Consequential improvements on extending a building
Constructing a new free-standing building on an existing site (e.g. a new out-patients building at an existing hospital site, or a new classroom block at a school) is not an extension. These should be treated as new buildings.
6.6 Where a building is extended, or the habitable area is increased, a way of complying with regulation 28 would be to adopt measures such as those in Table 6 to the extent that their value is not less than 10 per cent of the value of the principal works. The value of the principal works and the value of the consequential improvements should be established using prices current at the date the proposals are made known to the BCB. They should be made known by way of a report signed by a suitably qualified person as part of the initial notice or deposit of plans.
An example of a suitably qualified person would be a chartered quantity surveyor.
Consequential improvements on installing building services
6.7 Where it is proposed to install a fixed building service as a first installation, or as an installation which increases the installed capacity per unit area of an existing service, reasonable provision would be to:
a. firstly improve the fabric of those parts of the building served by the service, where this is economically feasible; and
This means for example that if heating systems are to be installed for the first time in a building or part thereof, or the installed heating capacity per unit area of an existing system is to be increased, the fabric should be improved. The aim in these cases is to make cost-effective improvements to the performance of the fabric so that the installed capacity (and the initial cost) of the fixed building services and their subsequent energy consumption are not excessive.
b. additionally, make improvements in line with the guidance in paragraph 6.6. The cost of any improvement made as a result of following the guidance in sub-paragraph a above cannot be taken as contributing to the value of the consequential improvements specified in paragraph 6.3.
If only the improvements under a) were made, then the CO2 emissions from the building might well increase as a result of the higher level of servicing. By also requiring the general improvements in b), an overall improvement should be achieved.
6.8 For the purposes of this Approved Document, the installed capacity of a fixed building service is defined as the design output of the distribution system output devices (the terminal units) serving the space in question, divided by the total useful floor area of that space.
This means that if (e.g.) the size of central boiler plant is increased to serve a new extension rather than to increase the heating provision in the existing building, the consequential improvements in paragraph 6.6 would be required but those in the following paragraphs would not apply.
6.9 Reasonable provision for improving the fabric of those parts of the building served by the service in line with paragraph 6.7a above would be to follow the guidance in paragraphs 6.10 and 6.11 to the extent that the work is technically, functionally and economically feasible. The extent of such work is not limited by the 10 per cent threshold. The following paragraphs give guidance on what in normal circumstances would be economically feasible.
6.10 Where the installed capacity per unit area of a heating system is increased:
a. the thermal elements within the area served which have U-values worse than those set out in column (a) of Table 5 should be upgraded following the guidance in paragraphs 5.12 and 5.13; and
b. existing windows, roof windows or rooflights (but excluding display windows) or doors (but excluding high-usage entrance doors) within the area served and which have U-values worse than 3.3 W/m².K should be replaced following the guidance in paragraphs 4.23 to 4.28.
6.11 Where the installed capacity per unit area of a cooling system is increased:
a. thermal elements within heated areas which have U-values worse than those set out in column (a) of Table 5 should be upgraded following the guidance in paragraphs 5.12 and 5.13; and
b. if the area of windows, roof windows (but excluding display windows) within the area served exceeds 40 per cent of the façade area or the area of rooflights exceeds 20 per cent of the area of the roof and the design solar load exceeds 25 W/m², then the solar control provisions should be upgraded such that at least one of the following four criteria is met:
i. the solar gain per unit floor area averaged over the period 0630 to 1630 GMT is not greater than 25 W/m2 when the building is subject to solar irradiances for July as given in the table of design irradiancies in CIBSE Design Guide A;
ii. the design solar load is reduced by at least 20 per cent;
iii. the effective g-value is no worse than 0.3;
iv. the zone or zones satisfies the criterion 3 check in Approved Document L2A based on calculations by an approved software tool; and
This will reduce the solar gain and hence the space cooling demand. Section 5.1 of TM 37 gives guidance on calculating solar gains, and Sections 4.4 and 4.5 give guidance on the effective g-value.
c. any general lighting system within the area served by the relevant fixed building service which has an average lamp efficacy of less than 45 lamp-lumens per circuit-watt should be upgraded with new luminaires and/or controls following the guidance in the Non-Domestic Building Services Compliance Guide.
This will reduce the lighting load and hence the space cooling demand.
 TM 37 Design for improved solar shading control, CIBSE, 2006.