Any lawful building, structure or use of premises existing at the time of enactment of this chapter, or any subsequent amendment thereof applying to such building, structure or use of premises, may be continued although such building, structure or use of premises does not conform to the provisions of this chapter; provided, however, that:

A building or structure of nonconforming use may be repaired or restored to a safe condition, except as specified in § 240-10.

Any building or structure for which a building permit was issued prior to the effective date of this chapter, or any subsequent amendment thereof applying, may be completed and used in accordance with the plans and specifications for such building and structure.

A nonconforming building may not be renovated or structurally altered during its life to an extent exceeding in aggregate value 50% of the replacement cost of the building, unless said building is changed to conform to the requirements of this chapter.

Any building damaged by fire or other causes to the extent of more than 50% of its replacement value may be repaired or rebuilt within a twelve-month period to conform to the building line of the original structure. Nothing in this chapter shall prevent the strengthening or restoring to a safe condition any wall, floor or roof which has been declared unsafe by the Code Enforcement Officer.