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non-rated floor assembly supporting new shaft enclosure

B

BillS

Member
Joined
Feb 18, 2015
Messages
44
Location
Pittsburgh
Inserting a new duct connecting three stories in an existing Type III-B building (wood floor joists). The floor/ceilings do not not need to be rated. 2018 IBC 716.6.3 says that this duct needs to be protected by a shaft enclosure complying with Section 713. 713.2 says this needs to be a fire barrier as per 707, and 707.5.1 says that supporting construction for a fire barrier needs to be rated, as well.

So, to confirm, does this mean that even though the floor is not required to be rated, I do need to also rate the portions of the floor supporting the shaft enclosure? It's not explicitly stated so and the commentaries often offer a good reminder in situations like this so I'm wondering if the requirement for rating that portion of the floor is not required.

Thoughts?
 
Shaft enclosures are required to be enclosed by fire barriers and horizontal assemblies (IBC Section 713.5), which means the horizontal assembly at the bottom of the shaft must be rated. Per IBC Section 711.2.3, horizontal assemblies must be supported by construction of equal or greater fire resistance.

The entire floor does not need to be rated--only that portion under the shaft. However, that portion must be supported by fire-resistance-rated walls and/or columns.
 
what if there are floor dampers in the ducts....you would no longer require a rated shaft enclosure...however that damper may need to be supported by a rated floor assembly.
 
if you use fire dampers at the floor slabs these would no longer require shaft enclosures, as far as the code is concerned you have a duct penetration through non fire rated floor assembly which is covered under 2018 IBC section 717.6.3.

717.6.3 Option #3 states:
In floor assemblies composed of noncombustible materials, a shaft shall not be required where the duct connects not more than three stories, the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion and a fire damper is installed at each floor line.
 
Thanks for pointing out the possibility of the dampers, Tim, but I have a combustible floor assembly so I can't make use of that option.
 
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