total of necessarily incurred labour, material (ISO 6707-1:2014, 6.1.1) and other related costs (ISO 6707-1:2014, 9.3.85) incurred to retain a building (ISO 6707-1:2014, 3.1.3)(3.1.10) or its parts in a state in which it can perform its required functions (3.1.43)