Vents

Vents and Venting

Reference text for the venting area. Every rule below is written from the printed line of the

2024 International Plumbing Code (IPC 2024) that carries it, and each rule names the section it comes

from. Where the printed line does not state a value, no value is stated here.

1. General

The chapter governs the materials, design, construction and installation of vent systems (IPC 2024,

901.1). The plumbing system must be provided with a system of vent piping that permits the admission

or emission of air so that the seal of any fixture trap is not subjected to a pressure differential of

more than 1 inch of water column (249 Pa) (IPC 2024, 901.2), and traps and trapped fixtures must be

vented in accordance with one of the venting methods specified in the chapter (IPC 2024, 901.2.1).

The purpose stated by the code for the whole chapter: the proper operation of a gravity flow drainage

system depends on maintaining an air path throughout the system, to prevent waste and odor blow back

into fixtures and siphoning of the trap seal in fixture traps (IPC 2024, Chapter 9, About this

chapter).

The vent system for a chemical waste drainage system must be independent of any sanitary drainage vent

system; its termination must be through the roof to the outdoors or to an air admittance valve

complying with ASSE 1049, and air admittance valves for chemical waste drainage systems must be

constructed of one of the materials indicated in Table 702.6 and be tested for chemical resistance in

accordance with ASTM F1412 (IPC 2024, 901.3). The plumbing vent system must not be used for purposes

other than the venting of the plumbing system (IPC 2024, 901.4). The vent system is tested in

accordance with Section 312 (IPC 2024, 901.5), and engineered venting systems must conform to

Section 919 (IPC 2024, 901.6).

2. Materials

Materials and methods for venting systems comply with the applicable provisions of Section 702

(IPC 2024, 902.1). For a chemical waste drainage vent system, pipe and fitting materials follow

Section 702.6 and the construction and installation methods follow the pipe and fitting manufacturer's

instructions (IPC 2024, 902.1.1).

Flashing materials carry their own weights: sheet copper for vent pipe flashings must conform to

ASTM B152 and weigh not less than 8 ounces per square foot (2.5 kg/m²) (IPC 2024, 902.2), and sheet

lead for vent pipe flashings must weigh not less than 3 pounds per square foot (15 kg/m²) for

field-constructed flashings and not less than 2 1/2 pounds per square foot (12 kg/m²) for

prefabricated flashings (IPC 2024, 902.3).

3. Vent terminals

The vent pipe must terminate by extending to the outdoors through the roof or the side wall in

accordance with one of the methods of Sections 903.1.1 through 903.1.4 (IPC 2024, 903.1).

this document does not carry a numeric height on that line (IPC 2024, 903.1.1).

deck, or for similar purposes, open vent pipes must terminate not less than 7 feet (2134 mm) above

the roof (IPC 2024, 903.1.2).

(such as a solar collector or photovoltaic panel mounted over the vent opening) or a roof element

(such as an architectural feature or a decorative shroud), the vent pipe must terminate not less

than 2 inches (51 mm) above the roof surface. Such roof elements must be designed to prevent the

adverse effects of snow accumulation and wind on the function of the vent. The placement of a panel

over a vent pipe, and the design of a roof element covering it, must provide an open area for the

vent pipe to the outdoors not less than the area of the pipe as calculated from the inside diameter

of the pipe, and such vent terminals must be protected by a method that prevents birds and rodents

from entering or blocking the vent pipe opening (IPC 2024, 903.1.3).

line and 10 feet (3048 mm) above the highest adjacent grade within 10 feet (3048 mm) horizontally of

the vent terminal. They must not terminate under the overhang of a structure with soffit vents, and

sidewall vent terminals must be protected to prevent birds and rodents from entering or blocking the

vent opening (IPC 2024, 903.1.4).

Frost closure and cold climate: where the 97.5 percent value for outdoor design temperature is 0°F

(-18°C) or less, vent extensions through a roof or wall must be not less than 3 inches (76 mm) in

diameter, and any increase in the size of the vent must be made not less than 1 foot (305 mm) inside

the thermal envelope of the building (IPC 2024, 903.2). 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 must be protected against freezing by insulation, heat or both (IPC 2024, 903.6).

The juncture of each vent pipe with the roof line must be made watertight by an approved flashing

(IPC 2024, 903.3), and a vent terminal must not be used for any purpose other than a vent terminal

(IPC 2024, 903.4).

Location: an open vent terminal from a drainage system must not be located directly beneath any door,

openable window, or other air intake opening of the building or of an adjacent building, and such a

vent terminal must 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 that opening (IPC 2024, 903.5).

