(Note that Chapter 9 has been reorganized to present the main sections in a more logical order. For clarity of presentation, the star and double-star scheme normally used to indicate text that has been relocated was not used for this text reorganization.)
The provisions of this chapter shall govern the materials, design, construction and installation of vent systems.
901.2 Trap seal protection.
The plumbing system shall be provided with a system of vent piping that will permit the admission or emission of air so that the seal of any fixture trap shall not be subjected to a pneumatic pressure differential of more than 1 inch of water column (249 Pa).
901.2.1 Venting required.
Traps and trapped fixtures shall be vented in accordance with one of the venting methods specified in this chapter.
901.3 Chemical waste vent systems.
The vent system for a chemical waste system shall be independent of the sanitary vent system and shall terminate separately through the roof to the outdoors or to an air admittance valve that complies with ASSE 1049. Air admittance valves for chemical waste systems shall be constructed of materials approved in accordance with Section 702.5 and shall be tested for chemical resistance in accordance with ASTM F 1412.
901.4 Use limitations.
The plumbing vent system shall not be utilized for purposes other than the venting of the plumbing system.
The vent system shall be tested in accordance with Section 312.
901.6 Engineered systems.
Engineered venting systems shall conform to the provisions of Section 919.
The materials and methods utilized for the construction and installation of venting systems shall comply with the applicable provisions of Section 702.
902.2 Sheet copper.
Sheet copper for vent pipe flashings shall conform to ASTM B 152 and shall weigh not less than 8 ounces per square foot (2.5 kg/m2).
902.3 Sheet lead.
Sheet lead for vent pipe flashings shall weigh not less than 3 pounds per square foot (15 kg/m2) for field-constructed flashings and not less than 21/2 pounds per square foot (12 kg/m2) for prefabricated flashings.
903.1 Roof extension.
Open vent pipes that extend through a roof shall be terminated not less than [NUMBER] inches (mm) above the roof, except that where a roof is to be used for any purpose other than weather protection, the vent extensions shall terminate not less than 7 feet (2134 mm) above the roof.
903.2 Frost closure.
Where the 97.5-percent value for outside design temperature is 0°F (-18°C) or less, every vent extension through a roof or wall shall be not less than 3 inches (76 mm) in diameter. Any increase in the size of the vent shall be made inside the structure at a point not less than 1 foot (305 mm) below the roof or inside the wall.
The juncture of each vent pipe with the roof line shall be made water-tight by an approved flashing.
903.4 Prohibited use.
A vent terminal shall not be used for any purpose other than a vent terminal.
903.5 Location of vent terminal.
An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet (3048 mm) horizontally of such an opening unless it is 3 feet (914 mm) or more above the top of such opening.
903.6 Extension through the wall.
Vent terminals extending through the wall shall terminate at a point not less than 10 feet (3048 mm) from a lot line and not less than 10 feet (3048 mm) above average ground level. Vent terminals shall not terminate under the overhang of a structure with soffit vents. Side wall vent terminals shall be protected to prevent birds or rodents from entering or blocking the vent opening.
903.7 Extension outside a structure.
In climates where the 97.5-percent value for outside design temperature is less than 0°F (-18°C), vent pipes installed on the exterior of the structure shall be protected against freezing by insulation, heat or both.
OUTDOOR VENT EXTENSIONS
904.1 Required vent extension.
The vent system serving each building drain shall have not less than one vent pipe that extends to the outdoors.
The required vent shall be a dry vent that connects to the building drain or an extension of a drain that connects to the building drain. Such vent shall not be an island fixture vent as allowed by Section 916.
The required vent shall be sized in accordance with Section 906.2 based on the required size of the building drain.
904.2 Vent stack required.
A vent stack shall be required for every drainage stack that has five branch intervals or more.
Exception: Drainage stacks installed in accordance with Section 913.
904.3 Vent termination.
Vent stacks or stack vents shall terminate outdoors to the open air or to a stack-type air admittance valve in accordance with Section 918.
