The nonconforming use of a structure, land, or water existing on the effective date of adoption or amendment of this Ordinance may be continued although the use does not conform with the provisions of this Ordinance, except that:

The alteration or structural repair of, or addition to any existing structure being used for a nonconforming use, in excess of fifty (50) percent of the assessed value as defined in section 12.39.020(a) of this Ordinance, is prohibited.

The nonconforming use of a structure may be changed to a use of the same or more restricted classification, but where the nonconforming use of a structure is hereafter changed to a use of a more restricted classification, it shall not thereafter be changed to a use of a less restricted classification.

When a structure being used for a nonconforming use is damaged by fire, explosion, flood, or other calamity, to the extent of more than fifty (50) percent of its assessed value, as defined in section 12.39.020(a) of this Ordinance, it shall not be restored except so as to comply with the use provisions of this Ordinance. If a nonconforming use is discontinued or terminated for a period of twelve (12) months, any future use of the structure, land, or water shall conform to the provisions of this Ordinance.

Parcels containing a nonconforming use of land or water may be maintained or repaired including grading, paving, and surfacing, or the repair and replacement of bumper or wheel stops, fences, screening and drainage ways; provided, that the amount of land, water or storage (i.e. vehicles, equipment and/or materials) devoted to such nonconforming use as it existed prior to the date of this Ordinance is not extended, enlarged, or moved. [Code § 12.28-8.]