(1) The performance level of an existing building is reduced where after proposed construction in all or part of an existing building,
(a) the major occupancy will change to a different major occupancy,
(b) the occupant load will increase by more than 15%, or
(c) the live load will increase due to change in use within the same major occupancy,
and the existing structural floor and roof framing systems and their supporting members after the construction are not adequate to support the proposed dead loads and live loads.