904.4 Vent connection at base.
Vent stacks shall connect to the base of the drainage stack. The vent stack shall connect at or below the lowest horizontal branch. Where the vent stack connects to the building drain, the connection shall be located downstream of the drainage stack and within a distance of 10 times the diameter of the drainage stack.
904.5 Vent headers.
Stack vents and vent stacks connected into a common vent header at the top of the stacks and extending to the open air at one point shall be sized in accordance with the requirements of Section 906.1. The number of fixture units shall be the sum of all fixture units on all stacks connected thereto, and the developed length shall be the longest vent length from the intersection at the base of the most distant stack to the vent terminal in the open air, as a direct extension of one stack.
VENT CONNECTIONS AND GRADES
All individual, branch and circuit vents shall connect to a vent stack, stack vent, air admittance valve or extend to the open air.
All vent and branch vent pipes shall be so graded and connected as to drain back to the drainage pipe by gravity.
905.3 Vent connection to drainage system.
Every dry vent connecting to a horizontal drain shall connect above the centerline of the horizontal drain pipe.
905.4 Vertical rise of vent.
Every dry vent shall rise vertically to a point not less than 6 inches (152 mm) above the flood level rim of the highest trap or trapped fixture being vented.
Exception: Vents for interceptors located outdoors.
905.5 Height above fixtures.
A connection between a vent pipe and a vent stack or stack vent shall be made at not less than 6 inches (152 mm) above the flood level rim of the highest fixture served by the vent. Horizontal vent pipes forming branch vents, relief vents or loop vents shall be located not less than 6 inches (152 mm) above the flood level rim of the highest fixture served.
905.6 Vent for future fixtures.
Where the drainage piping has been roughed-in for future fixtures, a rough-in connection for a vent shall be installed. The vent size shall be not less than one-half the diameter of the rough-in drain to be served. The vent rough-in shall connect to the vent system, or shall be vented by other means as provided for in this chapter. The connection shall be identified to indicate that it is a vent.
VENT PIPE SIZING
906.1 Size of stack vents and vent stacks.
The minimum required diameter of stack vents and vent stacks shall be determined from the developed length and the total of drainage fixture units connected thereto in accordance with Table 906.1, but in no case shall the diameter be less than one-half the diameter of the drain served or less than 11/4 inches (32 mm).
SIZE AND DEVELOPED LENGTH OF STACK VENTS AND VENT STACKS
DIAMETER OF SOIL
OR WASTE STACK
TOTAL FIXTURE UNITS
BEING VENTED (dfu)
MAXIMUM DEVELOPED LENGTH OF VENT (feet)a
DIAMETER OF VENT (inches)
11/4 11/2 2 21/2 3 4 5 6 8 10 12 11/4
— — — — — — — — — 2
— — — — — — — 3
— — — — — — 3
— 25 86
— — — — — 4
— — 23
— — — — 5
— — — 21
— — — — 6
— — — — 33
— — — 6
— — — — 20
— — 8
— — — — — 20
— — — — — — 24
— — — — — — — 31
— — — — — — — 18
— — — — — — — — 26
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm. a. The developed length shall be measured from the vent connection to the open air.
906.2 Vents other than stack vents or vent stacks.
The diameter of individual vents, branch vents, circuit vents and relief vents shall be not less than one-half the required diameter of the drain served. The required size of the drain shall be determined in accordance with Table 710.1(2). Vent pipes shall not be less than 11/4 inches (32 mm) in diameter. Vents exceeding 40 feet (12 192 mm) in developed length shall be increased by one nominal pipe size for the entire developed length of the vent pipe. Relief vents for soil and waste stacks in buildings having more than 10 branch intervals shall be sized in accordance with Section 908.2.
906.3 Developed length.
The developed length of individual, branch, circuit and relief vents shall be measured from the farthest point of vent connection to the drainage system to the point of connection to the vent stack, stack vent or termination outside of the building.
