# Penetrations followed by flex duct within rated floor-ceiling assembly



## BayPointArchitect (Feb 5, 2014)

Given:2009 IBCFour story apartments = R2 occupancy.Fully sprinkled 13R.1 hour fire-rated ceiling assembly.Several penetrations are located within the ceiling membrane.  Floor decks are 3/4" gypcrete over 3/4" plywood.  The ceiling consists of 5/8" Type "X" gyp.bd. attached to resilient channels = altogether a 1 hr. fire-rated assembly.  Duct penetrations are limited to no more than 6" diameter.  Ceiling radiation dampers are installed at each and every supply diffuser.  However, some of these small 6" supply ducts extend from the main supply trunk line located below this drywall ceiling and then penetrate into this ceiling membrane.  After the penetration, the HVAC Contractor and Mechanical Engineer would like to use flex duct throughout the floor truss system.Where a cluster of four 6" diameter penetrations are together (29 square inches each), then one of those four penetrations are protected with a damper so as not to exceed the combined 100 square inches maximum allowable within any given area of 100 square feet.  A few ceiling electrical boxes will need to be UL rated for this reason also.Question:Am I interpreting Chapter 7 correctly by requiring that the material used for these small supply ducts to be limited to 1) steel, 2) copper, 3) concrete, or 4) masonry as indicated by the list of specified materials?  Although one could argue that plastic is "non-combustible", I am thinking that a plastic flex duct would be acceptable if only it were part of a tested and classified UL assembly.See attachment.Thanks!ICC Certified Plan ReviewerNFPA Certified Fire Plan Examiner

View attachment 2031


713-MembranePenetration.pdf

713-MembranePenetration.pdf


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## BayPointArchitect (Feb 5, 2014)

Here is a better sketch of the problemI did not intend to attach my scribbles but this should make a little more sense.

View attachment 997


713-MembranePenetration.pdf

713-MembranePenetration.pdf


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## cda (Feb 5, 2014)

What UL assembly is the ceiling / floor assembly?

Does that UL design say anything about what can be in it


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## cda (Feb 5, 2014)

Also do you have a """"THROUGH PENETRATION. An opening that passes through an entire assembly""""??


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## BayPointArchitect (Feb 5, 2014)

CDA,

I knew that the question of which UL design we are using needed to be answered first.

Take your pick of one-hour rated floor-ceiling assemblies:

UL Design 558 = Optional ceiling damper (refer to manufacturer for information on this type of damper).

UL Design 563 = Optional ceiling damper (refer to manufacturer for information on this type of damper).

UL Design 574 = Optional ceiling damper (refer to manufacturer for information on this type of damper).

Let's say we opt out of using any kind of damper and take advantage of the exceptions provided within the 2009 IBC Section 713.

With regards to what goes on inside the interstitial space, we have combustible wood trusses.  So it would seem reasonable that we could also have combustible, flexible ductwork.

The way I read it, all openings within the membrane need to be protected... EXCEPTIONS allow for relatively small openings.  It is obvious to me that if a radiation damper is installed, then we can pretend that there is no opening and move onto other problems.  But the building code allows me to take a sledge hammer and poke a hole into the drywall ceiling and just walk away provided that the hole does not measure more than 6 inches in diameter.  Maybe I poke three holes close together and insert into each one a short steel pipe inside the holes for whatever reason I don't know.  Beyond those steel pipes or jagged openings or unprotected small holes, can I connect a plastic tube?  Perhaps a flexible piece of 6" diameter ductwork?


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## BayPointArchitect (Feb 5, 2014)

Currently, we are requiring that the HVAC Contractor install metal ductwork.  The challenge from the Mechanical Contractor is "why not flexible duct"?


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## cda (Feb 5, 2014)

1. do you have a "membrane penetration" and not a ""through penetrartion"??

If membrane thatn do you start with 713.3.2?

Maybe 713.3.3 is the section that you need to not allow the plastic flex.

and if dealing with a membrane penetration, than it appears to jump to 713.4.1.2

and, 713.4.1.3 which moves you to 716   and check 716.1.1

they are using "plastic flex" or metal flex"??


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## BayPointArchitect (Feb 5, 2014)

Plastic flex duct beyond unprotected 6 inch diameter opening in the membrane.

This is not a through penetration.

This is a membrane penetration.


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## cda (Feb 5, 2014)

Maybe 713.3.3                  is the section that you need      to not allow the plastic flex.

"""""This section limits the common practice of using a short metal nipple to penetrate a rated assembly, firestopping for the metal penetration (which is substantially less expensive than firestopping for plastic) and then connecting to plastic pipe or conduit on the room side of the wall. Arguably, there is a distance at which such connection is safe; however, this distance is variable and cannot be specified in the body of the code, hence the requirement for demonstration of fire-resistance integrity. An identical provision is found in Section 713.4.1.4 regarding penetrations of horizontal assemblies."""""


