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 Deciphering wind design approaches With the advent of the new International Building Code, which has already been adopted in about 20 states and will be phased into more states over time, code enforcement has reportedly been stepped up in the last couple of years in many jurisdictions. Now, not only new construction projects are going through plan review by local building inspectors, but more and more reroofing projects are being reviewed as a matter of course. In fact, the new code is quite clear in calling for plan review when more than 25% of the existing roof is undergoing construction. This puts more demand on contractors to be familiar with the building code's provisions. One approach that SPRI is taking to help upgrade the industry's general level of knowledge regarding building codes is through our comprehensive new seminar highlighting how wind loads are calculated. SPRI, the organization representing sheet membrane and component suppliers to the commercial roofing industry, developed this course identifying factors to consider regarding the wind resistance of low-slope roofing systems. Wind loading on roofs is an important but often misunderstood aspect of design. To fill this void, SPRI has drawn on its member companies' extensive resources to develop this seminar on wind design. SPRI's own publications on wind issues, which include the SPRI Wind Design Guide as well as its ANSI/SPRI RP-4 and ES-1 standards, are also discussed. The well-illustrated course covers a wide range of topics, from wind effects on buildings and how they act on different types of roof systems to the ways that wind loads are referenced by industry organizations like Factory Mutual (FM) Research Corp., Norwood, MA, and the American Society of Civil Engineers (ASCE). For instance, the ASCE 7-98 formula considers the environment in which a building is located. It has subdivided this into four different categories of exposures. Exposure A covers large city centers with a majority of buildings being taller than 70 feet. Exposure B includes urban and suburban areas as well as single-family dwellings. Exposure C refers to open terrain with scattered obstructions. And Exposure D covers flat, unobstructed areas plus those by open water for one mile or more. FM, by comparison, looks at six basic wind design factors:
An interactive portion of the program leads seminar participants through real-world examples, step by step. In this way, SPRI's program conveys both the science and the practice of calculating wind loads. About 300 slides, divided into seven sections, thoroughly showcase these design concepts. A course manual reinforces the topics discussed during the seminar and includes copies of all these slides. SPRI Technical Director Dave Roodvoets explains, "Our goal is to educate people who are involved in roof design so that they fully understand wind loads and their designs comply with local building codes. Instead of arbitrarily specifying FM 1-90 roofs, whether they're needed or not," Roodvoets continues, "this program aims to help people avoid over-engineering their roofs, which makes them cost more than they should, as well as to prevent roofs from being under-engineered." "There really isn't anything around like this program," agrees Ken Wolford, chairman of the task force that developed the program. "Wind design can be a confusing science. We've put a lot of effort into simplifying these confusing issues with graphics and sample problems based on actual conditions," Wolford says. "We've tried to make this program as user-friendly as possible." In fact, Wolford continues, "This program showcases the talent of SPRI. It is a true product of the association, having been conceived by SPRI staff and developed by its members." This program is now available for presentation to interested associations and related industry groups. For more information, contact SPRI's headquarters in Needham, MA at 781-444-0242 or e-mail info@spri.org. This article previously appeared in the May 2002 edition of RSI Magazine. |
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