If any nonconforming building, structure or use is destroyed by reason of wind storm, fire, explosion or other acts of God or the public enemy, and the foundation and at least two walls of the building or structure survive, a permit shall be issued for the reconstruction of a nonconforming building, structure or use. Nothing in this subsection shall prevent the strengthening or restoring to a safe condition of any wall, floor or roof which has been declared unsafe by the Construction Official.