Criterion 4 – Building performance consistent with the BER
3.1 Buildings should be constructed and equipped so that performance is consistent with the calculated BER. As indicated in paragraph 2.15, a calculation of the BER is required to be submitted to the BCB after completion to take account of:
a. any changes in performance between design and construction; and
b. the achieved air permeability, ductwork leakage and commissioned fan performance.
NOTE: The following paragraphs in this section set out what in normal circumstances would be reasonable provision to ensure that the actual performance of the building is consistent with the BER. The results referred to in paragraph 2.14 would assist the BCB in checking that the key features of the design are included as specified during the construction process.
3.2 The building fabric should be constructed to a reasonable quality so that:
a. the insulation is reasonably continuous over the whole building envelope; and
b. the air permeability is within reasonable limits.
Continuity of insulation
3.3 The building fabric should be constructed so that there are no reasonably avoidable thermal bridges in the insulation layers caused by gaps within the various elements, at the joints between elements and at the edges of elements such as those around window and door openings.
3.4 Reductions in thermal performance can occur where the air barrier and the insulation layer are not contiguous and the cavity between them is subject to air movement. To avoid this problem, either:
a. the insulation layer should be contiguous with the air barrier at all points in the building envelope; or
b. the space between the insulation layer and air barrier should be filled with solid material such as in a masonry wall.
3.5 Where linear thermal transmittances and temperature factors are calculated in support of the approaches set out in paragraph 3.7a, follow the guidance set out in BRE Report BR 497 Conventions for calculating linear thermal transmittance and temperature factors. Reasonable provision is to demonstrate that the specified details achieve a temperature factor that is no worse than the performance set out in BRE Information Paper IP 1/06 Assessing the effects of thermal bridging at junctions and around openings in the external elements of buildings.
3.6 Similarly, in support of the approaches set out in paragraph 3.7a, the builder would have to demonstrate that an appropriate system of site inspection is in place to give confidence that the construction procedures achieve the required standards of consistency.
3.7 Ways of demonstrating that reasonable provision has been made are:
a. To use construction joint details that have been calculated by a person with suitable expertise and experience following the guidance set out in BR 497 and following a process flow sequence that has been provided to the BCB indicating the way in which the detail should be constructed. The calculated value can then be used in the BER calculation.
NOTE: Evidence of suitable expertise and experience for calculating linear thermal transmittance would be to demonstrate that the person has been trained in the software used to carry out the calculation, has applied that model to the example calculations set out in BR 497 and has achieved results that are within the stated tolerances.
b. To use construction joints with no specific quantification of the thermal bridge values. In such cases, the generic linear thermal bridge values as given in IP 1/06 increased by 0.04 W/(m.K) or 50 per cent, whichever is greater, must be used in the BER calculation.
Air permeability and pressure testing
3.8 In order to demonstrate that an acceptable air permeability has been achieved, regulation 43 states:
43. (1) This regulation applies to the erection of a building in relation to which paragraph L1(a)(i) of Schedule 1 imposes a requirement.
(2) Where this regulation applies, the person carrying out the work shall, for the purpose of ensuring compliance with regulation 26 and paragraph L1(a)(i) of Schedule 1:
(a) ensure that:
(i) pressure testing is carried out in such circumstances as are approved by the Secretary of State; and
(ii) the testing is carried out in accordance with a procedure approved by the Secretary of State; and
(b) subject to paragraph (5), give notice of the results of the testing to the local authority.
(3) The notice referred to in paragraph (2)(b) shall:
(a) record the results and the data upon which they are based in a manner approved by the Secretary of State; and
(b) be given to the local authority not later than seven days after the final test is carried out.
(4) A local authority is authorised to accept, as evidence that the requirements of paragraph (2)(a)(ii) have been satisfied, a certificate to that effect by a person who is registered by the Independent Air Tightness Testing Scheme Limited or the Air Tightness and Testing and Measuring Association in respect of pressure testing for the air tightness of buildings.
(5) Where such a certificate contains the information required by paragraph (3)(a), paragraph (2)(b) does not apply.
NOTE: Where the BCB is an approved inspector see regulation 20 of the Building (Approved Inspectors etc.) Regulations 2010 (as amended).
3.9 The approved procedure for pressure testing is given in the Air Tightness Testing and Measurement Association (ATTMA) publication Measuring air permeability of building envelopes and, specifically, the method that tests the envelope area. The preferred test method is that trickle ventilators should be temporarily sealed rather than just closed. BCBs should be provided with evidence that test equipment has been calibrated within the previous 12 months using a UKAS-accredited facility. The manner approved for recording the results and the data on which they are based is given in Section 4 of that document.
