Fire rating of shared apartment wall.

[John DeBruyne]

Goal: To determine if the two side-by-side apartment structures are their own "buildings".

Existing 3-story 12-unit side-by-side apartment structures that we are assuming were constructed at the same time in the 1970's. Type V-B construction (wood-framed with wood trusses) with the primary structural members parallel with the shared side-by-side walls which makes each structure structurally-independent of each other. The shared wall is comprised of two rows of 2X4 studs, not connected and not sharing base/top plates... you could pull one structure down without affecting the other structure.

1. Would the side-by-side walls be considered exterior walls for each structure? If we are trying to make them individual buildings, I think "yes", therefore Section 705 applies.
2. 705.5 says to refer to Tables 601 (0-hour) and 602 (1-hour) for fire separation distance <5 feet.
3. Where is the correct positioning of the fire rating? Options 1, 2 or 3 (or something I'm not considering) per the attached sketches.
4. The side-by-side walls to do not extend to create a parapet per 705.11 nor does it terminate at the underside of the roof deck per Exception 5.
5. Is the construction simply a fire rated exterior wall, or would it fall under "fire wall", "fire barrier", etc.?

 

[classicT]

1. Would the side-by-side walls be considered exterior walls for each structure? If we are trying to make them individual buildings, I think "yes", therefore Section 705 applies.
2. 705.5 says to refer to Tables 601 (0-hour) and 602 (1-hour) for fire separation distance <5 feet.
3. Where is the correct positioning of the fire rating? Options 1, 2 or 3 (or something I'm not considering) per the attached sketches.
4. The side-by-side walls to do not extend to create a parapet per 705.11 nor does it terminate at the underside of the roof deck per Exception 5.
5. Is the construction simply a fire rated exterior wall, or would it fall under "fire wall", "fire barrier", etc.?

1. Yes.
2. Correct.
3. Option #3 - the exterior wall of both structures must be 1-hr and rated for exposure from both faces. See 705.5 - "The required fire-resistance rating of exterior walls with a fire separation distance of less than or equal to 10 feet (3048 mm) shall be rated for exposure to fire from both sides."
4. That would be a problem.
5. If they are treated as separate buildings, than it is simply two exterior walls with no FSD.

 

[Paul Sweet]

What is the reason for considering them as separate buildings?

Check the code edition they were built under to see if the combined building would have met the height and area limits when they were built.

IBC 503.1.2 Buildings on same lot
"Two or more buildings on the same lot shall be regulated as separate buildings or shall be considered as portions of one building where the building height, number of stories of each building and the aggregate building area of the buildings are within the limitations specified in Sections 504 and 506. The provisions of this code applicable to the aggregate building shall be applicable to each building."

 

[John DeBruyne]

What is the reason for considering them as separate buildings?

Check the code edition they were built under to see if the combined building would have met the height and area limits when they were built.

IBC 503.1.2 Buildings on same lot
"Two or more buildings on the same lot shall be regulated as separate buildings or shall be considered as portions of one building where the building height, number of stories of each building and the aggregate building area of the buildings are within the limitations specified in Sections 504 and 506. The provisions of this code applicable to the aggregate building shall be applicable to each building."

One half of the entire structure and a small portion of the other half suffered fire damage and we are trying to determine Work Area sizes under the Rehabilitation Code. If it is all a single building, then the Work Area is over 50% of the building area. If it is two buildings, then the building/side that suffered the least damage would be much less than 50%.

 

[Paul Sweet]

The Work Area is defied as reconfigured spaces. If you're putting it back together the way it was it should be considered a repair, or at most a Level 1 alteration, so the 50% wouldn't apply.

 

[John DeBruyne]

The Work Area is defied as reconfigured spaces. If you're putting it back together the way it was it should be considered a repair, or at most a Level 1 alteration, so the 50% wouldn't apply.

Do you have any insight on the fact that the term "work area" is not italicized in 505.1? At least it is not in the 2015 Michigan version of this code. It is my understanding that if a term is not italicized, then that use of that term doe not impart the code-defined meaning (per the code's preface).

 

[Paul Sweet]

Work Area is italicized in 501.2. I think the lack of italics in 505.1 is a typo, since it is italicized in the 2018 IEBC, and the 2021 IEBC has user notes explaining the difference between the 3 levels of alterations in chapters 7 - 9.

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