13.3 Island Fixture Venting and Air Admittance Valves
Key Takeaways
- IPC 916.1 limits island fixture venting to sinks and lavatories, expressly permitting a residential kitchen sink with a dishwasher waste connection, a food waste disposer, or both.
- IPC 916.3 requires cleanouts in the island fixture vent to permit rodding of all vent piping below the flood level rim, with rodding permitted in both directions through a cleanout.
- IPC 918.1 requires stack-type air admittance valves to conform to ASSE 1050 and individual and branch-type valves to conform to ASSE 1051.
- IPC 918.4 locates individual and branch-type air admittance valves not less than 4 inches above the horizontal branch drain or fixture drain, and stack-type valves not less than 6 inches above the flood level rim of the highest fixture vented.
- IPC 918.3.2 prohibits stack-type air admittance valves from serving as the vent terminal for stacks having more than six branch intervals.
Island fixture venting — IPC Section 916
An island sink has no wall to run a vent up. Section 916 permits a loop that rises above the fixture outlet, turns over, and drops back down to the drain.
916.1 Limitation
Island fixture venting shall not be permitted for fixtures other than sinks and lavatories. Residential kitchen sinks with a dishwasher waste connection, a food waste disposer, or both, in combination with the kitchen sink waste, shall be permitted to be vented in accordance with this section.
Sinks and lavatories only. No water closets, no bathtubs, no showers, no floor drains.
916.2 Vent connection
The island fixture vent shall connect to the fixture drain as required for an individual or common vent. The vent shall rise vertically to above the drainage outlet of the fixture being vented before offsetting horizontally or vertically downward. The vent or branch vent for multiple island fixture vents shall extend to a point not less than 6 inches above the highest island fixture being vented before connecting to the outside vent terminal.
Two distinct heights:
- The individual island vent rises above the drainage outlet of the fixture before turning.
- The vent or branch vent for multiple island fixture vents rises to 6 inches above the highest island fixture before connecting to the outside terminal.
916.3 Vent installation below the fixture flood level rim
The vent located below the flood level rim of the fixture being vented shall be installed as required for drainage piping in accordance with Chapter 7, except for sizing. The vent shall be sized in accordance with Section 906.2. The lowest point of the island fixture vent shall connect full size to the drainage system. The connection shall be to a vertical drain pipe or to the top half of a horizontal drain pipe. Cleanouts shall be provided in the island fixture vent to permit rodding of all vent piping located below the flood level rim of the fixtures. Rodding in both directions shall be permitted through a cleanout.
Because the descending leg of the loop sits below the flood level rim, it can and will collect waste. So the code treats it as drainage piping for installation purposes — drainage fittings, drainage slope, drainage support — while sizing it as a vent.
The cleanout requirement is what distinguishes a compliant island vent from the common defect: an island loop with no access is impossible to clear when it fouls.
IPC 904.1.1 adds the limit noted in Chapter 12 of this guide: the required outdoor vent for a building drain shall not be an island fixture vent.
Air admittance valves — IPC Section 918
A one-way valve that opens under negative pressure to admit air and closes by gravity, sealing against sewer gas. It relieves backsiphonage only — it can do nothing about back pressure, which is why 918.7 still requires an open vent.
918.1 Standards
| Type | Standard |
|---|---|
| Stack-type air admittance valves | ASSE 1050 |
| Individual and branch-type air admittance valves | ASSE 1051 |
| Chemical waste air admittance valves | ASSE 1049, materials per 702.6, chemical resistance per ASTM F1412 |
918.2 Installation
The valves shall be installed in accordance with this section and the manufacturer's instructions. Air admittance valves shall be installed after the DWV testing required by Section 312.2 or 312.3 has been performed.
An AAV diaphragm will not hold a 5 psi air test or a 10-foot water head. Install them after the test, not before.
918.3 Where permitted
- 918.3.1 Horizontal branches: individual and branch-type AAVs shall vent only fixtures that are on the same floor level and connect to a horizontal branch drain. Where the horizontal branch is located more than four branch intervals from the top of the stack, the branch shall be provided with a relief vent connecting to a vent stack or stack vent, or extending outdoors. The relief vent connects to the horizontal branch between the stack and the most downstream fixture drain, is sized per 906.2, installed per 905, and may serve as the vent for other fixtures.
- 918.3.2 Stack: stack-type AAVs shall be prohibited from serving as the vent terminal for vent stacks or stack vents that serve drainage stacks having more than six branch intervals.
918.4 Location
| Type | Minimum height |
|---|---|
| Individual and branch-type | not less than 4 inches above the horizontal branch drain or fixture drain being vented |
| Stack-type | not less than 6 inches above the flood level rim of the highest fixture being vented |
| All types | Within the maximum developed length permitted for the vent, and not less than 6 inches above insulation materials |
918.5 Access and ventilation
Access shall be provided to all air admittance valves. Such valves shall be installed in a location that allows air to enter the valve.
An AAV sealed inside a finished cabinet with no air path is inoperative. Both halves of the rule matter — access for service, and an air path for function.
918.6 Size
The AAV shall be rated in accordance with the standard for the size of the vent to which it connects.
918.7 Vent required
Within each plumbing system, not less than one stack vent or vent stack shall extend outdoors to the open air.
This is the rule that makes AAVs a supplement rather than a substitute. Because an AAV cannot relieve positive pressure, a system with no open vent has no path for compressed air at the base of a stack to escape except through a trap seal.
918.8 Prohibited installations
Air admittance valves shall not:
- Be installed in nonneutralized special waste systems described in Chapter 8, except where they comply with ASSE 1049, are of materials approved under Section 702.5, and are tested for chemical resistance per ASTM F1412.
- Be located in spaces utilized as supply or return air plenums.
- Be used to vent sumps or tanks, except where the vent system for the sump or tank has been designed by an engineer.
- Be installed on outdoor vent terminals for the sole purpose of reducing clearances to gravity air intakes or mechanical air intakes.
Item 4 closes an obvious loophole: capping a sidewall vent with an AAV to dodge the 903.5 separation requirement.
Engineered vent systems — IPC Section 919
919.1: engineered vent systems shall comply with Section 919 and the design, submittal, approval, inspection and testing requirements of Section 316.1 (alternative engineered design, covered in Chapter 2 of this guide).
919.2 covers individual branch fixture and individual fixture header vents, with Table 919.2 sizing them. 920 addresses computerized vent system design: the design of the vent system is by approved computer design methods, with system capacity based on the design criteria.
Choosing between an island vent and an AAV
| Consideration | Island fixture vent (916) | Air admittance valve (918) |
|---|---|---|
| Fixtures served | Sinks and lavatories only | Fixtures on the same floor connecting to a horizontal branch (individual/branch type) |
| Moving parts | None | A sealing membrane that wears |
| Relieves back pressure | Yes, it is an open vent | No — backsiphonage only |
| Can serve as the required outdoor vent | No (904.1.1) | No (918.7) |
| Access required | Cleanouts for rodding below the rim (916.3) | Access to the valve, and an air path (918.5) |
| Prohibited locations | — | Plenums, sumps and tanks without engineered design, nonneutralized special waste, outdoor terminals to dodge clearances (918.8) |
| Height | Above the fixture drainage outlet before offsetting | 4 in above the branch drain, or 6 in above the flood level rim for stack type |
Which fixtures may be vented by an island fixture vent under IPC 916.1?
At what height must an individual-type air admittance valve be located under IPC 918.4?
A drainage stack has eight branch intervals. May a stack-type air admittance valve serve as its vent terminal?
When must air admittance valves be installed relative to the required drainage and vent test?