obstruction to shaft

[TJacobs]

Greetings:

Have a project under 2003 IBC. 5-story pedestal building per 508.2. 2-story parking garage Type IA, 3-stories of R-2 apartments Type VA fully sprinklered per NFPA 13. Most (60%+) of the areas where shafts would be in the building have an open-web floor truss running thru them. Shafts in question would be bath fans, B-vents, clothes dryer vents.

Any suggestions?

 

[steveray]

Cut the truss....? If the wooden truss runs through it, how is the shaft rated and the structure?(5A)

 

[Dr. J]

1) are you sure they need to be rated shafts? Can IBC 716.6 be used (quoting 2006 code since I do not have electronic access to the 2003)

716.6.1 Through penetrations.

In occupancies other than Groups I-2 and I-3, a duct constructed of approved materials in accordance with the International Mechanical Code that penetrates a fire-resistance-rated floor/ceiling assembly that connects not more than two stories is permitted without shaft enclosure protection, provided a listed fire damper is installed at the floor line or the duct is protected in accordance with Section 712.4. For air transfer openings, see Exception 7 to Section 707.2.

Exception: A duct is permitted to penetrate three floors or less without a fire damper at each floor, provided it meets all of the following requirements:

1. The duct shall be contained and located within the cavity of a wall and shall be constructed of steel not less than 0.019 inch (0.48 mm) (26 gage) in thickness.

2. The duct shall open into only one dwelling or sleeping unit and the duct system shall be continuous from the unit to the exterior of the building.

3. The duct shall not exceed 4-inch (102 mm) nominal diameter and the total area of such ducts shall not exceed 100 square inches (0.065 m2) in any 100 square feet (9.3 m2) of floor area.

4. The annular space around the duct is protected with materials that prevent the passage of flame and hot gases sufficient to ignite cotton waste where subjected to ASTM E 119 time-temperature conditions under a minimum positive pressure differential of 0.01 inch (2.49 Pa) of water at the location of the penetration for the time period equivalent to the fire-resistance rating of the construction penetrated.

5. Grille openings located in a ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with a listed ceiling radiation damper installed in accordance with Section 716.6.2.1.

The exception is usually used for exactly your situation (B vent, fart fans, dryer vents). the use of dampers at each floor is not practical with B vent and dryer exhaust, so you have to qualify for the exception.

2) if required to be rated, then as Steveray said, how is the structure supporting the shaft protected to the same level as the shaft if there are exposed (and I assume that means unprotected) trusses?

 

[steveray]

Dr.J...He said 5 story building......although I am not sure it is a five story shaft.....

 

[mtlogcabin]

Exception: A duct is permitted to penetrate three floors or less without a fire damper at each floor,

Not intending to hi-jack the thread however this language could be viewed as follows

Example: A bathroom exhaust located on the ground floor. The duct will penetrate the 2nd, 3rd and 4th floor assemblies. Since the 1st floor is never penetrated it meets the literal wording of the code. However it allows 4 stories to be connected.

Or should it say?

Exception: A duct is permitted to connect three stories or less without a fire damper at each floor,

Is the intent of the code to limit the connection to 3 stories or 4?

 

[Dr. J]

Steveray - it does not matter where in the building the duct is, or how high the building is, as long as only 3 floors or less are penetrated. It could be the 3rd, 4th, and 5th floors, or the 43rd, 44th, and 45th (and then outside).

MT - it does not matter what it should say, it does say "floor". It also doesn't say "connect". Besides, condition 2 limits this exception to ducts that only open into one dwelling unit, and is continuous to the exterior. So the duct can't connect ANY stories.

As long as we are off the rails, make sure you read the main part of this section correctly as well:

"...a duct ... that penetrates a fire-resistance-rated floor/ceiling assembly that connects not more than two stories ..."

It is the ceiling that is important here. If the issue was a duct connecting only 2 stories, then a duct that connected only the 1st and 2nd stories, then went on up 27 more stories, would not need a shaft. Penetrate any more than one floor/ceiling assembly and you need a shaft.

Words mean things.

 

[steveray]

DrJ......What you are saying is....They might not need the shaft if they run the correct ducts correctly....What I am saying is the shaft needs to be protected if it is there regardless of what is in it.....You are offering a design solution for the shaft not to be there...I am asuming they "need" it and then need to figure out how to do it correctly...

I can't get designers and cheap builders to use a 6" wet wall...maybe you will have better luck with bath fans and dryer vents

 

[Dr. J]

good point, I am a designer and come at these things from a design angle.

The situation in the OP sounds like it is past the paper stage and reality must be dealt with.

The structure needs to be protected if it is a shaft. However, perhaps that vertical assembly can be considered a wide wall rather than a shaft. Maybe they can just close off each floor within this wide wall, to meet condition #4 and confirm the other conditions, and apply the exception.