CPC · California Plumbing Code
When is vertical wet venting allowed and what are the sizing limits?
A vertical wet vent can only serve up to four fixtures on the same floor, cannot be longer than 6 feet, and must be sized one pipe size larger than the controlling waste size or fixture‑unit total but never smaller than 2 inches, per **§ 908.1**, **§ 908.1.1**, and **§ 908.1.2** of the CPC.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Vertical wet venting is permitted only where the vertical drainage pipe receives the discharge from the trap arm of one- and two–fixture-unit fixtures and the vertical wet vent serves no more than four fixtures on the same story. The wet vent’s developed length must not exceed 6 feet (1829 mm). Sizing of each wet‑vented section is based on the rule that the wet‑vented pipe be one pipe size larger than either (a) the required minimum waste pipe size of the upper fixture or (b) one size larger than the required size for the sum of the fixture units served — whichever is larger — and in no case less than 2 inches. These requirements are stated in § 908.1, § 908.1.1, and § 908.1.2 of the CPC.
The single most important rule: A vertical wet vent can only serve up to four fixtures on the same story, be no longer than 6 feet, and must be sized at one pipe size larger than the controlling waste/fixture‑unit requirement but never smaller than 2 inches (see § 908.1, § 908.1.1, § 908.1.2).
Requirements in detail
Scope and basic limits (what is allowed)
- Allowed only for vertical drainage piping that receives the discharge from the trap arm of fixtures that are one- or two‑fixture‑unit fixtures. § 908.1.
- The vertical wet vent may serve no more than four fixtures. § 908.1.
- All wet‑vented fixtures (and any fixtures with a continuous vent discharging into the wet vent) must be on the same story. § 908.1.
- The developed length of a wet vent shall not exceed 6 feet (1829 mm). § 908.1.
How to size the vertical wet‑vented section
- A wet‑vented section is the vertical piping between two consecutive inlet levels (that vertical segment is treated as the wet‑vented section). § 908.1.1.
- For each wet‑vented section, select the larger of:
- One pipe size larger than the required minimum waste pipe size of the upper fixture served; or
- One pipe size larger than the required size for the sum of the fixture units served by that wet‑vented section.
Then apply a final floor: in no case less than 2 inches (50 mm) diameter. § 908.1.1.
- When the wet vent also functions as a common vent, the common vent sizing is the sum of the fixture units served, but in no case may the common vent be smaller than the minimum vent size required for any fixture served (or the minimum required by Section 904.0). § 908.1.2.
Quick decision table (decision‑relevant dimensions / values)
| Issue / value | Code requirement | Code Reference |
|---|---|---|
| Maximum fixtures served by a vertical wet vent | No more than 4 fixtures | § 908.1 |
| Story requirement | All wet‑vented fixtures must be within the same story | § 908.1 |
| Maximum developed length | 6 ft (1829 mm) | § 908.1 |
| Minimum diameter for any wet‑vented section | Not less than 2 in (50 mm) | § 908.1.1 |
| Sizing rule for wet‑vented section | One pipe size larger than (a) required minimum waste size of the upper fixture OR (b) one size larger than required for the sum of fixture units — whichever is larger | § 908.1.1 |
| Sizing rule for common vent connection | Sum of fixture units served; but not smaller than minimum vent size required for any fixture or Section 904.0 | § 908.1.2 |
Exceptions & special cases
- Continuous vents that discharge into the wet vent: these fixtures still must be on the same story as the wet‑vented fixtures. § 908.1.
- The code establishes an absolute minimum diameter of 2 inches for any wet‑vented section regardless of what “one size larger” would otherwise produce. § 908.1.1.
- When a wet vent is used as a common vent, you must compare the vent sizing required by the fixture‑unit total to the minimum vent size that specific fixtures require; the vent cannot be reduced below that minimum (see § 908.1.2 referencing Section 904.0).
If you need to translate “one pipe size larger” into an actual diameter, consult the Chapter 7 tables (minimum waste pipe sizes and fixture‑unit tables) and the pipe‑size progression used locally; those numeric tables are not reproduced here. The CPC text that defines the sizing rule is in § 908.1.1 and § 908.1.2.
Common mistakes
- Assuming a wet vent may serve fixtures on different floors — the CPC requires all wet‑vented fixtures to be on the same story. § 908.1.
- Forgetting the 6‑foot developed length cap and designing a longer wet vent. § 908.1.
- Sizing the wet vent only to the upper fixture’s waste size without applying the “one size larger” rule or neglecting the requirement to be at least 2 inches. § 908.1.1.
- Using the wet vent as a common vent and reducing diameter below the minimum required by an individual fixture or Section 904.0. § 908.1.2.
Worked example — applying the rule step‑by‑step
Scenario: A vertical wet‑vented section will serve a small group of lavatories and sinks all on the same floor. The vertical piping segment connects two consecutive inlet levels.
