Extensions

4.1 Under regulation 28 of the Building Regulations, the construction of an extension triggers the requirement for consequential improvements in buildings with a total useful floor area greater than 1000m². In such cases, the guidance in Section 6 should be followed in addition to the following specific guidance.

Large extensions

4.2 Where the proposed extension has a total useful floor area that is both:

a. greater than 100 m², and

b. greater than 25 per cent of the total useful floor area of the existing building,
the work should be regarded as a new building and the guidance in Approved Document L2A (2010 edition)4 followed. The requirement for consequential improvements, if appropriate, should also be met by following the guidance in Section 6 of this Approved Document.

Other extensions - reference method

Fabric standards

4.3 Reasonable provision would be for the proposed extension to incorporate the following:

a. doors, windows, roof windows, rooflights and smoke vents that meet the standards set out in paragraphs 4.23 to 4.28;

b. newly constructed thermal elements that meet the standards set out in paragraphs 5.1 to 5.7;

c. existing opaque fabric which becomes a thermal element where previously it was not should be upgraded so that it meets the standards in paragraphs 5.12 to 5.14.

Opening area

4.4 The area of windows and rooflights in the extension should generally not exceed the values given in Table 2. However, where a greater proportion of glazing is present in the part of the building to which the extension is attached, reasonable provision would be to limit the proportion of glazing in the extension so that it is no greater than the proportion that exists in the part of the building to which it is attached.
Building services systems in the extension

4.5 Where fixed building services are provided or extended as part of constructing the extension, reasonable provision would be to follow the guidance in paragraphs 4.29 to 4.48.

****Table 2 Opening areas in the extension

Optional approaches with more design flexibility

4.6 The approach set out in paragraphs 4.3 to 4.5 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

4.7 The U-values given in paragraph 4.3 and the opening areas given in paragraph 4.4 may be varied provided 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 U-value standards referred to in paragraph 4.3 and the opening area standards in paragraph 4.4. Any fixed building service provided or extended as part of constructing the extension should follow the guidance in paragraphs 4.29 to 4.48.

4.8 The area-weighted U-value is given by the following expression:
{(U1 X A1) + (U2 X A2) + (U3 X A3) + ...)} / {(A1 + A2 X A3 + ...)}

Whole building calculation method

4.9 Where even greater design flexibility is required, reasonable provision would be to use an approved calculation tool to demonstrate that the calculated CO2 emissions from the building and proposed extension are no greater than for the building plus a notional extension complying with the standards of paragraphs 4.3 to 4.5.

Approved Document C gives limiting values for individual elements to minimise condensation risk.

4.10 The specification of the existing building used in conjunction with the notional extension as the basis of setting the CO2 target for the building work shall include all upgrades that will be included in fulfilment of the requirement for consequential improvements (see Section 6).

Otherwise all the low-cost measures would have been taken by the compensatory measures, leaving little leeway for overall improvement.

4.11 Where additional upgrades over and above the consequential improvements are proposed in the actual building to compensate for lower performance in the extension, then 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 upgrading retained thermal elements are as set out in column (b) of Table 5.

Where it is proposed to upgrade, 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 building may be better than that required by paragraphs 4.1 to 4.10.

Conservatories and porches

4.12 Where the extension is a conservatory or porch that is not exempt from the energy efficiency requirements (see paragraphs 3.21 and 3.22 above), then reasonable provision would be to provide:

a. Effective thermal separation between the heated area in the existing building, i.e. the walls, doors and windows between the building and the extension should be insulated and draught proofed to at least the same extent as in the existing building.

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 4.29 to 4.48.

c. Glazed elements should meet the standards set out in Table 3 and opaque elements should meet the standards set out in Table 4. However, the limitations on total area of windows, roof windows and doors as set out at paragraph 4.4 above do not apply.

4.13 Removing, and not replacing, any of the thermal separation between the building and an existing exempt extension, or extending the building's heating system into the extension, means that the extension ceases to be exempt (see paragraphs 3.21 and 3.22 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 4.11 above.

Swimming pool basins

4.14 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[5].

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.

[5] BS EN ISO 13370 Thermal performance of buildings – Heat transfer via the ground – Calculation methods [2007 incorporating corrigendum March 2009].

Material change of use

4.15 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 hotel or a boarding house, where previously it was not;

b. the building is used as an institution, where previously it was not;

c. the building is used as a public building, where previously it was not;

d. the building is not a building described in Classes I to VI in Schedule 2, where previously it was;

e. the building contains a room for residential purposes, where previously it did not;

f. the building, which contains at least one room for residential purposes, contains a greater or lesser number of such rooms than it did previously; or

g. the building is used as a shop where previously it was not.

Change of energy status

4.16 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.

4.17 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 Part L of Schedule 1.

4.18 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 a building's energy status.

