CPC · California Plumbing Code
How to wet-vent a bathroom group horizontally (requirements and trap arm limits)
A horizontal wet vent for a bathroom group is allowed only when the specific fixture connections, wet‑vent diameter (2" for ≤4 dfu; 3" for ≥5 dfu), and trap arm developed lengths in Table 1002.2 are followed; lavatories may serve as the wet vent but showers/tubs require individual dry vent connections and only one upstream wet‑vented trap arm is permitted (see §§ 908.2.1–908.2.3).
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
A bathroom group on the same floor may be vented by a horizontal wet vent only when it meets the conditions in § 908.2 and its subsections. Key limits: only specified fixtures may serve as the wet vent, the wet vent diameter is set by the total drainage fixture units (dfu), and trap arm lengths must comply with Table 1002.2. See § 908.2, § 908.2.1, § 908.2.2, § 908.2.3 for the controlling rules.
The single most important rule: a horizontal wet vent for a bathroom group is permitted only when the specific fixture-connection, sizing, and trap-arm limits in § 908.2.1–§ 908.2.3 are met.
Key defined terms (first mention bolded)
- Wet vent — a drainage pipe that carries both fixture waste and functions as a vent for one or more fixtures. § 908.2.
- Dry vent — the individual vent connection that must serve certain fixtures in the group as required by § 908.2.1.
- Trap arm — the horizontal developed length from the trap weir to the inner edge of the vent; governed by Table 1002.2 and § 908.2.3.
Requirements in detail
1) When a horizontal wet vent is allowed
- A bathroom group on the same floor level is permitted to be vented by a horizontal wet vent only when all requirements of § 908.2.1 through § 908.2.5 are met. § 908.2 (intro).
2) Which fixtures may be the wet vent and vent connections
- The dry vent connection to the wet vent must be an individual vent for the bidet, shower, or bathtub (i.e., those fixtures require their own dry vent connection to the horizontal wet vent). § 908.2.1.
- One or two vented lavatory(s) are permitted to serve as the wet vent for the bathroom group (i.e., lavs can be the wet-venting fixtures). § 908.2.1.
- Only one wet‑vented fixture drain or trap arm may discharge upstream of the dry‑vented fixture drain connection. § 908.2.1.
3) Wet vent sizing (flow capacity)
- Size the wet vent based on the total dfu (drainage fixture units) discharging into it. § 908.2.2.
- Minimum wet vent diameters: not less than 2 inches for 4 dfu or less, and not less than 3 inches for 5 dfu or more. § 908.2.2.
- The dry vent that connects to the horizontal wet vent must be sized per Table 702.1 and Table 703.2, based on the total fixture units discharging into the wet vent (see § 908.2.2).
4) Trap arm length and vent opening location
- The length of the trap arm shall not exceed the limits in Table 1002.2; the trap size is set by § 1003.3. § 908.2.3.
- The vent pipe opening from the horizontal wet vent (except for water closets and similar fixtures) must not be below the weir of the trap — i.e., the vent opening must be at or above the trap weir. § 908.2.3 and § 1002.4.
Decision‑relevant values (quick reference table)
| Item | Code requirement / value | Code Reference |
|---|---|---|
| Permission to use horizontal wet vent | Allowed for bathroom group on same floor when §§ 908.2.1–908.2.5 are satisfied | § 908.2 |
| Who may be wet vent | One or two vented lavatories may serve as the wet vent; bidet/shower/bathtub require individual dry vent connection | § 908.2.1 |
| Upstream wet‑vented fixtures | Only one wet‑vented fixture drain or trap arm may discharge upstream of dry‑vented connection | § 908.2.1 |
| Wet vent minimum size | 2 inches for ≤ 4 dfu; 3 inches for ≥ 5 dfu | § 908.2.2 |
| Dry vent sizing | Per Table 702.1 and Table 703.2 based on total dfu | § 908.2.2 |
| Trap arm maximum lengths (by trap arm diameter) | See Table 1002.2 (examples below) | Table 1002.2 / § 908.2.3 |
Table 1002.2 (selected rows — horizontal trap arm developed length maxima) — see the code for the full table:
- 1-1/4" trap arm: maximum 30 inches; minimum distance trap-to-vent 2-1/2". Table 1002.2.
- 1-1/2" trap arm: maximum 42 inches; min trap-to-vent 3". Table 1002.2.
- 2" trap arm: maximum 60 inches; min trap-to-vent 4". Table 1002.2.
- Note: water closets and similar fixtures have a separate limit: the developed length from the face of the closet flange to the inner edge of the vent shall not exceed 6 feet (1829 mm). (Table notes).
Exceptions & special cases
- The horizontal wet‑venting permission is limited to fixtures within the same bathroom group; additional fixtures must discharge downstream and be conventionally vented (§ 908.2.5).
