Reference method
Fabric standards
4.1 Reasonable provision would be for the proposed extension to incorporate the following:
a. newly constructed thermal elements that meet the standards set out in paragraphs 5.1 to 5.6;
b. doors, windows, roof windows and rooflights that meet the standards set out in paragraphs 4.19 to 4.23;
c. improvements to fabric elements that are to become thermal elements, following the guidance in paragraphs 5.6 to 5.11.
Area of windows, roof windows and doors
4.2 In most circumstances reasonable provision would be to limit the total area of windows, roof windows and doors in extensions so that it does not exceed the sum of:
a. 25 per cent of the floor area of the extension; plus
b. the total area of any windows or doors which, as a result of the extension works, no longer exist or are no longer exposed.
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 extension and especially the part of the dwelling it covers may experience poor levels of daylight, resulting in increased use of electric lighting. Areas of glazing greater than 25 per cent may be acceptable, especially if this is required to make the extension consistent with the external appearance or character of the host building. In such cases and where practical, either the U-value of the window should be improved relative to the standard set out in paragraph 4.1b, or other compensating measures applied following the guidance set out in paragraphs 4.4 to 4.7.
Heating and lighting in the extension
4.3 Where a fixed building service is provided or extended as part of constructing the extension, reasonable provision would be to follow the guidance in paragraphs 4.24 to 4.37.
Optional approaches with more design flexibility
4.4 The approach set out in paragraphs 4.1 to 4.3 is somewhat prescriptive. The following paragraphs offer more flexible approaches to demonstrating that reasonable provision has been made. These alternative approaches allow some elements of the design to be relaxed through compensating measures elsewhere.
Area-weighted U-value method
4.5 One way of complying would be to show that the area-weighted U-value of all the elements in the extension is no greater than that of an extension of the same size and shape that complies with the fabric standards referred to in paragraph 4.1 and the opening area standards in paragraph 4.2. Any fixed building service provided or extended as part of constructing the extension should follow the guidance in paragraphs 4.24 to 4.37.
The area-weighted U-value is given by the following expression:
{(U1 X A1) + (U2 x A2) + (U3 x A3) + ...)} 4 {(A1 + A2 + A3 + ...)}
Whole dwelling calculation method
4.6 Where even greater design flexibility is required, reasonable provision would be to use SAP 2012 to show that the calculated carbon dioxide (CO2) emission rate from the dwelling with its proposed extension is no greater than for the dwelling plus a notional extension built to the standards of paragraphs 4.1 to 4.3. The openings in the notional extension should conform with paragraph 4.2 with door area set equal to the door area of the proposed extension, with the remainder of the openings being classified as windows. The data in SAP 2012 Appendix S can be used to estimate the performance of the elements of the existing building where these are unknown.
Approved Document C gives limiting values for individual elements to minimise condensation risk.
4.7 If, as part of achieving the standard set out in paragraph 4.6, upgrades are proposed to the existing dwelling, such upgrades should be implemented to a standard that is no worse than set out in the relevant guidance contained in this Approved Document. The relevant standards for improving retained thermal elements are as set out in column (b) of Table 3.
Where it is proposed to upgrade the original building, the standards set out in this Approved Document are cost-effective and should be implemented in full. It will be worthwhile implementing them even if the improvement is greater than necessary to achieve compliance. In some cases, therefore, the standard of the extended dwelling may be better than that required by paragraph 4.6 alone. Paragraph 4.7 sets limits on design flexibility and ensures that no cost-effective improvement opportunities are traded away.
Conservatories and porches
4.8 Where the extension is a conservatory or porch that is not exempt from the energy efficiency requirements (see paragraphs 3.15 and 3.16 above), then reasonable provision would be to provide:
a. Effective thermal separation between the heated area in the existing dwelling, i.e. the walls, doors, and windows between the dwelling and the extension, should be insulated and draught proofed to at least the same extent as in the existing dwelling.
b. Independent temperature and on/off controls to any heating system installed within the extension. Any fixed building service installed within the extension should also conform to the standards set out in paragraphs 4.24 to 4.37.
c. Glazed elements should meet the standards set out in Table 1 and opaque elements should meet the standards set out in Table 2. However, the limitations on total area of windows, roof windows and doors as set out at paragraph 4.2 above do not apply.
4.9 Removing, and not replacing, any or all of the thermal separation between the dwelling and an existing exempt extension, or extending the dwelling's heating system into the extension, means the extension ceases to be exempt (see paragraphs 3.15 and 3.16 above). In such situations, the extension should be treated as a conventional extension and reasonable provision would be to demonstrate that the extension meets the guidance set out in paragraphs 4.1 to 4.7 above.
Swimming pool basins
4.10 Where a swimming pool is being provided in a building, the U-value of the basin (walls and floor) should be not worse than 0.25 W/m².K as calculated according to BS EN ISO 13370[4].
