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Metal Bldg has no bearing walls - Is it always a type III-B?

N

nealderidder

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Joined
Dec 7, 2010
Messages
420
Location
Sacramento, CA
The requirements for a type 3b building are that the exterior walls be noncombustible. That's it, it's a short paragraph.

The only fire rating listed in Table 601 for type 3b is 2hrs for exterior bearing walls. I think what most of us expect when we see this type is a building with exterior bearing walls of CMU.

Consider a metal building. Rigid metal frames are the structure, there are no bearing walls.

Is a metal building a type 3b? If yes, is it also true that there is no fire rating required for any element since there are no bearing walls? Assuming of course the rating isn't required by some other provision (fire separation etc.).

I'm trying to classify an existing metal building. The only combustible in the place is second floor plywood floor sheathing. Is it a type 3b?

Thanks,

Neal
 
IIIB has a 2hr exterior wall if I am not mistaken table 601....And it can be FRTW....FWIW. I would have to look at it a lot more closely. I believe the intent of the rating is to keep the fire contained, which is why you get similar size to IIB. I believe we debated this previously....
 
V-B unless you can't meet the area and height for the use.

Why complicate it. Big box stores are usually II-B in construction but the designer chooses a V-B because it will work. In other words don't assign a higher rating then what is needed to meet code.
 
steveray said:
IIIB has a 2hr exterior wall if I am not mistaken table 601....And it can be FRTW....FWIW. I would have to look at it a lot more closely. I believe the intent of the rating is to keep the fire contained, which is why you get similar size to IIB. I believe we debated this previously....
Click to expand...

The 2 hr rating is for exterior bearing walls only. That's really the crux of my question. I don't have exterior bearing walls (I have rigid metal frames that everything hangs off) then I have NO fire rating requirement, right?

I'm trying to classify an existing metal building. It has no rated assemblies but I think it still qualifies as a 3b. Would you agree?

Sorry I missed the earlier debate, can you point me to a thread? I did a search but didn't find anything...

Thanks,
Neal
 
IMO it is IIB, The metal is non-combustible and the table does not require ratings of walls, of course unless it's required by the code somewhere else.
 
nealderidder said:
The 2 hr rating is for exterior bearing walls only. That's really the crux of my question. I don't have exterior bearing walls (I have rigid metal frames that everything hangs off) then I have NO fire rating requirement, right?
Click to expand...

Correct or like mtlogcabin said go with V-B
 
Thank you all for the input. What's driving all of this is required fire-flow. We're adding on to an existing building (the metal building). Our Fire Marshall is telling us we have a very limited available fire-flow. If the metal building is V-B we don't have enough fire-flow available to increase the floor area, if it's 3B we are good to go.

We can't call it 2B because of existing wood floor sheathing.

I really just wanted to see how wacky my idea was before I approached the Fire Marshall with it. I think I'm meeting the letter of the code, I'm just so used to a III-B being a CMU bearing wall building.
 
Can be 3B, however typically there are load bearing structural members to support the roof within the wall shall be protected in accordance with Section 704.10

704.10 Exterior structural members. Load-bearing structural members located within the exterior walls or on the outside of a building or structure shall be provided with the highest fire-resistance rating as determined in accordance with the following:

1. As required by Table 601 for the type of building element based on the type of construction of the building;

2. As required by Table 601 for exterior bearing walls based on the type of construction; and

3. As required by Table 602 for exterior walls based on the fire separation distance.

[ ] Exterior load-bearing structural members, such as columns or girders, must have the same fire-resistance rating required for exterior load-bearing walls. As such, the required fire-resistance rating is the higher rating of that found in Table 601 for type of construction for structural elements or bearing walls or as required in Table 602 based on the fire separation distance.
 
Francis Vineyard said:
Can be 3B, however typically there are load bearing structural members to support the roof within the wall shall be protected in accordance with Section 704.10

704.10 Exterior structural members. Load-bearing structural members located within the exterior walls or on the outside of a building or structure shall be provided with the highest fire-resistance rating as determined in accordance with the following:

1. As required by Table 601 for the type of building element based on the type of construction of the building;

2. As required by Table 601 for exterior bearing walls based on the type of construction; and

3. As required by Table 602 for exterior walls based on the fire separation distance.

[ ] Exterior load-bearing structural members, such as columns or girders, must have the same fire-resistance rating required for exterior load-bearing walls. As such, the required fire-resistance rating is the higher rating of that found in Table 601 for type of construction for structural elements or bearing walls or as required in Table 602 based on the fire separation distance.
Click to expand...

Now that's interesting... If I go through the list;

1. For 3B table 601 calls out 0 for structural frame
2. For 3B table 601 calls out 2 hrs for exterior bearing walls
3. In this case I've got plenty of separation so 0 there too.

So what does "within" mean? (I feel like Bill Clinton) My frames are not actually "within" the walls. If I'm not within then 704.10 doesn't apply, right?

Is this frame within?

15s0sra.jpg


9
 
You have a building with a primary structure that is not required to be rated under Table 601
You have non-bearing exterior walls which are not required to be rated per Table 601

704.10 sends you to 601. You meet the requirements in 601 for a IIIB building classification
 
Thank you all for chiming in. We will see if the Fire Marshall reaches the same conclusion... Hopefully he doesn't diagree and give me the reason "because I said so" like mom used to.
 
Table 602 is for fire separation requirements not to classify the building. Footnote "a" sends you back to Table 601 for exterior bearing walls because the type may be more restrictive. Similar to Table 601 footnote "e" sends you to Table 602 to get the highest fire rating required from each table
The OP stated there is plywood sheathing on the second floor so that ruled out a II-B construction type

BTW Ben welcome to the forum
 
I was told by Code Congress some time ago that the Construction Type is based on the size of the building and its occupancy use group. If you have a small building, say constructed as a Type II-B and it could be classified as a lower construction type, then per the Building Code you are suppose to classify it for the minimum Construction Type allowed for the Occupancy Use Group allowed. However, if the building is ever to be expanded then the Architect should take that into consideration and list the Construction Type desired. If the building is an existing building then its actual construction type and its actual size with any allowable increases in area and building height requires evaluation to see if the intended occupancy use group can be in the building. The building's location to the property lines does not have anything to do with the building's construction classification. You have to comply with any ratings required as you get closer to the property lines.
 
I disagree.
The size and use requires certain construction types as defined in 602. The designer can always identify a lower type of construction classification if he/she chooses but is is not the AHJ's call to classify it in a lower construction type. An unlimited M occupancy can be a V-B but typically are a II-B construction. That makes a big difference in the rates when the insurance adjuster comes by to check the file to verify the type of construction to use for the premium rate.

CONSTRUCTION TYPES. See Section 602.

Type I. See Section 602.2.

Type II. See Section 602.2.

Type III. See Section 602.3.

Type IV. See Section 602.4.

Type V. See Section 602.5.

507 will allow unlimited areas under certain conditions
 
Back in prehistoric and BOCA days, Type III construction used to be "Ordinary Construction" which required masonry exterior walls and either wood or metal (or both) for interior construction. When the codes changed to Type III they changed the requirement from prescriptive masonry exterior walls to a performance based 2 hour rated exterior walls, probably because 8" (required for structural stability) masonry walls had a 2 hour or greater fire rating. I think the intent of the code is to require framing in or at exterior walls to have a 2 hour rating, however this may have vanished over the years as the verbiage has been massaged.
 
Francis, I believe there was the Southern Building Code Congress. I'm not sure how BOCA or UBC were run. I was on the Virginia AIA codes committee in the 1980s and took part in getting some state amendments adopted, but never got involved nationally.
 
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