- The code explicitly limits how many fixtures may be upstream of the dry vent: only one wet‑vented fixture drain or trap arm may discharge upstream of the dry‑vented connection (§ 908.2.1).
- Table 1002.2 contains special notes for bathtubs/showers when horizontally wet‑vented: maxima of 6 feet for 1½" drains and 8 feet for 2" drains (maintaining 1/4" per foot slope). (Table notes).
If a condition or fixture not covered by §§ 908.2.1–908.2.5 applies (for example, island fixtures, combination waste & vent systems, or circuit venting), refer to the separate code sections that control those systems (e.g., § 909, § 910, § 911).
Common mistakes
- Assuming any fixture in a bathroom can act as the wet vent — only one or two vented lavatories are permitted to serve as the wet vent; showers/bathtubs require individual dry vent connections per § 908.2.1.
- Undersizing the wet vent by ignoring the total dfu: the wet vent minimum is 2" for ≤4 dfu and 3" for ≥5 dfu per § 908.2.2.
- Exceeding trap arm developed lengths in Table 1002.2 (e.g., using a 1-1/4" lavatory trap arm longer than 30 in.) — this is a code violation.
- Placing the vent opening below the trap weir (the vent must open at or above the weir except for water closets) — see § 908.2.3 and § 1002.4.
Worked example — concrete scenario
Scenario: One private bathroom group on the same floor contains a water closet, one lavatory, and one shower.
- Determine total dfu for the bathroom group: Appendix C lists a typical 1 bathroom group = 5.0 dfu (private‑use example). Use that dfu total for sizing the wet vent.
- Wet vent sizing per § 908.2.2: for 5 dfu, the wet vent must be not less than 3 inches. Result: provide a 3" wet vent.
- Fixture connections per § 908.2.1: the lavatory may serve as the wet vent (allowed: one or two lavs); shower requires an individual dry‑vent connection to the horizontal wet vent. Ensure only one wet‑vented fixture is upstream of the dry‑vented connection.
- Trap arm checks per Table 1002.2:
- Lavatory trap arm (commonly 1‑1/4") — max 30 in.; ensure vent is within that developed length.
- Shower trap arm (commonly 1‑1/2") — max 42 in.; horizontal wet‑vent note also limits shower trap developed length to 6 ft if it is 1½" drain.
- Water closet trap arm: the developed length from face of closet flange to inner edge of vent must not exceed 6 ft (table note).
If all these conditions are met (3" wet vent, proper individual dry vent for the shower, trap arms ≤ the Table 1002.2 limits, vent openings at/above trap weirs), the horizontal wet vent installation complies with §§ 908.2.1–908.2.3.
Related provisions
- § 908.2 — Horizontal Wet Venting for a Bathroom Group (general permission & cross‑reference)
- § 908.2.1 — Vent Connection (which fixtures may be wet‑vented and upstream rule)
- § 908.2.2 — Size (wet vent and dry vent sizing requirements)
- § 908.2.3 — Trap Arm (trap arm limits and vent opening location)
- Table 1002.2 — Horizontal Lengths of Trap Arms (numerical trap arm maxima)
- § 1002.4 — Vent Pipe Opening location relative to trap weir (vent opening must not be below the weir)
- Appendix C, Table C303.3 — Typical dfu values for bathroom groups (used to size wet vent)
Code references
Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:
CPC § 904.0. High relevance — show source text
VENTS
smaller than the minimum vent pipe size required for a fixture served, or by Section 904.0. 908.2 Horizontal Wet Venting for a Bathroom Group. A bathroom group located on the same floor level shall be permitted to be vented by a horizontal wet vent where all of the conditions of Section 908.2.1 through Section 908.2.5 are met.
908.2.1 Vent Connection. The dry vent connection to the wet vent shall be an individual vent for the bidet, shower, or bathtub. One or two vented lavatory(s) shall be permitted to serve as a wet vent for a bathroom group. Only one wet-vented fixture drain or trap arm shall discharge upstream of the dry-vented fixture drain connection. Dry vent connections to the horizontal wet vent shall be in accordance with Section 905.2 and Section
905.3.
908.2.2 Size. The wet vent shall be sized based on the fixture unit discharge into the wet vent. The wet vent shall be not less than 2 inches (50 mm) in diameter for 4 drainage fixture units (dfu) or less, and not less than 3 inches (80 mm) in diameter for 5 dfu or more. The dry vent shall be sized in accordance with Table 702.1 and Table 703.2 based on the total fixture units discharging into the wet vent.
908.2.3 Trap Arm. The length of the trap arm shall not exceed the limits in Table 1002.2. The trap size shall be in accordance with Section 1003.3. The vent pipe opening from the horizontal wet vent, except for water closets and similar fixtures, shall not be below the weir of the trap.