3.10 BCBs are authorised to accept, as evidence of compliance, a certificate offered under regulation 43(4). It should be confirmed to the BCB that the person has received appropriate training and is registered to test the specific class of building concerned. See http://www.bindt.org/att_list/ and https://attma.org/join-attma/registered_members/
3.11 The approved circumstances under which the Secretary of State requires pressure testing to be carried out are set out in paragraphs 3.12 to 3.14.
3.12 All buildings that are not dwellings (including extensions which are being treated as new buildings for the purposes of complying with Part L) must be subject to pressure testing, with the following exceptions:
a. Buildings less than 500 m² total useful floor area; in this case the developer may choose to avoid the need for a pressure test provided that the air permeability used in the calculation of the BER is taken as 15 m³/(h.m²) at 50 Pa.
NOTE: Compensating improvements in other elements of the building fabric and building services will be needed to keep the BER no worse than the TER.
b. A factory-made modular building of less than 500 m2 floor area, with a planned service life of more than two years at more than one location, and where no site assembly work is needed other than making linkages between standard modules using standard link details. Compliance with regulation 43 can be demonstrated by giving a notice to the local authority confirming that the building as installed conforms to one of the standard configurations of modules and link details for which the installer has pressure test data from a minimum of five in-situ measurements incorporating the same module types and link details as utilised in the actual building. The results must indicate that the average test result is better then the design air permeability as specified in the BER calculation by not less than 1.0 m³/(h.m²) at 50 Pa.
c. Large extensions (whose compliance with Part L is being assessed as if they were new buildings – see Approved Document L2B) where sealing off the extension from the existing building is impractical. The ATTMA publication gives guidance both on how extensions can be tested and on situations where pressure tests are inappropriate. Where it is agreed with the BCB that testing is impractical, the extension should be treated as a large, complex building, with the guidance in paragraph 3.12d applying.
d. Large complex buildings, where due to building size or complexity it may be impractical to carry out pressure testing of the whole building. The ATTMA publication indicates those situations where such considerations might apply. Before adopting this approach developers must produce in advance of construction work in accordance with the approved procedure a detailed justification of why pressure testing is impractical. This should be endorsed by a suitably qualified person such as a competent person approved for pressure testing. In such cases, a way of showing compliance would be to appoint a suitably qualified person to undertake a detailed programme of design development, component testing and site supervision to give confidence that a continuous air barrier will be achieved. It would not be reasonable to claim air permeability better than 5.0 m³/(h.m²) at 50 Pa has been achieved.
NOTE: One example of a suitably qualified person would be an ATTMA member. The 5.0 m3/(h.m2) at 50 Pa limit has been set because at better standards the actual level of performance becomes too vulnerable to single point defects in the air barrier.
e. Compartmentalised buildings. Where buildings are compartmentalised into self-contained units with no internal connections it may be impractical to carry out whole building pressure tests. In such cases reasonable provision would be to carry out a pressure test on a representative area of the building as detailed in the ATTMA guidance. In the event of a test failure, the provisions of paragraphs 3.13 and 3.14 would apply, but it would be reasonable to carry out a further test on another representative area to confirm that the expected standard is achieved in all parts of the building.
3.13 Compliance with the requirement in paragraph L1(a)(i) of Schedule 1 to the Building Regulations would be demonstrated if:
a. the measured air permeability is not worse than the limiting value of 10 m³/(h.m²) at 50 Pa; and
b. the BER calculated using the measured air permeability is not worse than the TER.
NOTE: If it proves impractical to meet the design air permeability, any shortfall must be compensated through improvements to subsequent fit-out activities. Builders may therefore wish to schedule pressure tests early enough to facilitate remedial work on the building fabric, e.g. before false ceilings are up.
Consequences of failing a pressure test
3.14 If satisfactory performance is not achieved, then remedial measures should be carried out on the building and new tests carried out until the building achieves the criteria set out in paragraph 3.13.
NOTE: If the measured air permeability on retest is greater than the design air permeability but less than the limiting value of 10 m³/(h.m²) then other improvements may be required to achieve the TER. This means that builders would be unwise to claim a design air permeability better than 10 m³/(h.m²) unless they are confident of achieving the improved value.
Commissioning of the building services systems
3.15 Paragraph L1(b)(iii) of Schedule 1 to the Building Regulations requires fixed building services to be commissioned by testing and adjusting them as necessary to ensure that they use no more fuel and power than is reasonable in the circumstances. In order to demonstrate that the heating and hot water systems have been adequately commissioned, regulation 44 states:
44. (1) This regulation applies to building work in relation to which paragraph F1(2) of Schedule 1 imposes a requirement, but does not apply to the provision or extension of any fixed system for mechanical ventilation or any associated controls where testing and adjustment is not possible.
(2) This regulation applies to building work in relation to which paragraph L1(b) of Schedule 1 imposes a requirement, but does not apply to the provision or extension of any fixed building service where testing and adjustment is not possible or would not affect the energy efficiency of that fixed building service.
