Rubb buildings support energy efficiency

Rubb’s white translucent PVC cladding allows natural light to illuminate the interior of our buildings, while reducing the heat island effect on the structure.

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The picture below is an external view of a Rubb fabric building used in some recent infrared tests. It is a 70ft x 80ft x 16.4ft BVE type structure, used as a salt storage shed for the City of Sanford, ME. It was built in 2009 and has performed well for the public works department.

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Thermal images were taken on a sunny spring day, where the sun was hitting the wall and roof at approximately the same angle. Results show that the reflective but translucent white roof is 12°f cooler than the sandstone-colored sidewalls.

The image below illustrates the results of the infrared surface temperature tests on the structure – a typical Rubb storage facility.

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The outcome: a cool and comfortable indoor temperature while avoiding any need for lighting power consumption during a regular working day. These double energy savings help greatly reduce the Rubb structure’s operating costs.

Independent building science consultant Lew Harriman also notes: “We measured the air tightness of this building using a blower door. When its rolling overhead door is closed, it meets and exceeds the U.S. Army’s air tightness requirement to leak less than 0.25 cfm at a pressure difference of 75 Pascals (0.3” W.C). That means the building won’t have uncomfortable drafts, even in the highest winter winds. It also means its air tightness is better than half of the very air tight commercial buildings measured for ASHRAE’s recent research project RP-1478. When any building must be heated, that level of air tightness means big energy cost savings for every year of that building’s long life.”

This is just another advantage of choosing a Rubb building. For more information about Rubb building solutions visit us at www.rubbusa.com or call 207-324-2877.

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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.