908.2.4 Water Closet. The water closet fixture drain or trap arm connection to the wet vent shall be downstream of fixture drain or trap arm connections to the horizontal wet vent.
908.2.5 Additional Fixtures. Additional fixtures shall discharge downstream of the wet vent system and be conventionally vented. Only the fixtures within the bathroom group shall connect to the wet-vented horizontal branch.
909.0 Special Venting for Island Fixtures. 909.1 General. Traps for island sinks and similar equipment shall be roughed in above the floor and shall be permitted to be vented by extending the vent as high as possible, but not less than the drainboard height and then returning it downward and connecting it to the horizontal sink drain immediately downstream from the vertical fixture drain. The return vent shall be connected to the horizontal drain through a wyebranch fitting and shall, in addition, be provided with a foot vent taken off the vertical fixture vent by means of a wye branch immediately below the floor and extending to the nearest partition and then through the roof to the open air, or shall be permitted to be connected to other vents at a point not less than 6 inches (152 mm) above the flood-level rim of the fixtures served. Drainage fittings shall be used on the vent below the floor level, and a slope of not less than [1] ⁄ 4 inch per foot (20.8 mm/m) back to the drain shall be maintained. The return bend used under the drainboard shall be a one-piece
CPC § 907.2 High relevance — show source text
907.2 Yoke Vent. The yoke vent connection to the vent stack shall be placed not less than 42 inches (1067 mm) above the floor level, and the yoke vent connection to the drainage stack shall be using a wye-branch fitting placed below the lowest drainage branch connection serving that floor.
908.0 Wet Venting. 908.1 Vertical Wet Venting. Wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one and two fixture unit fixtures that also serves as a vent not exceeding four fixtures. Wet-vented fixtures shall be within the same story; provided, further, that fixtures with a continuous vent discharging into a wet vent shall be within the same story as the wet-vented fixtures. No wet vent shall exceed 6 feet (1829 mm) in developed length. 908.1.1 Size. The vertical piping between two consecutive inlet levels shall be considered a wet-vented sec tion. Each wet-vented section shall be not less than one pipe size exceeding the required minimum waste pipe size of the upper fixture or shall be one pipe size exceeding the required minimum pipe size for the sum of the fixture units served by such wet-vented section, whichever is larger, but in no case less than 2 inches (50 mm) in diameter. 908.1.2 Vent Connection. Common vent sizing shall be the sum of the fixture units served but, in no case,
190 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
VENTS
smaller than the minimum vent pipe size required for a fixture served, or by Section 904.0. 908.2 Horizontal Wet Venting for a Bathroom Group. A bathroom group located on the same floor level shall be permitted to be vented by a horizontal wet vent where all of the conditions of Section 908.2.1 through Section 908.2.5 are met.
908.2.1 Vent Connection. The dry vent connection to the wet vent shall be an individual vent for the bidet, shower, or bathtub. One or two vented lavatory(s) shall be permitted to serve as a wet vent for a bathroom group. Only one wet-vented fixture drain or trap arm shall discharge upstream of the dry-vented fixture drain connection. Dry vent connections to the horizontal wet vent shall be in accordance with Section 905.2 and Section
905.3.
908.2.2 Size. The wet vent shall be sized based on the fixture unit discharge into the wet vent. The wet vent shall be not less than 2 inches (50 mm) in diameter for 4 drainage fixture units (dfu) or less, and not less than 3 inches (80 mm) in diameter for 5 dfu or more. The dry vent shall be sized in accordance with Table 702.1 and Table 703.2 based on the total fixture units discharging into the wet vent.
908.2.3 Trap Arm. The length of the trap arm shall not exceed the limits in Table 1002.2. The trap size shall be in accordance with Section 1003.3. The vent pipe opening from the horizontal wet vent, except for water closets and similar fixtures, shall not be below the weir of the trap.
CPC § 25.4 High relevance — show source text
For SI units: 1 inch = 25.4 mm
Notes: 1 Maintain 1 ⁄ 4 inch per foot slope (20.8 mm/m). 2 The developed length between the trap of a water closet or similar fixture (measured from the face of the closet flange to the inner edge of the vent) and its vent shall not exceed 6 feet (1829 mm). 3 Horizontally wet vented bathtubs, showers and similar fixtures shall be limited to a maximum of 6 feet (1829 mm) for 1½ inch (40 mm) fixture drains and 8 feet (2438 mm) for 2 inch (50 mm) fixture drains, maintaining ¼ inch per foot slope (20.8 mm/m).
