Existing nonconforming uses. The lawful nonconforming use of a structure or land existing at the time of the adoption or amendment of this chapter may be continued although the use does not conform with the provisions of this chapter; however:

Abolishment or replacement. If such nonconforming use is discontinued or terminated for 12 months, any future use of the structure or land shall conform to the provisions of this chapter. When a nonconforming use or structure is damaged by fire, explosion, flood, the public enemy or other calamity, to the extent of more than 50% of its fair market value, it shall not be restored except so as to comply with the use provisions of this chapter. A current file of all nonconforming uses shall be maintained by the Building Inspector listing the following at the time of its becoming a nonconforming use:

Existing nonconforming structures. The lawful nonconforming structure existing at the time of the adoption or amendment of this chapter may be continued although its size or location does not conform with the lot width, lot area, yard, height, parking and loading and access provisions of this chapter; however, it shall not be extended, enlarged, reconstructed, 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.

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

Substandard lots. In any residential district, a one-family detached dwelling and its accessory structures may be erected on any legal lot or parcel, provided such lot or parcel was of record in the County Register of Deeds office before the effective date or amendment of this chapter. Such lot or parcel shall be in separate ownership from abutting lands. If abutting lands and the substandard lot are owned by the same owner, the substandard lot shall not be sold or used without full compliance with the provisions of this chapter. If in separate ownership, all the district requirements shall be complied with insofar as practical, but shall not be less than the following:

Nonconforming lots, structures and uses in industrial district. In the B-I and I Districts, single-family detached dwellings and their accessory structures may be erected on any legal lot or parcel of record at the time of the adoption of this chapter. The burden of proof shall be on the applicant for a building permit or certificate of zoning compliance to show that said lot was of record in the County Register of Deeds office prior to the adoption of this chapter. No further subdivision for residential purposes is permitted in the Industrial District. Any building or structure erected after the adoption of this chapter under this section shall conform to the requirements of subs. (3) and (5) above, but shall not be subject to the repair and termination provisions of subs. (1) and (2) above.