Fire Dampers in Duplexes

[Michael Brown]

I know that if the builder separates the units of a two family dwelling with a 1 hour wall, I do not need to install fire dampers in the ductwork. However, the builder has the option to install rated ceilings in each unit instead of the separation wall. In my experience, anytime I penetrate a rated ceiling with ductwork, I need to install a a fire damper. But, I am unable to find a specific code reference stating this requirement. Is this a requirement or is it not taken into consideration for a two family dwelling?

 

[classicT]

I know that if the builder separates the units of a two family dwelling with a 1 hour wall, I do not need to install fire dampers in the ductwork. However, the builder has the option to install rated ceilings in each unit instead of the separation wall.

Correct. For a two family dwelling, the separation wall is not required to extend through the attic space where the ceiling has 5/8-in Type X, a draft stop is provided above the separation wall, and supporting construction for the ceiling has 1/2-in GWB or equivalent. See GA R302.3, Exception #2.

In my experience, anytime I penetrate a rated ceiling with ductwork, I need to install a a fire damper. But, I am unable to find a specific code reference stating this requirement. Is this a requirement or is it not taken into consideration for a two family dwelling?

The requirement in GA R302.3, Exception #2 is not specifying rated construction for the ceiling, only the 5/8-in Type X material. While we understand that this has some fire resistance level, a fire-resistance rating is not specified nor achieved via the specification of the 5/8ths.

Therefore, under GA R302.4, there is no requirement to protect penetrations of the ceiling assembly.

That said, with two family dwellings, the intent of the code is not to create separate structures or a defensible fire compartment. The intent is to slow the spread of fire sufficiently to permit egress of both units. In the case presented, the draft stop is considered sufficient to prevent the movement of hot gasses and smoke into the adjacent unit while the rated wall separating the two dwelling spaces provides sufficient protection between the occupied spaces.

GA R302.3 Two-Family Dwellings​

Dwelling units in two-family dwellings shall be separated from each other by wall and floor assemblies having not less than a 1-hour fire-resistance rating where tested in accordance with ASTM E119, UL 263 or Section 703.3 of the International Building Code. Fire-resistance-rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.
Exceptions:

1. A fire-resistance rating of 1/2 hour shall be permitted in buildings equipped throughout with an automatic sprinkler system installed in accordance with NFPA 13.
2. Wall assemblies need not extend through attic spaces where the ceiling is protected by not less than 5/8-inch (15.9 mm) Type X gypsum board, an attic draft stop constructed as specified in Section R302.12.1 is provided above and along the wall assembly separating the dwellings and the structural framing supporting the ceiling is protected by not less than 1/2-inch (12.7 mm) gypsum board or equivalent.

GA R302.4 Dwelling Unit Rated Penetrations​

Penetrations of wall or floor-ceiling assemblies required to be fire-resistance rated in accordance with Section R302.2 or R302.3 shall be protected in accordance with this section.

 

[steveray]

Just ran across the same thing...Attic access hatches create another "issue"....Not rated, no requirement to rate...Might try to submit a change to treat this like a garage with it's arbitrary "not rated protection"