Sanitary Drainage Systems

Sanitary Drainage Systems

Reference text for the sanitary drainage 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 sanitary drainage systems

(IPC 2024, 701.1). Sanitary drainage piping from plumbing fixtures in buildings, and sanitary drainage

piping systems from premises, must be connected to a public sewer; where a public sewer is not

available they must be connected to a private sewage disposal system in compliance with state or local

requirements, and, where such requirements do not exist, to an approved private sewage disposal system

in accordance with the International Private Sewage Disposal Code (IPC 2024, 701.2). The exception

covers piping and systems that convey only the discharge from bathtubs, showers, lavatories, clothes

washers and laundry trays, provided they are connected to a system in accordance with Chapter 13 or 14

(IPC 2024, 701.2, Exception).

A building having plumbing fixtures installed and intended for human habitation, occupancy or use on

premises abutting on a street, alley or easement in which there is a public sewer must have a separate

connection with the sewer; where located on the same lot, multiple buildings may connect to a common

building sewer that connects to the public sewer (IPC 2024, 701.3). Sewage or other waste deleterious

to surface or subsurface waters must not be discharged into the ground or into any waterway unless

first rendered innocuous through an approved form of treatment (IPC 2024, 701.4), and waste

detrimental to the public sewer system or to the functioning of the sewage-treatment plant must be

treated and disposed of in accordance with Section 1003 as directed by the code official (IPC 2024,

701.5). The sanitary drainage system is tested in accordance with Section 312 (IPC 2024, 701.6), and

engineered sanitary drainage systems must conform to Sections 316 and 713 (IPC 2024, 701.7).

2. Materials and joints

Sections 702.1 (above-ground sanitary drainage and vent pipe), 702.2 (underground building sanitary

drainage and vent pipe), 702.3 (building sewer pipe) and 702.4 (fittings) publish the materials and

the standards for those applications. Where the wastewater temperature will be greater than 140°F

(60°C), the sanitary drainage piping material must be rated for the highest temperature of the

wastewater (IPC 2024, 702.5). Section 702.6 governs chemical waste systems and Section 702.7 lead

bends and traps.

Section 705 contains the provisions applicable to joints specific to sanitary drainage piping

(IPC 2024, 705.1): 705.2 ABS plastic, 705.3 cast iron, 705.4 concrete joints, 705.5 copper pipe,

705.6 copper tubing, 705.7 borosilicate glass joints, 705.8 steel, 705.9 lead, 705.10 PVC plastic,

705.11 vitrified clay, 705.12 polyethylene plastic pipe, 705.13 polyolefin plastic, 705.14

polyvinylidene fluoride plastic, 705.15 polypropylene plastic, 705.16 joints between different

materials, 705.17 drainage slip joints, 705.18 caulking ferrules, 705.19 soldering bushings and

705.20 stainless steel drainage systems. Prohibited joints and connections in

drainage piping are: cement or concrete joints; mastic or hot-pour bituminous joints; joints made

with fittings not approved for the specific installation; joints between different diameter pipes made

with elastomeric rolling O-rings; solvent-cement joints between different types of plastic pipe except

where provided for in Section 705.16.4; and saddle-type fittings (IPC 2024, 707.1).

3. Building sewer

The proximity of a sewer to a water service must comply with Section 603.2 (IPC 2024, 703.1). Where a

building sewer or building drain is installed on filled or unstable ground, the drainage pipe must

conform to one of the standards for ABS plastic pipe, cast-iron pipe, copper or copper-alloy tubing,

PVC plastic pipe or polypropylene plastic pipe indicated in Table 702.3 (IPC 2024, 703.2). Where

separate systems of sanitary drainage and storm drainage are installed in the same property, the

sanitary and storm building sewers or drains may be laid side by side in one trench (IPC 2024, 703.3).

Where the entire sanitary drainage system of an existing building is replaced, existing building

drains under concrete slabs and existing building sewers that will serve the new system must be

internally examined to verify that the piping is sloping in the correct direction, is not broken, is

not obstructed and is sized for the drainage load of the new plumbing drainage system to be installed

(IPC 2024, 703.4). Cleanouts on building sewers are located as indicated in Section 708 (IPC 2024,

703.5), and where the public sewer is a combined system for both sanitary and storm water the sanitary

sewer must be connected independently to the public sewer (IPC 2024, 703.6).

4. Drainage piping installation

4.1 Slope

Horizontal drainage piping must be installed in uniform alignment at uniform slopes. The slope must be

not less than Table 704.1 shows, except that where the drainage piping is upstream of a grease

interceptor the slope must be not less than 1/4 inch per foot (2 percent slope) (IPC 2024, 704.1).

For SI: 1 inch = 25.4 mm, 1 inch per foot = 83.33 mm/m. Slopes for piping draining to a grease

interceptor comply with Section 704.1 (IPC 2024, Table 704.1, footnote a).

4.2 Size reduction, offsets and future fixtures

The size of the drainage piping must not be reduced in the direction of flow. The following are not

considered a reduction in size in the direction of flow: a 4-inch by 3-inch (102 mm by 76 mm) water

closet flange; a water closet bend fitting having a 4-inch (102 mm) inlet and a 3-inch (76 mm) outlet,

provided the 4-inch leg of the fitting is upright and below, but not necessarily directly connected

to, the water closet flange; and an offset closet flange (IPC 2024, 704.2).

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

diameter of the drainage stack downstream from the stack, and must connect to horizontal stack offsets

at a point located not less than 10 times the diameter of the drainage stack downstream from the

upper stack (IPC 2024, 704.3). Drainage piping for future fixtures must terminate with an approved cap

or plug (IPC 2024, 704.4).

5. Connections and fittings

Connections and changes in direction of the sanitary drainage system must be made with approved

drainage fittings; connections between drainage piping and fixtures conform to Section 405 (IPC 2024,

706.1). Fittings must not have ledges, shoulders or reductions capable of retarding or obstructing

flow in the piping, and threaded drainage pipe fittings must be of the recessed drainage type; the

section does not apply to tubular waste fittings used to convey vertical flow upstream of the trap

seal liquid level of a fixture trap (IPC 2024, 706.2).

Fittings must be installed to guide sewage and waste in the direction of flow, and changes in

direction must be made by fittings installed in accordance with Table 706.3. Change in direction by

combination fittings, side inlets or increasers must be installed in accordance with Table 706.3 based

on the pattern of flow created by the fitting. Double sanitary tee patterns must not receive the

discharge of back-to-back water closets and fixtures or appliances with pumping action discharge;

back-to-back water closet connections to double sanitary tees are permitted where the horizontal

developed length between the outlet of the water closet and the connection to the double sanitary tee

pattern is 18 inches (457 mm) or greater (IPC 2024, 706.3 and Exception).

Table 706.3 — fittings for change in direction ("X" = permitted):

Fitting limitations, as the printed table carries them on the marked cells (IPC 2024,

Table 706.3, footnotes a, b and c): the fittings marked a are only permitted for a 2-inch or smaller

fixture drain; the cell marked b carries "three inches or larger"; and the double sanitary tee

limitation is Section 706.3.

Heel-inlet quarter bends are an acceptable means of connection except where the quarter bend serves a

water closet; a low-heel inlet must not be used as a wet-vented connection; side-inlet quarter bends

are an acceptable means of connection for drainage, wet venting and stack venting arrangements

(IPC 2024, 706.4).

6. Cleanouts

Cleanouts must be provided for drainage piping in accordance with Sections 708.1.1 through 708.1.12

(IPC 2024, 708.1). The principal requirements:

100 feet (30 480 mm), and building drains must have cleanouts at intervals of not more than 100 feet

(30 480 mm) except where manholes are used instead of cleanouts, in which case the manholes must be

located at intervals of not more than 400 feet (122 m); the interval is measured from the cleanout

or manhole opening, along the developed length of the piping, to the next drainage fitting providing

access for cleaning, the end of the horizontal drain or the end of the building drain (IPC 2024,

708.1.1).

100 feet (30 480 mm); building sewers 8 inches (203 mm) and larger must have a manhole located not

more than 200 feet (60 960 mm) from the junction of the building drain and building sewer and at

intervals of not more than 400 feet (122 m) (IPC 2024, 708.1.2).

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

junction; removal of the water closet must not be required to provide cleanout access (IPC 2024,

708.1.3).

direction greater than 45 degrees, a cleanout must be installed at the change of direction; where

more than one such change occurs within 40 feet (12 192 mm) of developed length, the cleanout

installed for the first change serves all changes in direction within that 40 feet (IPC 2024,

708.1.4).