906.4 Multiple branch vents.
Where multiple branch vents are connected to a common branch vent, the common branch vent shall be sized in accordance with this section based on the size of the common horizontal drainage branch that is or would be required to serve the total drainage fixture unit (dfu) load being vented.
906.5.1 Sewage pumps and sewage ejectors other than pneumatic.
Drainage piping below sewer level shall be vented in the same manner as that of a gravity system. Building sump vent sizes for sumps with sewage pumps or sewage ejectors, other than pneumatic, shall be determined in accordance with Table 906.5.1.
SIZE AND LENGTH OF SUMP VENTS
DISCHARGE CAPACITY OF
MAXIMUM DEVELOPED LENGTH OF VENT (feet)a Diameter of vent (inches) 11/4 11/2 2 21/2 3 4 10 No limitb No limit No limit No limit No limit No limit 20 270 No limit No limit No limit No limit No limit 40 72 160 No limit No limit No limit No limit 60 31 75 270 No limit No limit No limit 80 16 41 150 380 No limit No limit 100 10c 25 97 250 No limit No limit 150 Not permitted 10c 44 110 370 No limit 200 Not permitted Not permitted 20 60 210 No limit 250 Not permitted Not permitted 10 36 132 No limit 300 Not permitted Not permitted 10c 22 88 380 400 Not permitted Not permitted Not permitted 10c 44 210 500 Not permitted Not permitted Not permitted Not permitted 24 130 For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m. a. Developed length plus an appropriate allowance for entrance losses and friction due to fittings, changes in direction and diameter. Suggested allowances shall be obtained from NBS Monograph 31 or other approved sources. An allowance of 50 percent of the developed length shall be assumed if a more precise value is not available. b. Actual values greater than 500 feet. c. Less than 10 feet.
906.5.2 Pneumatic sewage ejectors.
The air pressure relief pipe from a pneumatic sewage ejector shall be connected to an independent vent stack terminating as required for vent extensions through the roof. The relief pipe shall be sized to relieve air pressure inside the ejector to atmospheric pressure, but shall not be less than 11/4 inches (32 mm) in size.
VENTS FOR STACK OFFSETS
907.1 Vent for horizontal offset of drainage stack.
Horizontal offsets of drainage stacks shall be vented where five or more branch intervals are located above the offset. The offset shall be vented by venting the upper section of the drainage stack and the lower section of the drainage stack.
907.2 Upper section.
The upper section of the drainage stack shall be vented as a separate stack with a vent stack connection installed in accordance with Section 904.4. The offset shall be considered the base of the stack.
907.3 Lower section.
The lower section of the drainage stack shall be vented by a yoke vent connecting between the offset and the next lower horizontal branch. The yoke vent connection shall be permitted to be a vertical extension of the drainage stack. The size of the yoke vent and connection shall be a minimum of the size required for the vent stack of the drainage stack.
RELIEF VENTS—STACKS OF MORE THAN 10
908.1 Where required.
Soil and waste stacks in buildings having more than 10 branch intervals shall be provided with a relief vent at each tenth interval installed, beginning with the top floor.
908.2 Size and connection.
The size of the relief vent shall be equal to the size of the vent stack to which it connects. The lower end of each relief vent shall connect to the soil or waste stack through a wye below the horizontal branch serving the floor, and the upper end shall connect to the vent stack through a wye not less than 3 feet (914 mm) above the floor.
909.1 Distance of trap from vent.
Each fixture trap shall have a protecting vent located so that the slope and the developed length in the fixture drain from the trap weir to the vent fitting are within the requirements set forth in Table 909.1.
Exception: The developed length of the fixture drain from the trap weir to the vent fitting for self-siphoning fixtures, such as water closets, shall not be limited.