Step 1 — Confirm applicability:
- All fixtures are on the same story and the vertical pipe receives discharge from the trap arms of the fixtures → wet vent is permissible under § 908.1 (but limited to ≤ 4 fixtures and ≤ 6 ft developed length).
Step 2 — Establish the controlling sizes (what the code requires you to compare):
- Determine (A) the required minimum waste pipe size for the upper fixture (from Chapter 7 tables), and (B) the required size for the sum of fixture units that will discharge into the wet‑vented section (also from Chapter 7 / fixture‑unit tables). These numeric tables are not reproduced here; the CPC sizing rule that tells you how to use them is in § 908.1.1.
Step 3 — Apply the sizing rule from § 908.1.1:
- Compute: SizeOption1 = one pipe size larger than the upper fixture’s minimum waste size.
SizeOption2 = one pipe size larger than the pipe size required for the sum of the fixture units served.
Choose the larger of SizeOption1 or SizeOption2. Then enforce the minimum: final wet‑vent diameter must be at least 2 inches. § 908.1.1.
Step 4 — Check common vent sizing (if the wet vent also serves as a common vent):
- If the wet vent functions as a common vent, size it per the sum of the fixture units served, but do not reduce it below the minimum vent pipe size required for any fixture served or the minimum in Section 904.0, per § 908.1.2.
Note: This worked example shows the procedural steps required by the CPC sections cited. To compute concrete diameters you must use the numeric fixture‑unit and minimum waste‑pipe tables in Chapter 7 (these tables were not included in the retrieved snippet of the CPC used here).
Related provisions
- Vertical wet venting rules: § 908.1, § 908.1.1, § 908.1.2.
- Horizontal wet venting for bathroom groups: § 908.2.
- Minimum vent size and vent opening rules: § 904.0 (referenced by § 908.1.2).
- Vent terminations and roof termination requirements: § 905.4, § 906.0 (context for vent systems).
- Definitions and fixture unit tables (Chapter 7 / Table 703.2) — used to determine the required sizes that feed into § 908.1.1 and § 908.1.2.
(For the authoritative text of the exact provisions quoted above, see § 908.1, § 908.1.1, and § 908.1.2 in the CPC.)
Code references
Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:
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 § 906.4 High relevance — show source text
906.4 Outdoor Installations. Vent pipes for outdoor installations shall extend not less than 10 feet (3048 mm) above the surrounding ground and shall be securely supported.
906.5 Joints. Joints at the roof around vent pipes shall be made watertight by the use of approved flashings or flashing material.
906.6 Lead. (See Chapter 17) Sheet lead shall comply with the following:
(1) For safe pans – not less than 4 pounds per square foot (lb/ft [2] ) (19 kg/m [2] ) or [1] ⁄ 16 of an inch (1.6 mm) thick. (2) For flashings or vent terminals – not less than 3 lb/ft [2] (15 kg/m [2] ) or 0.0472 of an inch (1.2 mm) thick. (3) Lead bends and lead traps shall be not less than [1] ⁄ 8 of an inch (3.2 mm) in wall thickness.
906.7 Frost or Snow Closure. Where frost or snow closure is likely to occur in locations having minimum design temperature below 0°F (-17.8°C), vent terminals shall be not less than 3 inches (76 mm) in diameter, but in no event smaller than the required vent pipe. The change in diameter shall be made inside the building not less than 1 foot (305 mm) below the roof in an insulated space and terminate not less than 10 inches (254 mm) above the roof, or in accordance with the Authority Having Jurisdiction.
907.0 Vent Stacks and Relief Vents.
907.1 Drainage Stack. Each drainage stack that extends 10 or more stories shall be served by a parallel vent stack, which shall extend undiminished in size from its upper terminal and connect to the drainage stack at or immediately below the lowest fixture drain. Each such vent stack shall also be connected to the drainage stack at each fifth floor, counting down from the uppermost fixture drain, using a yoke vent, the size of which shall be not less in diameter than either the drainage or the vent stack, whichever is smaller.
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.
CPC § 12.7.4.1 High relevance — show source text
(4) For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.
(5) Engineering methods. [NFPA 54:12.7.4.1] 509.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60 degree (1.05 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 509.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions. [NFPA 54:12.7.4.3] 509.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 509.6.3 Gas Vents Serving Appliances on More than One Floor. Where a common vent is installed in a multistory installation to vent Category I appliances located on more than one floor level, the venting system shall be designed and installed in accordance with engineering methods. Crawl spaces, basements, and attics shall be considered as floor levels. [NFPA 54:12.7.5.1]
509.6.3.1 Occupiable Space. All appliances connected to the common vent shall be located in rooms separated from occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from occupiable space. [NFPA 54:12.7.5.2] (See Figure 509.6.3.1)
FIGURE 509.6.3.1
PLAN VIEW OF PRACTICAL SEPARATION
METHOD FOR MULTISTORY GAS VENTING
[NFPA 54: FIGURE A.12.7.5.2]
509.6.3.2 Multistory Venting System. The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 510.2(1), provided all of the following apply:
(1) The available total height ( H ) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection
tee.
