A shaft and floor dampers for ducts in Type II-B

[Firestop Guy]

I have been asked to inspect the firestopping in a 4-story, Type II-B university classroom building that is undergoing moderate renovation. Other than the stairwells, elevator shaft, an emergency electrical room and a BDA room, there are no rated walls in the building. Two new large vertical ducts start on the third floor and run through the fourth floor to the roof. The architect has required them to be enclosed in a 2-hour shaft (just on the fourth floor) AND has required fire dampers at the fourth floor. From a 2015 IBC Chapter 7 standpoint, I cannot see a reason for the 2-hour shaft or the dampers. The dampers are particularly odd since the ducts are in a fire-rated shaft. Is there something in the mechanical code that requires this?? Is the architect incorrect or am I missing something, probably that is blindingly obvious?

 

[Yankee Chronicler]

Who are you inspecting for? What's your role?

There is nothing in any law, regulation, or code that says an architect can't design to exceed code requirements. If there is a contract with construction documents calling for both a rated shaft enclosure and a fire damper at the floor -- then that's the contractual requirement and that's what must be built. In addition, if that's what is shown on the construction documents approved for the permit, then the code requires that it be built that way.

 

[Firestop Guy]

Who are you inspecting for? What's your role?

There is nothing in any law, regulation, or code that says an architect can't design to exceed code requirements. If there is a contract with construction documents calling for both a rated shaft enclosure and a fire damper at the floor -- then that's the contractual requirement and that's what must be built. In addition, if that's what is shown on the construction documents approved for the permit, then the code requires that it be built that way.

I am conducting special inspection of the firestopping as required by the AHJ under section 1705.1.1 Special Cases. I am contracted through the university.

I fully agree that the architect can exceed the code, and that the approved construction documents are what must be built. I am not trying to challenge the architect at all. I only do that when aspects of the design do NOT meet the code requirements, and I work through the AHJ when that occurs since my role is an extension of the AHJ. No matter who I am contracted through I am directly responsible first and foremost to the AHJ and the code. I am simply trying to further my understanding and make sure I am not missing something the code requires, something I need to be aware of moving forward.

 

[klarenbeek]

IMC section 607 which covers fire dampers/shafts/penetrations is basically taken almost word for word from IBC chapter 7. Unless there is some reason the floor/ceiling is rated, there is no code requirement for the shaft and damper other than to meet the design professional's approved plans.
Even if the floor was rated, just the damper would be required, not the shaft if its standard HVAC duct. That would change if it is hazardous exhaust or some other system where dampers can't be installed.

 

[Yankee Chronicler]

IBC 2015 section 713.4 says shafts connecting 4 stories or more shall be rated at 2-hours, shafts connecting fewer than 4 stories shall be rated 1-hour. Shaft enclosures shall have a rating not less than that of the floor assembly penetrated but need not exceed 2-hours.

If this is Type II-B construction, can we assume the floors are unrated? If so, the required shaft rating would be 1-hour.

Fire dampers are not required for floor penetrations within a rated shaft enclosure. If the rated shaft occurs only on the fourth floor, then the fire damper at the floor is required to complete the rated enclosure. [IBC 2015 section 713.11 #3]

 

[Firestop Guy]

IBC 2015 section 713.4 says shafts connecting 4 stories or more shall be rated at 2-hours, shafts connecting fewer than 4 stories shall be rated 1-hour. Shaft enclosures shall have a rating not less than that of the floor assembly penetrated but need not exceed 2-hours.

If this is Type II-B construction, can we assume the floors are unrated? If so, the required shaft rating would be 1-hour.