MAXIMUM DISTANCE OF FIXTURE TRAP FROM VENT
SIZE OF TRAP
(inch per foot)
DISTANCE FROM TRAP
11/4 1/4 5 11/2 1/4 6 2 1/4 8 3 1/8 12 4 1/8 16 For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 inch per foot = 83.3 mm/m
909.2 Venting of fixture drains.
The total fall in a fixture drain due to pipe slope shall not exceed the diameter of the fixture drain, nor shall the vent connection to a fixture drain, except for water closets, be below the weir of the trap.
909.3 Crown vent.
A vent shall not be installed within two pipe diameters of the trap weir.
910.1 Individual vent permitted.
Each trap and trapped fixture is permitted to be provided with an individual vent. The individual vent shall connect to the fixture drain of the trap or trapped fixture being vented.
911.1 Individual vent as common vent.
An individual vent is permitted to vent two traps or trapped fixtures as a common vent. The traps or trapped fixtures being common vented shall be located on the same floor level.
911.2 Connection at the same level.
Where the fixture drains being common vented connect at the same level, the vent connection shall be at the interconnection of the fixture drains or downstream of the interconnection.
911.3 Connection at different levels.
Where the fixture drains connect at different levels, the vent shall connect as a vertical extension of the vertical drain. The vertical drain pipe connecting the two fixture drains shall be considered the vent for the lower fixture drain, and shall be sized in accordance with Table 911.3. The upper fixture shall not be a water closet.
COMMON VENT SIZES
MAXIMUM DISCHARGE FROM UPPER
FIXTURE DRAIN (dfu)
11/2 1 2 4 21/2 to 3 6 For SI: 1 inch = 25.4 mm.
912.1 Horizontal wet vent permitted.
Any combination of fixtures within two bathroom groups located on the same floor level is permitted to be vented by a horizontal wet vent. The wet vent shall be considered the vent for the fixtures and shall extend from the connection of the dry vent along the direction of the flow in the drain pipe to the most downstream fixture drain connection to the horizontal branch drain. Each wet-vented fixture drain shall connect independently to the horizontal wet vent. Only the fixtures within the bathroom groups shall connect to the wet-vented horizontal branch drain. Any additional fixtures shall discharge downstream of the horizontal wet vent.
912.1.1 Vertical wet vent permitted.
Any combination of fixtures within two bathroom groups located on the same floor level is permitted to be vented by a vertical wet vent. The vertical wet vent shall be considered the vent for the fixtures and shall extend from the connection of the dry vent down to the lowest fixture drain connection. Each wet-vented fixture shall connect independently to the vertical wet vent. Water closet drains shall connect at the same elevation. Other fixture drains shall connect above or at the same elevation as the water closet fixture drains. The dry-vent connection to the vertical wet vent shall be an individual or common vent serving one or two fixtures.
912.2.1 Horizontal wet vent.
The dry-vent connection for a horizontal wet-vent system shall be an individual vent or a common vent for any bathroom group fixture, except an emergency floor drain. Where the dry-vent connects to a water closet fixture drain, the drain shall connect horizontally to the horizontal wet-vent system. Not more than one wet-vented fixture drain shall discharge upstream of the dry-vented fixture drain connection.
912.2.2 Vertical wet vent.
The dry-vent connection for a vertical wet-vent system shall be an individual vent or common vent for the most upstream fixture drain.
The dry vent serving the wet vent shall be sized based on the largest required diameter of pipe within the wet-vent system served by the dry vent. The wet vent shall be of a size not less than that specified in Table 912.3, based on the fixture unit discharge to the wet vent.
WET VENT SIZE
WET VENT PIPE SIZE
DRAINAGE FIXTURE UNIT LOAD (dfu) 11/2 1 2 4 21/2 6 3 12 For SI: 1 inch = 25.4 mm.
WASTE STACK VENT
913.1 Waste stack vent permitted.
A waste stack shall be considered a vent for all of the fixtures discharging to the stack where installed in accordance with the requirements of this section.
