Indirect and Special Waste

Indirect and Special Waste

Reference text for the indirect and special waste 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. Why indirect waste exists

There are drainage applications in buildings where a backup of liquid waste in a drainage system could

contaminate equipment and appliances. Chapter 8 covers the applications that require an indirect

discharge connection to the building's drainage system, and it carries the provisions for the types of

indirect connections and waste receptor configurations (IPC 2024, Chapter 8, About this chapter).

The chapter governs indirect waste piping and special wastes, and further controls food-handling

establishments, sterilizers, humidifiers, clear-water waste, swimming pools, methods of providing air

breaks or air gaps, and neutralizing devices for corrosive wastes (IPC 2024, 801.1). Devices,

appurtenances, appliances and apparatus intended to serve some special function — such as

sterilization, humidification, distillation, processing, cooling, or storage of ice or foods — and

that discharge to the drainage system, must be provided with protection against backflow, flooding,

fouling, contamination and stoppage of the drain (IPC 2024, 801.2).

2. Where an indirect waste connection is required

Food-handling equipment (in other than dwelling units), clear-water waste, humidifiers, dishwashing

machines and utensils, pots, pans and dishwashing sinks must discharge through an indirect waste pipe

as specified in Sections 802.1.1 through 802.1.7. Fixtures not required to be indirectly connected by

that section, and the exception to Section 301.6, must be directly connected to the plumbing system in

accordance with Chapter 7 (IPC 2024, 802.1). (Section 301.6 prohibits plumbing systems in an elevator

shaft or elevator equipment room, with an exception permitting floor drains, sumps and sump pumps at

the base of the shaft where they are indirectly connected to the plumbing system and comply with

Section 1003.4 — IPC 2024, 301.6 and Exception.)

The specific applications:

discharge through an indirect waste pipe by means of an air gap, and each well of a

multiple-compartment sink must discharge independently to a waste receptor (IPC 2024, 802.1.1).

food service and food establishments must be indirectly connected to the sanitary drainage system by

means of an air gap. Where a floor drain is located within an area subject to freezing, the waste

line serving the floor drain must not be trapped and must indirectly discharge into a waste receptor

located outside of the area subject to freezing. Exception: where protected against backflow by a

backwater valve, such floor drains must be indirectly connected to the sanitary drainage system by

means of an air break or an air gap (IPC 2024, 802.1.2).

discharge potable water to the building drainage system, the discharge must be through an indirect

waste pipe by means of an air gap (IPC 2024, 802.1.3).

deck drains discharge to the building drainage system, the discharge must be through an indirect

waste pipe by means of an air gap (IPC 2024, 802.1.4).

boilers discharge nonpotable water to the building drainage system, the discharge must be through an

indirect waste pipe by means of an air break or an air gap (IPC 2024, 802.1.5).

an air gap or air break into a waste receptor in accordance with Section 802.3 (IPC 2024, 802.1.6).

washing, rinsing or sanitizing of utensils, dishes, pots, pans or service ware used in the

preparation, serving or eating of food, must discharge indirectly through an air gap or an air break

to the drainage system (IPC 2024, 802.1.7).

3. Air gap against air break

The distinction the chapter draws is which method is required, not which is convenient:

The two connections are defined by measurement: the air gap between the indirect waste pipe and the

flood level rim of the waste receptor must be not less than twice the effective opening of the

indirect waste pipe (IPC 2024, 802.3.1), while an air break must be provided between the indirect

waste pipe and the trap seal of the waste receptor (IPC 2024, 802.3.2).

4. Materials and installation of indirect waste piping

Materials, joints, connections and methods used for the construction and installation of indirect

waste piping systems must comply with the applicable provisions of Chapter 7 (IPC 2024, 802.2).

Indirect waste piping must discharge through an air gap or air break into a waste receptor; waste

receptors must be trapped and vented and must connect to the building drainage system (IPC 2024,

802.3). Indirect waste piping that exceeds 30 inches (762 mm) in developed length measured

horizontally, or 54 inches (1372 mm) in total developed length, must be trapped. The exception: where

a waste receptor receives only clear-water waste and does not directly connect to a sanitary drainage

system, the receptor does not require a trap (IPC 2024, 802.3 and Exception).

5. Waste receptors

For other than hub drains that receive only clear-water waste and standpipes, a removable strainer or

basket must cover the outlet of waste receptors. Waste receptors must not be installed in concealed

spaces, and must not be installed in plenums, crawl spaces, attics, interstitial spaces above ceilings

and below floors. Ready access must be provided to waste receptors (IPC 2024, 802.4).

Sizing: a waste receptor must be sized for the maximum discharge of all indirect waste pipes served by

the receptor, and receptors must be installed to prevent splashing or flooding (IPC 2024, 802.4.1).

For the drainage load, 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 drainage fixture unit value given for

the indirect waste receptor in Table 709.1 or 709.2 (IPC 2024, 709.4); and 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).

(25 mm) above a water-impervious floor (IPC 2024, 802.4.2).

but not greater than 42 inches (1067 mm) above the trap weir, and access must be provided to

standpipes and drains for rodding (IPC 2024, 802.4.3).

directly to a drainage system, a laundry tray waste line without a fixture trap may connect to a

standpipe for an automatic clothes washer drain. The standpipe must extend not less than 30 inches

(762 mm) above the weir of the standpipe trap and must extend above the flood level rim of the

laundry tray; the outlet of the laundry tray must not be greater than 30 inches (762 mm) horizontal

distance from the side of the standpipe (IPC 2024, 802.4.3.1).

6. Special wastes

Corrosive liquids, spent acids or other harmful chemicals that destroy or injure a drain, sewer, soil

or waste pipe, or create noxious or toxic fumes, or interfere with sewage treatment processes, must

not be discharged into the plumbing system without being thoroughly diluted, neutralized or treated by

passing through an approved dilution or neutralizing device. Such devices must be automatically

provided with a sufficient supply of diluting water or neutralizing medium so as to make the contents

noninjurious before discharge into the drainage system, and the nature of the corrosive or harmful

waste and the method of its treatment or dilution must be approved prior to installation (IPC 2024,

803.1).

A chemical drainage and vent system must be designed and installed in accordance with the code, and

chemical drainage and vent systems must be completely separated from the sanitary systems. Chemical

waste must not discharge to a sanitary drainage system until it has been treated in accordance with

Section 803.1 (IPC 2024, 803.2). The vent system for a chemical waste drainage system must be

independent of any sanitary drainage vent system, and its termination must be through the roof to the

outdoors or to an air admittance valve complying with ASSE 1049 (IPC 2024, 901.3).

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

(IPC 2024, 918.8).

7. The indirect connection in the drainage load calculation

An indirect waste receptor is a drainage point of the building drain, so its load is computed as the

greater of the sum of the fixture units discharging to it and the value given for the receptor itself

in Table 709.1 or 709.2 (IPC 2024, 709.4). Where the discharge is known only as a flow rate, drainage

fixture unit values 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).