(3) Where this regulation applies the person carrying out the work shall, for the purpose of ensuring compliance with paragraph F1(2) or L1(b) of Schedule 1, give to the local authority a notice confirming that the fixed building services have been commissioned in accordance with a procedure approved by the Secretary of State.
(4) The notice shall be given to the local authority–
(a) not later than the date on which the notice required by regulation 16(4) is required to be given; or
(b) where that regulation does not apply, not more than 30 days after completion of the work.
NOTE: Where the BCB is an approved inspector see regulation 20 of the Building (Approved Inspectors etc.) Regulations 2010 (as amended).
3.16 It would be useful to prepare a commissioning plan, identifying the systems that need to be tested and the tests that will be carried out and provide this with the design-stage TER/BER calculation so that the BCB can check that the commissioning is being done as the work proceeds.
NOTE: The use of the templates in the Model Commissioning Plan (BSRIA BG 8/2009) is a way of documenting the process in an appropriate way.
3.17 Not all fixed building services will need to be commissioned. With some systems it is not possible as the only controls are ‘on’ and ‘off’ switches. Examples of this would be some mechanical ventilation systems or single fixed electrical heaters. In other cases commissioning would be possible but in the specific circumstances would have no effect on energy use.
3.18 Where commissioning is carried out it should be done in accordance with procedures approved by the Secretary of State comprising:
a. the CIBSE Commissioning Code M: Commissioning management; and
NOTE: This provides guidance on the overall process and includes a schedule of all the relevant guidance documents relating to the commissioning of specific building services systems.
b. the procedures for air leakage testing of ductwork given in paragraphs 3.26 and 3.27.
3.19 Commissioning must be carried out in such a way as not to prejudice compliance with any applicable health and safety requirements.
3.20 Commissioning is often carried out by the person who installs the system. Sometimes it may be carried out by a subcontractor or even by a specialist firm. It is important that whoever carries it out follows the relevant approved procedure.
Notice of completion
3.21 The Building Regulations (regulation 44(3)) and the Building (Approved Inspectors etc) Regulations (regulation 20(6)) require that a notice be given to the relevant BCB that commissioning has been carried out according to a procedure approved by the Secretary of State.
3.22 The notice should include a declaration confirming that:
a. a commissioning plan has been followed so that every system has been inspected and commissioned in an appropriate sequence and to a reasonable standard; and
b. the results of tests confirm that the performance is reasonably in accordance with the actual building design, including written commentaries where excursions are proposed to be accepted.
NOTE: It would be helpful to BCBs if such declarations were to be signed by someone suitably qualified by relevant training and experience. A way of achieving this would be to employ a member of the Commissioning Specialists Association or the Commissioning Group of the Building and Engineering Services Association (B&ES) in respect of heating, ventilation and air-conditioning (HVAC) systems, or a member of the Lighting Industry Commissioning Scheme in respect of fixed internal or external lighting. The use of the templates in the Model Commissioning Plan is a way of documenting the process in an appropriate way.
3.23 Where a building notice or full plans have been given to a local authority, the notice should be given within five days of the completion of the commissioning work; in other cases, for example where work is carried out by a person registered with a competent person scheme, it must be given within 30 days.
3.24 Where an approved inspector is the BCB, the notice should generally be given within five days of the completion of the building work. However, where the work is carried out by a person registered with a competent person scheme the notice must be given within 30 days. Where the installation of fixed building services which require commissioning is carried out by a person registered with a competent person scheme the notice of commissioning will be given by that person.
3.25 Until the BCB receives the commissioning notice it may not be able to be reasonably satisfied that Part L has been complied with and consequently is unlikely to be able to give a completion/final certificate.
NOTE: Energy efficiency in practice can often be enhanced by a sustained period of fine tuning to ensure the systems are operating as intended and controls are configured to the needs of the occupier. The Soft Landings initiative is an example of an appropriate fine tuning process (see https://www.bsria.co.uk/services/design/soft-landings/).
Air leakage testing of ductwork
3.26 Ductwork leakage testing should be carried out where required by and in accordance with the procedures set out in B&ES DW/143 and B&ES DW/144 on systems served by fans with a design flow rate greater than 1 m³/s.
NOTE: DW/143 does not call for any testing of low-pressure (class A) ductwork. However, where at least 10 per cent of low-pressure ductwork is tested at random and achieves the low-pressure standard as defined by DW/143 the National Calculation Methodology recognises an improvement in the BER. A decision to test low-pressure ductwork should be made at the initial design phase prior to commencement on site.
Membership of the B&ES specialist ductwork group or the Association of Ductwork Contractors and Allied Services (ADCAS) could be a way of demonstrating suitable qualifications for this testing work.
Table 4 Ductwork pressure classes
3.27 If a ductwork system fails to meet the leakage standard, remedial work should be carried out as necessary to achieve satisfactory performance in retests and further ductwork sections should be tested as set out in DW/143