913.2 Stack installation.
The waste stack shall be vertical, and both horizontal and vertical offsets shall be prohibited between the lowest fixture drain connection and the highest fixture drain connection. Fixture drains shall connect separately to the waste stack. The stack shall not receive the discharge of water closets or urinals.
913.3 Stack vent.
A stack vent shall be provided for the waste stack. The size of the stack vent shall be not less than the size of the waste stack. Offsets shall be permitted in the stack vent, shall be located not less than 6 inches (152 mm) above the flood level of the highest fixture and shall be in accordance with Section 905.2. The stack vent shall be permitted to connect with other stack vents and vent stacks in accordance with Section 904.5.
913.4 Waste stack size.
The waste stack shall be sized based on the total discharge to the stack and the discharge within a branch interval in accordance with Table 913.4. The waste stack shall be the same size throughout its length.
WASTE STACK VENT SIZE
MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS
Total discharge into one
Total discharge for
11/2 1 2 2 2 4 21/2 No limit 8 3 No limit 24 4 No limit 50 5 No limit 75 6 No limit 100 For SI: 1 inch = 25.4 mm.
914.1 Circuit vent permitted.
A maximum of eight fixtures connected to a horizontal branch drain shall be permitted to be circuit vented. Each fixture drain shall connect horizontally to the horizontal branch being circuit vented. The horizontal branch drain shall be classified as a vent from the most downstream fixture drain connection to the most upstream fixture drain connection to the horizontal branch.
914.1.1 Multiple circuit-vented branches.
Circuit-vented horizontal branch drains are permitted to be connected together. Each group of a maximum of eight fixtures shall be considered a separate circuit vent and shall conform to the requirements of this section.
914.2 Vent connection.
The circuit vent connection shall be located between the two most upstream fixture drains. The vent shall connect to the horizontal branch and shall be installed in accordance with Section 905. The circuit vent pipe shall not receive the discharge of any soil or waste.
914.3 Slope and size of horizontal branch.
The slope of the vent section of the horizontal branch drain shall be not greater than one unit vertical in 12 units horizontal (8.3-percent slope). The entire length of the vent section of the horizontal branch drain shall be sized for the total drainage discharge to the branch.
914.3.1 Size of multiple circuit vent.
Each separate circuit-vented horizontal branch that is interconnected shall be sized independently in accordance with Section 914.3. The downstream circuit-vented horizontal branch shall be sized for the total discharge into the branch, including the upstream branches and the fixtures within the branch.
914.4 Relief vent.
A relief vent shall be provided for circuit-vented horizontal branches receiving the discharge of four or more water closets and connecting to a drainage stack that receives the discharge of soil or waste from upper horizontal branches.
914.4.1 Connection and installation.
The relief vent shall connect to the horizontal branch drain between the stack and the most downstream fixture drain of the circuit vent. The relief vent shall be installed in accordance with Section 905.
914.4.2 Fixture drain or branch.
The relief vent is permitted to be a fixture drain or fixture branch for fixtures located within the same branch interval as the circuit-vented horizontal branch. The maximum discharge to a relief vent shall be four fixture units.
914.5 Additional fixtures.
Fixtures, other than the circuit-vented fixtures, are permitted to discharge to the horizontal branch drain. Such fixtures shall be located on the same floor as the circuit-vented fixtures and shall be either individually or common vented.
COMBINATION WASTE AND VENT SYSTEM
915.1 Type of fixtures.
A combination waste and vent system shall not serve fixtures other than floor drains, sinks, lavatories and drinking fountains. Combination waste and vent systems shall not receive the discharge from a food waste grinder or clinical sink.
The only vertical pipe of a combination waste and vent system shall be the connection between the fixture drain and the horizontal combination waste and vent pipe. The vertical distance shall not exceed 8 feet (2438 mm).
The slope of a horizontal combination waste and vent pipe shall not exceed one-half unit vertical in 12 units horizontal (4-percent slope) and shall not be less than that indicated in Table 704.1.
