IBC 717.5.1
Fire dampers in fire walls (IBC 717.5.1)
Fire walls are the strictest walls for ducts. Where the code lets a duct or air transfer opening through one at all, it needs a fire damper. Openings are also limited in size and total width by IBC 706.8.
What counts as a fire wall: A wall that divides a building into separate buildings for code purposes, running from foundation to roof.
Rules last reviewed October 12, 2026. How the rules are checked
Check your case in the tool (2024 IBC)Start the tool with the 2021 IBC · Start the tool with the 2018 IBC
When each damper is required
Every result the tool can give for a duct carrying heating, cooling or ventilation air, or an air transfer opening, through this assembly. Labels show where a result applies only to ducts, only to air transfer openings, or only in some editions.
Fire damper
- Required
Ducts and air transfer openings that IBC 706.11 allows through a fire wall need a listed fire damper. Section 717.5.1 has no exceptions.
IBC 717.5.1, IBC 706.11
Smoke damper
- Required
The fire wall serves as a horizontal exit, so a listed smoke damper is also required.
IBC 717.5.1.1
- Not required
The fire wall is not a horizontal exit.
IBC 717.5.1.1
When a damper is not the answer
- Not permitted
Ducts and air transfer openings are not allowed through a fire wall on a lot line. Reroute the duct so it does not cross the fire wall.
Also required
- Where the fire wall is not on a lot line, openings through it must stay within the size limits of IBC 706.8. IBC 706.11, IBC 706.8
- The size and total width of openings in the fire wall are limited by IBC 706.8. IBC 706.8
- Flexible ducts and flexible air connectors may not pass through any fire-resistance-rated assembly, and flexible air connectors may not go through any wall, floor or ceiling at all. (ducts only) IBC 717.7
Common situations by edition
| Situation | 2024 IBC | 2021 IBC | 2018 IBC |
|---|---|---|---|
| Duct through a 2-hour fire wall | Fire damper required | Fire damper required | Fire damper required |
| Duct through a 3-hour fire wall that is also a horizontal exit | Combination fire/smoke damper required | Combination fire/smoke damper required | Combination fire/smoke damper required |
| Air transfer opening through a 2-hour fire wall | Fire damper required | Fire damper required | Fire damper required |
| Duct through a fire wall on a lot line | Not permitted | Not permitted | Not permitted |
| Clothes dryer exhaust duct through a fire wall | Not permitted | Not permitted | Not permitted |
Select a result to open it in the tool with every answer filled in, including the conditions not listed here.
Exceptions and conditions the tool checks
These are the questions the tool asks, in order, with the explanation it gives. Section numbers are shown for each edition where they differ.
Is the fire wall on a lot line?
A fire wall on a lot line separates buildings on different properties, often as a party wall. The code does not allow ducts or air transfer openings through it.
IBC 706.11
Does this wall serve as a horizontal exit?
A horizontal exit is a fire wall, fire barrier or horizontal assembly rated at least 2 hours, with doors, that lets people move to another building or a refuge area on the same level (IBC 1026). It is shown on the egress plans.
IBC 1026
What is the required fire-resistance rating of the assembly?
Use the rating the code requires for this wall or floor, shown on the life safety plans.
Code changes that affect this assembly
- Static and dynamic fire dampers: Since 2021 the testing list no longer requires a dynamic label for fire dampers; a new section limits static-listed dampers to systems that shut down in a fire.
- Damper access: Since 2021 dampers with fusible links or internal operators need a 12-inch access door or a removable duct section.
Questions
Are there exceptions to the fire damper requirement in a fire wall?
No.
Fire damper: requiredAll three editions
Fire damper: required. Ducts and air transfer openings that IBC 706.11 allows through a fire wall need a listed fire damper. Section 717.5.1 has no exceptions. IBC 717.5.1, IBC 706.11
Also: The size and total width of openings in the fire wall are limited by IBC 706.8. IBC 706.8
Full result in the tool: Fire damper required
When does a fire wall need a smoke damper as well?
When the fire wall also serves as a horizontal exit.
Smoke damper: requiredAll three editions
Smoke damper: required. The fire wall serves as a horizontal exit, so a listed smoke damper is also required. IBC 717.5.1.1
Also: The size and total width of openings in the fire wall are limited by IBC 706.8. IBC 706.8
Full result in the tool: Combination fire/smoke damper required
Can a duct pass through a fire wall on a lot line?
No.
Not permittedAll three editions
Ducts and air transfer openings are not allowed through a fire wall on a lot line. Reroute the duct so it does not cross the fire wall.
Also: Where the fire wall is not on a lot line, openings through it must stay within the size limits of IBC 706.8. IBC 706.11, IBC 706.8
Can a clothes dryer exhaust duct pass through a fire wall?
Not permittedAll three editions
IBC 717.5.1 requires a fire damper at every duct through a fire wall, and the mechanical code prohibits fire dampers in clothes dryer exhaust. There is no code-prescribed way to take a dryer duct through a fire wall. Reroute the duct, or obtain approval of an alternative from the building official.