Change of occupancy from residential to commercial

[Yankee Chronicler]

The question here then revolves around how to calculate FSD for both the commercial and residential buildings. This is difficult given the lack of separating property lines. Imaginary lot lines have to be used. Further complicating the issue is that the IRC under which it was built required a FSD of 3', but it is now 5'.

Placement of the imaginary lot line for purposes of determining the FSD is going to be critically important for this project.

IMHO, I would suggest that the FSD be placed at the mid-point between the structures. As the SFD is not being modified, I would allow it to remain as is, even if the FSD would prohibit openings or would require a rated exterior wall. As for the shop building, which is now commercial, I would ask that it fully comply with the FSD requirements. If the designer proposed to push the imaginary lot line right up to the exterior wall of the SFD, I would push that the SFD comply with the rated exterior wall and opening limitations.

But you don't have to even consider the fire separation distance (the imaginary lot line) unless the IEBC tells you to do so in Chapter 10. Where does chapter 10 tell us to consider that?

 

[Sifu]

But you don't have to even consider the fire separation distance (the imaginary lot line) unless the IEBC tells you to do so in Chapter 10. Where does chapter 10 tell us to consider that?

This is my approach, agree or disagree this is the only way I have been able reconcile changing from an IRC regulated structure in the IEBC.

The IEBC tells us to go to the IBC when there is a change in occupancy to a higher hazard category at 1011.6. The problem with converting anything from the IRC to the IEBC is that the IEBC does not identify an IRC regulated building in t1011.6 (any of the tables). So we have to stretch. The original accessory "garage" has no classification under the IRC...it is just an IRC accessory structure. But in order to use the IEBC for this we MUST assign it a classification. I would consider it a U, so changing it to a mixed use, B or M it is moving to a higher hazard category, which 1011.6.1 then directs us to the IBC, and by extension t602.

The new idea is to set the FSD at 3' from the SFD. This enables the house walls and projections to remain unchanged based on the 2003 IRC. This will locate the FSD approximately 1'6" from the newly christened commercial building, and per t602 will require a 2-hr wall since the building is a non-separated B & M. This was discussed with the CBO, who may have suggested it in a vague way to the architect.

 

[steveray]

This is my approach, agree or disagree this is the only way I have been able reconcile changing from an IRC regulated structure in the IEBC.

The IEBC tells us to go to the IBC when there is a change in occupancy to a higher hazard category at 1011.6. The problem with converting anything from the IRC to the IEBC is that the IEBC does not identify an IRC regulated building in t1011.6 (any of the tables). So we have to stretch. The original accessory "garage" has no classification under the IRC...it is just an IRC accessory structure. But in order to use the IEBC for this we MUST assign it a classification. I would consider it a U, so changing it to a mixed use, B or M it is moving to a higher hazard category, which 1011.6.1 then directs us to the IBC, and by extension t602.

The new idea is to set the FSD at 3' from the SFD. This enables the house walls and projections to remain unchanged based on the 2003 IRC. This will locate the FSD approximately 1'6" from the newly christened commercial building, and per t602 will require a 2-hr wall since the building is a non-separated B & M. This was discussed with the CBO, who may have suggested it in a vague way to the architect.

Shouldn't it be 5'? Or was it different in the 2003?

 

[Sifu]

Different in the 2003, which helps a lot. I believe the actual distance is 4'6, so if it were to be measured using current code there would be no option but to rate, But since 3', I think they can "imagine" the line closer to the commercial building and only rate those walls.

 

[classicT]

But you don't have to even consider the fire separation distance (the imaginary lot line) unless the IEBC tells you to do so in Chapter 10. Where does chapter 10 tell us to consider that?

Yes you do. Check out IEBC 1011.7...

In the case mentioned, I too would classify the SFD-accessory building as Group-U. Therefore, the Change of Occupancy is to a higher hazard per Table 1011.7. Exterior walls thereby must conform to the IBC, which would drive you towards IBC Section 705 (Exterior Walls), and ultimately to Table 705.5 - Fire-Resistance Rating Requirements for Exterior Walls Based on Fire Separation Distance.

2021 IEBC ​

1011.7 Exterior Wall Fire-Resistance Ratings​

Hazard categories in regard to fire-resistance ratings of exterior walls shall be in accordance with Table 1011.7.

TABLE 1011.7
EXPOSURE OF EXTERIOR WALLS HAZARD CATEGORIES​

RELATIVE HAZARD	OCCUPANCY CLASSIFICATION
1 (Highest Hazard)	H
2	F-1; M; S-1
3	A; B; E; I; R
4 (Lowest Hazard)	F-2; S-2; U

1011.7.1 Exterior Wall Rating for Change of Occupancy Classification to a Higher-Hazard Category​

Where a change of occupancy classification is made to a higher hazard category as shown in Table 1011.7, exterior walls shall have fire resistance and exterior opening protectives as required by the International Building Code.​

Exception: A 2-hour fire-resistance rating shall be allowed where the building does not exceed three stories in height and is classified as one of the following groups: A-2 and A-3 with an occupant load of less than 300, B, F, M or S.​

1011.7.2 Exterior Wall Rating for Change of Occupancy Classification to an Equal or Lesser-Hazard Category​

Where a change of occupancy classification is made to an equal or lesser-hazard category as shown in Table 1011.7, existing exterior walls, including openings, shall be accepted.​

1011.7.3 Opening Protectives​

Openings in exterior walls shall be protected as required by the International Building Code. Where openings in the exterior walls are required to be protected because of their distance from the lot line, the sum of the area of such openings shall not exceed 50 percent of the total area of the wall in each story.​

Exceptions:​

1. Where the International Building Code permits openings in excess of 50 percent.
2. Protected openings shall not be required in buildings of Group R occupancy that do not exceed three stories in height and that are located not less than 3 feet (914 mm) from the lot line.
3. Exterior opening protectives are not required where an automatic sprinkler system has been installed throughout.
4. Exterior opening protectives are not required where the change of occupancy group is to an equal or lower hazard classification in accordance with Table 1011.7.

 

[Yankee Chronicler]

In the case mentioned, I too would classify the SFD-accessory building as Group-U. Therefore, the Change of Occupancy is to a higher hazard per Table 1011.7. Exterior walls thereby must conform to the IBC, which would drive you towards IBC Section 705 (Exterior Walls), and ultimately to Table 705.5 - Fire-Resistance Rating Requirements for Exterior Walls Based on Fire Separation Distance.

Fair enough. I agree.