(a)

The lawful use of the land exiting at the time of the passage of this ordinance, although such use does not conform to the provisions hereof, may be continued, provided, however, that nonconforming commercial and industrial uses operated on open land not accessory to a permanent building on the site may be continued for a period not longer than five years after such uses become nonconforming.

(b)

In all "R" districts, every nonconforming building or structure which was designed, arranged or intended for a use permitted only in districts other than "R" districts shall be completely removed, or altered and converted to a conforming building, structure or use when such buildings or structures have reached or may hereafter reach, the ages hereinafter specified, computed from the date the building was erected. In the case of buildings defined in the Building Code effective in the city at the effective date of this ordinance: Class I and II, forty years; Class III and VI, thirty years; Class V, twenty years. Provided, however, that this regulation shall not become operative until twenty years from the effective date of this article.

(c)

If any nonconforming use is abandoned or discontinued for any reason, subsequent use of such land shall be in conformity with the provisions of this ordinance. The discontinuance of a nonconforming use for a period of six months or more is, in itself prima facie evidence of abandonment.

If no external structural alternations are made, a nonconforming use of a building may be changed to another nonconforming use of the same or more restricted classification.

Except in cases where a use permit is approved, no existing building designed, arranged or intended for or devoted to a use not permitted under the regulations of this ordinance for the district in which such building or premises is located shall be enlarged, extended, reconstructed or structurally altered, unless such use is changed to a use permitted under the regulations specified by this ordinance for such district in which said building is located; provided, however, that authorized maintenance shall be permitted not exceeding a total amount, during a period of five years, or fifty percent of the assessed value of the building according to the assessments thereof by the assessor of the city.

Except in cases where a use permit is approved any building in existence or maintained at the time of the adoption of this ordinance which does not conform to the regulations for the district in which it is located which is destroyed by fire, explosion, act of God, or act of the public enemy to the extent of more than one-half the value thereof, then and without further action by the city council the said building and the land on which said building was located or maintained shall from and after the date of such destruction be subject to all the regulations of the district in which such land and/or building is located. For the purposes of this ordinance, the value of any building shall be the estimated cost of the replacement of the building in kind, as determined by the building inspector.

The foregoing provisions shall also apply to nonconforming uses in districts hereafter changed or established and any time limit for the suspension of a non-conforming use of land shall date from the date of the enactment of this ordinance or any amendment of district boundaries which first creates a nonconforming use or uses.