72 Pa. Stat. § 4711-205
Any person desiring tax exemption pursuant to ordinances or resolutions adopted pursuant to this article, shall notify each local taxing authority granting such exemption in writing on a form provided by it submitted at the time he secures the building permit, or if no building permit or other notification of improvement is required, at the time he commences construction. A copy of the exemption request shall be forwarded to the board of assessment and revision of taxes or other appropriate assessment agency. The assessment agency shall, after completion of the improvement, assess separately the improvement and calculate the amounts of the assessment eligible for tax exemption in accordance with the limits established by the local taxing authorities and notify the taxpayer and the taxing authorities of the reassessment and amounts of the assessment eligible for exemption. Appeals from the reassessment and the amounts eligible for the exemption may be taken by the taxpayer or the local taxing authorities as provided by law.
The cost of improvements per dwelling unit to be exempted and the schedule of taxes exempted existing at the time of the initial request for tax exemption shall be applicable to that exemption request, and subsequent amendments to the ordinance, if any, shall not apply to requests initiated prior to their adoption.
72 P.S. § 4711-205