Criterion 4 – Building performance consistent with DER and DFEE rate
3.1 Dwellings should be constructed and equipped so that performance is consistent with the calculated DER and DFEE rate. As indicated in paragraph 2.13, a final calculation of the DER and DFEE rate is required to take account of any changes in performance between design and construction, and to demonstrate that the building, as constructed, meets the TER and TFEE rate as required by regulations 26 and 26A. The following paragraphs in this section set out what in normal circumstances is reasonable provision to ensure that the performance of the building is consistent with the DER and DFEE rate.
NOTE: The information referred to in paragraph 2.12 will help BCBs check that the key features of the design are included during the construction process.
3.2 In accordance with Part L and regulation 7, the building fabric should be constructed to a reasonable standard so that:
a. the insulation is reasonably continuous over the whole building envelope; and
b. the air permeability is within reasonable limits.
Party walls and other thermal bypasses
3.3 Contrary to previous assumptions, party cavity walls may not be zero heat loss walls; this is because air flow in the cavity provides a heat-loss mechanism.
NOTE: Where outside air flows into the party wall cavity, a cold zone is created which causes heat loss through the wall sectionson either side. The extent of air flow and heat changes depends on external conditions such as wind and temperature, and also on the effect caused by the warmed air rising in the cavity to be replaced by cooler air drawn in from outside. The air movements involved can be significant and, if no steps are taken to restrict flows, the resulting heat losses can be large.
3.4 Heat loss can be reduced by restricting air movement through the cavity, which can be achieved by fully filling the cavity and/or by effective sealing around the perimeter. Further guidance is available at www.buildingcontrolalliance.org
The extent to which heat loss can be reduced depends on the detailed design and the quality of construction. In the absence of any specific independent scientific field evidence, reasonable provision is to adopt the guidance on U-values in paragraph 3.5.
NOTE: Fully filling the cavity may affect sound transmission through party walls. Developers who plan to fill a party wall cavity must satisfy the BCB that the requirements of Part E (Sound) of Schedule 1 to the Building Regulations will be satisfied, either by adopting a full-fill detail accredited under the Robust Details scheme or through specific site testing.
3.5 When calculating the DER and DFEE rate for a dwelling, a party wall U-value for the type of construction adopted, as set out in Table 3, should be applied.
3.6 When applying the U-values in Table 3, it is important that if edge sealing is adopted, either on its own or in conjunction with a fully filled cavity, the seal is effective in restricting air flow and is aligned with the thermal envelope. Although effective sealing may be part of a cavity barrier provided in order to comply with Part B (Fire) of Schedule 1 to the Building Regulations, a cavity barrier on its own may not be effective in restricting air flow. In order to claim a reduced U-value (0.2 or 0.0), it is necessary to demonstrate that the design adopted is likely to be robust under normal site conditions.
It is also important that the sealing system is applied in such a way as to be in line with the thermal envelope. Any solution to reducing party wall heat loss must take into account all the requirements in Schedule 1 to the Building Regulations, but particular attention should be given to the requirements of Part E.
NOTE: For example, in a room-in-roof design, the insulation layer may follow the sloping roof sections to a horizontal ceiling then continue at ceiling level. In such a case it is important that the party wall cavity seal follows the line of the insulation in the slope and horizontal ceiling sections(although for the purposes of Part B (Fire), it may be necessary to ensure that the fire cavity barrier follows the slope to the ridge). In the case of flats, the sealing system should follow the line of party floors and other party structures as well as the main thermal envelope.
3.7 In considering heat losses via party walls, it is important to remember that wherever the wall penetrates an insulation layer, such as when the blockwork of a masonry party wall penetrates insulation at ceiling level, a thermal bridge is likely to exist – even when the party wall U-value is zero. Any bridging at the party wall should be evaluated and then taken into account, along with other thermal bridges. It is important also to be satisfied that any solution to the party wall bypass does not contravene other parts of the regulations, in particular Part E (Sound).
Table 3 U-values for party walls
3.8 The party wall is a particular case of the more general thermal bypass problem that occurs if the air barrier and the insulation layer are not contiguous and the cavity between them is subject to air movement. To avoid the consequent reduction in thermal performance, either the insulation layer should be contiguous with the air barrier at all points in the building envelope, or the space between the air barrier and insulation layer should be filled with solid material, such as in a masonry wall.
3.9 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.
3.10 Reasonable provision would be to:
a. Adopt approved design details as set out in DCLG Approved Construction Details or those that are formally recognised by DCLG. The calculated linear thermal transmittance values can be used directly in the DER and DFEE rate calculations; or
b. Use construction joint details that have been calculated by a person with suitable expertise and experience following the guidance set out in BRE Report BR 497 Conventions for calculating linear thermal transmittance and temperature factors. The linear thermal transmittance values can be used directly in the DER and DFEE rate calculations. Reasonable provision for the temperature factors is that they should achieve a performance no worse than that 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; or
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.
c. Use the linear thermal transmittance values in the ‘default’ column of Table K1 in SAP 2012 directly in the DER and DFEE rate calculations; or
d. Use a conservative default y-value of 0.15 W/(m².K), rather than linear transmittance values for each construction joint, in the DER and DFEE rate calculation.
