When zoning changes, existing lawful uses that no longer comply become legal nonconforming uses. They may continue, subject to limits designed to encourage their eventual elimination.

Establishing the status requires proof that the use existed lawfully before the change and has continued. The burden is on the owner, and the evidence — permits, tax records, aerial photographs, affidavits — should be assembled before it is needed.

Expansion and change. Most ordinances prohibit enlargement or intensification of a nonconforming use, and permit a change only to a use that is equally or less nonconforming. What counts as intensification, as opposed to normal fluctuation in business volume, is a common dispute.

Discontinuance. Abandonment or cessation for a stated period terminates the status. Many jurisdictions require intent to abandon in addition to the lapse of time; others treat the period as conclusive. Which rule applies matters greatly to a seasonal or interrupted operation.

Destruction. Ordinances commonly permit rebuilding if damage is below a percentage of value, and prohibit it above.

Amortization — requiring termination after a period sufficient to recoup investment — is permitted in some states and rejected in others.

Nonconforming structures and nonconforming lots are governed separately and should not be conflated with nonconforming uses.