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domestic kichen exhaust duct in multifamily

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spector51

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Oct 22, 2012
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Location
DC, Northern VA
Given- Kitchen hood penetration in cieling of wood framed multifamily.

Penetrates 1 hour horizontal floor cieling assembly and runs in joist space to exterior wall so is a membrane penetration.

Question- Any way around the radiation damper or any damper for that matter.

I seem to remembers something about when complying with duct construction ( Listed tape, proper support, thickness and joints) the duct is the protection and only the annular space needs protection.

Does that only apply to wall membrane penetrations?
 
backdraft damper is required (IMC 505). Since it's multi family, there are STC considerations as well, so there is more to it than just the duct.
 
the backdraft damper is a totally seperate issue as i don't think the backdraft damper is to protect the opening in the fire rated construction. anyone else care to chime in?
 
spector51 said:
the backdraft damper is a totally seperate issue as i don't think the backdraft damper is to protect the opening in the fire rated construction. anyone else care to chime in?
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[F] 502.10.2 Penetrations.

Exhaust ducts penetrating fire barriers constructed in accordance with Section 707 of the International Building Code or horizontal assemblies constructed in accordance with Section 711 of the International Building Code shall be contained in a shaft of equivalent fire-resistance-rated construction. Exhaust ducts shall not penetrate fire walls. Fire dampers shall not be installed in exhaust ducts.
 
You Do Not put a "Fire or Radiation" damper on a kitchen exhaust duct.

Ceiling "radiation dampers" are installed in the throat of a ceiling diffuser or return grille.

They are required where a "suspended ceiling" is part of a fire rating for the floor or roof above the suspended ceiling.

The purpose of that exhaust is to get rid of excess heat, vapors and fumes, not to shut down when there is a kitchen fire.
 
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SECTION 716 DUCTS AND AIR TRANSFER OPENINGS

716.1 General. The provisions of this section shall govern the protection of duct penetrations and air transfer openings in assemblies required to be protected.

716.1.1 Ducts that penetrate fire-resistance-rated assemblies without dampers. Ducts that penetrate fire-resistance-rated assemblies and are not required by this section to have dampers shall comply with the requirements of Sections 713.2 through 713.3.3. Ducts that penetrate horizontal assemblies not required to be contained within a shaft and not required by this section to have dampers shall comply with the requirements of Sections 713.4 through 713.4.2.2.

713.2 Installation details. Where sleeves are used, they shall be securely fastened to the assembly penetrated. The space between the item contained in the sleeve and the sleeve itself and any space between the sleeve and the assembly penetrated shall be protected in accordance with this section. Insulation and coverings on or in the penetrating item shall not penetrate the assembly unless the specific material used has been tested as part of the assembly in accordance with this section.

713.4 Horizontal assemblies. Penetrations of a floor, floor/ceiling assembly or the ceiling membrane of a roof/ceiling assembly not required to be enclosed in a shaft by Section 708.2 shall be protected in accordance with Sections 713.4.1 through 713.4.2.2.

713.4.1.4 Dissimilar materials. Noncombustible penetrating items shall not connect to combustible materials beyond the point of firestopping unless it can be demonstrated that the fire-resistance integrity of the horizontal assembly is maintained.
 
so again does that mean just annular space protection is all that is required as mentioned in my first post. I get the idea of no damper in exhaust ducts bt the code now calls domectic kitchen exhaust environmental air. I think if you follow the reason for the change it is to confuse all and sell more handbooks. Seriously, i thoght it had to do with damper issue.
 
spector51 said:
so again does that mean just annular space protection is all that is required as mentioned in my first post. I get the idea of no damper in exhaust ducts bt the code now calls domectic kitchen exhaust environmental air. I think if you follow the reason for the change it is to confuse all and sell more handbooks. Seriously, i thoght it had to do with damper issue.
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Protect the annular space same way you protect every other penetration. That prevents the fire from entering the annular space, not the duct.
 
spector 51, for annular space construction, we typically line the joist bay with two layers 5/8" type X.

Another alternative is to modify a fire-rated fan box, but a about $150 apiece, you're probably spending less money just to do the preliminary drywall in the joist bay.
 
Yikes said:
spector 51, for annular space construction, we typically line the joist bay with two layers 5/8" type X.Another alternative is to modify a fire-rated fan box, but a about $150 apiece, you're probably spending less money just to do the preliminary drywall in the joist bay.
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Same deal here. Do the same thing with recessed cans, but only 1 layer of 5/8

Brent
 
MASSDRIVER, what UL or ICC assembly do you use that allows the single layer in an annular space?

I find that most of the single layer horizontal assemblies are for 2x10 or larger. When I line the inside of the joist bay, my "joist" depth is virtually nil, so I think I need a different assembly.