915.2.2 Size and length.
The size of a combination waste and vent pipe shall not be less than that indicated in Table 915.2.2. The horizontal length of a combination waste and vent pipe shall be unlimited.
SIZE OF COMBINATION WASTE AND VENT PIPE
MAXIMUM NUMBER OF DRAINAGE
FIXTURE UNITS (dfu)
Connecting to a horizontal
branch or stack
Connecting to a building
drain or building subdrain
2 3 4 21/2 6 26 3 12 31 4 20 50 5 160 250 6 360 575 For SI: 1 inch = 25.4 mm.
The combination waste and vent system shall be provided with a dry vent connected at any point within the system or the system shall connect to a horizontal drain that is vented in accordance with one of the venting methods specified in this chapter. Combination waste and vent systems connecting to building drains receiving only the discharge from a stack or stacks shall be provided with a dry vent. The vent connection to the combination waste and vent pipe shall extend vertically to a point not less than 6 inches (152 mm) above the flood level rim of the highest fixture being vented before offsetting horizontally.
915.2.4 Vent size.
The vent shall be sized for the total drainage fixture unit load in accordance with Section 906.2.
915.2.5 Fixture branch or drain.
The fixture branch or fixture drain shall connect to the combination waste and vent within a distance specified in Table 909.1. The combination waste and vent pipe shall be considered the vent for the fixture.
ISLAND FIXTURE VENTING
Island fixture venting shall not be permitted for fixtures other than sinks and lavatories. Residential kitchen sinks with a dishwasher waste connection, a food waste grinder, or both, in combination with the kitchen sink waste, shall be permitted to be vented in accordance with this section.
916.2 Vent connection.
The island fixture vent shall connect to the fixture drain as required for an individual or common vent. The vent shall rise vertically to above the drainage outlet of the fixture being vented before offsetting horizontally or vertically downward. The vent or branch vent for multiple island fixture vents shall extend to a point not less than 6 inches (152 mm) above the highest island fixture being vented before connecting to the outside vent terminal.
916.3 Vent installation below the fixture flood level rim.
The vent located below the flood level rim of the fixture being vented shall be installed as required for drainage piping in accordance with Chapter 7, except for sizing. The vent shall be sized in accordance with Section 906.2. The lowest point of the island fixture vent shall connect full size to the drainage system. The connection shall be to a vertical drain pipe or to the top half of a horizontal drain pipe. Cleanouts shall be provided in the island fixture vent to permit rodding of all vent piping located below the flood level rim of the fixtures. Rodding in both directions shall be permitted through a cleanout.
SINGLE STACK VENT SYSTEM
917.1 Where permitted.
A drainage stack shall serve as a single stack vent system where sized and installed in accordance with Sections 917.2 through 917.9. The drainage stack and branch piping shall be the vents for the drainage system. The drainage stack shall have a stack vent.
917.2 Stack size.
Drainage stacks shall be sized in accordance with Table 917.2. Stacks shall be uniformly sized based on the total connected drainage fixture unit load. The stack vent shall be the same size as the drainage stack. A 3-inch (76 mm) stack shall serve not more than two water closets.
SINGLE STACK SIZE
MAXIMUM CONNECTED DRAINAGE FIXTURE UNITS Stacks less than
75 feet in height
Stacks 75 feet to
less than 160 feet
Stacks 160 feet
and greater in
3 24 NP NP 4 225 24 NP 5 480 225 24 6 1,015 480 225 8 2,320 1,015 480 10 4,500 2,320 1,015 12 8,100 4,500 2,320 15 13,600 8,100 4,500 For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
917.3 Branch size.
Horizontal branches connecting to a single stack vent system shall be sized in accordance with Table 710.1(2). Not more than one water closet shall discharge into a 3-inch (76 mm) horizontal branch at a point within a developed length of 18 inches (457 mm) measured horizontally from the stack.