Design consideration should be taken with regards to compressive creep, insulation boards not being fully supported and the effects of point loading. Care should be taken to avoid thermal bridging particularly around basin wall and floor junctions with foundations.
[4] BS EN ISO 13370 Thermal performance of buildings – Heat transfer via the ground – Calculation methods [2007 incorporating corrigendum March 2009].
Material change of use
4.11 Material changes of use (see regulation 5 of the Building Regulations) covered by this document are where, after the change:
a. the building is used as a dwelling, where previously it was not;
b. the building contains a flat, where previously it did not; or
c. the building, which contains at least one dwelling, contains a greater or lesser number of dwellings than it did previously.
Change of energy status
4.12 A change to a building's energy status is defined in regulation 2(1) as:
any change which results in a building becoming a building to which the energy efficiency requirements of these Regulations apply, where previously it was not.
4.13 The requirements relating to a change to energy status are in regulation 22:
Where there is a change in a building's energy status, such work, if any, shall be carried out to ensure that the building complies with the applicable requirements of regulation 40 and Part L of Schedule 1.
4.14 In this regulation 'building' means the building as a whole or parts of the building that have been designed or altered to be used separately.
For example, this could occur where a previously unheated building, or parts of the building that have been designed or altered to be used separately, were to be heated in future, or where a previously exempt building were no longer within the exempted categories. A material alteration (regulation 3(2) and (3)) may result in a change in buildings energy status.
4.15 In normal circumstances, reasonable provision where there is a material change of use or a change to the building's energy status would be:
a. Where controlled services or fittings are being provided or extended, to meet the standards set out in paragraphs 4.17 to 4.37. If the area of openings in the newly created dwelling is more than 25 per cent of the total floor area, either the area of openings should be reduced to be not greater than 25 per cent, or the larger area should be compensated for in some other way using the procedure described in paragraph 4.16.
b. Where the work involves the provision of a thermal element, to meet the standards set out in paragraphs 5.1 to 5.6.
For the purposes of Building Regulations, provision means both new and replacement elements.
c. Where any thermal element is being retained, to upgrade it following the guidance given in paragraphs 5.11 to 5.13.
d. Where an existing window (including roof window or rooflight) or door which separates a conditioned space from an unconditioned space or the external environment has a U-value that is worse than 3.3 W/(m².K), to provide replacement units following the guidance in paragraphs 4.19 to 4.23.
Option providing more design flexibility
4.16 To provide more design flexibility, SAP 2012 can be used to demonstrate that the total CO2 emissions from all the dwellings in the building as it will become are no greater than if each dwelling had been improved following the guidance set out in paragraph 4.15.
4.17 Controlled services or fittings are defined in regulation 2 as follows:
Controlled service or fitting means a service which part G,H,J,L or P of schedule 1 imposes a requirement;
Controlled service or fitting means a service or fitting in relation to which Part G, H, J, L or P of schedule 1 imposes a requirement;
Controlled fittings
4.18 In the context of this Approved Document, the application of the term controlled fitting to a window, roof window, rooflight or door refers to a whole unit, i.e. including the frame. Consequently, replacing the glazing whilst retaining an existing frame is not providing a controlled fitting, and so such work is not notifiable and does not have to meet the Part L standards, although where practical it would be sensible to do so. Similar arguments apply to doors, where the controlled fitting refers to the complete doorset (leaf plus frame). Replacing a door leaf whilst retaining the existing frame is not notifiable and does not have to meet the Part L standards, although where practical it would be sensible to do so.
4.19 Where windows, roof windows, rooflights or doors are to be provided, reasonable provision in normal cases would be the installation of draught-proofed units whose performance is no worse than given in Table 1. In addition, insulated cavity closers should be installed where appropriate. Where the windows or fully glazed external pedestrian doors are unable to meet the requirements of Table 1 because of the need to maintain the external appearance of the façade or the character of the building, such fittings should meet a centre pane U-value of 1.2 W/(m².K), where the centre-pane U-value is defined as the U-value determined in the central area of the glazing unit, making no allowance for edge spacers or window frame. As an alternative, single glazing should be supplemented with low-e secondary glazing. In this latter case, the weather stripping should be on the secondary glazing to minimise condensation risk between the primary and secondary glazing. Where enhanced performance requirements (e.g. wind load, safety, security or acoustic attenuation) require thicker glass to be used, reasonable provision would be demonstrated if the window unit with the equivalent standard glazing thickness can be shown to comply.
4.20 U-values shall be calculated using the methods and conventions set out in BR 443[5], and should be based on the whole unit (i.e. in the case of a window, the combined performance of the glazing and frame). The U-value of the window can be calculated for:
a. the smaller of the two standard windows defined in BS EN 14351-1[6]; 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.
