11.2 Vent Terminals, Roof Penetrations, and Sidewall Terminations
Key Takeaways
- IPC 903.1.2 requires open vent pipes to terminate not less than 7 feet above a roof used as a promenade, restaurant, bar, sunbathing deck or observation deck.
- IPC 903.1.3 permits a vent covered by a roof-mounted panel or architectural element to terminate not less than 2 inches above the roof surface, with an open area not less than the pipe area and bird and rodent protection.
- IPC 903.1.4 requires sidewall vent terminals to be not less than 10 feet from the lot line and 10 feet above the highest adjacent grade within 10 feet horizontally.
- IPC 903.2 requires vent extensions through a roof or wall to be not less than 3 inches in diameter where the 97.5 percent outdoor design temperature is 0 degrees F or less, with the increase made at least 1 foot inside the thermal envelope.
- IPC 903.5 prohibits an open vent terminal directly beneath a door, openable window or air intake, and within 10 feet horizontally unless it is 3 feet or more above the top of the opening.
The terminal is the system's only opening
IPC 903.1: the vent pipe shall terminate by extending to the outdoors through the roof or the side wall by one of the four methods in 903.1.1 through 903.1.4. Everything the vent system does depends on that opening staying open, unobstructed, and away from places where sewer gas can re-enter the building.
Roof terminations
903.1.1 Roof extension unprotected
Open vent pipes that extend through a roof shall be terminated not less than [NUMBER] inches above the roof.
The number is bracketed in the model code, meaning the adopting jurisdiction fills it in. The exam is based on the model 2021 IPC, so an item asking for a specific unprotected-roof height would have to supply the jurisdiction's number.
Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(qq) fills the bracket with 6 inches: "All open vent pipes that extend through a roof shall be terminated at least 6 inches above the roof."
903.1.2 Roof used for recreational or assembly purposes
Where a roof is to be used as a promenade, restaurant, bar, or sunbathing deck, as an observation deck, or for similar purposes, open vent pipes shall terminate not less than 7 feet above the roof.
Seven feet puts the opening above the breathing zone of people standing on the deck.
903.1.3 Protected vent terminal
Where a vent terminates above a sloped roof and is covered by either a roof-mounted panel (a solar collector or photovoltaic panel mounted over the vent opening) or a roof element (an architectural feature or decorative shroud), the vent pipe shall terminate not less than 2 inches above the roof surface. Four conditions attach:
- Roof elements must be designed to prevent the adverse effects of snow accumulation and wind on the vent's function.
- The panel placement or roof element design must provide an open area to the outdoors not less than the area of the pipe, calculated from the inside diameter.
- The terminal must be protected by a method that prevents birds and rodents from entering or blocking the opening.
- The roof must be sloped.
Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(rr) changes 2 inches to 4 inches for the protected vent terminal in Colorado.
903.1.4 Sidewall vent terminal
| Requirement | Value |
|---|---|
| Distance from the lot line | not less than 10 feet |
| Height above the highest adjacent grade within 10 feet horizontally | not less than 10 feet |
| Under an overhang with soffit vents | Prohibited |
| Bird and rodent protection | Required |
Both 10-foot dimensions must be satisfied, and the soffit prohibition exists because a soffit vent pulls air directly into the attic and then into the building.
Frost closure — IPC 903.2
Where the 97.5-percent value for outdoor design temperature is 0 degrees F or less, vent extensions through a roof or wall shall be not less than 3 inches in diameter. Any increase in the size of the vent shall be made not less than 1 foot inside the thermal envelope of the building.
The physics: warm, saturated sewer gas rising through a cold vent deposits frost on the inside wall of the pipe. On a 2-inch pipe in sustained sub-zero weather the frost ring can close the opening entirely in a day. A 3-inch opening takes far longer to close, and making the transition 1 foot inside the thermal envelope puts the enlargement where the pipe is still warm, so the joint itself does not become the frost point.
