If any nonconforming building shall be destroyed by reason of windstorm, fire, explosion or other act of God or the public enemy to an extent of more than 60% of the recorded true value as appraised in the records of the tax assessor, then such destruction shall be deemed complete destruction, and the structure may not be rebuilt, restored or repaired except in conformity with this chapter. Nothing in this chapter shall prevent the strengthening or restoring to a safe condition of any wall, floor, or roof which has been declared unsafe by the Building Official.