4.19 In normal circumstances, reasonable provision when 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 4.22 to 4.48. If the area of openings in the newly created building is more than 25 per cent of the total floor area, the area of openings should either 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 4.21.

b. Where the work involves the provision of a thermal element, to meet the standards set out in paragraphs 5.1 to 5.7.

For the purposes of the 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 5.12 to 5.14. This guidance should also be followed in respect of any existing element that becomes part of the thermal envelope of the building where previously it was not.

As an example, this would include the party wall between units in a terrace of industrial units which originally were unheated, but heating is to be provided to one of the units.

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 follow the guidance in paragraphs 4.23 to 4.28 unless it is a display window or high usage entrance door. It would be reasonable in these latter cases to make some lesser provision for energy efficiency.

4.20 As well as satisfying the energy efficiency requirements in respect of the material change of use or change in energy status, such building work may be one of the triggers for consequential improvements - see regulation 28 and Section 6.

Option providing more design flexibility

4.21 To provide more design flexibility, an approved calculation tool can be used to demonstrate that the CO2 emissions from the building as it will become are no worse than if the building had been improved following the guidance set out in paragraph 4.19.

WORK ON CONTROLLED FITTINGS AND SERVICES

4.22 A controlled service or fitting is defined in Regulation 2(1) as follows:
'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

4.23 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 a new door in an existing frame.

4.24 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 3. In addition, insulated cavity closers should be installed where appropriate. If a window, pedestrian door or rooflight is enlarged or a new one created, then the area of the windows and pedestrian doors and of rooflights expressed as a percentage of the total floor area of the building should not exceed the relevant value from Table 2, or should be compensated for in some other a way. Where the windows or fully glazed external pedestrian doors are unable to meet the requirements of Table 3 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.

****Table 3 Standards for controlled fittings

4.25 U-values of windows, roof-windows, rooflights and doors shall be calculated using the methods and conventions set out in BR 443[6], 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 for windows can be taken as that for:

a. the smaller of the two standard windows defined in BS EN 14351-1[7]; or

b. the standard configuration referred to 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.

For domestic type construction, SAP 2012 Table 6e gives values for different window configurations that can be used in the absence of test data or calculated values.

4.26 The U-values for roof windows and rooflights given in this Approved Document are based on the particular 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 a U-value adjustment following the guidance given in BR 443.

The stated standard for a replacement plastic rooflight as given in Table 3 is 1.8 W/(m².K). This is for the unit assessed in the vertical plane. If the performance of a triple-skin rooflight was assessed in the horizontal plane, then, based on the guidance given in BR 443, the standard would be adjusted by 0.3 W/(m2.K) (the value from BR 443 for a horizontal triple-skin rooflight), requiring the rooflight as assessed in the horizontal plane to achieve a standard of 1.8 + 0.3 = 2.1 W/(m².K).

4.27 In certain classes of building with high internal gains, a less demanding U-value for glazing may be an appropriate way of reducing overall CO2 emissions. If this case can be made, then the average U-value for windows, doors and rooflights can be relaxed from the values given in Table 3, but the value should not exceed 2.7 W/(m².K).

4.28 The overall U-value of curtain walling should be no greater than the better of 1.8

W/(m².K) or a limiting U-value Ulimit given by:

Ulimit = 0.8 + {(1.2 + (FOL X 0.5)) X GF}

where FOL is the fraction of opening lights and GF is the glazed fraction.

This means that if an area of curtain walling is to be 60 per cent glazed and 40 per cent opaque, with 50 per cent opening lights, the U-value standard should be 0.8 + (1.2 + 0.5 X 0.5) X 0.6 = 1.7 W/(m².K).

[6] BR 443 Conventions for U-value calculations, BRE, 2006

[7] 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)].

Controlled services

4.29 Where the work involves the provision or extension of controlled services, reasonable provision would be demonstrated by following the guidance set out in the Non-Domestic Building Services Compliance Guide. 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; note that as detailed in Schedule 4, the work is not notifiable if the floor area that is to be provided with new fixed lighting is not greater than 100m2. Although not notifiable, the work should still meet the standards set out in the compliance guide.

e. renewable energy systems.

4.30 In general terms, the aim should be to:

a. provide new fixed building services that meet reasonable standards of energy efficiency, which in normal circumstances would be:

i. an efficiency not less than set out in the Non-Domestic Building Services Compliance Guide. The efficiency claimed for the fixed building service should be based on the appropriate test standard as set out in the 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. If a particular technology is not covered in the 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; and

ii. an efficiency not less than that of the controlled service being replaced. If the new service uses a different fuel, the efficiency of the new appliance should be multiplied by the ratio of the CO2 emission factor of the fuel used in the appliance being replaced to that of the fuel used in the new appliance before making this check.