4. Outdoor vent extensions

The vent system serving each building drain must have not less than one vent pipe that extends to the

outdoors (IPC 2024, 904.1). That required vent must be a dry vent connecting to the building drain or

to an extension of a drain that connects to the building drain, and must not be an island fixture vent

as allowed by Section 916 (IPC 2024, 904.1.1). It must be sized in accordance with Section 906.2

based on the required size of the building drain (IPC 2024, 904.1.2).

A vent stack is required for every drainage stack that has five branch intervals or more, except for

drainage stacks installed in accordance with Section 913 (IPC 2024, 904.2). Vent stacks or stack vents

must terminate outdoors to the open air or to a stack-type air admittance valve in accordance with

Section 918 (IPC 2024, 904.3). Vent stacks must connect to the base of the drainage stack, at or below

the lowest horizontal branch; where the vent stack connects to the building drain, the connection must

be located downstream of the drainage stack and within a distance of 10 times the diameter of the

drainage stack (IPC 2024, 904.4).

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 must be sized in accordance with Section 906.1, with the number of

fixture units equal to the sum of all fixture units on all stacks connected to the header, and the

developed length equal to 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 (IPC 2024,

904.5).

5. Vent connections and grades

Individual, branch and circuit vents must connect to a vent stack, stack vent, air admittance valve or

extend to the open air (IPC 2024, 905.1). Vent and branch vent pipes must be graded and connected so

as to drain back to the drainage pipe by gravity (IPC 2024, 905.2). Every dry vent connecting to a

horizontal drain must connect above the centerline of the horizontal drain pipe (IPC 2024, 905.3).

Every dry vent must 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 (IPC 2024, 905.4); the exception is vents for

interceptors located outdoors. A connection between a vent pipe and a vent stack or stack vent must be

made at not less than 6 inches (152 mm) above the flood level rim of the highest fixture served by the

vent, and horizontal vent pipes forming branch vents, relief vents or loop vents must be located not

less than 6 inches (152 mm) above the flood level rim of the highest fixture served (IPC 2024, 905.5).

Where drainage piping has been roughed-in for future fixtures, a rough-in connection for a vent must

be installed, of a size not less than one-half the diameter of the rough-in drain to be served; the

vent rough-in must connect to the vent system or be vented by other means provided for in the chapter,

and the connection must be identified to indicate that it is a vent (IPC 2024, 905.6).

6. Vent pipe sizing

6.1 Stack vents and vent stacks

The minimum required diameter of stack vents and vent stacks is determined from the developed length

and the total drainage fixture units connected to them in accordance with Table 906.1; in no case

may the diameter be less than one-half the diameter of the drain served, or less than 1 1/4 inches

(32 mm) (IPC 2024, 906.1). Table 906.1 is a grid of maximum developed length of vent per soil or waste

stack diameter, total fixture units being vented and vent diameter; the value is read at the

intersection of those conditions (IPC 2024, Table 906.1).

6.2 Vents other than stack vents or vent stacks

The diameter of individual vents, branch vents, circuit vents and relief vents must be not less than

one-half the required diameter of the drain served, with the required size of the drain determined in

accordance with Table 710.1(2). Vent pipes must be not less than 1 1/4 inches (32 mm) in diameter.

Vents exceeding 40 feet (12 192 mm) in developed length must be increased by one nominal pipe size for

the entire developed length of the vent pipe, and relief vents for soil and waste stacks in buildings

having more than 10 branch intervals are sized in accordance with Section 908.2 (IPC 2024, 906.2).

The developed length of individual, branch, circuit and relief vents is 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 (IPC 2024, 906.3). Where multiple branch vents are

connected to a common branch vent, the common branch vent must be sized on the basis of the size of

the common horizontal drainage branch that is, or would be, required to serve the total drainage

fixture unit load being vented (IPC 2024, 906.4).

Sump vents: drainage piping below sewer level must be vented in the same manner as that of a gravity

system, and building sump vent sizes for sumps with sewage pumps or sewage ejectors, other than

pneumatic, are determined in accordance with Table 906.5.1 (IPC 2024, 906.5.1).

7. Vents for stack offsets and relief vents

Horizontal offsets of drainage stacks must be vented where five or more branch intervals are located

above the offset; the offset is vented by venting the upper section and the lower section of the

drainage stack (IPC 2024, 907.1). The upper section must be vented as a separate stack with a vent

stack connection installed in accordance with Section 904.4, and the offset is considered to be the

base of the stack (IPC 2024, 907.2). The lower section must be vented by a yoke vent connecting

between the offset and the next lower horizontal branch; the yoke vent connection may be a vertical

extension of the drainage stack, and the size of the yoke vent and connection must be not less than

the size required for the vent stack of the drainage stack (IPC 2024, 907.3).

