For example, a zoning ordinance may permit professional offices in a residential zone, if at least four off-street parking places are provided. When a use is conditional, the zoning ordinance often will require the property owner to file an application with local officials so that they may determine whether the conditions have been met. When a zoning ordinance is validly adopted, all future development in the locality governed by the ordinance must conform to its requirements. However, existing properties in a locality are often used in a manner inconsistent with a new zoning ordinance. Generally, an existing non-conforming use is not required to cease and may continue after the adoption of a zoning ordinance.
Amortization is another device used to limit the duration of non-conforming uses.
Under this approach, a non-conforming use may be permitted to continue for a specific period of time, after which it must be converted to a conforming use. A variance or special use permit is an exception to the requirements of a zoning ordinance. Most statutes permitting the adoption of zoning ordinances also specify the circumstances under which variances may be granted. Usually, some kind of hardship must be shown to justify the grant of a variance. Once a plan and ordinance has been adopted, property owners may seek to obtain exceptions to the requirements and limitations, either through an amendment to the plan or ordinance, or through an application for a variance or special use permit.