Where a water closet is within 18 inches (457 mm) measured horizontally from the stack and not more than one fixture with a drain size of not more than 11/2 inch (38 mm) connects to a 3-inch (76 mm) horizontal branch, the branch drain connection to the stack shall be made with a sanitary tee.
917.4.1 Water closet connection.
Water closet connections shall be not greater than 4 feet (1219 mm) in developed length measured horizontally from the stack.
Exception: Where the connection is made with a sanitary tee, the maximum developed length shall be 8 feet (2438 mm).
917.4.2 Fixture connections.
Fixtures other than water closets shall be located not greater than 12 feet (3657 mm) in developed length, measured horizontally from the stack.
917.4.3 Vertical piping in branch.
The length of vertical piping in a fixture drain connecting to a horizontal branch shall not be considered in computing the fixture’s distance in developed length measured horizontally from the stack.
917.5 Minimum vertical piping size from fixture.
The vertical portion of piping in a fixture drain to a horizontal branch shall be 2 inches (51 mm). The minimum size of the vertical portion of piping for a water-supplied urinal or standpipe shall be 3 inches (76 mm). The maximum vertical drop shall be 4 feet (1219 mm). Fixture drains that are not increased in size, or have a vertical drop in excess of 4 feet (1219 mm) shall be individually vented.
917.6 Additional venting required.
Additional venting shall be provided where more than one water closet discharges to a horizontal branch and where the distance from a fixture trap to the stack exceeds the limits in Section 917.4. Where additional venting is required, the fixture(s) shall be vented by individual vents, common vents, wet vents, circuit vents, or a combination waste and vent pipe. The dry vent extensions for the additional venting shall connect to a branch vent, vent stack, stack vent, air admittance valve, or shall terminate outdoors.
917.7 Stack offsets.
Where fixture drains are not connected below a horizontal offset in a stack, a horizontal offset shall not be required to be vented. Where horizontal branches or fixture drains are connected below a horizontal offset in a stack, the offset shall be vented in accordance with Section 907. Fixture connections shall not be made to a stack within 2 feet (610 mm) above or below a horizontal offset.
917.8 Prohibited lower connections.
Stacks greater than 2 branch intervals in height shall not receive the discharge of horizontal branches on the lower two floors. There shall be no connections to the stack between the lower two floors and a distance of not less than 10 pipe diameters downstream from the base of the single stack vented system.
917.9 Sizing building drains and sewers.
The building drain and building sewer receiving the discharge of a single stack vent system shall be sized in accordance with Table 710.1(1).
AIR ADMITTANCE VALVES
Vent systems utilizing air admittance valves shall comply with this section. Stack-type air admittance valves shall conform to ASSE 1050. Individual and branch-type air admittance valves shall conform to ASSE 1051.
The valves shall be installed in accordance with the requirements of this section and the manufacturer’s installation instructions. Air admittance valves shall be installed after the DWV testing required by Section 312.2 or 312.3 has been performed.
918.3 Where permitted.
Individual, branch and circuit vents shall be permitted to terminate with a connection to an individual or branch-type air admittance valve in accordance with Section 918.3.1. Stack vents and vent stacks shall be permitted to terminate to stack-type air admittance valves in accordance with Section 918.3.2.
918.3.1 Horizontal branches.
Individual and branch-type air admittance valves shall vent only fixtures that are on the same floor level and connect to a horizontal branch drain. Where the horizontal branch is located more than four branch intervals from the top of the stack, the horizontal branch shall be provided with a relief vent that shall connect to a vent stack or stack vent, or extend outdoors to the open air. The relief vent shall connect to the horizontal branch drain between the stack and the most downstream fixture drain connected to the horizontal branch drain. The relief vent shall be sized in accordance with Section 906.2 and installed in accordance with Section 905. The relief vent shall be permitted to serve as the vent for other fixtures.
