You must file a Catastrophic Loss application in order to report the loss, so that the Office of Property Assessment (OPA) can determine the new market value for the property. Any adjustment in the assessment of real property will be reflected in the form of a credit for the next tax year.
This application must be submitted to the OPA “within the remainder of the county fiscal year* in which the catastrophic loss occurred, or within six months of the date on which the catastrophic loss occurred, whichever time period is longer.”

*"The fiscal year for the City of Philadelphia...beginning July 1 and ending June 30." Ordinance #2789, December 14, 1967.