While the terminology may be similar, the code does not actually link the occupancy classification of a building or space to the applicable occupant load factor for means of egress design requirements. This is a common misconception we see many designers make that can have a significant impact on the required number or size of exits in a building. When determining the occupant loads for your facility’s egress requirements, it is important to consider the difference between the occupancy classification of the building, and function of the space for the area you are evaluating.
- Occupancy Classification – based on a building’s use and purpose as determined by Chapter 3 of the International Building Code (IBC). This classification (or several if the facility is a mixed occupancy) is applied throughout all areas of a building.
- Occupant Load – based on the “function of space”, which is defined independently of the building’s occupancy classification.
While in most cases, the occupancy classification of a building or space aligns with its intended function, this is not always the case. For example, in a typical office building, the office space and any small conference/meeting rooms with less than 50 people will be classified as a Group B Business Occupancy (IBC 303.1, 304.1). However, the function of space for the small conference/meeting rooms align themselves most closely with “assembly without fixed seats, unconcentrated (tables and chairs)” in IBC Table 1004.1.1 and should be loaded with the corresponding occupant load factor accordingly. When calculating the occupant load factor for the conference/meeting rooms, 15 net square feet per occupant should be applied. Often times, we see designers loading these spaces at 100 gross square feet per occupant for “business areas” since they are defined as Group B Occupancies, however this is not technically correct and can have a significant impact on egress design. We often get asked if this same approach would apply to a “breakout” space that, while looking very similar to the conference room described above, differs in that its intended to only act as collaboration space for employees sitting in adjacent cubicles/offices. While the language in the IBC does not directly address this distinction, we often find in practice that the building official is accepting of utilizing an occupant load factor of 100 gross square feet for this type of breakout space if it can be illustrated that it is in-fact a non-simultaneous use with the surrounding offices. This is just one small facet of occupant loads. Stay tuned for Part II which will address the difference between net and gross calculations.