1003.2 Slip Joint Fittings. A maximum of one approved slip joint fitting shall be permitted to be used on the outlet side of a trap, and no tubing trap shall be installed without a listed tubing trap adapter. Listed plastic trap adapters shall be permitted to be used to connect listed metal tubing traps.
1003.3 Size. The size (nominal diameter) of a trap for a given fixture shall be sufficient to drain the fixture rapidly but in no case less than nor more than one pipe size larger than given in Table 702.1. The trap shall be the same size as the trap arm to which it is connected.
TABLE 1002.2
HORIZONTAL LENGTHS OF TRAP ARMS (EXCEPT FOR WATER CLOSETS AND SIMILAR FIXTURES) [1, 2, 3]
For SI units: 1 inch = 25.4 mm
Notes: 1 Maintain 1 ⁄ 4 inch per foot slope (20.8 mm/m). 2 The developed length between the trap of a water closet or similar fixture (measured from the face of the closet flange to the inner edge of the vent) and its vent shall not exceed 6 feet (1829 mm). 3 Horizontally wet vented bathtubs, showers and similar fixtures shall be limited to a maximum of 6 feet (1829 mm) for 1½ inch (40 mm) fixture drains and 8 feet (2438 mm) for 2 inch (50 mm) fixture drains, maintaining ¼ inch per foot slope (20.8 mm/m).
2025 CALIFORNIA PLUMBING CODE 195
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
TRAPS AND INTERCEPTORS
1004.0 Traps.
1004.1 Prohibited. No form of trap that depends for its seal upon the action of movable parts shall be used. No trap that has concealed interior partitions, except those of plastic, glass, or similar corrosion-resisting material, shall be used. “S” traps, bell traps, and crown-vented traps shall be prohibited. No fixture shall be double trapped. Drum and bottle traps shall be installed for special conditions. No trap shall be installed without a vent, except as otherwise provided in this code.
1004.2 Movable Parts. Bladders, check valves or another type of devices with moveable parts shall be prohibited to serve as a trap.
CPC § 908.2.4 Medium relevance — show source text
908.2.4 Water Closet. The water closet fixture drain or trap arm connection to the wet vent shall be downstream of fixture drain or trap arm connections to the horizontal wet vent.
908.2.5 Additional Fixtures. Additional fixtures shall discharge downstream of the wet vent system and be conventionally vented. Only the fixtures within the bathroom group shall connect to the wet-vented horizontal branch.
909.0 Special Venting for Island Fixtures. 909.1 General. Traps for island sinks and similar equipment shall be roughed in above the floor and shall be permitted to be vented by extending the vent as high as possible, but not less than the drainboard height and then returning it downward and connecting it to the horizontal sink drain immediately downstream from the vertical fixture drain. The return vent shall be connected to the horizontal drain through a wyebranch fitting and shall, in addition, be provided with a foot vent taken off the vertical fixture vent by means of a wye branch immediately below the floor and extending to the nearest partition and then through the roof to the open air, or shall be permitted to be connected to other vents at a point not less than 6 inches (152 mm) above the flood-level rim of the fixtures served. Drainage fittings shall be used on the vent below the floor level, and a slope of not less than [1] ⁄ 4 inch per foot (20.8 mm/m) back to the drain shall be maintained. The return bend used under the drainboard shall be a one-piece
fitting or an assembly of a 45 degree (0.79 rad), a 90 degree (1.57 rad), and a 45 degree (0.79 rad) elbow in the order named. Pipe sizing shall be as elsewhere required in this code. The island sink drain, upstream of the returned vent, shall serve no other fixtures. An accessible cleanout shall be installed in the vertical portion of the foot vent.
910.0 Combination Waste and Vent Systems. 910.1 Where Permitted. Combination waste and vent systems shall be permitted where structural conditions preclude the installation of conventional systems as otherwise prescribed by this code. 910.2 Approval. Construction documents for each combination waste and vent system shall first be approved by the Authority Having Jurisdiction before a portion of such system is installed.
910.3 Vents. Each combination waste and vent system, as defined in Chapter 2, shall be provided with a vent or vents adequate to ensure free circulation of air. A branch exceeding 15 feet (4572 mm) in length shall be separately vented in an approved manner. The area of a vent installed in a combination waste and vent system shall be not less than one-half the inside cross-sectional area of the drainpipe served. The vent connection shall be downstream of the uppermost fixture. 910.4 Connections and Size. Branches serving traps shall connect to the main line at an angle not exceeding 2 percent. Each waste pipe and each trap in such a system shall be not less than two pipe sizes exceeding the sizes required by Chapter 7 of this code, and not less than two pipe sizes exceeding a fixture tailpiece or connection. 910.5 Vertical Waste Pipe. No vertical waste pipe shall be used in such a system, except the tailpiece or connection between the outlet of a plumbing fixture and the trap. Such tailpieces or connections shall be as short as possible, and in no case shall exceed 2 feet (610 mm).