SAP 2012 Table 6e gives values for different window configurations that can be used in the absence of test data or calculated values.
4.21 The U-values for roof windows and rooflights given in this Approved Document are based on the U-value having been assessed with the roof window or rooflight 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 in BR 443.
Table 1 Standards for controlled fittings
4.22 The calculation of Window Energy Rating (WER) and the Doorset Energy Rating (DSER) are set out in the GGF Guide to the Calculation of Energy Ratings for Windows, Roof Windows and Doors[7]. The guide provides different procedures for windows, roof windows, external pedestrian doors and patio/French/ sliding/folding doors. BCBs may accept a WER and/or DSER declaration from a certification scheme that provides a quality assured process and supporting audit trail from calculating the performance of the window through to installation as evidence of compliance. Notwithstanding the suggested performance values set out in Table 1, guidance on energy efficient windows is available from the Energy Saving Trust[8].
4.23 If a window is enlarged or a new one created, then the area of windows, roof windows, rooflights and doors should not exceed 25 per cent of the total floor area of the dwelling unless compensating measures are included elsewhere in the work.
[5] BR 443 Conventions for U-value calculations, BRE, 2006.
[6] BS EN 14351-1 Windows and doors – Product standard, performance characteristics. Windows and external pedestrian doorsets without resistance to fire and/or smoke leakage characteristics [2006 (+AMD 1:2010)].
[7] Guide to the Calculation of Energy Ratings for Windows, Roof Windows and Doors, GGF, 2013.
[8] http://www.energysavingtrust.org.uk/Insulation/Windows.
[9] Domestic Building Services Compliance Guide, DCLG, 2013.
Controlled services
4.24 Whenever a fixed building service is extended or provided, reasonable provision would be demonstrated by following the guidance set out in the Domestic Building Services Compliance Guide[9]. The Guide covers the following services:
a. heating and hot water systems (including insulation of pipes, ducts and vessels;
b. mechanical ventilation;
c. mechanical cooling/air-conditioning;
d. fixed internal lighting;
e. fixed external lighting;
f. renewable energy systems.
4.25 The efficiency claimed for the fixed building service should be based on the appropriate test standard as set out in the Domestic Building Services Compliance Guide and the test data should be certified by a notified body. It would be reasonable for BCBs to accept such data at face value. In the absence of such quality-assured data, BCBs should satisfy themselves that the claimed performance is justified.
4.26 When replacing an existing appliance, the efficiency of the new appliance should not be significantly less than the efficiency of the appliance being replaced. If the replacement involves a fuel switch, then the relative carbon emissions associated with the new and existing fuels should be considered when assessing the reasonableness of the proposed new appliance. The Domestic Building Services Compliance Guide contains the detailed guidance on this issue.
4.27 If a renewable energy generator such as a wind turbine or photovoltaic array is being replaced, the new system should have an electrical output that is not less than the original installation.
4.28 When replacing a heating appliance, consideration should be given to connecting to any existing local heat networks. If the work involves pipework changes, consideration should be given to providing capped off connections to facilitate subsequent connection to a planned local heat network.
4.29 If a particular technology is not covered in the Domestic Building Services Compliance Guide, reasonable provision would be demonstrated by showing that the proposed technology gives a performance that is no worse than a reference system of the same type whose details are given in the Guide.
[9] Domestic Building Services Compliance Guide, DCLG, 2013.
COMMISSIONING OF FIXED BUILDING SERVICES
4.30 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 Commissioning
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.
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.
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.
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.
4.31 Reasonable provision would be to prepare a commissioning plan, identifying the systems that need to be tested and the tests that will be carried out. the notice required by regulation 44 should confirm that the commissioning plan has been followed and that every system has been inspected in an appropriate sequence and to a reasonable standard and that the test results confirm that performance is reasonably in accordance with the design requirements.
4.32 Not all fixed building services will need to be commissioned. with some systems adjustment 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.
4.33 Where commissioning is carried out it must be done in accordance with a procedure approved by the Secretary of State. For heating and hot water systems the approved procedures are set out in the Domestic Building Services Compliance Guide. For ventilation systems, an approved procedure would be to follow the guidance in the Domestic Ventilation Compliance Guide[10].
4.34 Commissioning is often carried out by the person who installs the system. 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.
4.35 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 5 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 (see paragraphs 3.19 to 3.22), it must be given within 30 days.
4.36 Where an approved inspector is the BCB, the notice of completion of commissioning should generally be given to the approved inspector within 5 days of the completion of work. However, where the work is carried out by a person registered with a competent person scheme (see paragraph 3.19 to 3.22), 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.
4.37 Until the BCB receives the commissioning notice it cannot be reasonably satisfied that Part l has been complied with and consequently is unlikely to be able to give a completion/final certificate.
