The lawful nonconforming use of a structure or land, including but not limited to fences, parking and zoning setbacks existing on the date of adoption of the City Zoning Code may be continued although the use does not conform with the provisions of this chapter. However, only that portion of the land in actual use may be so continued and the structure may not be extended, enlarged, reconstructed, substituted, moved or structurally altered except when required to do so by law or order or so as to comply with the provisions of this chapter.

If no structural alterations are made, a nonconforming use of a building may be changed to any use permitted in the same use district as that in which the use existing is permitted according to the provisions of this chapter; provided when a use district is changed, any existing, nonconforming use in such changed district may be continued or changed to a use permitted in the same use district as that in which the existing use is permitted, provided all other regulations governing the new use are complied with.

Substitution of new equipment may be permitted by the Zoning Board of Appeals if such equipment will reduce the incompatibility of the nonconforming use with the neighboring uses.

Termination. If such nonconforming use is discontinued or terminated for a period of 12 months for residential districts and 12 months for commercial and industrial districts, any future use of the structure or land shall conform to the provisions of this chapter.

Building destroyed by fire. Where a building located in a district restricted against its use has been destroyed by fire or other calamity to the extent of not more than 50% of its assessed or fair market value, whichever is higher, the same may be rebuilt; but where such a building is destroyed to the extent of more than 50% of its assessed or fair market value, a building permit, following specific Common Council approval, may be granted for its reconstruction within 12 months from the date of such fire or other calamity, except any public utility located in a restricted district shall be permitted to rebuild, alter or enlarge in any business or industrial district as the interest of the public demands.

Pursuant to § 62.23(7)(hc), Wis. Stats., and notwithstanding any other provision of this chapter, a nonconforming structure damaged or destroyed by violent wind, vandalism, fire, flood, ice, snow, mold or infestation after March 2, 2006, may be restored to, or replaced at, the size, location, and use that it had immediately before the damage or destruction occurred, and no limits may be imposed on the costs of the repair, reconstruction, or improvement of said structure. The size of the structure may be larger than the size it was immediately before the damage or destruction if necessary for the structure to comply with applicable state or federal requirements.

A nonconforming use may be changed to a use of higher classification but not to a use of lower classification, nor shall a nonconforming use be changed to another use of the same classification unless the new use shall be deemed by the Zoning Board of Appeals, after public notice and hearing, to be no more harmful to the surrounding neighborhood from the standpoint of the purposes of this chapter than the existing nonconforming use.

Once a nonconforming use or structure has been changed to conform, it shall not revert back to a nonconforming use or structure. Once the Zoning Board of Appeals has permitted the substitution of a more restrictive nonconforming use for an existing nonconforming use, the substituted use shall lose its status as a legal nonconforming use and become subject to all the conditions required by the Zoning Board of Appeals.