Restoration. If any nonconforming building or use shall be destroyed to an extent of 50% or less of the recorded true valuation, then such destruction shall be deemed partial destruction and may be rebuilt, restored or repaired. Such restoration shall take place within 12 months of the time of destruction. 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 Building Inspector. If this time period is exceeded, a building permit shall only be issued for a conforming use.