Soil and waste stacks in buildings having more than 10 branch intervals must be provided with a relief

vent at each tenth interval installed, beginning with the top floor (IPC 2024, 908.1). The size of the

relief vent must be equal to the size of the vent stack to which it connects; the lower end of each

relief vent must connect to the soil or waste stack through a wye below the horizontal branch serving

the floor, and the upper end must connect to the vent stack through a wye not less than 3 feet

(914 mm) above the floor (IPC 2024, 908.2).

8. Fixture vents

Each fixture trap must 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 of Table 909.1;

the developed length of the fixture drain from the trap weir to the vent fitting is not limited for

self-siphoning fixtures, such as water closets (IPC 2024, 909.1 and Exception).

The total fall in a fixture drain due to pipe slope must not exceed the diameter of the fixture drain,

and the vent connection to a fixture drain, except for water closets, must not be below the weir of

the trap (IPC 2024, 909.2). A vent must not be installed within two pipe diameters of the trap weir

(IPC 2024, 909.3).

9. Individual and common vents

Each trap and trapped fixture may be provided with an individual vent, which must connect to the

fixture drain of the trap or trapped fixture being vented (IPC 2024, 910.1). An individual vent may

vent two traps or trapped fixtures as a common vent, provided the traps or trapped fixtures being

common vented are located on the same floor level (IPC 2024, 911.1). Where the fixture drains being

common vented connect at the same level, the vent connection must be at the interconnection of the

fixture drains or downstream of the interconnection (IPC 2024, 911.2). Where the fixture drains

connect at different levels, the vent must connect as a vertical extension of the vertical drain; the

vertical drain pipe connecting the two fixture drains is considered to be the vent for the lower

fixture drain and must be sized in accordance with Table 911.3, and the upper fixture must not be a

water closet (IPC 2024, 911.3).

10. Wet venting

Any combination of fixtures within two bathroom groups located on the same floor level may be vented

by a horizontal wet vent. The wet vent is considered to be the vent for the fixtures and must 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 must

connect independently to the horizontal wet vent; only the fixtures within the bathroom groups may

connect to the wet-vented horizontal branch drain, and any additional fixtures must discharge

downstream of the horizontal wet vent (IPC 2024, 912.1).

Any combination of fixtures within two bathroom groups on the same floor level may also be vented by a

vertical wet vent, which extends from the connection of the dry vent down to the lowest fixture drain

connection, each wet-vented fixture connecting independently. Water closet drains must connect at the

same elevation, other fixture drains must connect above or at the same elevation as the water closet

fixture drains, and the dry-vent connection to the vertical wet vent must be an individual or common

vent serving one or two fixtures (IPC 2024, 912.1.1).

The dry-vent connection for a horizontal wet-vent system must 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 must connect horizontally to the horizontal wet-vent system, and

not more than one wet-vented fixture drain may discharge upstream of the dry-vented fixture drain

connection (IPC 2024, 912.2.1). For a vertical wet-vent system, the dry-vent connection must be an

individual vent or common vent for the most upstream fixture drain (IPC 2024, 912.2.2).

The dry vent serving the wet vent must be sized on the basis of the largest required diameter of pipe

within the wet-vent system served by the dry vent, and the wet vent must be of a size not less than

Table 912.3 specifies, based on the fixture unit discharge to the wet vent (IPC 2024, 912.3).

11. Waste stack vent

A waste stack is considered to be a vent for all of the fixtures discharging to the stack where

installed in accordance with Section 913 (IPC 2024, 913.1). The waste stack must be vertical, and both

horizontal and vertical offsets are prohibited between the lowest fixture drain connection and the

highest fixture drain connection; fixture drains must connect separately to the waste stack, and the

stack must not receive the discharge of water closets or urinals (IPC 2024, 913.2).

A stack vent must be provided for the waste stack, of a size not less than the size of the waste

stack. Offsets are permitted in the stack vent, must be located not less than 6 inches (152 mm) above

the flood level of the highest fixture and must be in accordance with Section 905.2; the stack vent

may connect with other stack vents and vent stacks in accordance with Section 904.5 (IPC 2024, 913.3).

The waste stack must be sized on the basis of the total discharge to the stack and the discharge

within a branch interval in accordance with Table 913.4, and must be the same size throughout its

length (IPC 2024, 913.4).