When I use the IBC 721.1(3) item #2 - - the assembly with 2 layers type X - - it mentions no minimum joist thickness, so that's why I can use it.
 
you are going to lose your required STC rating with most of what is being proposed.
 
See IMC 607.6.2 (2012) Going straight up through the drywall membrane, the only way to not have a radiation damper in ANY duct is to have the duct in a shaft from the membrane penetration to the exterior. This is not an application where a fire or radiation damper is not required in a duct.

The only way to avoid either a radiation damper (bad idea on residential kitchen exhaust) or building a shaft is to have the duct enter a wall cavity below the membrane and the turn up so it enters the truss space above the drywall lid membrane through the top plate of the wall. See IMC 607.6.2.1, #2.
 
bhale7wv said:
Use 26 gauge metal for the duct per 716.5.2; Ex. 3
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607.5.2 Fire barriers. Ducts and air transfer openings that

penetrate fire barriers shall be protected with listed fire

dampers installed in accordance with their listing. Ducts

and air transfer openings shall not penetrate exit enclosures

and exit passageways except as permitted by Sections

1022.5 and 1023.6, respectively, of the International

Building Code.

Exception: Fire dampers are not required at penetrations

of fire barriers where any of the following apply:

1. Penetrations are tested in accordance with ASTM

E 119 or UL 263 as part of the fire-resistancerated

assembly.

2. Ducts are used as part of an approved smoke control

system in accordance with Section 513 and

where the fire damper would interfere with the

operation of the smoke control system.

3. Such walls are penetrated by ducted HVAC systems,

have a required fire-resistance rating of 1

hour or less, are in areas of other than Group H

and are in buildings equipped throughout with an

automatic sprinkler system in accordance with

Section 903.3.1.1 or 903.3.1.2 of the International

Building Code. For the purposes of this

exception, a ducted HVAC system shall be a duct

system for the structure’s HVAC system. Such a

duct system shall be constructed of sheet steel not

less than 26 gage [0.0217 inch (0.55 mm)] thickness

and shall be continuous from the air-handling

appliance or equipment to the air outlet and

inlet terminals.

This is out of the IMC, but 716.5 of the IBC reads the same. This exception is for fire barrier walls, not ceiling membrane penetrations. Exception 3 applies to "such walls" not ceiling membranes.
 
I would argue that walls are specifically addressed in 716.5.1 -Fire Walls and that section 716.5.2- Fire Barriers pertains to ALL Fire Barriers, both horizonal & vertical. The intent in the section is that you provide a non-combusible "chase" for the air to flow through of sufficient thickness to contain any flames or smoke from getting into the rated assembly. The easiest thing to do would be to build a chase / bulkhead over the cabinets AFTER the rated Shett Rock is completed so that the duct is completely within the rating of the unit.
 
How can the code be silent on such a common issue. I think the code addresses it. The problem is there are to many differing interpetations, one being correct and the others all wet. With that line of thought one of us here is right, unfortunately most of us though are wrong.

The question is, which 1 (or so) of us is right?

I bring this up because i used to permit the penetration with proper duct construction, thickness, support, and tape with just annular space protection but i am starting to rethink this issue.

Peach, I see we are both from the same area. What has been approved in this region here in the past? Is there any consistancy here?
 
The annular space is protected which protects the structure. The 26 gauge metal duct will not provide fuel for the fire to burn inside the duct. How far do you think the fire will go without a fuel source? In theory the 26 gauge duct is all the protection that is needed.
 
A better method of compliance is to place all ducts and vents either kitchen or bath below the required floor ceiling assembly and then enclose them in a transverse bulkhead or soffitt above the kitchen cabinets or shower tub enclosure directed to an exterior wall. This may actually involve a bit of forethought about the placement of such spaces and thier required breathing conditions on the part of the designer.
 
Beating this thread back to life, I'm looking for a code-compliant way of exhausting residential range hoods through the rated ceiling/roof assembly at the top floor of a type V-A apartment building. I wanted to add another alternative code analysis - - feel free to pick it apart:

If the kitchen hood meets the mechanical code definition of "ventilation system", the sheet metal exhaust is thus a type of "vent",

and CBC 714.4.1.1 exception #1 allows "vents" of up to 6" diameter to penetrate a floor assembly. 144 sq in of vent max in 100 SF of membrane.
 
= $ =

Yikes,

The Section that you listed [ RE: CBC 714.1.1, Exception # 1 ] refers

to a [ rated ] floor assembly, however, ...you are desiring to penetrate

a [ rated ] ceiling \ roof assembly.........Does the same code section

apply to ceilings & roofs, as the floor assemblies, or is there one for

the ceilings \ roofs too ? :?:

= $ =
 
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