When are sprinklers required in mixed-use buildings?
Like most questions in the engineering world the answer to this is “it depends.” First it's important to realize that there is a difference between use and occupancy. When people say “mixed use buildings” they generally are referring to buildings that the code would consider “mixed occupancy.” The building code has many requirements for mixed occupancy buildings but there are few to no requirements for a mixed-use building. For more information on this difference, you can check out the module entitled “difference between use and occupancy.”
Assuming your building does have multiple occupancy types, the first step in determining sprinkler requirements is to verify if any of the individual occupancies requires sprinkler protection. In the 2021 IBC these requirements are found in section 903.2. Requirements in this section are based on the occupancy type of the building, the fire area in the building and other factors such as the occupant load and where in the building the fire area is located.
It's important to note that some of the requirements in Section 903.2 apply only to certain floors or fire areas, while other requirements apply to the entire building.
For example, if you have a group A-3 occupancy in your building, the sprinkler requirements found in Section 903.2.1.3 apply to the story containing the Group A-3 occupancy and all stories between that story and the exit discharge. But if you have a Group R-2 occupancy in your building, the requirements of Section 903.2.8 apply to the entire building.
Once you have reviewed the IBC section 903.2 requirements for the occupancies present in your building, you also need to check IBC chapter 4 special detailed requirements based on occupancy and use.
If any of these subsections apply to your building, you need to check for potential sprinkler requirements. For example, Section 403, High-Rise Buildings, requires a sprinkler system throughout the building, independent of any requirements found in Section 903.2.
The final item step is determining what mixed occupancy approach to use for the building. In Section 508, the IBC provides three options for mixed occupancy: Separated, non-separated and accessory. Choosing a mixed occupancy approach is typically based on the allowable height, area and number of stories for the occupancies involved, but all of these values do depend on the presence of sprinkler protection. Check out the module on mixed occupancy approaches for more info on this topic.
Once you have reviewed Chapters 4 and 9 for sprinklers requirements based on your specific building, and once you have determined which mixed occupancy approach to take, there are a number of scenarios that your building call fall into:
1. The first, and most restrictive scenario, is where of one the occupancies in your building, or one of the characteristics of the building, triggers a sprinkler requirement for the whole building. So if you have a Group R-2 building, or if your building is a high-rise, you will need to fully-sprinkler the building, regardless of what other occupancies are present.
2. The second scenarios is based on the mixed occupancy approach that you are using for your building.
a. If you are using a nonseparated mixed occupancy approach, the most restrictive requirements of any of the occupancies involved apply to the entire building. So if any of the applicable Chapter 4 or 9 sections require a sprinkler system, even if just for a specific fire area or floor, those requirements would apply to the entire building if you are taking a non-separated mixed occupancy approach.
b. If you are taking a separated mixed occupancy approach, you would apply the applicable requirements from Chapter 4 and 9 to each separated area within the building. This requirement could be to just provide sprinklers for a specific fire area, or it could be for the entire floor or floors between the occupancy and the level of exit discharge. With this approach, you may end up with sprinklers in certain parts of the building but not others. Keep in mind that the requirements for separating occupancies and/or fire areas can vary, so you’ll need to review Table 508.4 and 707.3.10 for these requirements to make sure you are providing sufficient separation.
c. If you are taking an accessory occupancy approach, the requirements are based on each individual occupancy. While Section 508.2 allows you to base the allowable height and area on the main occupancy, the requirements for sprinklers are based on each individual occupancy, even the ones considered to be accessory. So you need to apply the applicable requirements from Chapter 4 and 9 to each occupancy within the building.
3. The final scenario is where nothing in your building triggers a requirement for sprinkler protection in Chapter 4 or 9. In this case, there is no requirement to provide sprinkler protection in any part of the building.
In conclusion, sprinkler requirements for a mixed occupancy building depend on the occupancies involved, the characteristics of the building, and is being used.
I’m Chris Campbell, this is MeyerFire University.
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