53 Pa. Stat. § 4652
In tenement-houses, lodging-houses, factories, workshops, and all public buildings (except single family homes), the entire water-closet apartments and side-walls, to a height of six inches from the floor, except at the door, must be made waterproof with asphalt, cement, tile, or other waterproof material, as approved by the board or bureau of health. In tenement-houses and lodging-houses, the water-closet and urinal apartments must have a window or windows opening into the outer air, of sufficient size, all of which shall be shown on plans, and shall be subject to the approval of the board or bureau of health. Except that tenement- or lodging-house, three stories or less in height, may have such window opening on a ventilating shaft, not less than ten square feet in area. If over three stories, then said shaft must not be less than twenty-five square feet. In all buildings, the outer partition of such apartments must extend to the ceiling, or be independently ceiled over, and these partitions must be air-tight. The outside partitions must include a window opening to outer air on the lot whereon the building is situated; or some other approved mechanical means of ventilation must be provided to change the air at least six times per hour. When necessary to properly light such apartments, the upper part of the partitions must be of glass. The interior partitions of such apartments must be drawfed partitions.
53 P.S. § 4652