3.11 The alternative approaches for using linear transmittance values in paragraphs 3.10 (a), (b) and (c) are not mutually exclusive. For example, a builder could use approved design details for the majority of the junctions, but use a calculated bespoke detail for the window head. Furthermore, where design details via paragraph 3.10 (a) or (b) are adopted for some junctions but not for all junctions, the linear thermal transmittance values in the ‘default’ column of Table K1 in SAP 2012 should be used for the other junctions.
NOTE: The effect of using linear transmittance values that are poorer than those in the notional dwelling specification at SAP 2012 Appendix R should be compensated for by improved standards elsewhere in the dwelling design. When default linear transmittance values from Table K1 in SAP 2012 are used for the majority of the construction joints in a dwelling, or when the conservative default y-value of 0.15 W/(m².K) is used, the builder would need to significantly improve upon the notional dwelling values elsewhere in the design to meet the TER and TFEE rate.
3.12 When adopting the approaches in paragraphs 3.10 (a) and (b), the builder should demonstrate to the BCB that an appropriate system of site inspection is in place to give confidence that the construction procedures achieve the required standard of consistency.
Air permeability and pressure testing
3.13 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).
3.14 The approved procedure for pressure testing is given in the Air Tightness Testing and Measurement Association (ATTMA) publication Measuring air permeability of building envelopes (dwellings) 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.
3.15 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 who completed the testing has received appropriate training and is registered to test the specific class of building concerned. See http:// www.bindt.org/att_list/ and https://atorg/join-attma/registered_members/
3.16 The approved circumstances under which the Secretary of State requires pressure testing to be carried out are set out in paragraphs 3.17 to 3.22.
3.17 On each development, an air pressure test should be carried out on three units of each dwelling type or 50 per cent of all instances of that dwelling type, whichever is the less. For the purposes of this approved document, a block of flats should be treated as a separate development, irrespective of the number of blocks on the site. The dwelling(s) to be tested should be taken from the first completed batch of units of each dwelling type.
NOTE: Most larger developments include many dwelling types. Multiple units of each type should be tested to confirm the robustness of the designs and the construction procedures.
3.18 The specific dwellings making up the test sample should be selected by the BCB in consultation with the pressure tester. Dwellings should be selected so that about half of the scheduled tests for each dwelling type are carried out during construction of the first 25 per cent of each dwelling type. The results of all tests on dwellings in the sample should be reported to the BCB, including any test failures (see paragraphs 3.19 to 3.21).
NOTE: The aim is to enable lessons to be learned and adjustments to the design and/or site procedures to be made before the majority of the dwellings are built.
Showing compliance with regulation 43, and the consequences of failing a pressure test
3.19 The dwelling is shown to comply with the requirements if:
a. the measured air permeability is not worse than the limit value of 10 m³/(h.m²) at 50 Pa; and
b. the DER and the DFEE rate calculated using the measured air permeability are not worse than the TER and the TFEE rate.
NOTE: If a low (i.e. better) design air permeability is used in order to achieve a performance that is better than the TER and the TFEE rate, the design will not fail to comply with the energy efficiency requirements if the pressure test achieves the limit value and the TER and the TFEE rate are achieved.
3.20 If satisfactory performance is not achieved, then remedial measures should be carried out on the dwelling and new tests carried out until the dwelling achieves the criteria set out in paragraph 3.19. In addition, a further dwelling of the same dwelling type should be tested, thereby increasing the overall sample size.
3.21 When a dwelling fails the initial pressure test, other dwellings of the same dwelling type that have not been tested should be examined and, where appropriate, remedial measures applied.
Alternative to pressure testing on small developments
3.22 On development sites where no more than two dwellings are to be erected, reasonable provision is to:
a. demonstrate that during the preceding 12-month period, a dwelling of the same dwelling type constructed by the same builder was pressure tested according to the procedures given in paragraphs 3.13 to 3.18 and achieved the design air permeability; or
b. use a value of 15 m3/(h.m2) at 50 Pa for the air permeability when calculating the DER and the DFEE rate, which then avoids the need for pressure testing.
NOTE: The effect of using this cautious value in option b should be compensated for by improved standards elsewhere in the dwelling design.
Commissioning of heating and hot water systems
3.23 Paragraph L1(b)(iii) of Schedule 1 to the Building Regulations requires fixed building services to be commissioned by testing and adjustment 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).
3.24 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/DER and TFEE/ DFEE rate calculations 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.
3.25 Not all fixed building services will need to be With some systems it is not possible as the only controls are ‘on’ and ‘off’ switches. Examples of this would be some mechanical extraction 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.
Fixed building services which do not require commissioning should be identified in the commissioning plan, along with the reason for not requiring commissioning.
3.26 Where commissioning is carried out, it should be done in accordance with procedures approved by the Secretary of State:
(a) For heating and hot water systems, the approved procedures are set out in the Domestic Building Services Compliance Guide.
(b) For ventilation systems, the approved procedure is set out in the Domestic Ventilation Compliance Guide.
3.27 Commissioning is often carried out by the person who installs the In other cases, it may be carried out by a subcontractor or by a specialist firm. It is important that whoever carries it out follows the relevant approved procedure in doing so.
3.28 Where a building notice or full plans have been given to a local authority BCB the notice of completion of commissioning should be given to that BCB within five days of the completion of the commissioning 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.
3.29 Where an approved inspector is the BCB the notice of completion of commissioning should generally be given to the approved inspector within five days of the completion of 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.
3.30 Until the BCB receives the commissioning notice, it may not consider it appropriate to give a completion/final certificate.