12. Circuit venting

Not more than eight fixtures connected to a horizontal branch drain may be circuit vented. Each

fixture drain must connect horizontally to the horizontal branch being circuit vented, and the

horizontal branch drain is classified as a vent from the most downstream fixture drain connection to

the most upstream fixture drain connection to the horizontal branch (IPC 2024, 914.1). Circuit-vented

horizontal branch drains may be connected together, each group of not more than eight fixtures being

considered a separate circuit vent conforming to the section (IPC 2024, 914.1.1).

The circuit vent connection must be located between the two most upstream fixture drains; the vent

must connect to the horizontal branch and be installed in accordance with Section 905, and the circuit

vent pipe must not receive the discharge of any soil or waste (IPC 2024, 914.2). The slope of the vent

section of the horizontal branch drain must be not greater than one unit vertical in 12 units

horizontal (8.3 percent slope), and the entire length of the vent section of the horizontal branch

drain must be sized for the total drainage discharge to the branch (IPC 2024, 914.3). Each separate

circuit-vented horizontal branch that is interconnected must be sized independently, and the

downstream circuit-vented horizontal branch must be sized for the total discharge into the branch,

including the upstream branches and the fixtures within the branch (IPC 2024, 914.3.1).

A relief vent must 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 (IPC 2024, 914.4). The relief vent must connect to the horizontal

branch drain between the stack and the most downstream fixture drain of the circuit vent, and be

installed in accordance with Section 905 (IPC 2024, 914.4.1); it may be a fixture drain or fixture

branch for fixtures located within the same branch interval as the circuit-vented horizontal branch,

and the maximum discharge to a relief vent is four fixture units (IPC 2024, 914.4.2). Fixtures other

than the circuit-vented fixtures may discharge to the horizontal branch drain, provided they are

located on the same floor as the circuit-vented fixtures and are either individually or common vented

(IPC 2024, 914.5).

13. Combination waste and vent system

A combination waste and vent system must not serve fixtures other than floor drains, sinks, lavatories

and drinking fountains, and must not receive the discharge from a clinical sink (IPC 2024, 915.1). The

only vertical pipe of the system is the connection between the fixture drain and the horizontal

combination waste and vent pipe, and that vertical distance must not exceed 8 feet (2438 mm)

(IPC 2024, 915.2). The slope of a horizontal combination waste and vent pipe must not exceed one-half

unit vertical in 12 units horizontal (4 percent slope) and must be not less than Table 704.1

indicates (IPC 2024, 915.2.1).

The size of a combination waste and vent pipe must be not less than Table 915.2.2 indicates, and the

horizontal length of the system is unlimited (IPC 2024, 915.2.2):

The system must be provided with a dry vent connected at any point within the system, or must connect

to a horizontal drain that serves vented fixtures located on the same floor; combination waste and

vent systems connecting to building drains receiving only the discharge from one or more stacks must

be provided with a dry vent. The vent connection to the combination waste and vent pipe must 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 (IPC 2024, 915.2.3). The vent must be sized for the total

drainage fixture unit load in accordance with Section 906.2 (IPC 2024, 915.2.4), and the fixture

branch or drain must connect to the combination waste and vent within a distance specified in

Table 909.1, the combination waste and vent pipe being considered to be the vent for the fixture

(IPC 2024, 915.2.5).

14. Island fixture venting

Island fixture venting is not permitted for fixtures other than sinks and lavatories; residential

kitchen sinks with a dishwasher waste connection, a food waste disposer, or both, in combination with

the kitchen sink waste, may be vented in accordance with Section 916 (IPC 2024, 916.1). The island

fixture vent must connect to the fixture drain as required for an individual or common vent; it must

rise vertically to above the drainage outlet of the fixture being vented before offsetting horizontally

or vertically downward, and the vent or branch vent for multiple island fixture vents must 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 (IPC 2024, 916.2).

The part of the vent located below the flood level rim of the fixture being vented must be installed

as required for drainage piping in accordance with Chapter 7, except for sizing: it is sized in

accordance with Section 906.2, its lowest point must connect full size to the drainage system, and the

connection must be to a vertical drain pipe or to the top half of a horizontal drain pipe. Cleanouts

must be provided in the island fixture vent to permit rodding of all vent piping located below the

flood level rim of the fixtures, and rodding in both directions must be permitted through a cleanout

(IPC 2024, 916.3).

15. Single-stack vent system

A drainage stack serves 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 are the vents for the drainage

system, and the drainage stack must have a stack vent (IPC 2024, 917.1). Drainage stacks must be sized

in accordance with Table 917.2, uniformly sized on the basis of the total connected drainage fixture

unit load; the stack vent must be the same size as the drainage stack, and a 3-inch (76 mm) stack

serves not more than two water closets (IPC 2024, 917.2).

