Incidental Use vs Accessory Use vs Mixed Use

Hi all,

I have a client that currently occupies a three story ±300,000 sf building located in California. The construction type of the building is Type I-A w/ fire sprinklers. We have been remodeling the entire interior of the building for the past few years and are constantly running into new issues, whether it be from the original building construction or new code interpretations.

My Building Official has been concerned with rooms that are classifid as "Storage" and are larger than 100sf. He believes that they need to be classified as "Incidental Uses" and therefore being required to be seperated from the rest of the B Occupancy per CBC 508.2.2 & 508.2.2.1 with some means that resists the passoge of smoke. I don't see how a storage room (and in some cases file rooms) are to be considered an Incidental Use when they are part of an overall B Occupancy. I can't even get a clear definition for what qualifies as Incidental or Accessory. And it looks like the 2010 CBC has combined them to now be Incidental Accessory Occupancies.

So, my questtions are as follows: 1)Can they rooms be classified as an Accessory Occupancy or even classified as a completely different use (i.e. and S-1 for book storage or furniture storage)and then not require any occupancy seperation? 2) Are all "storage rooms" governed by table 508.2 and consided incidental uses?

I have attached a drawing of the current area of concern for your review. Thanks for any help in advance.

Greg Frank


Original Post
The designer has the option of handling mixed uses and occupancies in 4 ways:
1. Incidental use
2. Accessory occupancy
3. Nonseparated occupancies
4. Separated occupancies

I usually start with #1 and work my way down to #4 to see which one would apply.

In my opinion, the rooms in question can be considered incidental use areas.

Table 508.2 states that incidental storage rooms over 100 sq. ft. shall be separated by 1-hour fire barriers or provide an automatic fire extinguishing system. Since the building is already sprinklered throughout, the second option is provided; therefore, no additional protection is required. Additionally, incidental use areas are to be classified in accordance with the occupancy in which they are located. Since they are associated with the B occupancy, they can be considered B occupancies, too.

Also, since the building is Type IA construction, and you have no H occupancies (apparently), then you have an unlimited area building with unlimited height. Which means you can call your building a nonseparated occupancy building, since no single occupancy group would be considered the most restrictive.
Ron is right on the money!

Here are some previous discussions that are helpful on this subject (incidental uses, occupancy separation): (Is storage less than 100SF still "incidental use") (CBC 2007 - 508.3.2) (Required Separation of Occupancy?)
Ron & needtolearn,

Thank you for the response. My problem now lies with Section 508.2.2.1 which states "Where Table 508.2 permits an automatic fire-extinguishing system without a fire barrier, the incidental use area shall be separated from the remainder of the building by construction capable of resisting the passage of smoke". Unfortunately, due to existing conditions it would be extremely difficult to create the full height walls and/or hardlid ceilings. Plus there are 100's of these type of rooms throughout the building.

Would classifing the building as a Nonseperated Occupancy Building be sufficient for eliminating the seperation from the storage rooms from the rest of the spaces? Do I have the ability to pick and choose?

Greg Frank
Yes, you have the choice.

Section 508.2.1 states, "An incidental use area shall be classified in accordance with the occupancy of that portion of the building in which it is located or the building shall be classified as a mixed occupancy and shall comply with Section 508.3."

If you call it a nonseparated occupancy building, then the requirements for incidental use areas are not applicable.
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