CPC § 908.1 Medium relevance — show source text
908.1 Vertical Wet Venting . . . . . . . . . . .190
908.2 Horizontal Wet Venting for a Bathroom Group . . . . . . . . . . . . . .191
909.0 Special Venting for Island Fixtures . . . . . . . . . . . . . . . . . . . . .191
909.1 General . . . . . . . . . . . . . . . . . . . . .191
910.0 Combination Waste and Vent
Systems . . . . . . . . . . . . . . . . . . . .191
910.1 Where Permitted . . . . . . . . . . . . . .191
910.2 Approval . . . . . . . . . . . . . . . . . . . .191
910.3 Vents . . . . . . . . . . . . . . . . . . . . . .191
910.4 Connections and Size . . . . . . . . .191
910.5 Vertical Waste Pipe . . . . . . . . . . .191
910.6 Cleanouts . . . . . . . . . . . . . . . . . . .191
910.7 Fixtures . . . . . . . . . . . . . . . . . . . . .191
911.0 Circuit Venting . . . . . . . . . . . . . . .191
911.1 Circuit Vent Permitted . . . . . . . . .191
911.2 Circuit Vent Size and
Connection . . . . . . . . . . . . . . . . . .192
911.3 Relief Vent . . . . . . . . . . . . . . . . . .192
911.4 Slope and Size of Horizontal Branch . . . . . . . . . . . . . . . . . . . . .192
911.5 Additional Fixtures . . . . . . . . . . . .192
912.0 Engineered Vent System . . . . . . .192
912.1 General . . . . . . . . . . . . . . . . . . . . .192
912.2 Minimum Requirements . . . . . . . .192
CHAPTER 10 TRAPS AND
INTERCEPTORS . . . . . . . . . . . . .193
1001.0 General . . . . . . . . . . . . . . . . . . . . .195
1001.1 Applicability . . . . . . . . . . . . . . . . . .195
1001.2 Where Required . . . . . . . . . . . . . .195
1002.0 Traps Protected by Vent Pipes . .195
1002.1 Vent Pipes . . . . . . . . . . . . . . . . . .195
1002.2 Fixture Traps . . . . . . . . . . . . . . . .195
1002.3 Change of Direction . . . . . . . . . . .195
1002.4 Vent Pipe Opening . . . . . . . . . . . .195
1003.0 Traps – Described . . . . . . . . . . . .195
1003.1 General Requirements . . . . . . . . .195
California Plumbing Code Medium relevance — show source text
IN THOUSANDS OF BTU PER HOUR**|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR| |VENT
HEIGHT
H
(feet)|CONNECTOR
RISE
R
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |VENT
HEIGHT
H
(feet)|CONNECTOR
RISE
R
(feet)|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|1
2
3|292
301
309|366
432
491|200
231
269|362
373
381|474
557
634|252
299
348|499
509
519|594
696
793|316
376
437| |8|1
2
3|313
323
332|407
465
509|207
238
274|387
397
407|530
607
663|263
309
356|529
540
551|672
766
838|331
391
450| |10|1
2
3|333
343
352|434
489
530|213
244
279|410
420
430|571
640
694|273
317
363|558
569
580|727
813
880|343
403
459| |15|1
2
3|349
359
368|502
548
586|225
256
289|445
456
466|646
706
755|291
334
378|623
634
646|808
884
945|366
424
479| |20|1
2
3|345
355
365|569
610
644|235
266
298|439
450
461|734
787
831|306
348
391|614
627
639|921
986
1042|387
443
496| |30|1
2
3|338
348
358|665
699
729|250
282
312|430
442
452|864
908
946|330
372
412|600
613
626|1089
1145
1193|421
473
524| |50|1
2CPC § 19.19 Medium relevance — show source text
Exception s :
(1) Drawn-copper alloy tubing traps shall not be used for urinals. Each trap shall have the manufacturer’s name stamped legibly in the metal of the trap, and each tubing trap shall have the gauge of the tubing in addition to the manufacturer’s name. A trap shall have a smooth and uniform interior waterway.
(2) [HCD 1 & HCD 2] Non-water supplied urinals conform- ing to ASME A112.19.19-2016, Standard for Vitreous China Nonwater Urinals, or reference standards in Table 1701.1 for non-vitreous ceramic or plastic urinal fixtures.
