19. ‘deep renovation’ means a renovation in line with the energy efficiency first principle and efforts to reduce whole life-cycle greenhouse gas emissions generated during the renovation, which focuses on essential building items, such as wall insulation, roof insulation, low floor insulation, replacement of external joinery, ventilation and heating or heating systems and treatment of thermal bridges, to ensure the necessary comfort of the occupants in summer and winter or a renovation resulting in a reduction of at least 60 % primary energy demand for worst-performing buildings for which it is technically and economically not feasible to achieve a zero-emission building standard, and which transforms a building or building unit:
(a) before 1 January 2027, into a nearly zero-energy building
(b) from 1 January 2027, into a zero-emission building