2021 IPC Chapter 3
Chapter 3 of the 2021 IPC gathers the rules that apply to every plumbing job, whatever the system: how materials are marked, how pipe is protected from damage, corrosion and the soil around it, how it is supported, and what a toilet room needs beyond fixtures. Inspectors lean on this chapter at underground and rough-in inspections, because a pipe that would pass a pressure test can still fail here: bad bedding, a missing nail plate, a hanger every eight feet instead of every four.
Every length of pipe, fitting, trap, fixture, material and device carries the manufacturer's identification and the markings the referenced standard requires (303.1). Materials are installed under the standards they were approved under, or by the manufacturer's instructions where there are none, and if those fall short of the code, the code wins (303.2). Plastic pipe, fittings and components are third-party certified to NSF 14 (303.3), products required to meet a referenced standard are third-party listed (303.4), and cast-iron soil pipe, fittings and couplings are third-party listed and labeled (303.5). The inspector reads the print on the pipe, and an unmarked fitting earns a correction notice even when it looks fine.
Strainer plates on drain inlets have openings no larger than 1/2 inch in least dimension (304.2). Meter boxes must not give rodents a path along the water service into the building (304.3), and the annular space around a pipe through a wall, floor or ceiling is sealed with caulking or a gasketing system compatible with the pipe (304.4).
Metallic pipe must not touch steel framing, concrete, cinder walls or floors, other masonry, or corrosive soil, except cast iron, ductile iron and galvanized steel; where sheathing is used to prevent contact it is plastic, at least 0.008 inch (8 mil) thick, and where it passes through concrete or masonry it must allow the pipe to move (305.1). Piping is installed to avoid stress and strain, with provision for expansion, contraction and settlement (305.2). A pipe through a foundation wall gets a relieving arch or a sleeve two pipe sizes larger (305.3).
Pipe is not placed where it freezes unless protected by insulation or heat. Exterior water supply piping goes at least 6 inches below the frost line and at least 12 inches below grade (305.4), so where frost depth is shallow the 12-inch minimum below grade is the number that controls. Building sewer depth is left blank in the model code (305.4.1), so the local number governs. Roof and vent joints are made watertight with flashing (305.5). In concealed locations, where pipe other than cast iron or galvanized steel passes through a hole or notch in a stud, joist or rafter less than 1-1/4 inches from the nearest edge, it gets a steel shield plate, at least 0.0575 inch (No. 16 gage) thick, extending at least 2 inches above sole plates and below top plates (305.6). Components along alleys, driveways and parking garages are recessed or protected (305.7).
Buried pipe is supported along its entire length, on a solid, continuous bed, with bell holes at joints and never on blocks (306.1, 306.2). If the trench is overexcavated, it is brought back to pipe level with sand or fine gravel in layers no thicker than 6 inches, compacted after each (306.2.1). Rock is removed at least 3 inches below the pipe and replaced with tamped sand, and the pipe and joints never rest on rock (306.2.2). If the bottom is soft, overexcavate at least two pipe diameters and rebuild with fine gravel, crushed stone or a concrete foundation bedded in sand (306.2.3).
Backfill is free of construction debris. Loose earth without rocks, broken concrete or frozen chunks goes in 6-inch layers, tamped until the crown of the pipe is covered by 12 inches of tamped earth, and it is brought up evenly on both sides so the pipe stays aligned (306.3). Tunneled pipe is protected from damage and uneven loading (306.4). A trench beside a footing must stay out of the footing's bearing plane, which runs down at 45 degrees from horizontal from the outside bottom edge of the footing (307.5).
Whatever floors, walls, ceilings or tile the plumber disturbs must be left structurally safe under the International Building Code (307.1). Framing members are not cut, notched or bored past the IBC limits (307.2), and penetrations of floor and ceiling assemblies and rated assemblies are protected as the IBC requires (307.3). Truss members are never cut, drilled, notched, spliced or altered without written concurrence and approval of a registered design professional, and added loads such as a water heater on a truss need verification that the truss can carry them (307.4).
Hangers, anchors and supports carry the pipe and its contents, use approved material that does not promote galvanic action, and attach to the building in an approved manner (308.3, 308.4). Table 308.5 sets the maximum spacing by material. Stiff, heavy pipe spans farther, and flexible plastic needs more support. Some rows depend on size (CPVC, PEX and copper tubing), and cast iron is 5 feet, rising to 10 feet where 10-foot lengths are installed. For plastic vertical pipe 2 inches and smaller, a guide goes midway between the vertical supports.
Drainage pipe has extra rules. Horizontal drain or waste pipe 4 inches and larger needs rigid bracing at a fitting that turns the flow more than 45 degrees, to resist upstream movement, though a turn into a vertical pipe does not (308.6). Drain pipe over 4 inches is anchored against axial movement at every change in direction and every diameter change of more than two pipe sizes (308.7). Thermal expansion tanks are supported per the manufacturer, not by the piping they connect to (308.10).
