Number of Exits Within a Room – Building Codes

As an Architect, I interact with clients, engineers and contractors who have acquired bits of information about Building Codes.  Sometimes, those bits are misconceptions and regurgitated information.  The building codes can be intimidating and have no beginning or end. To learn the code, the best way is jumping in feet first.  

Upcoming Blog Posts

In the next series of blog posts, I will explore common simple and more complex Building Codes.    Each City has adopted a code but most in Arizona use the IBC (International Building Code).

The issues addressed in the following Blog Posts are:

1. Door swing direction.  Which way should the door swing, out of a room or in?
2. Number of exits within a room?
3. Size of the door.  Who said “size doesn’t matter.”
4. Exit corridor width.  How wide or narrow can a hallway be?
5. Clearances around a door?  Door arrangement between two doors. 
6. Door fire ratings.  Is your door fire rated?
7. Exit Travel Distance.  
8. Do I need an Elevator?
9. Should my door have panic hardware? 
10. Do I need a drinking Fountain?
11. Minimum size of a single person toilet room?
12. Small commercial space, is one bathroom enough?

Item in bold is addressed in this post.  As an Arizona Architect, most City’s jurisdictions work with the IBC (International Building Code).   The code analysis is based upon the IBC.

Number of Exits within a Room

The number of exits within a room is determined by the occupancy and the level of hazardous condition.  The type of Occupancy (ie.  office, retail, industrial etc.) generally determine quantity of occupants based upon a load calculation. For example:

Portion of Occupancy Table

Once the number of occupants is determined, a maximum number of occupants are allowed before second or possibly third exit is required.  The general rule of thumb are as follows:

Number of Exits Rule of thumb

In occupancy’s such as business group (offices), Assembly (Theaters, night clubs, restaurants), Educational (Schools), Factory (manufacturing), Mercantile (stores, markets, retail) and Utility (agriculture buildings, barns, sheds), if occupant load stays below 49 people, one exit is required.  Other factors may play into the requirement, such as travel distance, but  that will discussed in a later blog.

In hazardous occupancy’s, the maximum occupant load is greatly reduced to either 3 or 10, depending upon the use, before a second exit is required.  In storage occupancy the number of occupants allowed before a second exit is required is 29.

Once occupant loads reach greater numbers, such as 501 – 1,000 occupants, minimum 3 exits are required.  Beyond 1,000 occupants, four exits are required.  An example of this may be a large conference room or convention center where spaces are large enough to hold these quantities.

Another requirement to take into account is location of the exits themselves.  A good rule of thumb to follow is that the distance separating the exits must be greater than 1/2 the distance of the overall diagonal dimension of the room.  So in a large office space that is an open plan with no walls, such as the one depicted below,  the number of occupants possible by code would be 12,000 s.f. / 100 s.f. per person = 120 occupants.  this exceeds 49 occupants therefore 2 exits required.  See graphic below.

Exit calculation

Summary

Number of exits and their separation are dependent upon occupant loads.  Once a threshold of occupants are met, exit quantities increase.  Separations of those exits are required to allow for occupants to safely exit in time of emergency.  For example, if a fire occurs within one side of the room, having adequate separation ensures that both exits are not blocked.

When learning building codes, once you begin digging into the code, it begins to make sense.  However when in doubt, rely on an Architect to explore the code and assist you.