IBC 717.6.3
Fire dampers in floors that are not rated (IBC 717.6.3)
Floors that are not fire-resistance rated still limit how far a duct may run between stories without a shaft. The answer depends on how many stories the duct connects and what the floors are built of.
What counts as a floor that is not rated: A floor with no required fire-resistance rating, common in smaller buildings.
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
- RequiredDucts only
A duct connecting three stories through noncombustible floors needs a fire damper at each floor line.
Or enclose the duct in a shaft that complies with IBC 713.
IBC 717.6.3 item 3
- Not requiredDucts only
A duct through one floor that is not rated, connecting two stories, needs no damper if the space around it is filled with approved noncombustible material that resists flame and combustion products.
IBC 717.6.3 item 2
- Not requiredDucts only
Ducts that stay within one residential dwelling unit do not need fire dampers at the floor lines. This applies only where the floors are noncombustible, the duct connects no more than three stories and the space around it is filled with approved noncombustible material; combustible floors or more stories need a shaft.
IBC 717.6.3 Exception
When a damper is not the answer
- Shaft enclosure requiredDucts only
A duct connecting three stories through combustible floors that are not rated must be enclosed in a shaft.
- Shaft enclosure requiredDucts only
A duct connecting more than three stories must be enclosed in a shaft.
- Vertical opening rules applyAir transfer openings only
An air transfer opening through a floor is a vertical opening, not a damper question. It is allowed only inside a shaft enclosure or where a vertical opening rule in IBC 712.1 permits it.
Also required
- Fill the space around the duct at each floor with approved noncombustible material that stops flame and combustion products from passing. (ducts only) IBC 717.6.3
- Flexible air connectors may not go through any wall, floor or ceiling at all. (ducts only) IBC 717.7
- Only floors built of noncombustible materials may use fire dampers at each floor line instead. (ducts only) IBC 717.6.3, IBC 713
- Unrated floors allow unenclosed ducts only up to three stories. (ducts only) IBC 717.6.3, IBC 713
Common situations by edition
| Situation | 2024 IBC | 2021 IBC | 2018 IBC |
|---|---|---|---|
| Duct through one unrated floor, connecting two stories | No damper required | No damper required | No damper required |
| Duct through two noncombustible unrated floors, connecting three stories | Fire damper required | Fire damper required | Fire damper required |
| Duct through two combustible (wood) unrated floors | Shaft enclosure required | Shaft enclosure required | Shaft enclosure required |
| Duct through three or more unrated floors | Shaft enclosure required | Shaft enclosure required | Shaft enclosure required |
| Duct within one dwelling unit through two noncombustible floors | No damper required | No damper required | No damper required |
| Air transfer opening through an unrated floor | Vertical opening rules apply | Vertical opening rules apply | Vertical opening rules apply |
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.
How many floors does the duct pass through outside of a shaft?
IBC 717.6.3
Are all the floors the duct passes through built of noncombustible materials?
For example concrete or steel deck floors. A wood floor with a concrete topping is combustible.
IBC 717.6.3 item 3
Is the duct entirely within one residential dwelling unit?
A dwelling unit is an apartment or house. Hotel rooms and other sleeping units are not dwelling units.
IBC 717.6.3 Exception
Questions
Does a duct through a floor that is not rated need a fire damper?
Not for a duct connecting two stories.
Fire damper: not requiredAll three editions
Fire damper: not required. A duct through one floor that is not rated, connecting two stories, needs no damper if the space around it is filled with approved noncombustible material that resists flame and combustion products. IBC 717.6.3 item 2
Also: Fill the space around the duct at each floor with approved noncombustible material that stops flame and combustion products from passing. IBC 717.6.3
Full result in the tool: No damper required
When does a duct through unrated floors need a fire damper at each floor?
Fire damper: requiredAll three editions
Fire damper: required. A duct connecting three stories through noncombustible floors needs a fire damper at each floor line. Or enclose the duct in a shaft that complies with IBC 713. IBC 717.6.3 item 3
Also: Fill the space around the duct at each floor with approved noncombustible material that stops flame and combustion products from passing. IBC 717.6.3
Full result in the tool: Fire damper required
When does a duct through unrated floors need a shaft?
Shaft enclosure requiredAll three editions
A duct connecting three stories through combustible floors that are not rated must be enclosed in a shaft.
Also: Only floors built of noncombustible materials may use fire dampers at each floor line instead. IBC 717.6.3, IBC 713
Do ducts inside a house or apartment need fire dampers?
Fire damper: not requiredAll three editions
Fire damper: not required. Ducts that stay within one residential dwelling unit do not need fire dampers at the floor lines. This applies only where the floors are noncombustible, the duct connects no more than three stories and the space around it is filled with approved noncombustible material; combustible floors or more stories need a shaft. IBC 717.6.3 Exception
Also: Fill the space around the duct at each floor with approved noncombustible material that stops flame and combustion products from passing. IBC 717.6.3
Full result in the tool: No damper required