TABLE 1002.2
HORIZONTAL LENGTHS OF TRAP ARMS (EXCEPT FOR WATER CLOSETS AND SIMILAR FIXTURES) [1, 2, 3]
TRAP ARM PIPE
DIAMETER (inches)DISTANCE TRAP TO
VENT MINIMUM
(inches)LENGTH MAXIMUM
(inches)11⁄4 21⁄2 30
11⁄23 42
24 60
36 72
48 120
Exceeding 42 x Diameter 120 For SI units: 1 inch = 25.4 mm
Notes: 1 Maintain 1 ⁄ 4 inch per foot slope (20.8 mm/m). 2 The developed length between the trap of a water closet or similar fixture (measured from the face of the closet flange to the inner edge of the vent) and its vent shall not exceed 6 feet (1829 mm). 3 Horizontally wet vented bathtubs, showers and similar fixtures shall be limited to a maximum of 6 feet (1829 mm) for 1½ inch (40 mm) fixture drains and 8 feet (2438 mm) for 2 inch (50 mm) fixture drains, maintaining ¼ inch per foot slope (20.8 mm/m).
1003.2 Slip Joint Fittings. A maximum of one approved slip joint fitting shall be permitted to be used on the outlet side of a trap, and no tubing trap shall be installed without a listed tubing trap adapter. Listed plastic trap adapters shall be permitted to be used to connect listed metal tubing traps.
1003.3 Size. The size (nominal diameter) of a trap for a given fixture shall be sufficient to drain the fixture rapidly but in no case less than nor more than one pipe size larger than given in Table 702.1. The trap shall be the same size as the trap arm to which it is connected.
TABLE 1002.2
HORIZONTAL LENGTHS OF TRAP ARMS (EXCEPT FOR WATER CLOSETS AND SIMILAR FIXTURES) [1, 2, 3]
For SI units: 1 inch = 25.4 mm
CPC § 1002.2 Medium relevance — show source text
1002.2 Fixture Traps. Each fixture trap shall have a protecting vent so located that the developed length of the trap arm from the trap weir to the inner edge of the vent shall be within the distance given in Table 1002.2 but in no case less than two times the diameter of the trap arm. 1002.3 Change of Direction. A trap arm shall be permitted to change direction without the use of a cleanout where such change of direction does not exceed 90 degrees (1.57 rad). Horizontal changes in the direction of trap arms shall be in accordance with Section 706.3.
Exception: For trap arms, 3 inches (80 mm) in diameter and larger, the change of direction shall not exceed 135 degrees (2.36 rad) without the use of a cleanout. 1002.4 Vent Pipe Opening. The vent pipe opening from soil or waste pipe, except for water closets and similar fixtures, shall not be below the weir of the trap.
1003.0 Traps – Described. 1003.1 General Requirements. Each trap, except for traps within an interceptor or similar device shall be selfcleaning. Traps for bathtubs, showers, lavatories, sinks, laun
dry sinks, floor drains, urinals, drinking fountains, dental units, and similar fixtures shall be of standard design, weight and shall be of ABS, cast-brass, cast-iron, lead, PP, PVC, or other approved material. An exposed and readily accessible drawn-copper alloy tubing trap, not less than 17 B & S Gauge (0.045 inch) (1.143 mm), shall be permitted to be used on fixtures discharging domestic sewage.
Exception s :
(1) Drawn-copper alloy tubing traps shall not be used for urinals. Each trap shall have the manufacturer’s name stamped legibly in the metal of the trap, and each tubing trap shall have the gauge of the tubing in addition to the manufacturer’s name. A trap shall have a smooth and uniform interior waterway.
(2) [HCD 1 & HCD 2] Non-water supplied urinals conform- ing to ASME A112.19.19-2016, Standard for Vitreous China Nonwater Urinals, or reference standards in Table 1701.1 for non-vitreous ceramic or plastic urinal fixtures.
