(a) A sign or a substantial part of a sign that is blown down, destroyed, taken down, or removed for any purpose other than for maintenance or for changing a letter, symbol, or other matter on the sign may not be reerected, reconstructed, or rebuilt unless the sign conforms with this chapter.
(b) For purposes of this section, a sign or substantial part of a sign is considered destroyed only if the cost of repairing the sign is more than 50 percent of the cost of erecting a new sign of the same type at the same location.