This will prevent an existing low-carbon component being replaced by a lesser provision when fuel switching. For example, if an existing electric chiller with a Co-efficient of Performance (CoP) of 2.5 is replaced by an absorption chiller with a CoP of 0.8 but fired by waste heat, the equivalent efficiency of the absorption chiller would be 0.8 x (0.519/0.058) = 7.2, and so test (ii) would be satisfied. 0.519 and 0.058 kgCO2/kWh are the emission factors for electricity and waste heat respectively[8].

b. provide new HVAC systems with appropriate controls to achieve reasonable standards of energy efficiency. In normal circumstances reasonable provision would be to provide the following control features on each system in addition to the system-specific controls detailed in subsequent paragraphs:

i. the fixed building services systems should be sub-divided into separate control zones to correspond to each area of the building that has a significantly different solar exposure, occupancy period, or type of use;

ii. each separate control zone should be capable of independent switching and control of set-point;

iii. the provision of the service should respond to the requirements of the space it serves. If both heating and cooling are provided, they should be controlled so they do not operate simultaneously;

iv. central plant serving the zone-based systems should operate only as and when required. The default condition should be off;

v. in addition to these general control requirements, the systems should meet the specific control requirements and general energy efficiency criteria as set out in the Non-Domestic Building Services Compliance Guide.

c. demonstrate the new service has been effectively commissioned (see paragraphs 4.36 to 4.48);

d. demonstrate that reasonable provision of energy meters has been made for effective monitoring of the performance of newly installed plant (see paragraphs 4.33 to 4.35);

e. demonstrate that the relevant information has been recorded in a new log book or incorporated into an update of the existing one as described in Section 7.

4.31 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.

4.32 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.

Energy meters

4.33 The aim for buildings as a whole is to enable building occupiers to assign at least 90 per cent of the estimated annual energy consumption of each fuel to the various end-use categories (heating, lighting, etc.).

4.34 Reasonable provision for energy meters in existing buildings would be to install energy metering systems in the building service systems provided as part of the works in accordance with the recommendations in CIBSE TM 39[9].

4.35 In addition to this:

a. meters should be provided to enable the performance of any renewable energy system provided as part of the works to be separately monitored;

b. in buildings with a total useful floor area greater than 1000 m², the metering system should enable automatic meter reading and data collection;

c. the metering provisions should be designed such as to facilitate the benchmarking of energy performance as set out in TM 46[10].

Following implementation of the Energy Services Directive, there are likely to be legal obligations for persons commissioning building work on existing buildings with floor areas in excess of 1000 m² to notify their intentions to the energy supply companies.

[8] See Table 12 at http://www.bre.co.uk/sap2012.

[9] TM 39 Building energy metering, CIBSE, 2009.

[10] TM 46 Energy benchmarks, CIBSE, 2008.

COMMISSIONING OF FIXED BUILDING SERVICES

4.36 Regulation 44 (Commissioning) 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.

4.37 Reasonable provision could 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.

4.38 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 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.

4.39 Commissioning must be carried out in such a way as not to prejudice compliance with any applicable health and safety requirements.

4.40 In existing buildings other than dwellings commissioning is most often carried out by the person who installs the system. Sometimes 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.

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 http://www.bsria.co.uk/services/design/soft-landings/.

Notice of completion of commissioning

4.41 The Building Regulations (regulation 44(3)) and the Building (Approved Inspectors etc) Regulations (regulation 20(1) and (5)) 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.

4.42 The procedure approved by the Secretary of State is set out in:

a. CIBSE Commissioning Code M on commissioning management[11]; and
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. for leakage testing of ductwork, paragraphs 4.47 and 4.48.

4.43 Where a building notice or full plans have been given to a BCB, the notice should be given 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, it must be given within 30 days.

4.44 Where an approved inspector is the BCB, the notice should generally be given within 5 days of the completion of the commissioning work. However, where the work is carried out by a person registered with a competent person scheme (see paragraphs 3.25 to 3.28) the notice must be given within 30 days.

4.45 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.

4.46 Until the BCB receives the commissioning notices it may be unable to be reasonably satisfied that Part L has been complied with and consequently may be unable to give a completion/final certificate.

Membership of the Commissioning Specialists Association or the Commissioning group of the HVCA may be a way of demonstrating suitability to sign the report in respect of the HVAC systems. For lighting control systems, suitability may be demonstrated by accreditation under the Lighting Industry Commissioning Scheme.

4.47 Ductwork leakage testing should be carried out on new or refurbished ducting where practicable in accordance with the procedures set out in HVCA DW/143[12] on systems served by fans with a design flow rate greater than 1 m3/s and for those sections of ductwork where the pressure class is such that DW/143 recommends testing.
Membership of the HVCA specialist ductwork group or the Association of Ductwork Contractors and Allied Services could be a way of demonstrating suitable qualifications for this testing work.

4.48 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.

[11] CIBSE Commissioning Code M: Commissioning management, CIBSE, 2003.

[12] DW/143 A Practical Guide to Ductwork Leakage Testing, HVCA, 2000.

Guidance relating to building work