4 inches (102 mm) need not be larger than 4 inches (102 mm); a removable P-trap with slip or ground

joint connections can serve as a cleanout for drain piping one size larger than the P-trap size;

cleanouts located on stacks can be one size smaller than the stack size; and the size of cleanouts

for cast-iron piping can be in accordance with the referenced standards for cast-iron fittings in

Table 702.4 (IPC 2024, 708.1.5 and Exceptions).

acceptable as a cleanout equivalent (IPC 2024, 708.1.6). Cleanout plugs must be of copper-alloy,

plastic or other approved materials (borosilicate glass for borosilicate glass piping systems),

copper-alloy plugs conforming to ASTM A74 and limited to metallic piping systems, plastic plugs

conforming to the referenced standards for plastic pipe fittings in Table 702.4, with a raised

square head, a countersunk square head or a countersunk slot head, and manufactured with a blind

end threaded hole where a trim cover screw will be installed (IPC 2024, 708.1.7).

must have gas-tight covers that require tools for removal (IPC 2024, 708.1.8). The installation

arrangement of a cleanout must enable cleaning of drainage piping only in the direction of drainage

flow, except for test tees serving as cleanouts and a two-way cleanout installation approved for

meeting Section 708.1.3 (IPC 2024, 708.1.9).

less than 18 inches (457 mm) from, and perpendicular to, the face of the opening to any

obstruction; cleanouts for 8-inch (203 mm) and larger piping must have a clearance of not less than

36 inches (914 mm) (IPC 2024, 708.1.10).

inside of plenums, within walls, within floor/ceiling assemblies, below grade and in crawl spaces

where the height from the crawl space floor to the nearest obstruction along the path from the

crawl space opening to the cleanout is less than 24 inches (610 mm). Cleanouts with openings at a

finished wall must have the face of the opening within 1 1/2 inches (38 mm) of the finished wall

surface; cleanouts located below grade must be extended to grade level so that the top of the

cleanout plug is at or above grade; and a cleanout installed in a floor or walkway without a trim

cover must have a countersunk plug installed so the top surface of the plug is flush with the

finished surface of the floor or walkway (IPC 2024, 708.1.11).

trim cover fasteners that thread into cleanout plugs must be corrosion resistant, and cleanout plugs

must not be covered with mortar, plaster or any other permanent material (IPC 2024, 708.1.11.1).

Cleanout assemblies in accordance with ASME A112.36.2M must be installed where it is necessary to

protect a cleanout plug from the loads of vehicular traffic (IPC 2024, 708.1.11.2).

where another cleanout of equal size is installed with the required access and clearance (IPC 2024,

708.1.12).

7. Fixture units

Drainage fixture unit values in Table 709.1 designate the relative load weight of different kinds of

fixtures, to be used in estimating the total load carried by a soil or waste pipe and in connection

with Tables 710.1(1) and 710.1(2) (IPC 2024, 709.1).

Table notes that carry rules: a showerhead over a bathtub or whirlpool bathtub attachment does not

increase the drainage fixture unit value (footnote b); trap size must be consistent with the fixture

outlet size (footnote d); and for traps larger than 3 inches, Table 709.2 is used (footnote a).

Showers are rated on the total flow rate through showerheads and body sprays: 5.7 gpm or less = 2 dfu

with a 1 1/2-inch trap; greater than 5.7 gpm to 12.3 gpm = 3 dfu with a 2-inch trap; greater than

12.3 gpm to 25.8 gpm = 5 dfu with a 3-inch trap; greater than 25.8 gpm to 55.6 gpm = 6 dfu with a

4-inch trap (IPC 2024, Table 709.1).

Where discharges to a waste receptor or to a drainage system are known only in gallons per minute, the

drainage fixture unit values for those flows are computed on the basis that 1 gpm (0.06 L/s) of flow

is equivalent to two drainage fixture units (IPC 2024, 709.3). The drainage fixture unit load of an

indirect waste receptor receiving the discharge of indirectly connected fixtures is the sum of the

drainage fixture unit values of the fixtures that discharge to the receptor, but not less than the

value given for the indirect waste receptor in Table 709.1 or 709.2 (IPC 2024, 709.4). Waste receptors

such as floor drains, floor sinks and hub drains that receive only clear-water waste from display

cases, refrigerated display cases, ice bins, coolers and freezers have a drainage fixture unit value

of one-half (IPC 2024, 709.4.1).