CPC § 907.0 High relevance — show source text
907.0, 911.3, 1009.4
Required . . . . . . . . . . . . . . . . . . . . . . . . . . .901.2, 904.1
Required separately
on every trap . . . . . . . . . . . . . . . .901.2, 1002.1, 1002.2 Sizing . . . . . . . . . . . . . .Table 702.1, 703.0, Table 703.2,
904.0, 908.1.1, 908.1.2,
908.2.2, 910.4, C 401.0,
Table C 401.1, C 601.2
Special . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .909.0
Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224.0, 906.1,
907.0, C 401.2, C 601.2
Sump . . . . . . . . . . . . . . . . . . . .710.7, 710.10, 710.13.3,
810.1, Table 810.1
System, definition . . . . . . . . . . . . . . . . . . . . . . . . .224.0
Termination . . . . . . . . . . . . . . . . . .905.4, 906.0, 906.2.1
Testing . . . . . . . . . . . . . . . . . . . . . . . . . .712.0, 1504.10 Trap seal protection . . . . . . . . . . . . . . . . . .901.3, 1002.0
Undiminished in
size through roof . . . . . . . . . . . . . . . . . . .905.4, 907.1 Unit loading . . . . . . . . . . . . . . . . . . . . . . . . .Table 703.2
Wet, Horizontal . . . . . . . . . . . . . . . . . . . . . . . . . . .908.2
Wet, Vertical . . . . . . . . . . . . . . . . . . . . . . . . . . . . .908.1
Yoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227.0, 907.0
VENTED APPLIANCE, DEFINITION . . . . . . . . . . . . . .224.0
Category I Vented Appliance, definition . . . . . . . . .224.0 Category II Vented Appliance, definition . . . . . . . .224.0 Category III Vented Appliance, definition . . . . . . . .224.0 Category IV Vented Appliance, definition . . . . . . .224.0 VENTILATING HOODS . . . . . . . . . . . . . . . .509.2.4, 509.3.4
VERTICAL-TO-HORIZONTAL
CPC § 25.4 Medium relevance — show source text
For SI Units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
509.6.1.1 Insulation Protection Shield. Where a vent passes through an insulated assembly, an approved metal shield constructed of steel having a thickness of not less than 26 gauge (0.0179 inch) (0.45 mm) (No. 26 gauge) shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the
manufacturer’s installation instructions.
509.6.2 Size of Gas Vents. Venting systems shall be sized and constructed in accordance with Section
2025 CALIFORNIA PLUMBING CODE 95
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
WATER HEATERS
509.6.2.1 through Section 509.6.2.3 and the appliance manufacturer’s instructions. [NFPA 54:12.7.4] 509.6.2.1 Category I Appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following:
(1) The provisions of Section 510.0.
(2) Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances, shall be sized in accordance with Section 510.0 or other engineering methods.
(3) For sizing an individual gas vent for a single, draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times the draft hood outlet area.
(4) For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.
(5) Engineering methods. [NFPA 54:12.7.4.1] 509.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60 degree (1.05 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 509.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions.
CPC § 904.0. Medium 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
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 § 2025 Medium relevance — show source text
Chapter 7 Sanitary Drainage.
This chapter regulates the design and installation of sanitary drainage systems to ensure they will work as intended. Drainage piping should not be oversized nor undersized, and constructed of approved materials to guard against fouling, deposit of solids, clogging, and with cleanouts so arranged that the pipes may be readily cleaned. The purpose of the sanitary drainage system is to remove effluent discharged from plumbing fixtures and other equipment to an approved point of disposal, such as a public sanitary system or private sewage disposal system.
The basics of a sanitary drainage system include public and private sewage disposal; selection of materials; installation of the building drain and sewer; joining methods for pipe and fittings; drainage fixture units for sizing the drainage system; sumps and ejectors; vent sizing and length of vents; and testing.
Chapter 8 Indirect Wastes.
Chapter 8 regulates indirect waste connections that are required for plumbing fixtures and plumbing appliances dealing with food preparation, dishwashing, potable liquids, and similar equipment. An indirect connection prevents sewage from backing up into a fixture or appliance, thus providing protection against potential health hazards. The waste pipe discharges through an air gap or air break into a waste receptor or standpipe. The protection in the form of an air gap is necessary when the contamination is a potential health hazard or cross connection with the potable water system. Where there is no possibility of contaminating the potable water (nonpotable discharge), the indirect waste pipe may connect in the form of an air break. This method is often preferred to prevent splashing. In addition, health care facilities and special wastes must be protected from contamination that may result from the connection to the drainage system. The waste must be treated to prevent any damage to the piping or sewage treatment process. Waste receptors are sized and designed to prevent splashing and allow for peak discharge conditions.
