Do accessory occupancies apply in a nonseparated analysis?

[Redmund]

A designer of an office building is proposing a nonseparated occupancy analysis for their project, and the occupancies involved are B, A-3 and S-2. However, the designer is also stating that the A-3 occupancy shall be accessory to the main B occupancy in the office building.

Does it make any sense to designate some areas as accessory in a nonseparated occupancy approach since the most restrictive occupancy group will determine the allowable height, area and number of stories? Additionally, the accessory occupancy section is IBC 508.2, with the separated occupancy section being 508.2.4 (i.e.: the separated occupancy section is one of the 508.2 series of accessory occupancy subsections). The nonseparated occupancy approach is in section 508.3 (i.e.: a different series of code subsections).

Is there any role for accessory occupancies when the nonseparated occupancy approach will be used?

 

[Yankee Chronicler]

A designer of an office building is proposing a nonseparated occupancy analysis for their project, and the occupancies involved are B, A-3 and S-2. However, the designer is also stating that the A-3 occupancy shall be accessory to the main B occupancy in the office building.

What's the size and the occupant load of the A-3 space? If it qualifies as an accessory space, then it's not an A-3, it's a B.

303.1.1 Small buildings and tenant spaces. A building
or tenant space used for assembly purposes with an occupant
load of less than 50 persons shall be classified as a
Group B occupancy.
303.1.2 Small assembly spaces. The following rooms
and spaces shall not be classified as Assembly
occupancies:
1. A room or space used for assembly purposes with
an occupant load of less than 50 persons and
accessory to another occupancy shall be classified
as a Group B occupancy or as part of that
occupancy.
2. A room or space used for assembly purposes that
is less than 750 square feet (70 m2) in area and
accessory to another occupancy shall be classified
as a Group B occupancy or as part of that
occupancy.

Does it make any sense to designate some areas as accessory in a nonseparated occupancy approach since the most restrictive occupancy group will determine the allowable height, area and number of stories? Additionally, the accessory occupancy section is IBC 508.2, with the separated occupancy section being 508.2.4 (i.e.: the separated occupancy section is one of the 508.2 series of accessory occupancy subsections). The nonseparated occupancy approach is in section 508.3 (i.e.: a different series of code subsections).

No, section 508.2.4 addresses specifically separation of accessory occupancies from the main occupancies to which they are accessory. For the overall, building-wide approaches, nonseparated occupancies are in section 508.3 and separated occupancies are in 508.4. It would seem that the only time it makes sense to treat spaces as accessory in a nonseparated building is if you want/need to NOT have the overall building height and area governed by a more restrictive occupancy classification that can be made to go away by using the accessory occupancy provisions.

Is there any role for accessory occupancies when the nonseparated occupancy approach will be used?

Yes. If the accessory space is small enough to qualify under 303.1.1 or 303.1.2, then using the accessory provision allows classifying the accessory space as B rather than A-3.

 

[CR Design]

What's the size and the occupant load of the A-3 space? If it qualifies as an accessory space, then it's not an A-3, it's a B.





No, section 508.2.4 addresses specifically separation of accessory occupancies from the main occupancies to which they are accessory. For the overall, building-wide approaches, nonseparated occupancies are in section 508.3 and separated occupancies are in 508.4. It would seem that the only time it makes sense to treat spaces as accessory in a nonseparated building is if you want/need to NOT have the overall building height and area governed by a more restrictive occupancy classification that can be made to go away by using the accessory occupancy provisions.



Yes. If the accessory space is small enough to qualify under 303.1.1 or 303.1.2, then using the accessory provision allows classifying the accessory space as B rather than A-3.

Note: even if the proposed A-3 space exceeds the area and occupant load limits of 303.1.1 and/or 303.1.2, the space could qualify as accessory per 508.2 provided the space does not occupy more than 10 percent of the floor area of the story in which the accessory use(s) are located and does not exceed the tabular values for nonsprinklered buildings in Table 506.2 for each such accessory occupancy."

 

[Sifu]

If an individual space is under the 10% limitation for the floor, but the aggregate of all spaces on the floor exceeds 10% then does the individual space need to separated?

For example, there is an A3 space on one end of a building that is less than 10%, and several other accessory spaces on the floor. Combined they exceed 10%. Is separation still required using the separated occupancies strategy? If so, then could separating the A3 per t508.4 to bring the aggregate down work and then the rest would require no separation.

Is this an example where one could use the separated AND accessory strategies?

 

[Sifu]

Struggling to articulate this.

To expand on this, if multiple different accessory occupancies are present on the end of a building, must they be separated from each other? So using the previous example, there is a lobby (A) office (B), storage (S1) and mechanical room (U) at one end. Assume the combined spaces are less than 10%, but other areas on the floor combined with this area exceed 10%. If the plan north end is separated along the heavy red highlight to get the accessory percentage to less than 10% from the rest of the building then it works for as a separated occupancy from the R2 side. But do those individual occupancies require a mixed use analysis in and of themselves? If so, they would then need to meet either accessory, separated per 508.4, or non-separated.

 

[CR Design]

IBC 2021 s. 508.1 states that a mixed-use building can be evaluated according to 508.2 (accessory), 508.3 (nonseparated), or 508.4 (separated), or a combination of the three. Is the separation shown in red a fire wall or a fire barrier? Is the area "south" of that red line all R-2?

 

[Sifu]

IBC 2021 s. 508.1 states that a mixed-use building can be evaluated according to 508.2 (accessory), 508.3 (nonseparated), or 508.4 (separated), or a combination of the three. Is the separation shown in red a fire wall or a fire barrier? Is the area "south" of that red line all R-2?

The red highlight follows a separation that is a fire barrier in some places, a fire partition in other places, and not identified at all in one location. My question originates in the belief that the some or all of the area should be separated by a fire barrier since the exceed the 10% for accessory occupancies. FB = fire barrier (blue), FP1 = fire partition (green), over the double door it is not identified, but assume it is the FP1 at this point.

Mostly R2 below the line. About 500sf² of other accessory space, which puts them about 499sf² over 10%. If the strategy I outline is valid, they might be better off separating those spaces out, but that is up to them.