6.1 Regulation 28 of the Building Regulations may require additional work to be undertaken to make an existing building more energy efficient when certain types of building work are proposed.
6.2 This requirement arises in existing buildings with a total useful floor area of over 1,000 m² where the proposed work consists of or includes:
a. an extension;
b. the initial provision of any fixed building service (other than a renewable energy generator);
c. an increase to the installed capacity of any fixed building service (other than a renewable energy generator).
6.3 Where regulation 28 applies, consequential improvements, in addition to the proposed building work (the principal works), should be made to ensure that the building complies
with Part L, to the extent that such improvements are technically, functionally and economically feasible. Paragraphs 6.4 to 6.11 below set out guidance on what will constitute technically, functionally and economically feasible consequential improvements in various circumstances.
The principal works must comply with the energy efficiency requirements in the normal way.
6.4 Where improvement works other than the 'trigger activities' listed in regulation 28(1) are planned as part of the building work, owners can use these as contributing to the consequential improvements. The exception
to this is if additional work is being done to the existing building to compensate for a poorer standard of an extension (see paragraphs 4.9 to 4.11).
For example, if, as well as extending the building, the proposals included total window replacement, then the window replacement work would satisfy the requirement for consequential improvements, provided the cost was at least 10 per cent of the cost of the extension.
6.5 Measures such as those listed in Table 6 that achieve a simple payback not exceeding 15 years will be economically feasible unless there are unusual circumstances.
For example, if the remaining life of the building is less than 15 years it would be economic to carry out only improvements with payback periods within that life.
Table 6 Improvements that in ordinary circumstances are practical and economically feasible