53 Pa. C.S. § 8585
(a) Authorization.--The exclusion for farmstead property shall be authorized pursuant to section 2(b)(i) of Article VIII of the Constitution of Pennsylvania. This exclusion shall apply uniformly to each farmstead property within the taxing jurisdiction.
(b) General rule.--Any governing body that excludes a portion of the value of homestead property under section 8583 (relating to exclusion for homestead property) shall exclude a portion of the assessed value of each farmstead property in the political subdivision by a fixed dollar amount established by its governing body, not to exceed the amount of the exclusion for homestead property under section 8583. The exclusion for farmstead property shall be in addition to any exclusion for homestead property for which the dwelling on the farm may qualify.
(c) Farmstead crossing county lines.--If a political subdivision is located in more than one county, the exclusion for farmstead property computed under subsection (a) for each county portion of the political subdivision shall be uniform after adjustment for the common level ratios in the respective counties.
(d) New construction.--The exclusion allowed under subsection (b) for a building constructed during the taxable year and used as farmstead property shall be prorated in a manner consistent with the assessment of real property taxes on that building.
(e) Reassessment.--After a revision of assessments by means of revaluing all properties, the governing body of the political subdivision providing an evaluation under this section shall adjust the amount of the exclusion for farmstead property as follows:
(1) if the assessment base is revised by applying a change in the established predetermined ratio, the exclusion for farmstead property shall be adjusted by the percentage change between the existing predetermined ratio and the newly established predetermined ratio; or
(2) if performing a revision of assessments by revaluing all properties and applying an established predetermined ratio, the exclusion for farmstead property shall be adjusted by dividing the exclusion for farmstead property for the year preceding the revision of assessments by the common level ratio and multiplying the quotient of that calculation by the newly established predetermined ratio.
53 Pa.C.S. § 8585