# 2018 IMC - Is a 1 hour shaft required?



## redbird11 (Sep 9, 2021)

I have an AHU in a basement with duct penetrating a 1 hour floor assembly and then supplying the plenum of the 1st floor. Type II-A Construction. Is a 1 hour shaft required? If not, what are the section references?


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## classicT (Sep 9, 2021)

Why the 1-hr floor assembly? Is it a horizontal assembly or is it just the 1-hr construction due to the construction type (i.e. Table 601))?

We are going to need some more info here before we can answer this one.


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## redbird11 (Sep 9, 2021)

Yes, the 1 hour floor assembly is due to the construction type of II-A (Table 601).


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## mtlogcabin (Sep 9, 2021)

2018 IMC
[BF] 607.6 Horizontal assemblies.
Penetrations by air ducts 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 713 and Sections 717.6.1 through 717.6.3 of the International Building Code or shall comply with Sections 607.6.1 through 607.6.3.

[BF] 607.6.1 Through penetrations.
In occupancies other than Groups I-2 and I-3, a duct constructed of approved materials in accordance with Section 603 that penetrates a fire-resistance-rated floor/ceiling assembly* that connects not more than two stories is permitted without shaft enclosure protection provided that a listed fire damper is installed at the floor line or the duct is protected in accordance with Section 714.5 of the International Building Code*. For air transfer openings, see Item 6, Section 712.1.9 of the International Building Code.

Is your horizontal assembly also being used to divide the 2 floors into separate fire areas? If it is then you do not have the proper floor rating see 
TABLE 707.3.10
FIRE-RESISTANCE RATING REQUIREMENTS FOR
FIRE BARRIERS, FIRE WALLS OR HORIZONTAL
ASSEMBLIES BETWEEN FIRE AREAS


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## classicT (Sep 9, 2021)

mtlogcabin said:


> 2018 IMC
> [BF] 607.6 Horizontal assemblies.
> Penetrations by air ducts 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 713 and Sections 717.6.1 through 717.6.3 of the International Building Code or shall comply with Sections 607.6.1 through 607.6.3.
> 
> ...


I haven't gotten to the book yet, but I do not believe that this will apply, as a horizontal assembly is not required by Table 601. Given Type II-A construction, the primary and secondary members of the floor have to be 1-hr rated construction. While they could encapsulate in a 1-hr floor/ceiling assembly, that is not required. It could be individual encapsulation of the primary and secondary members.

So again, we really need more info. How is the floor achieving the 1-hr rating? Is this opening going to be concealed?

Ideally, we really need to see a floor section and floor plan to better understand what we have going.


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## rgrace (Sep 10, 2021)

classicT said:


> I haven't gotten to the book yet, but I do not believe that this will apply, as a horizontal assembly is not required by Table 601. Given Type II-A construction, the primary and secondary members of the floor have to be 1-hr rated construction. While they could encapsulate in a 1-hr floor/ceiling assembly, that is not required. It could be individual encapsulation of the primary and secondary members.
> 
> So again, we really need more info. How is the floor achieving the 1-hr rating? Is this opening going to be concealed?
> 
> Ideally, we really need to see a floor section and floor plan to better understand what we have going.


I did look at Table 601 and it looks like the floor construction *and* the secondary members have to have a 1 hour rating in Type II-A construction, so mtlogcabin's response is appropriate.


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## classicT (Sep 10, 2021)

rgrace said:


> I did look at Table 601 and it looks like the floor construction *and* the secondary members have to have a 1 hour rating in Type II-A construction, so mtlogcabin's response is appropriate.


Isn't that exactly what I said?


classicT said:


> Given Type II-A construction, the primary and secondary members of the floor have to be 1-hr rated construction. While they could encapsulate in a 1-hr floor/ceiling assembly, that is not required. It could be individual encapsulation of the primary and secondary members.