Fire dampers are not required for floor penetrations within a rated shaft enclosure. If the rated shaft occurs only on the fourth floor, then the fire damper at the floor is required to complete the rated enclosure. [IBC 2015 section 713.11 #3]

Those are the sections I referred to from the start and part of why the 2-hour shaft surprised me. It is II-B so the floors are definitely non-rated. As further proof of that an extensive amount of sealing of a curtain wall joint was installed in conformance to §715.5. The GC and the architect queried me to ask if a firestop system needed to be installed at that joint and I said, "No, the code does not require a firestop system though you could opt for one. The code says the joint 'shall be filled with an approved material or system'". The GC opted for 4pcf mineral wool installed with a 33% compression ratio and an elastomeric smoke/acoustic spray, not a firestop system but more than just mineral wool.
The shaft runs just from the fourth-floor deck to the underside of the roof deck above which is not rated. The ducts, which are standard HVAC, start on the third floor and are not enclosed by a shaft there, only at the fourth floor. I checked the plans and confirmed with the GC that there is nothing in the room the shaft is being built in that needs separation from the duct for some reason, no fume hoods or hazardous materials, etc. Everything contributed thus far confirms my original thoughts, and your comment that the architect can exceed the code if they so choose. That seems to be the case here. I could not connect all the dots and wanted to make sure I was not missing something. Thanks for your help.

 

[TheCommish]

Flip it back to the RDP, if they want to lessen the design submitted the RDP should be submitting an amendment for review by the AHJ.

 

[Yankee Chronicler]

Those are the sections I referred to from the start and part of why the 2-hour shaft surprised me. It is II-B so the floors are definitely non-rated.

That's an incorrect conclusion. In Type II-B construction, floors do not have to be rated as a structural consideration. Depending on the use and occupancy of the spaces on the third and fourth floors, the floor may have to be rated as an occupancy separation issue.

Beyond that, shaft enclosures must be constructed as fire barriers. Fire barriers are addressed in section 707 of the 2015 IBC. Section 707.5.1 says the strcyure supporting a fire barrier must be constructed to the same rating as the fire barrier. There are a couple of exceptions, but neither appears to apply to this situation. So the floor should have a 2-hour rating.

 

[Firestop Guy]

The project is way past that. I was on site this week to inspect the joint firestopping at the shaft liner. We were engaged quite late (not unusual) and only had time for cursory plan review before the inspection. The 2-hour shaft did not register in my mind until I was on site.

 

[Yankee Chronicler]

The GC and the architect queried me to ask if a firestop system needed to be installed at that joint and I said, "No, the code does not require a firestop system though you could opt for one. The code says the joint 'shall be filled with an approved material or system'". The GC opted for 4pcf mineral wool installed with a 33% compression ratio and an elastomeric smoke/acoustic spray, not a firestop system but more than just mineral wool.

With all due respect, (a) neither the architect nor the general contractor has any business asking a special inspector what the code requires. The GC should ask the architect. If the architect doesn't know, he/she should ask the AHJ.

As to joints, section 707.9 says joints between fire barriers and non-rated roof assemblies shall be filled with an approved material or system. "Approved" is defined in the 2015 IBC as "Acceptable to the building official." So if the joint seal system was clearly shown or specified in the approved construction documents, before the GC did anything the proposed system should have been submitted to the architect and then to the AHJ for approval.

 

[Yankee Chronicler]

The project is way past that. I was on site this week to inspect the joint firestopping at the shaft liner. We were engaged quite late (not unusual) and only had time for cursory plan review before the inspection. The 2-hour shaft did not register in my mind until I was on site.

I had no doubt that the project was pretty far along. As a special inspector, don't go beyond your role. You are not the registered design professional in responsible charge. You are there to verify whether or not something was installed according to the approved construction documents -- nothing more. The contractor should not be asking you code questions. If he does, you should decline to answer. Don't make someone else's problem become your problem.

 

[Firestop Guy]

That's an incorrect conclusion. In Type II-B construction, floors do not have to be rated as a structural consideration. Depending on the use and occupancy of the spaces on the third and fourth floors, the floor may have to be rated as an occupancy separation issue.

