Flexibility is added to zoning ordinances through variances and special exceptions, both administered by the Board of Zoning Appeals or Adjustment, and zoning amendments enacted by the municipal legislature.
Zoning ordinances permit the board of adjustment to grant variances. A variance, if granted, allows a landowner to build on land or use the land in a manner otherwise not permitted by the zoning ordinance. The variance is an administrative order waiving application of the zoning ordinance in order to keep the ordinance from denying a landowner all reasonable use of his property. It also serves as a safety valve that prevents the city or county from being held liable under the Takings Clause of the Constitution, or the zoning ordinance from being declared unconstitutional under the substantive Due Process Clause of the Constitution.
Variances are categorized as either use variances or area variances. Use variances permit a use otherwise prohibited in the district. A few jurisdictions prohibit use variances altogether. Area variances permit deviations from area, bulk, set-back, street frontage, floor space, and height and other nonuse requirements of the zoning ordinance. Boards of Adjustment or Zoning Appeals (and courts) are more receptive to area variances since they usually do not change a district's essential character.