Any building or structure declared unsafe by the City Engineer may be restored to a safe condition, provided, however, that if the damage or cost of reconstruction or restoration is in excess of 50% of the value of the building or structure, exclusive of foundations, such building or structure, if reconstructed or restored, shall be made to conform, with respect to materials and type of construction to the requirements for buildings and structures as set forth in the state building code, if applicable, but no change of use or occupancy shall be compelled by reason of such reconstruction or restoration.
(`63 Code, § 1309.03)