Beyond that, shaft enclosures must be constructed as fire barriers. Fire barriers are addressed in section 707 of the 2015 IBC. Section 707.5.1 says the strcyure supporting a fire barrier must be constructed to the same rating as the fire barrier. There are a couple of exceptions, but neither appears to apply to this situation. So the floor should have a 2-hour rating.

Excellent! You've hit on what I've been stuck on, why would the shaft have been required in the first place. There was nothing in the code analysis for the project or the plans indicating any need for an occupancy separation. but there is a new lecture hall below and the ducts originate from that space so that is an A-3 occupancy and the classrooms on the fourth floor are B. Correct?
To your point about a 2-hour rating on the floor, there are some conduit penetrations into the new shaft. The GC asked if they need to be firestopped and I said, "Yes, the shaft is 2-hour rated so the floor below it is now also 2-hour rated."

 

[Firestop Guy]

I had no doubt that the project was pretty far along. As a special inspector, don't go beyond your role. You are not the registered design professional in responsible charge. You are there to verify whether or not something was installed according to the approved construction documents -- nothing more. The contractor should not be asking you code questions. If he does, you should decline to answer. Don't make someone else's problem become your problem.

Agreed. At the same time, we encounter few AHJs or architects who understand firestopping well, or even at all, and we are frequently asked for advice. It is quite frustrating at times. We are very careful what we say and always kick things back to the AE and the AHJ. In this case the architect and GC jointly approached me about the curtain wall joint because neither was sure what was required. I gave him the code references that might apply. The GC asked me this week "So we are OK to install finish layers of GWB now?" to which I replied, "That is not my call. It is up to the AHJ." and was then told the AHJ had not been on site at all. I made no further comment.

 

[Yankee Chronicler]

Okay -- possibility number 1: The architects may have split the building into fire areas. If the third floor is an A occupancy and the fourth floor is a B occupancy, if they are considered to be separate fire areas a 2-hour separation is required:



Beyond that, unless the building was designed as non-separated mixed uses, Table 508.4 requires a separation between an A occupancy and a B occupancy. It's 1-hour in a sprinklered building, 2-hour in a non-sprinklered building.



So, whether it has to be 1-hour or 2-hour, the shaft is required and has to be rated because the duct connects an A occupancy with a B occupancy. Since the architect enclosed the duct(s) in a shaft on the fourth floor, the point where the ducts enter the protected (rated) enclosure is the fourth floor, so that's why a fire damper is required at that point.

 

[Yankee Chronicler]

The GC asked me this week "So we are OK to install finish layers of GWB now?" to which I replied, "That is not my call. It is up to the AHJ." and was then told the AHJ had not been on site at all. I made no further comment.

Good call. Back to what I said about not making someone else's problem become your problem.

Obviously, the GC wants to forge ahead. He wants someone to bless the firestopping so he can cover it up. It doesn't matter to him if the party he gets an okay from has any authority to "approve" anything -- he just wants something [somebody -- anybody] he can hang his hat on if there's a problem down the road and he gets sued.

 

[Tim Mailloux]

My gut is telling me that this building was designed as separated mixed-use, meaning there is a fire-rated separation between the A occupancy on the 3rd floor and the adjacent B occupancy spaces. If the building were designed as non-separated mixed-use under type IIB construction, it would be limited to just three stories due to the A occupancy classification.

 

[steveray]

My gut is telling me that this building was designed as separated mixed-use, meaning there is a fire-rated separation between the A occupancy on the 3rd floor and the adjacent B occupancy spaces. If the building were designed as non-separated mixed-use under type IIB construction, it would be limited to just three stories due to the A occupancy classification.

Unless the A is accessory....

 

[Tim Mailloux]

The OP said the A occupancy is a lecture hall and I am envisioning that as a pretty large space.

 

[steveray]

The OP said the A occupancy is a lecture hall and I am envisioning that as a pretty large space.

And you are PROBABLY right.....