NP = not permitted (IPC 2024, Table 917.2).

Horizontal branches connecting to a single-stack vent system must be sized in accordance with

Table 710.1(2); not more than one water closet may 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, and

where a water closet is within 18 inches measured horizontally from the stack and not more than one

fixture with a drain size of not more than 1 1/2 inches (38 mm) connects to a 3-inch horizontal

branch, the branch drain connection to the stack must be made with a sanitary tee (IPC 2024, 917.3).

Length of horizontal branches: water closet connections must be not greater than 4 feet (1219 mm) in

developed length measured horizontally from the stack, or 8 feet (2438 mm) where the connection is

made with a sanitary tee (IPC 2024, 917.4.1 and Exception); fixtures other than water closets must be

located not greater than 12 feet (3657 mm) in developed length, measured horizontally from the stack

(IPC 2024, 917.4.2); and the length of vertical piping in a fixture drain connecting to a horizontal

branch is not counted in computing the fixture's distance in developed length measured horizontally

from the stack (IPC 2024, 917.4.3).

The vertical portion of piping in a fixture drain to a horizontal branch must be 2 inches (51 mm); the

minimum size of the vertical portion of piping for a water-supplied urinal or standpipe must be

3 inches (76 mm); the maximum vertical drop is 4 feet (1219 mm); and fixture drains that are not

increased in size, or that have a vertical drop in excess of 4 feet, must be individually vented

(IPC 2024, 917.5).

Additional venting must 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

required, fixtures must be vented by individual vents, common vents, wet vents, circuit vents, or a

combination waste and vent pipe, and the dry vent extensions for that additional venting must connect

to a branch vent, vent stack, stack vent, air admittance valve, or terminate outdoors (IPC 2024,

917.6).

Stack offsets: where fixture drains are not connected below a horizontal offset in a stack, the

horizontal offset need not be vented; where horizontal branches or fixture drains are connected below

a horizontal offset in a stack, the offset must be vented in accordance with Section 907, and fixture

connections must not be made to a stack within 2 feet (610 mm) above or below a horizontal offset

(IPC 2024, 917.7). Stacks greater than 2 branch intervals in height must not receive the discharge of

horizontal branches on the lower two floors, and there must not be 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 (IPC 2024, 917.8). The building drain and building sewer receiving the

discharge of a single stack vent system must be sized in accordance with Table 710.1(1) (IPC 2024,

917.9).

16. Air admittance valves

Vent systems using air admittance valves must comply with Section 918. Stack-type air admittance

valves must conform to ASSE 1050, and individual and branch-type air admittance valves must conform to

ASSE 1051 (IPC 2024, 918.1). The valves must be installed in accordance with the section and the

manufacturer's instructions, and air admittance valves must be installed after the DWV testing

required by Section 312.2 or 312.3 has been performed (IPC 2024, 918.2).

Individual, branch and circuit vents may terminate with a connection to an individual or branch-type

air admittance valve (IPC 2024, 918.3), and stack vents and vent stacks may terminate to stack-type

air admittance valves (IPC 2024, 918.3). Individual and branch-type air admittance valves must 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 must be provided with a relief vent connecting to a vent stack or stack vent, or extending

outdoors to the open air. That relief vent must connect to the horizontal branch drain between the

stack and the most downstream fixture drain connected to the horizontal branch drain, be sized in

accordance with Section 906.2, be installed in accordance with Section 905, and may serve as the vent

for other fixtures (IPC 2024, 918.3.1). Stack-type air admittance valves are prohibited from serving as

the vent terminal for vent stacks or stack vents that serve drainage stacks having more than six

branch intervals (IPC 2024, 918.3.2).

Location: individual and branch-type air admittance valves must be located not less than 4 inches

(102 mm) above the horizontal branch drain or fixture drain being vented; stack-type air admittance

valves must be located not less than 6 inches (152 mm) above the flood level rim of the highest

fixture being vented; the valve must be located within the maximum developed length permitted for the

vent and installed not less than 6 inches (152 mm) above insulation materials (IPC 2024, 918.4).

Access must be provided to all air admittance valves, and such valves must be installed in a location

that allows air to enter the valve (IPC 2024, 918.5). The valve must be rated in accordance with the

standard for the size of the vent to which it is connected (IPC 2024, 918.6), and within each plumbing

system not less than one stack vent or vent stack must extend outdoors to the open air (IPC 2024,

918.7).