Worked example: a 30-foot horizontal run of cast-iron drain is hung with 10-foot lengths. With 10-foot lengths the spacing may reach 10 feet, so the run needs at least 30 divided by 10, or 3 spans. If the plumber used 5-foot lengths, the 5-foot limit applies and the same run needs at least 30 divided by 5, or 6 spans. A 24-foot run of PVC at 4 feet needs at least 24 divided by 4, or 6 spans.
In a flood hazard area, plumbing follows Section 309 and the IBC's flood provisions (IBC Section 1612). Water service pipes, sanitary and storm drainage, vents, fixtures, water heaters and similar systems are located as that section requires. They may sit below the required elevation only where designed to keep water out and to resist hydrostatic and hydrodynamic loads, including buoyancy, up to that elevation (309.2). In coastal high-hazard areas and Coastal A zones, plumbing does not mount on or pass through walls meant to break away under flood loads (309.3). For Gulf Coast rehab work, check the flood zone and design flood elevation before deciding where a new water heater or sewage ejector goes.
Toilet rooms and washrooms are lit and ventilated as the IBC and the International Mechanical Code require, finished per the IBC, and laid out per Section 405.3 for fixture location and compartments (310.1 to 310.3). Toilet facilities must be provided for construction workers and kept sanitary, and nonsewer types meet the PSAI Z4.3 standard (311.1).
Condensate from condensing appliances and from cooling coils drains to an approved place, sloped at least 1/8 inch per foot, or 1 percent (314.1, 314.2.1). It does not connect directly to a plumbing drain, waste or vent pipe. It may discharge to a floor sink, floor drain, trench drain, mop sink, hub drain, standpipe, utility sink or laundry sink, but a connection to a lavatory tailpiece or a bathtub overflow does not count (314.2.1.1). The pipe is at least 3/4 inch and never reduced downstream (314.2.2), and Table 314.2.2 sizes a manifolded line by capacity: up to 20 tons, 3/4 inch; over 20 to 40 tons, 1 inch; over 40 to 90 tons, 1-1/4 inches. Where overflow could damage the building, an auxiliary pan at least 1-1/2 inches deep and 3 inches larger than the unit, or a separate overflow drain, is added (314.2.3). Slope example: a 32-foot condensate line at 1/8 inch per foot needs 32 times 1/8, or 4 inches, of fall.
In the field
On a clinic walk-through, an inspector finds the rooftop unit's condensate line tied into the tailpiece of a staff lavatory with a wye. That is not a permitted discharge under 314.2.1.1: a lavatory tailpiece connection is not treated as a plumbing fixture connection, and the line may not tie directly to a drain. The fix is to run it to a floor sink or mop sink in the same tenant space, with a slope of at least 1/8 inch per foot and, if a stoppage could damage the ceiling below, an auxiliary pan or overflow line.
1. An inspector finds a box of drain fittings in a small commercial job with no manufacturer marking on them. Under Section 303.1, what is required on every pipe fitting?
2. A plumbing contractor bores a hole through a metal stud and runs copper water pipe through it. Under Section 305.1, if plastic sheathing is used to prevent direct contact, what is its minimum thickness?
3. A copper pipe is run through a hole in a wood stud, with the hole 1 inch from the nearest edge of the stud, in a Group B office wall. Under Section 305.6, what is required?
4. An underground drain for a small clinic is being installed and the trench bottom has a large rock. Under Section 306.2.2, what must be done?
5. Under Section 306.3, backfill over a buried pipe goes in layers of no more than 6 inches and is tamped until the crown of the pipe is covered by:
6. A trench for a new sewer runs parallel to an existing building footing. Under Section 307.5, the trench must not extend into the footing's bearing plane, which starts at the footing's outside bottom edge and slopes down at:
7. A plumber wants to cut a web member of a roof truss to pass a 4-inch vent in a new community building. Under Section 307.4, what is required?
8. An inspector finds a horizontal PVC drain in a Group B building supported every 6 feet. Under Table 308.5, the maximum horizontal spacing for PVC pipe is:
9. A run of horizontal cast-iron drain pipe is installed in 10-foot lengths. Under Table 308.5, the maximum hanger spacing is:
10. A 24-foot horizontal run of PVC drain is supported at the maximum spacing of 4 feet. How many spans between supports does it need at minimum?
11. Which piping systems must be sway braced under Section 308.6?
12. A new water heater is being located in a Gulf Coast community building inside a flood hazard area. Under Section 309.2, when may it sit below the required flood elevation?
13. An inspector finds a rooftop unit's condensate line connected to the tailpiece of a staff lavatory in a small clinic. Under Section 314.2.1.1, this is:
14. A 40-foot horizontal condensate line from a cooling coil must slope at least 1/8 inch per foot (1 percent). How much total fall does the line need?