hire agreement for the unit.

2.17 For modular or portable buildings of the type described in paragraph 2.16, a target primary energy rate and building primary energy rate calculation and target emission rate and building emission rate calculation should be carried out when the portable building or its modular components are first constructed. The calculation can be based on a standard generic configuration of modules.

Whenever the building is moved to a new location, in which its intended time of use is less than two years, these calculations can be provided as evidence that the energy efficiency requirements are met. The supplier should provide all the following in writing.

a. Details of the calculation.

b. Confirmation that the modules as provided meet or exceed the elemental energy standards of the generic module on which the calculation was based.

c. Confirmation that the activities assumed in the generic module are reasonably representative of the planned use of the actual module.

2.18 If the planned time of use of a modular or portable building in a single location is less than two years, the only practical heating technology may be electric resistance heating. In such cases, the notional building will use electric resistance heating.

2.19 If more than 70% of the external envelope of this type of building will be created from subassemblies manufactured before the date when this approved document came into force, the target primary energy rate and target emission rate should be multiplied by the relevant factors from Table 2.3.

NOTE: One way of demonstrating the date of manufacture of each sub-assembly is by relating the serial number to the manufacturer’s records.

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Table 2.3 Target emission rate multiplying factor for modular and portable buildings with a planned service life of more than two years but intended time of use at a single location of less than two years

Swimming pool basins

2.20 When calculating the building primary energy rate and building emission rate for a building with a swimming pool, the thermal performance of the pool basin should not be included in the calculation. Instead, the building primary energy rate and building emission rate should be calculated as if the area covered by the pool were replaced with the equivalent area of floor with the same U-value as the pool surround.

Shell and core developments

2.21 If a building is offered to the market as a shell for fit-out work by the incoming occupier, the developer should calculate a design-stage target primary energy rate, building primary energy rate, target emission rate and building emission rate. These calculations should be submitted to the building control body. The submission should demonstrate how the building could reasonably meet the energy efficiency requirements after fit-out.

2.22 If some systems are not installed when a building is put on the market, reasonable assumptions should be made in the calculation of the building primary energy rate and building emission rate and model for the efficiencies of services that will be installed during first fit-out work. The specification provided to the building control body should include all of the following.

a. Details of the services, including any on-site electricity generation, not provided in the base build.

b. The efficiency values assumed for these services.

c. A statement on how access to install any services, including on-site electricity generation, will be provided during first fit-out work.

2.23 At practical completion of the base building in a shell and core development, the as-built target primary energy rate, building primary energy rate, target emission rate and building emission rate calculations should be based only on the building and systems as constructed; the fit-out areas should be assumed to be conditioned to temperatures appropriate to their designated use, but no associated energy demand included.

2.24 If an incoming occupier does first fit-out work on all or part of a building in a shell and core development by providing or extending fixed services for any of the following:

a. heating

b. hot water

c. air-conditioning

d. mechanical ventilation

then a target primary energy rate, building primary energy rate, target emission rate and building emission rate submission should be made to the building control body after completion to demonstrate compliance for the part of the building covered by the fit-out work.

2.25 If fit-out work does not include providing or extending any of the fixed services for any of the following:

a. heating

b. hot water

c. air-conditioning

d. mechanical ventilation

then any lighting systems that are installed should be at least as efficient as those assumed in the shell developer’s initial submission.

NOTE: A new energy performance certificate is required for that part of the physical building covered by fit-out work.

NOTE: Paragraph 9.12 outlines requirements for the building log book to be completed for shell and core developments when first fit-out work takes place.

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

2.26 Special considerations may apply for industrial sites, workshops and non-residential agricultural buildings, where the National Calculation Methodology Modelling Guide cannot adequately account for the building’s use. For example, if using the National Calculation Methodology Modelling Guide would lead to negative impacts on cost-effectiveness and/or significant technical risk.

Buildings with low energy demand

2.27 Buildings with low energy demand are taken to be buildings or parts of buildings, which are not exempt from the energy efficiency requirements for reasons outlined in Section 0, where any of the following apply.

a. Fixed building services for heating and/or cooling are not provided.

b. Fixed building services for heating and/or cooling 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).

c. Fixed building services are used to heat space in the building to temperatures that are substantially lower than those normally provided for human comfort (e.g. to protect a warehouse from frost).

2.28 A target primary energy rate, target emission rate, building primary energy rate and the building emission rate should be calculated for non-exempt buildings with low energy demand. Zones corresponding to the definitions in paragraph 2.27 should be modelled as outlined in the National Calculation Methodology Modelling Guide paragraph 124 as ‘unconditioned’, i.e. not served by a space heating or space cooling system.

2.29 For a building with low energy demand both of the following apply.

a. Every fixed building service that is installed should meet the energy efficiency standards set out in Sections 5 and 6.

b. The building envelope should be insulated to a degree that is reasonable in the particular case. If some general heating is provided, as in paragraph 2.27c, then no part of the opaque fabric should have a U-value worse than 0.7W/(m2·K).

2.30 If part of a building with low energy demand is both:

a. partitioned off

b. heated normally

(for example, an office area in an unheated warehouse), then the separately heated area should be treated as a separate building or zone and the normal procedures for demonstrating compliance should be followed.

2.31 If a building with low energy demand subsequently changes to a building that no longer has a low energy demand, consequential improvements may need to be made in some circumstances. See Section 12.

2.32 If a building or part of a building with low energy demand was designed as a shell and core building, and first fit-out work is carried out which results in it no longer being classed as low energy demand (in line with paragraph 2.24), then normal procedures for demonstrating compliance should be followed.

Section 2: Calculating the building primary energy rate and building emission rate