Ask the Engineer: Occupancy Categories

Ask the Engineer is a blog segment presented by the engineering department at Rubb Building Systems. Our goal is to help Rubb customers to understand the world of structure engineering in a way that is free of jargon and easy to comprehend. We hope to educate, advise, and consult on best practices and why proper engineering is crucial to project safety and cost over the long term.

What is an “Occupancy Category”?

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:

Occupancy Categories

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.

Didn’t answer your question? You can contact us by leaving a comment, e-mailing us, or messaging us on Facebook, Twitter, Linkedin, or Google+ and we’ll be happy to respond as soon as possible. You can also contact us by phone at 1-800-289-7822 or visit us at 1 Rubb Lane, Sanford, ME 04073.


Hurricane Action Steps

This is a reminder to owners of Rubb Buildings in hurricane zones.

The 2014 hurricane season is upon us, and that means taking the proper precautions to help ensure your structure’s durability through the storm. During a hurricane or tropical storm, wind forces, especially with the presence of tornadoes, can sometimes exceed building code design requirements. Although Rubb Building range products are properly designed to code and engineered to resist substantial wind loads, we stress the importance of following the safety measures outlined below so that you can help to minimize or prevent damage to your Rubb Building and preserve the structure’s integrity and longevity.

  • Close and secure all doors to the Rubb Building. This applies to large equipment or hangar doors as well as smaller personnel doors.
  • Repair any loose or damaged PVC cladding. Excessively loose areas of fabric should be tightened if possible. Tears in the PVC should be patched with a PVC Repair Kit to strengthen the area around the tear and prevent flapping in the wind, which can lead to additional tearing. Cutting a circle in the fabric at the end of the tear will help spread out the tension in the fabric and prevent the tear from spreading.
  • Check base tension of the PVC. The PVC tensioning hardware around the base of the structure should be applying even tension on the covering. Any loose tensioning hardware along the sides should be tightened. Caution: PVC cladding should be tight but over tightening will stretch the fabric and is not recommended.
  • Secure debris in the area. Although a hurricane can carry wind-borne debris for miles, you can help to minimize damage to the PVC membrane and structural frame by securing any loose items on your site that could blow into the building and cause damage.
  • Make sure structure is properly anchored. Some Rubb products, especially non-code designed shelter range products such as the THA, are often secured with ballast blocks and/or around spikes. These should all be in place and properly secured to the structure baseplates, foundation beam or base angle. Check that the proper number of anchor spikes or bolts is being used to hold down the foundation. If needed, secure the frame of the shelter to ballast to help hold it in place.

In the event of emergency please contact our President at 207-651-7821, our Chief Operating Officer at 207-651-7354, or our Site Operations Manager at 207-651-7358.

10 Sports Facilities Questions Answered by Rubb

  1. What space is available at your location? Available in spans from 65′ to 262′ (20m to 80m) wide by any length, Rubb has over 30 years’ experience in meeting individual requirements for custom buildings. With this experience, we are able to provide a complete package for sports halls and training complexes, including help with planning approval and the installation of all services such as roads, drainage, mechanical and electrical services. As experts in space usage and efficiency, we offer a wide range of advice on how to maximize the potential of any sports facility.
  2. What will the facility be used for? Rubb can tailor designs to accommodate a variety of athletic activities. Whether its soccer, field hockey, lacrosse, football, ultimate frisbee, baseball, basketball, gymnastics, tennis, rock climbing, horseback riding enclosures or professional training facilities, Rubb Sportspans provide an economical building solution.
  3. Why play inside? Rubb sports buildings are highly cost-effective building and our use of translucent fabric gives the impression of playing and training outside. And now, with the development of our Thermohall Insulation System, teams and individuals are provided with first class illumination and full weather protection in any climate that also yields significant energy savings.
  4. What equipment will you need to ensure your activities can run smoothly? Rubb can provide features and equipment such as bleachers, rebound walls, division nets and curtains, scoreboards, and a variety of other customizable owner supplied options.
  5. What kind of flooring are you looking for? Rubb can accommodate any surface needs with state of the art floor solutions, including Synthetic Infill Sports Turf installed on a crushed gravel base, hard wood court or a multi-sport synthetic surface, and high density playing surfaces available in a choice of colors. Design the floor to function as one large playing surface or sub-divide it into smaller surfaces for younger age groups or training programs. Rubb takes pride in being flexible and partnering with trusted businesses, and is comfortable working with local providers for flooring and equipment needs.
  6. What building materials will be used? Rubb buildings are designed to meet or exceed local building, fire and safety codes, and use only the highest quality materials and components in the manufacturing process. Rubb’s traditional galvanized internal steel frame resists corrosion and is virtually maintenance free and PVC membrane cladding materials are sourced from reputable suppliers with long and proven track records of supplying architectural membranes. As a public service warning, Rubb does not condone the use of harmful or lesser materials, and urges clients to be cautious of companies promoting inferior substances.
  7. What are the energy savings and environmental benefits? Rubb’s Thermohall Insulation System offers great energy savings and is environmentally friendly, both in fabrication and operation. Elimination of air gaps in the cladding reduces heat loss and helps control condensation, non-combustible glass wool insulation encapsulated in air and water tight pockets offers protection for any climate, and all recyclable materials provide eco-friendly solutions. Structures can be temporary or permanent; readily adaptable to suit changing requirements, extendable, relocatable and reusable ensuring a cost effective solution in the long term.
  8. What experience does Rubb have with Sports Buildings? Take a look at projects, photos, videos, brochures, and building highlights on our website.
  9. How do I contact Rubb for my Sports Building needs? Send us a project inquiry, send us an e-mail at, or call toll free at 1-800-289-7822
  10. What sets Rubb apart from other Sports Buildings? Simply, we build structures to protect your assets…we take our commitment to service seriously and we do it right. Rubb has earned a reputation for tackling difficult and unique projects, and holds a number of certifications from reliable and trusted organizations. Rubb follows a strong commitment to: codes and standards, reducing impact to the environment, and above all, our valued clients.

Using Highway Barriers for Foundation Anchoring

The Maine Turnpike Authority recently posted to their Facebook page that they have hundreds of highway barriers, also known as Jersey barriers, for sale.  These are commonly used on Rubb shelters as ballast weights for the foundations, or even as the actual foundation itself, as pictured on the right.

One of the features of Rubb buildings and shelters is the flexibility in foundation requirements.  Many of our structures do not need a full concrete foundation, and can use our base angle or wide-flange beam foundations where they can be installed on earth or asphalt.  Highway barriers and other types of ballast weights can often be used with these foundations to resist wind uplift instead of driven earth anchors.  In addition to their low cost, they give the owner flexibility of relocating the building on their site.

Highway barriers are also a convenient way to anchor structures that are equipped with lifting kits, enabling them to be crane lifted around a construction site. The weights can be removed easily using a forklift and then replaced when the building is at its new location.  Contact us to discuss your project and how we can customize a structure to fit your needs.

The Maine Turnpike Authority’s original post is below: