7 Pa. Code § 137b.88
If enrolled land undergoes separation, and one of the tracts created through separation is converted to other than agricultural use, agricultural reserve or forest reserve 7 years or more after the date of the separation, the owner of the separated tract owes roll-back taxes and interest with respect to that separated tract, but does not owe roll-back taxes with respect to the remainder of the enrolled land. The separated tract may no longer receive preferential assessment under the act. The remaining enrolled land shall continue to receive a preferential assessment.
Example: Landowner A owns 100 acres of enrolled land, which is in agricultural use. Landowner A sells Landowner B a 50-acre portion of this enrolled land. Both 50-acre tracts continue in agricultural use, and preferential assessment continues with respect to both tracts. Eight years after the original 100-acre tract of enrolled land was separated, Landowner B converts his 50-acre tract to industrial use. Landowner B owes roll-back taxes and interest with respect to the 50-acre tract which he has converted to ineligible use. Landowner A's 50-acre tract continues to receive preferential assessment, and preferential assessment of Landowner B's 50-acre tract ends.
7 Pa. Code § 137b.88