Prohibited installations: air admittance valves must not be installed in nonneutralized special waste

systems as described in Chapter 8 except where such valves comply with ASSE 1049, are constructed of

materials approved in accordance with Section 702.5, and are tested for chemical resistance in

accordance with ASTM F1412; they must not be located in spaces used as supply or return air plenums;

they must not be used to vent sumps or tanks except where the vent system for the sump or tank has been

designed by an engineer; and they must not be installed on outdoor vent terminals for the sole purpose

of reducing clearances to gravity air intakes or mechanical air intakes (IPC 2024, 918.8).

17. Engineered vent systems

Engineered vent systems must comply with Section 919 and with the design, submittal, approval,

inspection and testing requirements of Section 316 (IPC 2024, 919.1). The maximum developed length of

individual fixture vents to vent branches and vent headers is determined in accordance with

Table 919.2 for the minimum pipe diameters at the indicated vent airflow rates, with the individual

vent airflow rate determined by the equation published in the section (IPC 2024, 919.2).

Developed Length

Reference text for the developed length area. Every rule below is written from the printed line of

the 2024 International Plumbing Code (IPC 2024) that carries it, and each rule names the section it

comes from. Where the printed line does not state a value, no value is stated here; where a sizing

table is printed under a number, the table is reproduced under that number with the values read from

the print. The text says what it does: the print read for this document carries no definition entry

of its own for the phrase "developed length", so the text does not invent one. It takes the phrase

where the code prints it — in the definitions of the chapter of definitions and in the sections whose

limits are expressed in it — and it sets out each printed limit with its address.

1. Where the phrase is printed in the definitions

The chapter of definitions uses the phrase in two of its entries (IPC 2024, 202).

The first is the branch interval: the vertical distance between the points where horizontal branches

meet a drainage stack, taken down the stack from the highest such point, where that distance measures

8 feet (2438 mm) or more in developed length (IPC 2024, 202). The second is the building drain: the

lowest piping of a drainage system, which takes the discharge from the soil, waste and other drainage

pipes inside the building and runs 30 inches (762 mm) in developed length of pipe past the exterior

walls of the building, carrying that discharge on to the building sewer (IPC 2024, 202).

The building sewer is defined as the piping that carries the discharge onwards from the end of the

building drain, to a public sewer, a private sewer, an individual sewage disposal system or another

point of disposal (IPC 2024, 202). The two definitions meet at a fixed

length: 30 inches (762 mm) of pipe beyond the exterior wall is what makes the building drain end and

the building sewer begin, and it is a developed length that fixes that boundary.

No further definition of the phrase is printed in the corpus read for this document. Every other use

of it in the code is a limit or a measurement rule inside a section, and those are what the rest of

this text collects.

2. Developed length in the drainage system

2.1 Cleanout intervals and locations

Horizontal drainage pipes inside buildings have cleanouts at intervals of not more than 100 feet

(30 480 mm), and building drains also at intervals of not more than 100 feet (30 480 mm), except where

manholes are used in place of cleanouts, in which case the manholes are at intervals of not more than

400 feet (122 m). That interval is taken from the cleanout or the manhole opening, follows the

developed length of the piping, and stops at whichever comes next: the drainage fitting that gives

access for cleaning, the end of the horizontal drain, or the end of the building drain

(IPC 2024, 708.1.1).

Building sewers smaller than 8 inches (203 mm) have cleanouts at intervals of not more than 100 feet

(30 480 mm), and building sewers 8 inches (203 mm) and larger have a manhole not more than 200 feet

(60 960 mm) from the junction of the building drain and the building sewer and at intervals of not

more than 400 feet (122 m); that interval again starts at the cleanout or the manhole opening and

follows the developed length, stopping at the next fitting that gives access for cleaning, at a

manhole, or at the end of the building sewer (IPC 2024, 708.1.2).

The junction of the building drain and the building sewer is served by a cleanout located at the

junction or within 10 feet (3048 mm) of the developed length of piping upstream of the junction

(IPC 2024, 708.1.3). A change of horizontal direction exceeding 45 degrees (0.79 rad) in a horizontal

drainage pipe, in a building drain or in a building sewer carries a cleanout at that change; where

two or more such changes fall inside 40 feet (12 192 mm) of developed length of piping, the cleanout

installed for the first change serves as the cleanout for every change inside that length

(IPC 2024, 708.1.4).

2.2 Slope and connection points

Horizontal drainage piping is installed in uniform alignment at uniform slopes, and the printed

minimum slope is a function of the pipe size (IPC 2024, 704.1 and Table 704.1):

Footnote a of that table sends piping draining to a grease interceptor back to the text of the

section, where the slope must be not less than 1/4 inch per foot (2 percent slope); for SI: 1 inch =

25.4 mm, 1 inch per foot = 83.33 mm/m (IPC 2024, 704.1 and Table 704.1). The slope is the second term

of the fall over a run: a developed length read off the plan, multiplied by the printed slope, gives

the fall of the pipe over that length.

