Retained thermal elements – upgrade requirements

Where – (a) an existing thermal element is part of a building subject to a material change of use or a change of energy status; (b) an existing thermal element is upgraded as part of a consequential improvement; or (c) an existing element becomes part of the thermal envelope where previously it was not, and where it has a U-value greater than the threshold value given in column (a) of Table 3.4, the element should be upgraded to the standard given in column (b) of Table 3.4 provided that this is technically, functionally and economically feasible. A reasonable test of economically feasible is to achieve a simple payback period of 15 years or less.