Navigating the Building Code – Part 1 (Use and Occupancy)

Today we are going to dive deeper into understanding what is really important in understanding key aspects of the building code.  We will examine two of the main factors that dictate what drives code compliance – use and occupancy.  Also, to reiterate a few important points from previous posts keep in mind that there are other regulations and rules set forth by the authorities having jurisdiction over your project.  You and the architect must identify what is in place for the project to ensure that the project is designed correctly (we will focus on the International Code Council family of codes as it is the most widely adopted).  Before we get into a more detailed look at the code let’s review the approach to navigating the building code (as described in previous GDS posts):


For years the building code has been viewed as something that tells architects and clients what they cannot do with their project.  Architects typically see it as a battle to design according to the code and the client’s wants simultaneously.  Also, most architect’s see it as a hindrance to “good design”.   However, in most cases the code is not in place to limit design, it is in place to allow design to happen within the framework of maintaining the health, safety, and welfare of the public.  Basically, the most productive way to approach the building codes are that, as long as certain conditions are met, then the project can be designed to function in the best way possible.  So, it is the set of regulations that describes what is allowed, not what isn’t allowed.

Let’s look at the terms and see how they will affect your project.


The Use Designation is a subordinate category of the Occupancy.  It is the designated use of a space.


The Occupancy is the formal designation of the primary purpose of the space, or portion of the space within a structure.  It is based on the nature of the hazards and risks associated with the purpose of the space.  Occupancy of a space is determined to be in one of the following categories:

  1. Assembly – Groups A-1 (spaces for the production and viewing of performing arts or motion pictures), A-2 (spaces for food and/or drink consumption), A-3 (spaces for worship, recreation, or amusement), A-4 (spaces for viewing indoor sporting events and activities with spectator seating), and A-5 (spaces for the participation in or viewing of outdoor activities)
  2. Business – Group B
  3. Educational – Group E
  4. Factory and Industrial – Group F-1 (moderate-hazard factory industrial), and F-2 (low-hazard factory industrial)
  5. High Hazard – Groups H-1 (structures containing materials that pose a detonation hazard), H-2 (structures containing materials that pose a deflagration hazard), H-3 (structures containing materials that support combustion), H-4 (structures containing materials that are health hazards), and H-5 (semi-conductor fabrication structures and research and development areas)
  6. Institutional – Groups I-1 (structures for more than 16 people who require 24 hours supervision and receive custodial care), I-2 (structures for medical care who require 24 hours supervision for more than five persons who are incapable of self preservation), I-3 (structures for more than more than five persons who are under restraint or security), and I-4 (structures for more than five people who require less than 24 hours and receive custodial care)
  7. Mercantile – Group M
  8. Residential – Groups R-1 (containing sleeping units where the occupants are primarily transient), R-2 (containing sleeping units or more than two dwelling units where occupants are permanent), R-3, and R-4
  9. Storage – Groups S-1, and S-2
  10. Utility and Miscellaneous – Group U

Within the code there are lists of the individual types of spaces that fall within these categories.

Applying Use and Occupancy

A building may be single Occupancy or mixed Occupancy (where more than one Occupancy make up the building).  A single Occupancy building may be an office building (Business Group), with a single or multiple tenants.  In the scenario of multiple tenants, the building could have many different Uses (determined by individual needs of each tenant) and just the one Occupancy – Business Group.

An example of a mixed Occupancy building would be a multi-level building that has restaurants (Assembly Groups) and retail stores (Mercantile Group) on the first floor and condos on the upper levels (Residential Groups).  Knowing the mixed Occupancy groups is important because there are specific requirements for keeping the different Occupancies “separated”.  One of the most important issues is the fire separation needed in order to keep the individual Occupancies isolated from damage when a problem occurs in an adjacent space.

One thing to note: typically, Use and Occupancy are used interchangeably but there are cases where it is not the case.  Most often, the Use vs. Occupancy designations factor into remodels of a space when the purpose of the space is changing.  For example a single family dwelling could be converted to a two family changing how the building is used, but not changing the occupancy. There are also sub-classifications in the occupancy that may not change the type of occupancy (Mercantile comes to mind) but could change in use (larger or smaller sub-class).  Regardless of whether the project is new construction, remodels, renovations, or additions, determining the use and occupancy of the spaces is an important step because it determines the subsequent processes and restrictions that will be applied to the construction of the facility.

As technology improves, and more construction methods and materials are developed, the building codes will be updated.  In order to maintain the health, safety, and welfare of the general public, the architect and client needs a thorough understanding of the building codes and be able to adapt the design practices to meet the needs of the code.  You are more than welcome to contact us regarding any questions you may have regarding building codes and the effect of regulations on your project –

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