reg 23 Requirements for the renovation or replacement of thermal elements
(1) Where the renovation of an individual thermal element— (a) constitutes a major renovation; or (b) amounts to the renovation of more than 50% of the element’s surface area; the renovation must be carried out so as to ensure that the whole of the element complies with paragraph L1(a)(i) of Schedule 1, in so far as that is technically, functionally and economically feasible. (2) Where the whole or any part of an individual thermal element is proposed to be replaced and the replacement— (a) constitutes a major renovation; or (b) (in the case of part replacement) amounts to the replacement of more than 50% of the thermal element’s surface area; the whole of the thermal element must be replaced so as to ensure that it complies with paragraph L1(a)(i) of Schedule 1, in so far as that is technically, functionally and economically feasible.