Philadelphia contains many buildings that were built over 100 years ago; some even date back to the early part of the 18th century. In 1955, the city created the Philadelphia Historical Commission (PHC) and charged it with preserving historically significant buildings. The PHC has two basic functions: identifying historically significant structures or parts of structures and reviewing projects that involve the modification or demolition of structures that have been or may be designated as historically significant.
The PHC regulates preservation through the city's zoning process. The PHC maintains a register of historically significant structures in the city. At the moment, the register contains over 20,000 properties. If physical changes are proposed for either the interior or exterior of a building on the register, and if the work requires a building permit, the owner or developer must obtain the PHC's approval before a building permit will be issued. If a project requires a rezoning or the issuance of a conditional use permit, the PHC must first review and approve the proposal. The city's Department of Licenses and Inspections will not issue a building permit for structure on either the national or city register of historical places unless and until the PHC has approved the project.