Stack-type air admittance valves shall be prohibited from serving as the vent terminal for vent stacks or stack vents that serve drainage stacks having more than six branch intervals.
Individual and branch-type air admittance valves shall be located a minimum of 4 inches (102 mm) above the horizontal branch drain or fixture drain being vented. Stack-type air admittance valves shall be located not less than 6 inches (152 mm) above the flood level rim of the highest fixture being vented. The air admittance valve shall be located within the maximum developed length permitted for the vent. The air admittance valve shall be installed not less than 6 inches (152 mm) above insulation materials.
918.5 Access and ventilation.
Access shall be provided to all air admittance valves. The valve shall be located within a ventilated space that allows air to enter the valve.
The air admittance valve shall be rated in accordance with the standard for the size of the vent to which the valve is connected.
918.7 Vent required.
Within each plumbing system, not less than one stack vent or vent stack shall extend outdoors to the open air.
918.8 Prohibited installations.
Air admittance valves shall not be installed in non-neutralized special waste systems as described in Chapter 8 except where such valves are in compliance with ASSE 1049, are constructed of materials approved in accordance with Section 702.5 and are tested for chemical resistance in accordance with ASTM F 1412. Air admittance valves shall not be located in spaces utilized as supply or return air plenums.
ENGINEERED VENT SYSTEMS
Engineered vent systems shall comply with this section and the design, submittal, approval, inspection and testing requirements of Section 105.4.
919.2 Individual branch fixture and individual fixture header vents.
The maximum developed length of individual fixture vents to vent branches and vent headers shall be determined in accordance with Table 919.2 for the minimum pipe diameters at the indicated vent airflow rates.
The individual vent airflow rate shall be determined in accordance with the following:
Qh,b = Nn, b Qν (Equation 9-1) For SI: Qh,b = Nn, b Qν (0.4719 L/s)
Nn, b = Number of fixtures per header (or vent branch) ÷ total number of fixtures connected to vent stack. Qh, b = Vent branch or vent header airflow rate (cfm). Qν = Total vent stack airflow rate (cfm). Qν(gpm) = 27.8 rs2/3 (1 – rs) D8/3 Qν(cfm) = 0.134 Qν(gpm)
D = Drainage stack diameter (inches). Qw = Design discharge load (gpm). rs = Waste water flow area to total area.
Individual vent airflow rates are obtained by equally distributing Qh,b into one-half the total number of fixtures on the branch or header for more than two fixtures; for an odd number of total fixtures, decrease by one; for one fixture, apply the full value of Qh,b.
Individual vent developed length shall be increased by 20 percent of the distance from the vent stack to the fixture vent connection on the vent branch or header.
MINIMUM DIAMETER AND MAXIMUM LENGTH OF INDIVIDUAL BRANCH FIXTURE VENTS AND
INDIVIDUAL FIXTURE HEADER VENTS FOR SMOOTH PIPES
INDIVIDUAL VENT AIRFLOW RATE (cubic feet per minute) Maximum developed length of vent (feet) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1/2 95 25 13 8 5 4 3 2 1 1 1 1 1 1 1 1 1 1 1 1 3/4 100 88 47 30 20 15 10 9 7 6 5 4 3 3 3 2 2 2 2 1 1 — — 100 94 65 48 37 29 24 20 17 14 12 11 9 8 7 7 6 6 11/4 — — — — — — — 100 87 73 62 53 46 40 36 32 29 26 23 21 11/2 — — — — — — — — — — — 100 96 84 75 65 60 54 49 45 2 — — — — — — — — — — — — — — — — — — — 100 For SI: 1 inch = 25.4 mm, 1 cubic foot per minute = 0.4719 L/s, 1 foot = 304.8 mm.
COMPUTERIZED VENT DESIGN
920.1 Design of vent system.
The sizing, design and layout of the vent system shall be permitted to be determined by approved computer program design methods.
920.2 System capacity.
The vent system shall be based on the air capacity requirements of the drainage system under a peak load condition.