All traps, except approved antisiphon traps connected to main waste or soil lines or to the house drain by branch piping not over seven feet in length with a fall not exceeding two inches per foot, shall be protected from siphonage and back pressure by special lines of vent pipes; provided that where approved back seal siphon-jet water closet or stop sink fixtures are installed with branch piping not over five feet in length from fixtures to main soil or waste line, the vent pipe may be omitted for such fixtures in buildings not over eight stories in height, and where the main soil or waste line is made one inch larger in diameter than required by these rules, the vent pipe may also be omitted for such fixtures in buildings over eight stories in height.
All vent pipe lines and main branches must be of cast iron, galvanized wrought iron, galvanized steel, brass or Type K or L or DWV copper. They must be extended above the roof as required for waste pipes. They may be connected with the adjoining soil or waste lines well above the highest fixture, but this will not be permitted when there are fixtures on more than six floors.
All offsets must he made at an angle of no less than 45° to the horizontal, and all lines must be connected at the bottom with a soil or waste pipe or with the drain in such a manner as to prevent the accumulation of rust scale.
Branch vent pipes shall be kept above the top of all connecting fixtures so as to prevent the use of vent pipes as soil pipes or waste pipes. Branch vent pipes should be connected not less than six inches nor more than two feet from crown of trap or side of lead hand.
A. 
Except where yoke-type ventilation is installed, vent connections for water closets and slop sinks must be made from the branch soil or waste pipe just below the trap of the fixture and the branch vent pipe must be so connected as to prevent obstruction and with no waste pipe connected between it and the fixture.
B. 
Yoke-type ventilation shall be taken to mean a cross-connection by means of a horizontal branch soil or waste pipe between the main soil or waste line and the vent line and in which the connection between the branch pipe and the vent line is made at least six inches above the line of fixtures discharging into such branch pipe.
No sheet metal, brick or other flue shall be used as a vent pipe.
The size of vent pipes throughout must not be less than the following:
A. 
Main vents. For main vents, two inches in diameter; for water closets on three or more floors, three inches in diameter; for other fixtures on less than seven floors, two inches in diameter; three-inch vent pipe will be permitted for less than nine stories; for more than eight and less than 16 stories, four inches in diameter; for more than 15 and less than 22 stories, five inches in diameter; for more than 20 stories, the size of the vent pipe shall be determined by the Superintendent of Buildings.
B. 
Fixtures. For fixtures other than water closets and slop sinks and for more than eight stories, vent pipes may be one inch smaller in diameter than above stated.
C. 
Water closets, etc. For water closets, slop sinks and shower stalls on less than three floors, branch vent pipes may be 1 1/2 inches in diameter.
D. 
Branch vents. For long branch vent pipes over 10 feet in length but not exceeding 25 feet, two inches in diameter; when over 25 feet in length but not exceeding 50 feet, three inches in diameter. No branch vent pipe can exceed 50 feet in length, nor can any main vent be of less diameter than the largest branch vent connection to same.
A. 
Yoke-type ventilation. When the plumbing fixtures installed in any building are arranged in groups or batteries, yoke-type ventilation may be installed; provided that for batteries of water closets, each fixture shall be set not more than two feet distant from the horizontal branch soil pipe into which it discharges, and for batteries of fixtures other than water closets, each fixture shall be so located that its trap will be not more than two feet distant from the horizontal branch waste line into which it discharges.
B. 
Ordinary venting. When the ordinary type of venting is installed and the number of branch or back vents from the traps of fixtures connecting to any main branch vent exceeds the number and size given in the following table, a three-inch main branch vent must be provided for the additional vent connections:
Number
Branch Size
(inches)
Main Branch Size
(inches)
2
1 1/2
1 1/2
4
2
2
7
1 1/2
2
2
2
2
4
1 1/2
2
1
2
2
5
1 1/2
2