TABLE 1002.2
HORIZONTAL LENGTHS OF TRAP ARMS (EXCEPT FOR WATER CLOSETS AND SIMILAR FIXTURES) [1, 2, 3]
TRAP ARM PIPE
DIAMETER (inches)DISTANCE TRAP TO
VENT MINIMUM
(inches)LENGTH MAXIMUM
(inches)11⁄4 21⁄2 30
11⁄23 42
24 60
36 72
48 120
Exceeding 42 x Diameter 120 For SI units: 1 inch = 25.4 mm
CPC § 905.1 Medium relevance — show source text
905.1 Grade . . . . . . . . . . . . . . . . . . . . . .190
905.2 Horizontal Drainage Pipe . . . . . . .190
905.3 Vent Pipe Rise . . . . . . . . . . . . . . .190
905.4 Roof Termination . . . . . . . . . . . . .190
905.5 Location of Opening . . . . . . . . . . .190
905.6 Common Vertical Pipe . . . . . . . . .190
906.0 Vent Termination . . . . . . . . . . . . .190
906.1 Roof Termination . . . . . . . . . . . . .190
906.2 Clearance . . . . . . . . . . . . . . . . . . .190
906.3 Use of Roof . . . . . . . . . . . . . . . . .190
906.4 Outdoor Installations . . . . . . . . . . .190
906.5 Joints . . . . . . . . . . . . . . . . . . . . . .190
906.6 Lead . . . . . . . . . . . . . . . . . . . . . . .190
906.7 Frost or Snow Closure . . . . . . . . .190
907.0 Vent Stacks and Relief Vents . . . .190
907.1 Drainage Stack . . . . . . . . . . . . . . .190
907.2 Yoke Vent . . . . . . . . . . . . . . . . . . .190
908.0 Wet Venting . . . . . . . . . . . . . . . . .190
908.1 Vertical Wet Venting . . . . . . . . . . .190
908.2 Horizontal Wet Venting for a Bathroom Group . . . . . . . . . . . . . .191
909.0 Special Venting for Island Fixtures . . . . . . . . . . . . . . . . . . . . .191
909.1 General . . . . . . . . . . . . . . . . . . . . .191
910.0 Combination Waste and Vent
Systems . . . . . . . . . . . . . . . . . . . .191
910.1 Where Permitted . . . . . . . . . . . . . .191
910.2 Approval . . . . . . . . . . . . . . . . . . . .191
910.3 Vents . . . . . . . . . . . . . . . . . . . . . .191
910.4 Connections and Size . . . . . . . . .191
910.5 Vertical Waste Pipe . . . . . . . . . . .191
910.6 Cleanouts . . . . . . . . . . . . . . . . . . .191
910.7 Fixtures . . . . . . . . . . . . . . . . . . . . .191
911.0 Circuit Venting . . . . . . . . . . . . . . .191
911.1 Circuit Vent Permitted . . . . . . . . .191
911.2 Circuit Vent Size and
Connection . . . . . . . . . . . . . . . . . .192
CPC § 910.7 Medium relevance — show source text
910.7 Fixtures. No water closet or urinal shall be installed on such a system. Other one, two, or three unit fixtures remotely located from the sanitary system and adjacent to a combination waste and vent system shall be permitted to be connected to such system in the conventional manner by means of waste and vent pipes of regular sizes, providing that the two pipe size increase required in Section 910.4 is based on the total fixture unit load connected to the system.
See Appendix B of this code for explanatory notes on the design of combination waste and vent systems.
911.0 Circuit Venting. 911.1 Circuit Vent Permitted. A maximum of eight flooroutlet water closets, showers, bathtubs, or floor drains con
2025 CALIFORNIA PLUMBING CODE 191
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
VENTS
nected to a horizontal branch shall be permitted to be circuit vented. Each trap arm shall connect horizontally to the horizontal branch being circuit vented in accordance with Table 1002.2. The horizontal branch shall be classified as a drain and a vent from the most downstream trap arm connection to the most upstream trap arm connection to the horizontal branch.
Exception: Back-outlet and wall-hung water closets shall be permitted to be circuit vented provided that no floor-outlet fixtures are connected to the same horizontal branch. Backoutlet and wall-hung water closets shall connect horizontally to the horizontal circuit vented drain.
911.2 Circuit Vent Size and Connection. The circuit vent size shall be in accordance with Table 703.2 according to the number of circuit vented fixtures connected to the horizontal branch but shall be not less than 2 inches (50 mm) in diameter. The vent shall connect to the horizontal branch on the vertical between the two most upstream trap arms. The circuit vent pipe shall not receive the discharge of soil or
waste.
911.2.1 Multiple Circuit Vents. When multiple circuit vents are interconnected according to Section 911.4.1, each individual circuit vent shall be sized according to Section 911.2. The vent pipe connecting each circuit vent shall be sized according to Table 703.2.
911.3 Relief Vent. A 2 inch (50 mm) relief vent shall be provided for circuit-vented horizontal branches receiving the discharge of four or more water closets when connecting to a drainage stack that receives the discharge of soil or waste from upper horizontal branches.
911.3.1 Connection and Installation. The relief vent
shall connect to the horizontal branch between the stack and the most downstream trap arm of the circuit vent. The relief vent shall be installed on the vertical to the
horizontal branch.
911.3.2 Fixture Drain. The relief vent is permitted to serve as a fixture drain. Fixtures discharging to a relief vent shall be one or two fixture unit fixtures but shall not
exceed a total of 4 fixture units.
911.4 Slope and Size of Horizontal Branch. The vented section of the horizontal branch shall be uniformly sloped and not more than 1 inch per foot (83.3 mm/m). The entire length of the vented section of the horizontal branch shall be sized for the total drainage discharge to the branch according to Table 703.2.
