53 Pa. Stat. § 14813
The smallest diameter of any soil-pipe permitted to be used shall be four-inch. The size of soil-pipes must be not less than those set forth in the following tables:
Maximum number of fixtures connected to--
| Size of Pipe. | Soil and Waste Combined. | Soil-Pipe Alone. | ||
| Branch. | Main. | Branch. | Main. | |
| 4 In. | 48 fixtures | 96 fixtures | 8 water-closets | 16 water-closets |
| 5 In. | 96 fixtures | 192 fixtures | 16 water-closets | 32 water-closets |
| 6 In. | 268 fixtures | 336 fixtures | 34 water-closets | 68 water-closets |
If the building is six (6), and less than twelve (12), stories in height, the diameter shall be not less than five (5) inches; if more than twelve (12) stories, it shall be six (6) inches in diameter. A building six or more stories in height, with fixtures, located below the sixth floor, soil-pipe four (4) inches in diameter will be allowed to extend through the roof; provided the number of fixtures does not exceed the number given in the table.
All soil-pipes must extend at least two feet above the highest window, and must not be reduced in size. Traps will not be permitted on main, vertical, soil, or waste lines. Each house must have a separate line of soil- and vent-pipes. No soil or waste line shall be constructed on the outside of a building.
Fixtures with--
One and one-quarter traps, count as one fixture;
Two-inch traps, count as two fixtures;
Two and one-half traps, count as three fixtures;
Three-inch traps (water-closets), count as four fixtures;
Four-inch traps, count as five fixtures.
53 P.S. § 14813