Building Codes – Number of Exits Within a Room


Building Codes

As an Arizona 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 heard along their travels.  Building Codes are generally clearly defined, however some codes have grey areas with interpretations.   If you are not an architect, you most likely would not pick up the local governing code book and use it as nightly reading.

When I first began my architectural career over 25 years ago, I found the code book very intimidating.  Graduating from the College of Architecture at the University of Arizona and learning to be an Arizona Architect, it took a few years before I cracked open the code book.  My first job was essentially drawing buildings already conceptually designed.  The codes were already figured out and I didn’t need to analyze zoning, determine fire ratings or look at number of exits or their locations etc.   There are classes and seminars to get a better understanding of the Building Codes, but just like many things, jumping in feet first is how you learn.  The code has no beginning or end, so the question is where to start.

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 to be 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.  Helpful if your using a wheelchair or trying to bring supplies to your space.
  6. Door fire ratings.  Is your door fire rated
  7. Exit Travel Distance.  There is a maximum number of feet one can travel before exiting a space.
  8. When is an elevator required?
  9. Number of plumbing fixtures required? 

The item in bold to be 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 dictated by the occupancy and whether their is some hazardous condition.  The type of Occupancy (ie.  office, retail, industrial etc.) generally determine quantity of occupants based upon a load calculation. For example:

Architect in Arizona - occupant load table

Portion of Occupancy Table

For example in a large office space that is an open plan with no walls of 12,000 s.f., the number of occupants possible by code would be 12,000 s.f. / 100 s.f. per person = 120 occupants.  See graphic below.

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:

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, 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.  See illustration below.

Building Codes - exit calculation

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.

Jeff Serbin

Jeff Serbin

Jeff Serbin is Vice President of Serbin Studio. His responsibilities include architectural design and project management. He coordinates the work of consultants and design team members, and is involved in design from concept through construction.

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