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## mtlogcabin (Feb 5, 2014)

You are not looking at the correct sections

713.4.1.3 Ducts and air transfer openings.

Penetrations of horizontal assemblies by ducts and air transfer openings shall comply with Section 716.



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.

716.6 Horizontal assemblies.

Penetrations by ducts and air transfer openings of a floor, floor/ceiling assembly or the ceiling membrane of a roof/ceiling assembly shall be protected by a shaft enclosure that complies with Section 708 or shall comply with Sections 716.6.1 through 716.6.3.

716.6.2 Membrane penetrations.

Ducts and air transfer openings constructed of approved materials in accordance with the International Mechanical Code that penetrate the ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with one of the following:

1.	A shaft enclosure in accordance with Section 708.

2.	A listed ceiling radiation damper installed at the ceiling line where a duct penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly.

3.	A listed ceiling radiation damper installed at the ceiling line where a diffuser with no duct attached penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly.

The code requires a listed ceiling radiation damper. Item 3 permits this diffuser without a duct attachment as long as the damper is installed inline with the rated ceiling assembly. The answer to the flex duct question is the flex duct shall not penetrate the ceiling line. If it does it is in violation of 

716.7 Flexible ducts and air connectors.

Flexible ducts and air connectors shall not pass through any fire-resistance-rated assembly. Flexible air connectors shall not pass through any wall, floor or ceiling.

You may have any duct material you choose located within the fire rated floor/ceiling assembly


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## bhale7wv (Feb 5, 2014)

First, is the penatration cimbustible or non-combustible?

If there is any flexiible duct being used in the system or fabric vibration isolators, then the system is treated as combustible and IMC 607.6.2  (IBC 716.6.2) comes into play.

If the entire duct system is constructed of steel having a minimum wall thickness of 0.0187 inch (0.4712 mm) (No. 26 gage), then it is a non-combustible penatration.

*607.6.2 Membrane penetrations.* Ducts and air transfer openings constructed of approved materials, in accordance

with Section 603, that penetrate the ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly

shall be protected with one of the following:

1. A shaft enclosure in accordance with Section 708 of the International Building Code.

2. A listed ceiling radiation damper installed at the ceiling line where a duct penetrates the ceiling of a fireresistance-

rated floor/ceiling or roof/ceiling assembly.

3. A listed ceiling radiation damper installed at the ceiling line where a diffuser with no duct attached penetrates

the ceiling of a fire-resistance-rated floor/ ceiling or roof/ceiling assembly.

*607.6.2.1 Ceiling radiation dampers*. Ceiling radiation dampers shall be tested as part of a fire-resistance-rated

floor/ceiling or roof/ceiling assembly in accordance with ASTME 119 orUL263. Ceiling radiation dampers shall be installed

in accordance with the details listed in the fire-resistance-rated assembly and the manufacturer’s installation instructions

and the listing. Ceiling radiation dampers are not required where either of the following applies:

1. Tests in accordance with ASTM E 119 or UL 263 have shown that ceiling radiation dampers are not necessary to

maintain the fire-resistance rating of the assembly.

2. Where exhaust duct penetrations are protected in accordance with Section 713.4.1.2 of the International Building

Code, are located within the cavity of a wall and do not pass through another dwelling unit or tenant space.


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## Builder Bob (Feb 5, 2014)

What does the manufacture of teh radiation dampers listed in accordance with UL C555... or as 2012 IBC states

3.6. A minimum 12-inch-long (305 mm) by 0.060-inch-thick (1.52 mm) steel sleeve shall be centered in each duct opening. The sleeve shall be secured to both sides of the wall and all four sides of the sleeve with minimum 11/2-inch by 11/2-inch by 0.060-inch (38 mm by 38 mm by 1.52 mm) steel retaining angles. The retaining angles shall be secured to the sleeve and the wall with No. 10 (M5) screws. The annular space between the steel sleeve and the wall opening shall be filled with mineral wool batting on all sides.

4. Such walls are penetrated by ducted HVAC systems, have a required fire-resistance rating of 1 hour or less, and are in buildings equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2. For the purposes of this exception, a ducted HVAC system shall be a duct system for conveying supply, return or exhaust air as part of the structure’s HVAC system. Such a duct system shall be constructed of sheet steel not less than No. 26 gage thickness and shall be continuous from the air-handling appliance or equipment to the air outlet and inlet terminals.


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## markw (Feb 5, 2014)

It says flex shall not pass thru any fire resistance rated assemby-not membrane.


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## markw (Feb 5, 2014)

the op is not concerned with walls, just the ceiling membrane-


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