10 Pa. Stat. § 34
And in ascertaining such value, all vacant lots or lands shall be taken to be of the annual value at which such lots or lands could be let upon ground rent, or at the interest of the price at which they would sell for cash and without sacrifice; and if occupied and yielding rent or income, then as if the annual value of such rent or income, or of the valuation as vacant ground, in manner aforesaid, whichsoever shall be of the greater amount; but no edifice used for worship, education or an hospital, or the unproductive ground contained within the curtilage of such building, shall be included in such valuation: Provided, That no bona fide purchaser, for a valuable consideration, shall take a defeasible title by reason of the grantors having held property in excess of the limit aforesaid: And provided, That any property now held as aforesaid, in excess of such value, shall not be hereby invalidated or prejudiced in title or otherwise.
10 P.S. § 34