8. Drainage system sizing

The maximum number of drainage fixture units connected to a given size of building sewer, building

drain or horizontal branch of the building drain is determined using Table 710.1(1), and the maximum

number connected to a given size of horizontal branch or vertical soil or waste stack is determined

using Table 710.1(2) (IPC 2024, 710.1).

Table 710.1(1) — building drains and sewers:

The minimum size of any building drain serving a water closet is 3 inches (IPC 2024,

Table 710.1(1), footnote a).

9. Offsets in drainage piping in buildings of five stories or more

If a horizontal branch connects to the stack within 2 feet (610 mm) above or below a vertical stack

offset, and the offset is located more than four branch intervals below the top of the stack, the

offset must be vented in accordance with Section 907; those vents are not required where the stack and

its offset are sized as a building drain (IPC 2024, 711.1 and 711.1.1).

A stack with a horizontal offset located more than four branch intervals below the top of the stack

must be vented in accordance with Section 907 and sized as follows: the portion of the stack above

the offset is sized as for a vertical stack based on the total number of drainage fixture units above

the offset; the offset is sized in accordance with Section 710.1.1; and the portion of the stack below

the offset is sized as for the offset or based on the total number of drainage fixture units on the

entire stack, whichever is larger (IPC 2024, 711.2). Those vents are not required where the stack and

its offset are one pipe size larger than required for a building drain and the entire stack and offset

are not less in cross-sectional area than that required for a straight stack plus the area of an

offset vent as provided in Section 907 (IPC 2024, 711.2.1).

Where a vertical offset occurs in a soil or waste stack below the lowest horizontal branch, a change

in diameter of the stack because of the offset is not required; if a horizontal offset occurs below

the lowest horizontal branch, the required diameter of the offset and of the stack below it must be

determined as for a building drain in accordance with Table 710.1(1) (IPC 2024, 711.3).

10. Sumps and ejectors

Building subdrains that cannot be discharged to the sewer by gravity flow must be discharged into a

tightly covered and vented sump from which the liquid is lifted and discharged into the building

gravity drainage system by automatic pumping equipment or other approved method; in other than

existing structures, the sump must not receive drainage from any piping within the building capable of

being discharged by gravity to the building sewer (IPC 2024, 712.1). A check valve and a full-open

valve located on the discharge side of the check valve must be installed in the pump or ejector

discharge piping between the pump or ejector and the gravity drainage system, with access to such

valves; they must be located above the sump cover required by Section 712.1 or, where the discharge

pipe from the ejector is below grade, accessibly outside the sump below grade in an access pit with a

removable access cover (IPC 2024, 712.2).

The sump pit must be not less than 18 inches (457 mm) in diameter and not less than 24 inches (610 mm)

in depth unless otherwise approved, provided with access, located so that all drainage flows into the

pit by gravity, constructed of tile, concrete, steel, plastic or other approved materials, with a

solid bottom providing permanent support for the pump, and fitted with a gastight removable cover

installed not more than 2 inches (51 mm) below grade or floor level, adequate to support anticipated

loads; the sump pit is vented in accordance with Chapter 9 (IPC 2024, 712.3.2). The effluent level

control must be adjusted and maintained to at all times prevent the effluent in the sump from rising

to within 2 inches (51 mm) of the invert of the gravity drain inlet into the sump (IPC 2024, 712.3.4).

Discharge pipe and fittings must be constructed of copper or copper-alloy, CPVC, ductile iron, PE or

PVC, rated for the maximum system operating pressure and temperature, compatible with the pipe

material, and suitable for burial where buried in the earth (IPC 2024, 712.3.3.1 and 712.3.3.2).

Pumps connected to the drainage system must connect to a building sewer, building drain, soil stack,

waste stack or horizontal branch drain; where the discharge line connects into horizontal drainage

piping, the connection must be made through a wye fitting into the top of the drainage piping, and

that wye fitting must be located not less than 10 pipe diameters from the base of any soil stack,

waste stack or fixture drain (IPC 2024, 712.3.5).

