Technical Booklet F1 Conservation of Fuel and Power in Dwellings·Page 10·42
Change of energy status
When a building's energy status changes, necessary work must be carried out to ensure the building complies with conservation requirements.
Where there is a change of energy status such work shall be carried out as is necessary to ensure that the building complies with the requirements of regulation 39.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet F1 - Conservation of Fuel and Power in Dwellings.pdf