IPC 903.6 Extension outside a structure: where the 97.5-percent outdoor design temperature is less than 0 degrees F, vent pipes installed on the exterior of the structure shall be protected against freezing by insulation, heat or both.
Colorado field note — an important divergence: Board Rule 1.2(E)(1)(ss) deletes IPC 903.2 Frost Closure in its entirety from the Colorado Plumbing Code. Colorado, a state with many jurisdictions well below a 0-degree design temperature, does not require the 3-inch vent extension. Board Rule 1.2(E)(2)(xx) does the same for IRC Section P3103.2.
On the exam, the model-code answer is the 3-inch rule. In a Colorado installation, the rule does not apply. This is one of the clearest cases where the exam answer and the field answer differ, and the PSI bulletin tells you which to use: the test is based solely on the model 2021 IPC and IRC.
Location of the terminal — IPC 903.5
An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet horizontally of such an opening unless it is 3 feet or more above the top of such opening.
Three tests, applied in order:
- Directly beneath an opening? Never permitted, at any height.
- Within 10 feet horizontally of an opening? Permitted only if the terminal is 3 feet or more above the top of the opening.
- More than 10 feet horizontally away? Permitted.
The rule protects adjacent buildings as well as the one being vented. A sidewall vent 6 feet from a neighbor's bedroom window is a violation even if it is nowhere near a window on its own building.
Flashings and prohibited uses
IPC 903.3 Flashings: the juncture of each vent pipe with the roof line shall be made watertight by an approved flashing. Materials come from IPC 902.2 and 902.3 — sheet copper not less than 8 ounces per square foot, field-constructed sheet lead not less than 3 pounds per square foot, prefabricated sheet lead not less than 2-1/2 pounds per square foot.
IPC 903.4 Prohibited use: a vent terminal shall not be used for any purpose other than a vent terminal. Anchoring a satellite dish, a guy wire or a lightning rod to a vent stack is a code violation, not merely bad practice.
Applying the rules to one roof
A two-story house in a jurisdiction with a 97.5-percent design temperature of minus 5 degrees F has a sloped roof. The plumber proposes:
| Proposal | Model IPC result |
|---|---|
| 2-inch vent through the roof | Fails 903.2 — the design temperature is 0 degrees F or less, so the extension must be not less than 3 inches |
| Increase from 2-inch to 3-inch at the roof deck | Fails 903.2 — the increase must be made not less than 1 foot inside the thermal envelope |
| Vent terminal 4 feet horizontally from an openable bedroom window, 1 foot above its head | Fails 903.5 — within 10 feet horizontally and not 3 feet or more above the top of the opening |
| Vent terminal 4 feet horizontally from the same window, 3 feet 6 inches above its top | Complies with 903.5 |
| Solar panel mounted over the vent, terminal 2 inches above the roof | Complies with 903.1.3 if the open area is not less than the pipe area, the assembly resists snow and wind, and birds and rodents are excluded |
| Exterior vent run up the gable wall, uninsulated | Fails 903.6 — the design temperature is less than 0 degrees F, so insulation, heat or both are required |
| Aluminum flashing at the roof line | Complies with 903.3 if approved; copper and lead have specified minimum weights |
Now change the jurisdiction to Colorado, and two of those answers change: 903.2 is deleted, so a 2-inch vent through the roof is acceptable, and the terminal must extend at least 6 inches above the roof under the Colorado amendment to 903.1.1. Everything else — 903.5 location, 903.1.4 sidewall, 903.3 flashing, 903.6 exterior freeze protection — is unchanged.
A roof is used as a sunbathing deck. How far above the roof must an open vent pipe terminate?
The 97.5 percent outdoor design temperature is minus 10 degrees F. What minimum vent extension diameter does IPC 903.2 require through the roof?
A vent terminal is located 6 feet horizontally from an openable window. Under IPC 903.5, what is required?
A sidewall vent terminal is proposed. Which of the following does IPC 903.1.4 prohibit?