Exterior Wall Separation

[Phil B]

In the sketch below, building 1 is a new, 2,100 small Type IIB food serving building with 8" cmu exterior walls, no openings, and a small overhang on the lower left corner. Buildings 2 and 3 are existing open air gathering places with about 4 to 5 feet overhangs. If I'm reading table 705.5 correctly, the walls of the new building need to be rated 1 hour, correct? If so, doesn't the block carry an inherent 1 hour rating and therefore I am OK?

 

[RLGA]

What are the construction types, occupancies, exterior wall fire-resistance ratings, and exterior opening protection ratings for the existing buildings? The location of the imaginary line cannot make an existing building non-compliant.

Most CMU walls will provide a 2-hour rating. Obtain the equivalent thickness and ratio of aggregates of the proposed CMU from the manufacturer to determine what the rating will be per IBC Table 722.3.2.

 

[Phil B]

Existing buildings 2 & 3 are Type VB per the 2o14 building code, and Assemble occupancy. They do not have any exterior walls, hence no openings, and they are not sprinklered. New building 1 is sprinklered.

 

[TheCommish]

How do the existing buildings not have exterior walls and a building construction type?

 

[Phil B]

It's a covered area with roof, columns, slab, etc. All those elements would be governed by the Type classification.

 

[RLGA]

In other words, Buildings 2 and 3 are canopies by IBC definition. As Type VB buildings, the required fire separation distance to avoid fire-resistance-rated construction is 10 feet. Thus, your imaginary line must be located at least 10 feet from the "exterior walls" (i.e., location of columns) of each building. Then, the exterior walls of the new building will be based on the fire separation remaining after the 10-foot separation, which still requires a 1-hour fire resistance rating.

 

[Yankee Chronicler]

Existing buildings 2 & 3 are Type VB per the 2o14 building code, and Assemble occupancy. They do not have any exterior walls, hence no openings, and they are not sprinklered. New building 1 is sprinklered.

No, they have 100% unprotected openings.

What's your role? Are you the architect, or the Building Official? Your sketch shows what appears to be a fire-separation line mid-way between the new building and the existing structures. Who decided where to draw that line? It does NOT have to be mid-way -- the owner (effectively meaning the architect) can put it anywhere, right up to zero inches off the face of the new building if that's what's most beneficial to the design. But the owner will have to understand that if the line is right at the new building, they can't come back later and just pop in unprotected doors or windows.

 

[Phil B]

No, they have 100% unprotected openings.

What's your role? Are you the architect, or the Building Official? Your sketch shows what appears to be a fire-separation line mid-way between the new building and the existing structures. Who decided where to draw that line? It does NOT have to be mid-way -- the owner (effectively meaning the architect) can put it anywhere, right up to zero inches off the face of the new building if that's what's most beneficial to the design. But the owner will have to understand that if the line is right at the new building, they can't come back later and just pop in unprotected doors or windows.

Thank you for that. I hadn't thought of it that way. I'm the Architect.

 

[Phil B]

In other words, Buildings 2 and 3 are canopies by IBC definition. As Type VB buildings, the required fire separation distance to avoid fire-resistance-rated construction is 10 feet. Thus, your imaginary line must be located at least 10 feet from the "exterior walls" (i.e., location of columns) of each building. Then, the exterior walls of the new building will be based on the fire separation remaining after the 10-foot separation, which still requires a 1-hour fire resistance rating.

RLGA - Looking at this from Yankee Chronicler's viewpoint that the existing building has 100% unprotected openings, and your comment that "The location of the imaginary line cannot make an existing building non-compliant", wouldn't it be correct that based on Table 705.8 for Unprotected, NonSprinklered nothing can be built within 30' of the existing building (unless some walls were added at the existing building)?

 

[RLGA]

No. Refer to Section 705.8.1, Exception 2.

At 10 feet, exterior nonbearing walls are not required to be fire-resistance-rated. With Type VB construction, exterior bearing walls and structural frame are not required to be fire-resistance rated. Thus, you are permitted to have unlimited unprotected openings at 10 feet.

 

[Yankee Chronicler]

And, as the designer, you get to draw that "imaginary property line" anywhere you want. If the proposed new building has exterior walls with the required fore-resistance rating and no openings, the line can be the exterior face of the new building.

Just remember that, once you draw it and submit it and it gets approved, it becomes part of the building (and site) record. Any future changes -- such as punching windows and doors into those walls -- will have to deal with the position of that line (unless you submit a new permit application to revise its location).

 

[Phil B]

No. Refer to Section 705.8.1, Exception 2.

At 10 feet, exterior nonbearing walls are not required to be fire-resistance-rated. With Type VB construction, exterior bearing walls and structural frame are not required to be fire-resistance rated. Thus, you are permitted to have unlimited unprotected openings at 10 feet.

Thank you very much for that info!

 

[Phil B]

No. Refer to Section 705.8.1, Exception 2.

At 10 feet, exterior nonbearing walls are not required to be fire-resistance-rated. With Type VB construction, exterior bearing walls and structural frame are not required to be fire-resistance rated. Thus, you are permitted to have unlimited unprotected openings at 10 feet.

I am just following up on this to make sure I understand it correctly:
The FSD line needs to be 10' feet away from Bldg 2 (with no walls, just columns) because anything closer would require the columns to be rated 1 hour per Table 705.5, even though Type VB doesn't require it, correct?
Thank you for your patience.

 

[RLGA]

I am just following up on this to make sure I understand it correctly:
The FSD line needs to be 10' feet away from Bldg 2 (with no walls, just columns) because anything closer would require the columns to be rated 1 hour per Table 705.5, even though Type VB doesn't require it, correct?
Thank you for your patience.

Correct, and exterior unprotected openings would be limited to 10% of the exterior wall if nonsprinklered and 25% if sprinklered.

 

[Phil B]

Correct, and exterior unprotected openings would be limited to 10% of the exterior wall if nonsprinklered and 25% if sprinklered.

I think that's the part I don't understand because exception 2 in 707.8.1. doesn't refer to a 10' limit.

 

[RLGA]

No, Table 705.5 does.

If the fire separation distance is less than 10 feet, per Table 705.5, a 1-hour exterior wall is required; thus, Exception 2 to Section 705.8.1 would no longer be applicable. Since Exception 2 does not state "per Table 601," the fire-resistance rating condition applies regardless of what provision requires those elements to be fire-resistance rated.

 

[Phil B]

No, Table 705.5 does.

If the fire separation distance is less than 10 feet, per Table 705.5, a 1-hour exterior wall is required; thus, Exception 2 to Section 705.8.1 would no longer be applicable. Since Exception 2 does not state "per Table 601," the fire-resistance rating condition applies regardless of what provision requires those elements to be fire-resistance rated.

Thank you sir