53 Pa. Stat. § 14822
All traps shall be protected from siphonage or air pressure by special vent-pipes, of a size not less than the following tables:
| Size of Pipe. | Maximum Developed Length in Feet. | Number of Traps Vented. | |
| Mains. | Branch. | Main Vertical. | |
| 1 1/4 inch vent | 20 | 1. | |
| 1 1/2 inch vent | 40 | 2 or less. | |
| 2 inch vent | 65 | 10 or less | 20 or less |
| 2 1/2 inch vent | 100 | 20 or less | 40 or less |
| 3 inch vent | 10 or more stories | 60 or less | 100 or less |
The branch vent-pipes shall be not less than the following sizes: One and one-fourth inches in diameter, for one and one-fourth inch traps. One and one-half inches in diameter, for one and one-half inch to two and one-half inch traps. Two inches in diameter, for three-inch to four-inch traps. One-half their diameter, for traps five inches and over.
Where two (2) or more water-closets are placed side by side on a horizontal branch, the branch line shall have a relief extended as a loop vent. A pipe two (2) inches in diameter will be sufficient as a loop vent for two (2) closets. A pipe three (3) inches in diameter shall be used as a relief for three (3) or four (4) closets; and where more than four (4) closets are located on the same branch the relief shall not be less than (4) inches in diameter. All house drains and soil lines on which a water-closet is located must have a four-inch main vent line. Where an additional closet is located in the cellar or basement, and within ten feet of main soil or vent line no relief vent will be required for said closet; but where it is more than ten (10) feet, a two-inch vent line will be required. Relief vent pipes for water-closets must not be less than two inches in diameter for a length of forty-feet, and not less than three inches in diameter for more than forty feet.
No revent from traps under bell-traps will be required.
Any building having a sewer connection with a public or private sewer used for bell-trap connections or floor drainage only, a two-inch relief line must be extended to the roof of building from rear end of main drain. House drains constructed for roof drainage only, will not require a relief vent.
A floor-trap for a shower shall be vented, unless located in cellar or ground floor, the paving of which renders the trap inaccessible. If the number of these fixtures on a branch is two (2) or more, the waste line shall be extended as a loop vent, instead of back venting the separate traps; and when located in basement floor, they shall be provided with a removable strainer or cleanout. Back-vent pipes, from traps above the floor, must either be connected with crown of trap with ground-in brass coupling, or, if connected solidly to trap, must have a ground-in brass coupling at wall.
53 P.S. § 14822