Horizontal branches connect to the bases of stacks at a point not less than 10 times the diameter of

the drainage stack downstream from the stack, and connect to horizontal stack offsets at a point not

less than 10 times the diameter of the drainage stack downstream from the upper stack

(IPC 2024, 704.3). That distance is a run along the pipe, measured in stack diameters rather than in

developed length, and it is the printed counterpart of the developed lengths that follow.

2.3 Indirect waste and combination waste and vent piping

Indirect waste piping discharges through an air gap or an air break into a waste receptor, and waste

receptors are trapped and vented and connect to the building drainage system; where indirect waste

piping exceeds 30 inches (762 mm) in developed length measured horizontally, or 54 inches (1372 mm) in

total developed length, it is trapped (IPC 2024, 802.3). Those two figures are printed side by side,

one for the horizontal run and one for the whole piping including its risers and drops.

In a combination waste and vent system, the only vertical pipe is the connection between the fixture

drain and the horizontal combination waste and vent pipe, and that vertical distance is not more than

8 feet (2438 mm) (IPC 2024, 915.2); the horizontal length of a combination waste and vent system is

unlimited (IPC 2024, 915.2.2).

In the subsurface graywater chapter, an individual seepage trench is not greater than 100 feet

(30 480 mm) in developed length, and the soil absorption area of a seepage trench is computed from the

bottom of the trench area (its width) multiplied by the length of the pipe

(IPC 2024, 1403.1.2).

3. Developed length in the vent system

3.1 Stack vents and vent stacks

The minimum required diameter of a stack vent or a vent stack is determined from the developed length

and the total of the drainage fixture units connected to it, in accordance with the sizing table for

stack vents and vent stacks; the diameter is in no case less than one-half the diameter of the drain

served, or less than 1 1/4 inches (32 mm) (IPC 2024, 906.1 and Table 906.1). That table is a grid: it

gives the maximum developed length of vent for a soil or waste stack diameter, a total of fixture

units being vented and a vent diameter, and the value is read at the intersection of those conditions

(IPC 2024, Table 906.1).

Where stack vents and vent stacks are connected into a common vent header at the top of the stacks and

extend to the open air at one point, the developed length that sizes the header is the longest vent

length, measured from the intersection at the base of the most distant stack to the vent terminal in

the open air, taken as a direct extension of one stack (IPC 2024, 904.5).

3.2 Vents other than stack vents and vent stacks

Individual vents, branch vents, circuit vents and relief vents are not less than one-half the required

diameter of the drain served, the required size of the drain being determined from the sizing table

for horizontal fixture branches and stacks, and vent pipes are not less than 1 1/4 inches (32 mm) in

diameter. Vents exceeding 40 feet (12 192 mm) in developed length are increased by one nominal pipe

size for the entire developed length of the vent pipe, and relief vents for soil and waste stacks in

buildings having more than 10 branch intervals are sized in accordance with Section 908.2

(IPC 2024, 906.2 and Table 710.1(2)).

For individual, branch, circuit and relief vents, the developed length runs from the furthest point at

which the vent meets the drainage system to the point where it joins the vent stack or the stack vent,

or where it terminates outside the building (IPC 2024, 906.3).

3.3 Sump vents

Drainage piping below the level of the sewer is vented in the same manner as the piping of a gravity

system, and the size of a building sump vent, for sumps with sewage pumps or with sewage ejectors

other than pneumatic ejectors, is determined from the printed table, which reads a maximum developed

length of vent against the discharge capacity of the pump and the diameter of the vent

(IPC 2024, 906.5.1 and Table 906.5.1):

TABLE 906.5.1 SIZE AND LENGTH OF SUMP VENTS — maximum developed length of vent (feet)

Footnote a of that table: the developed length is taken together with an appropriate allowance for

entrance losses and friction due to fittings, changes in direction and diameter; suggested allowances

are obtained from NBS Monograph 31 or other approved sources, and an allowance of 50 percent of the

developed length is assumed where a more precise value is not available. Footnotes b and c of the same

table: b. actual values greater than 500 feet; c. less than 10 feet. For SI: 1 inch = 25.4 mm,

1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m (IPC 2024, Table 906.5.1).