Chapter 9 Vents.
Chapter 9 regulates the material, design, and installation of vents. A vent system is a pipe or pipes installed in a drainage system that provide a flow of air to and from the system to ventilate it, provide a circulation of air to eliminate trap siphonage, and reduce back-pressure and vacuum surge. In addition, vents provide the rapid and silent flow of waste without exposing occupants of the building to any sewer gases. Proper installation of vents is crucial, as a telltale sign that there is a problem in the drain and vent system is related to the elevation of the horizontal portion of the venting. Venting is not limited to sanitary drainage systems. Venting methods are applicable to other drainage systems such as those for chemical waste, graywater waste, and clear water waste. Sizing the venting system is directly tied to the design of the drainage system. For example, the velocities in the drainage system and its peak flow rates affect the diameters in the venting system. Where the vertical distance between a fixture outlet and trap is excessive, velocities in the entire drainage system will be greater than those in the vent sizing table. All venting methods in this chapter are categorized as either dry vents or wet vents. Vent stacks, stack vents, branch vents, island vents, relief vents, and individual vents are dry vents. Wet vents (horizontal or vertical), circuit vents, combination drain and vents are versions of “wet venting” in which the vent is wetted by drainage flow.
2025 CALIFORNIA PLUMBING CODE xv
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
CPC § 9.595 Medium relevance — show source text
tonR**|PATH A|PATH B||105°F|120°F|140°F|140°F|105°F|120°F|140°F|140°F|140°F| |Air
source|All
sizes|≥9.595
FL
≥13.02
IPLV.IP|≥9.215
FL
≥15.01
IPLV.IP|47 db
43 wb4|≥3.290|≥2.770|≥2.310|NA|NA|NA|NA|NA|AHRI
550/590| |Air
source|All
sizes|≥9.595
FL
≥13.30
IPLV.IP|≥9.215
FL
≥15.30
IPLV.IP|17 db
15 wb4|≥2.230|≥1.950|≥1.630|NA|NA|NA|NA|NA|NA| |Water
source
electri-
cally
operated
positive
displace-
ment|<75|≤0.7885
FL
≤0.6316
IPLV.IP|≤0.7875
FL
≤0.5145
IPLV.IP|54/445|≥4.640|≥3.680|≥2.680|NA|≥8.330|≥6.410|≥4.420|NA|AHRI
550/590| |Water
source
electri-
cally
operated
positive
displace-
ment|<75|≤0.7885
FL
≤0.6316
IPLV.IP|≤0.7875
FL
≤0.5145
IPLV.IP|75/655|NA|NA|NA|≥3.550|NA|NA|NA|6.150|6.150| |Water
source
electri-
cally
operated
positive
displace-
ment|≥75
and
<150|≤0.7579
FL
≤0.5895
IPLV.IP|≤0.7140
FL
≤0.4620
IPLV.IP|54/445|≥4.640|≥3.680|≥2.680|NA|≥8.330|≥6.410|≥4.420|NA|NA| |Water
source
electri-
cally
operated
positive
displace-
ment|≥75
and
<150|≤0.7579
FL
≤0.5895
IPLV.IP|≤0.7140
FL
≤0.4620
IPLV.IP|75/655|NA|NA|NA|≥3.550|NA|NA|NA|6.150|6.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
Frequently asked questions
Can a wet vent serve a sink and a toilet on different floors?
No. Vertical wet‑vented fixtures and any fixtures with continuous vents into the wet vent must be located on the same story. Serving different floors is not permitted under § 908.1.
What if my “one size larger” calculation gives a 1½‑inch pipe?
Even if “one size larger” would produce 1½ inch, § 908.1.1 requires the wet‑vented section be not less than 2 inches in diameter. You must adopt 2 inches as the minimum.
How long may a vertical wet vent be?
The developed length of any wet vent shall not exceed 6 feet (1829 mm) measured along the piping. § 908.1.
If the wet vent doubles as a common vent, how do I size it?
Size the common vent by the sum of fixture units discharged into it, but do not reduce the vent below the minimum vent size required for any fixture served or that required by Section 904.0, per § 908.1.2.
Where do I find the numeric fixture‑unit and minimum waste sizes to apply the “one size larger” rule?
Numeric fixture‑unit values and minimum waste‑pipe sizes are in Chapter 7 (e.g., Table 703.2 and related tables). The CPC sections that set the wet‑venting rules tell you how to use those table results but do not list those numeric tables in § 908.1–§ 908.1.2.
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
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