A sewage pump or sewage ejector must automatically discharge the contents of the sump to the building

drainage system (IPC 2024, 712.4). Macerating toilet systems must comply with ASME A112.3.4/CSA B45.9

and be installed in accordance with the manufacturer's instructions (IPC 2024, 712.4.1). A sewage pump

or ejector must have the capacity and head for the application requirements: pumps or ejectors that

receive the discharge of water closets must be capable of handling spherical solids with a diameter of

up to and including 2 inches (51 mm), and other pumps or ejectors must be capable of handling

spherical solids up to and including 1/2 inch (13 mm). Capacity based on the diameter of the discharge

pipe must be not less than Table 712.4.2 shows; grinder pumps or grinder ejectors that receive the

discharge of water closets must have a discharge opening of not less than 1 1/4 inches (32 mm), and

macerating toilet assemblies that serve single water closets must have a discharge opening of not less

than 3/4 inch (19.1 mm) (IPC 2024, 712.4.2 and Exceptions).

11. Computerized drainage design, backwater valves and rehabilitation

The sizing, design and layout of the drainage system may be designed by approved computer design

methods; the load is computed from the simultaneous or sequential discharge conditions from fixtures,

appurtenances and appliances or the peak usage design condition; discharge profiles for flow rates

versus time follow the manufacturer's specifications; pipe must be sized to prevent full-bore flow;

pipe size calculations use the pipe wall roughness factor (ks) per the manufacturer's specifications

as modified for aging roughness factors with deposits and corrosion; and horizontal drainage piping

must be designed and installed at slopes in accordance with Table 704.1 (IPC 2024, 713.1, 713.2,

713.2.1, 713.3, 713.3.1 and 713.3.2).

Where plumbing fixtures are installed on a floor with a finished floor elevation below the elevation

of the manhole cover of the next upstream manhole in the public sewer, such fixtures must be protected

by a backwater valve installed in the building drain or horizontal branch serving such fixtures;

fixtures installed on a floor with a finished floor elevation above the elevation of that manhole

cover must not discharge through a backwater valve, except that in existing buildings fixtures above

that elevation are not prohibited from discharging through a backwater valve (IPC 2024, 714.1 and

Exception). Backwater valves must comply with ASME A112.14.1, CSA B181.1 or CSA B181.2 (IPC 2024,

714.2), and must be installed so that access is provided to the working parts (IPC 2024, 714.3).

Sections 715 through 718 govern vacuum drainage systems, replacement of underground building sewers

and building drains by pipe-bursting methods, relining of building sewers and building drains, and

rehabilitation of building sewers and building drains; vacuum drainage systems must be designed per

the manufacturer's instructions and the plans, specifications and other data submitted to the code

official for review and approval prior to installation (IPC 2024, 715.1, 715.2, 716.1, 717.1 and

718.1).

12. Testing the sanitary drainage system

Section 312 governs the tests (IPC 2024, 701.6):

openings in the piping tightly closed except the highest opening, the system filled with water to

the point of overflow; if tested in sections, each opening tightly plugged except the highest

openings of the section under test and each section filled with water, but no section tested with

less than a 10-foot (3048 mm) head of water; in testing successive sections, not less than the upper

10 feet of the next preceding section must be tested, so that no joint or pipe in the building,

except the uppermost 10 feet of the system, is submitted to a test of less than a 10-foot head of

water. The pressure must be held for not less than 15 minutes, and the system must then be tight at

all points (IPC 2024, 312.2).

forcing air into the system until there is a uniform gauge pressure of 5 psi (34.5 kPa) or enough

to balance a 10-inch (254 mm) column of mercury, held for not less than 15 minutes, with adjustments

for ambient temperature or gasket seating made before the test period begins (IPC 2024, 312.3).

uniform gauge pressure of negative 5 pounds per square inch or a negative 10 inches of mercury

column, held without removal of additional air for 15 minutes (IPC 2024, 312.4).

and in sufficient detail to determine compliance; where a smoke test is used it is made by filling

all traps with water and introducing into the entire system a pungent, thick smoke produced by one

or more smoke machines; when the smoke appears at stack openings on the roof, the stack openings

must be closed and a pressure equivalent to a 1-inch water column (248.8 Pa) held for a test period

of not less than 15 minutes (IPC 2024, 312.5).