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## steveray (Sep 13, 2021)

712.1.9 Two-story openings. In other than Groups I-2 and
I-3, a vertical opening that is not used as one of the applications
listed in this section shall be permitted if the opening
complies with all of the following items:
1. Does not connect more than two stories.
2. Does not penetrate a horizontal assembly that separates
fire areas or smoke barriers that separate
smoke compartments.
3. Is not concealed within the construction of a wall or
a floor/ceiling assembly.
4. Is not open to a corridor in Group I and R occupancies.
5. Is not open to a corridor on nonsprinklered floors.
6. Is separated from floor openings and air transfer
openings serving other floors by construction conforming
to required shaft enclosures.


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## mtlogcabin (Sep 13, 2021)

712.1 General.
Each vertical opening* shall comply in accordance with one *of the protection methods in Sections 712.1.1 through 712.1.16

717 is a specific section governing duct penetrations not floor openings.

717.1 General.
The provisions of this section shall govern the protection of duct penetrations and air transfer openings* in assemblies required to be protected and duct penetrations in nonfire-resistance-rated floor assemblies.*

717.6 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 713 *or shall comply with Sections 717.6.1 through 717.6.3*.

717.6.1 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 that a listed fire damper is installed at the floor line* or the duct is protected in accordance with Section 714.5. For air transfer openings, see Section 712.1.9.

Exception: A duct is permitted to penetrate three floors or less without a fire damper at each floor, provided that such duct 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 having a minimum wall thickness of 0.0187 inches (0.4712 mm) (No. 26 gage).

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 E119 or UL 263 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 717.6.2.1.


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## steveray (Sep 14, 2021)

mtlogcabin said:


> or the duct is protected in accordance with Section 714.5.


714.5 Horizontal assemblies. Penetrations of a fire-resistance-
rated floor, floor/ceiling assembly or the ceiling membrane
of a roof/ceiling assembly not required to be enclosed
in a shaft by Section 712.1 shall be protected in accordance
with Sections 714.5.1 through 714.5.4.
714.5.1 Through penetrations. Through penetrations of
horizontal assemblies shall comply with Section 714.5.1.1
or 714.5.1.2.
Exceptions:
1. Penetrations by steel, ferrous or copper conduits,
pipes, tubes or vents or concrete or masonry
items through a single fire-resistance-rated floor
assembly where the annular space is protected
with materials that prevent the passage of flame
and hot gases sufficient to ignite cotton waste
when subjected to ASTM E119 or UL 263 time temperature
fire 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. Penetrating
items with a maximum 6-inch (152 mm) nominal
diameter shall not be limited to the penetration of
a single fire-resistance-rated floor assembly, provided
that the aggregate area of the openings
through the assembly does not exceed 144 square

Anyone know why they use "Vents" here instead of ducts or air transfer?


Needless to say to the OP, there are several ways to get out of a shaft...But you may need a damper...


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## mtlogcabin (Sep 14, 2021)

He will definitely need a fire damper.

A vent is not a duct by definition

VENT. A pipe or other conduit *composed of factory-made components,* containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance.

Pellet vent. A vent listed and labeled for use with listed pellet-fuel-burning appliances.

Type L vent. A vent listed and labeled for use with the following:

1.    Oil-burning appliances that are listed for use with Type L vents.

2.    Gas-fired appliances that are listed for use with Type B vents.


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## steveray (Sep 14, 2021)

Just seems odd that you would put a damper in an open mezzanine floor with an exposed duct....Or for that matter an atrium...A lot of changes here, maybe we are fixing this in 2021-24?


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## mtlogcabin (Sep 14, 2021)

A mezzanine is not a story it is a floor area within a story so I agree a damper should not be necessary in that scenario.


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## steveray (Sep 14, 2021)

Yeah but it is penetrations of floors....not stories...


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## mtlogcabin (Sep 14, 2021)

712.1.7 Atriums.
In other than Group H occupancies, atriums complying with Section 404 shall be permitted.

Looking at 404 I do not see a where a fire damper would be required within the atrium only required in the fire barrier that protects the atrium


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