The effectiveness of a preservation ordinance depends on its scope and language, and ordinances vary greatly among jurisdictions.

Their basic provisions enable a community to designate significant local sites as historic, list them on a local listing of historic resources, and provide a level of protection through a design review process. These designated sites are referred to by a variety of names, such as “historic landmark” or “historic-cultural monument,” depending on the jurisdiction. 

A preservation ordinance outlines the criteria the community has established for designating such landmarks. These criteria are often based on those used by both the National Register of Historic Places and the California Register of Historical Places, which in turn are based on generally accepted preservation standards. Each community can tailor its designation criteria to reflect the specific significance of the community’s unique local resources.

Strong local historic preservation ordinances require that requests for building permits for designated structures be reviewed by city staff or a special local commission to ensure that proposed alterations conform to preservation standards. They also give the city the power to deny permits for inappropriate alterations or demolitions.

In order to protect a significant structure from demolition or severe alteration by its owner, a strong preservation ordinance does not require owner consent for a historic resource to be designated. Ordinances that require owner consent, or that allow the owner to have a designation removed, are far less effective in using landmark designation as a method for protecting threatened resources.

Weaker preservation ordinances do not prevent demolition of a designated resource, but merely delay demolition for a set number of days. The weakest ordinances contain no language regarding the protection of the designated resource: such designated sites enjoy only honorary status and no protections at all.

A few communities have a “scorched-earth” provision in their ordinances. This provision prohibits new construction on a site for a set period of time after an illegal demolition has occurred.

Once in place, an ordinance needs to be actively used to be most effective. Some communities have had landmark ordinances for several years yet have never designates any landmarks. Others have active programs and a growing list of designated landmarks, often fueled by the strong promotion of the benefits of owning a historic property, such as property tax relief under the Mills Act.