CPC § 910.0 Medium relevance — show source text
910.0 Combination Waste and Vent Systems. 910.1 Where Permitted. Combination waste and vent systems shall be permitted where structural conditions preclude the installation of conventional systems as otherwise prescribed by this code. 910.2 Approval. Construction documents for each combination waste and vent system shall first be approved by the Authority Having Jurisdiction before a portion of such system is installed.
910.3 Vents. Each combination waste and vent system, as defined in Chapter 2, shall be provided with a vent or vents adequate to ensure free circulation of air. A branch exceeding 15 feet (4572 mm) in length shall be separately vented in an approved manner. The area of a vent installed in a combination waste and vent system shall be not less than one-half the inside cross-sectional area of the drainpipe served. The vent connection shall be downstream of the uppermost fixture. 910.4 Connections and Size. Branches serving traps shall connect to the main line at an angle not exceeding 2 percent. Each waste pipe and each trap in such a system shall be not less than two pipe sizes exceeding the sizes required by Chapter 7 of this code, and not less than two pipe sizes exceeding a fixture tailpiece or connection. 910.5 Vertical Waste Pipe. No vertical waste pipe shall be used in such a system, except the tailpiece or connection between the outlet of a plumbing fixture and the trap. Such tailpieces or connections shall be as short as possible, and in no case shall exceed 2 feet (610 mm).
Exception: Branch lines shall be permitted to have 45 degree (0.79 rad) vertical offsets.
910.6 Cleanouts. An accessible cleanout shall be installed in each vent for the combination waste and vent system. Cleanouts shall not be required on a wet-vented branch serving a single trap where the fixture tailpiece or connection is not less than 2 inches (50 mm) in diameter and provides ready access for cleaning through the trap.
910.7 Fixtures. No water closet or urinal shall be installed on such a system. Other one, two, or three unit fixtures remotely located from the sanitary system and adjacent to a combination waste and vent system shall be permitted to be connected to such system in the conventional manner by means of waste and vent pipes of regular sizes, providing that the two pipe size increase required in Section 910.4 is based on the total fixture unit load connected to the system.
See Appendix B of this code for explanatory notes on the design of combination waste and vent systems.
911.0 Circuit Venting. 911.1 Circuit Vent Permitted. A maximum of eight flooroutlet water closets, showers, bathtubs, or floor drains con
2025 CALIFORNIA PLUMBING CODE 191
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
VENTS
nected to a horizontal branch shall be permitted to be circuit vented. Each trap arm shall connect horizontally to the horizontal branch being circuit vented in accordance with Table 1002.2. The horizontal branch shall be classified as a drain and a vent from the most downstream trap arm connection to the most upstream trap arm connection to the horizontal branch.
Exception: Back-outlet and wall-hung water closets shall be permitted to be circuit vented provided that no floor-outlet fixtures are connected to the same horizontal branch. Backoutlet and wall-hung water closets shall connect horizontally to the horizontal circuit vented drain.
Frequently asked questions
Can I wet-vent a tub and lavatory together horizontally?
Yes — lavatories are allowed to serve as the wet vent for a bathroom group, but the shower or bathtub requires an individual dry vent connection to the horizontal wet vent per § 908.2.1. Also confirm trap arm lengths and wet‑vent sizing per § 908.2.2 and Table 1002.2.
What diameter must my horizontal wet vent be for a typical 1‑bath group?
Use the total dfu. A typical private 1‑bath group is 5.0 dfu (Appendix C), so the wet vent must be not less than 3 inches by § 908.2.2.
How far can the lavatory trap be from its vent on a horizontal wet vent?
Refer to Table 1002.2: a 1‑1/4" trap arm is limited to 30 inches, a 1‑1/2" to 42 inches, etc. The developed length is from the trap weir to the inner edge of the vent.
Can more fixtures outside the bathroom group connect to the wet vent?
No. Only the fixtures within the bathroom group may connect to the wet‑vented horizontal branch; additional fixtures must discharge downstream and be conventionally vented (§ 908.2.5).
What if my trap arm length would exceed Table 1002.2 limits?
You must reconfigure the piping (shorten the trap arm, increase trap/trap‑arm diameter where appropriate, or add an accessible vent) so the developed length complies with Table 1002.2 and § 908.2.3.
More in California Plumbing Code
- Administration
- Definitions
- General Regulations
- Plumbing Fixtures and Fixture Fittings
- Water Heaters
- Water Supply and Distribution
- Sanitary Drainage (Drain, Waste, and Vent)
- Indirect Wastes
- Vents
- Traps and Interceptors
- Storm Drainage
- Fuel Gas Piping
- Health Care Facilities — Medical Gas and Medical Vacuum Systems
- Alternate Water Sources and Nonpotable Rainwater Catchment Systems
Ask about the CPC
Get cited, plain-English answers on the California Plumbing Code for your project — any code section, any scenario.
Start Free Trial