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Occupancy category is defined as the purpose for which a building or other structure, or part thereof, is used or intended to be used.

“It essentially breaks down to how many people are inside, whether it’s temporary or permanent, and the function of the building,” our engineer explained. There are four occupancy categories, each determined by the nature of the occupancy which is based on elements such as hazard to human life in the event of failure, economic impact, essentiality of the facility, and so on.

 

The basic breakdown is as follows:

 

For a complete table highlighting the Nature of Occupancy, click here.

 

Why do structural engineers need occupancy categories?

 

The purpose of occupancy categories is to calculate your design load, which is the maximum force a building must handle before being deemed unsafe. This is based on the combined weight of the building materials, occupants, and environmental effects such as snow, wind, rain, seismic activity, ice, etc.

 

 

What is an importance factor?

 

Importance factors are numeric values assigned to each occupancy category that will increase or decrease the design loads for snow, wind, rain, seismic activity, ice, etc. when multiplied by the base load. This calculation system is based on a minimum requirement in which the primary intent is to protect the life and safety of the public. Therefore, a higher hazard to human life will result in a higher design load, and a lower hazard to human life will result in a lower design load. Occupancy category II will always have an importance factor of 1.0, thus making the design load the same as the base load.

 

 

Who determines the occupancy category?

 

Occupancy category is determined by the authority having jurisdiction over the project. Although the engineer is not responsible for choosing the occupancy category, it is useful for them to know when calculating design loads for a structure.

 

 

How does occupancy category affect building costs?

 

Depending on the occupancy category, your price will fluctuate to account for the structural requirements and cost of materials. Higher occupancy categories will result in higher costs, and lower occupancy categories will result in lower costs. When researching and pricing out your building, it is important to compare “apples to apples”, and make sure the occupancy category is appropriate for the intended use of the building.

 

 

How does Rubb view occupancy categories?

 

Rubb Building Systems takes occupancy categories and the safety of those in our buildings very seriously. Unfortunately, others may not, capitalizing on technicalities in the wording of each occupancy category. Where does the line get drawn between “minor” and “major”, or “temporary” and “permanent”? “A responsible engineer determines the intended use and the customer needs, and uses their best judgment in determining occupancy category,” our engineer stressed. All of our engineers take the time and care to put the occupancy category on top of every cover sheet, so that our clients can see it up front and use it in correlation with other information. Our calculations are in accordance with the most current building codes, and all plans and drawings are documented and signed before sending them to our clients.

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Chuck Auger

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