3.4 Fixture vents

Every trap carries a protecting vent whose position holds two things inside the printed limits: the

slope of the fixture drain, and its developed length taken from the trap weir to the vent fitting

(IPC 2024, 909.1 and Table 909.1):

The exception printed with it: for self-siphoning fixtures, such as water closets, the printed

distance between trap weir and vent fitting is not a limit at all (IPC 2024, 909.1 and Exception).

Two further printed rules work on the same trap-to-vent geometry: the total fall a fixture drain

takes from its slope stays inside the diameter of that drain, and the vent connection to a fixture

drain, except for a water closet, is not below the weir of the trap (IPC 2024, 909.2), and no vent

goes within two pipe diameters of the trap weir (IPC 2024, 909.3). For SI: 1 inch = 25.4 mm,

1 foot = 304.8 mm, 1 inch per foot = 83.3 mm/m (IPC 2024, Table 909.1).

3.5 Horizontal branches of a single-stack vent system

Water closet connections are not greater than 4 feet (1219 mm) in developed length measured

horizontally from the stack, and where the connection is made with a sanitary tee the maximum

developed length is 8 feet (2438 mm) (IPC 2024, 917.4.1 and Exception). Fixtures other than water

closets are located not greater than 12 feet (3657 mm) in developed length, again measured horizontally

from the stack (IPC 2024, 917.4.2). The length of vertical piping in a fixture drain connecting to a

horizontal branch is not counted in computing the fixture's distance in developed length measured

horizontally from the stack (IPC 2024, 917.4.3). The vertical portion of piping in a fixture drain to a

horizontal branch is 2 inches (51 mm), the minimum size of the vertical portion for a water-supplied

urinal or standpipe is 3 inches (76 mm), and the maximum vertical drop is 4 feet (1219 mm); fixture

drains that are not increased in size, or that have a vertical drop in excess of 4 feet, are

individually vented (IPC 2024, 917.5). Extra venting comes in when a horizontal branch takes the

discharge of two or more water closets, and when the distance from a fixture trap to the stack runs

past the limits of Section 917.4 (IPC 2024, 917.6).

3.6 Engineered vent systems

The maximum developed length of individual fixture vents to vent branches and vent headers is

determined from the printed table for the minimum pipe diameters at the indicated vent airflow rates

(IPC 2024, 919.2 and Table 919.2). That table is a grid read against the diameter of the vent pipe and

the individual vent airflow rate in cubic feet per minute, and its values are the maximum developed

length of vent in feet (IPC 2024, Table 919.2). The airflow rate that enters that reading is computed

from the number of fixtures per header or vent branch, the total number of fixtures connected to the

vent stack, and the total vent stack airflow rate (IPC 2024, 919.2). One printed addition applies to

the developed length itself: for an individual vent, that length rises by 20 percent of the distance

measured from the vent stack to the fixture vent connection on the branch or header (IPC 2024, 919.2).

4. Developed length in the hot water system

The developed length of the hot or tempered water piping, measured from the source of hot water to the

fixtures that require hot or tempered water, is not more than 50 feet (15 240 mm); recirculating

system piping and heat-traced piping count as sources of hot or tempered water

(IPC 2024, 607.2). Where an occupancy is one that the commercial provisions of the International

Energy Conservation Code govern, that code sets the limit on the developed length of hot or tempered

water piping, in its sections C404.5.1 through C404.5.2.1 (IPC 2024, 607.2.1).

5. How a printed developed length is measured

Each of the sections that carries a developed-length limit also prints how the length is taken, and

the printed measurement rules differ in a way that matters when a drawing is read:

vent meets the drainage system and ends at the vent stack, at the stack vent, or at the outside

termination (IPC 2024, 906.3).

length, and stop at the next fitting that gives access for cleaning, at the end of the horizontal

drain, or at the end of the building drain (IPC 2024, 708.1.1).

piping in the fixture drain is not counted in it (IPC 2024, 917.4.3).

once on the total developed length (IPC 2024, 802.3).

stack, and it counts as an interval when the developed length between those connections reaches

8 feet (2438 mm) or more (IPC 2024, 202).

the building, and the building sewer starts at that point (IPC 2024, 202).

and the vent diameter (IPC 2024, 906.5.1 and Table 906.5.1).

entrance losses and friction due to fittings, changes in direction and diameter, an allowance of

50 percent of the developed length being assumed where a more precise value is not available

(IPC 2024, Table 906.5.1, footnote a).

6. The printed developed-length limits, gathered

The limits the code prints, each with the address of the line that carries it:

Where a limit above is expressed by a table rather than by a figure, the table is the limit: the

figure a designer takes from it is the printed value at the intersection of the conditions of the

installation, and no value is taken from a line that prints none (IPC 2024, Table 906.5.1 and

Table 919.2).