53 Pa. Stat. § 25010
In every such tenement house, whenever a connection with a public sewer is in any way possible (and of this possibility the bureau of health of said cities shall be the sole judge), there shall be one water closet for every tenement or suite of rooms, which has its own independent hallway, so separated that its rooms do not open into or connect with any other rooms; and in tenement houses so constructed that a tenement may consist of a single room or of two rooms, there shall be at least one water closet for every three rooms: Provided, That in the case of buildings existing at the date of this act, which shall hereafter be altered or converted into tenement houses, there shall be one water closet for every six rooms, but not less than one for each floor. Every water closet shall be separated from every other water closet, and shall have an entrance entirely independent of the entrance to every other water closet. Every such water closet shall be properly ventilated, in conformity with the regulations and requirements already in force in said cities of the second class. But when necessary (and of this necessity the bureau of health of said cities shall be the sole judge), such water closets may be located in the yard. Wherever located, the said water closets shall conform in design, materials and construction to the building and health regulations of said cities.
53 P.S. § 25010