How Will New Changes In the International Building Code For Wind Speeds Affect San Antonio Commercial Roofs

As the changes of seasons come, it’s a good idea to look back and see what changes have occurred this year. For San Antonio, one of the biggest changes is the adoption of the International Building Code 2012 Edition or IBC 2012. One of the more significant changes of IBC 2012 as it related to roofing occurs with the implementation of new wind speed maps which are derived from the American Society of Civil Engineers (ASCE 7-10) which have replaced the existing map in ASCE 7-05. The new maps use “Ultimate Wind Speeds” rather than “Nominal Wind Speeds” for determining wind load design pressures. In ASCE 7-10, different maps are provided for different “Risk Categories” instead of a single map with importance factors to be applied for each Risk Category.

In the past, San Antonio was assigned a basic wind speed of 90 mph as a design basis. Now agricultural and non-occupied buildings (Risk Category I), are assigned a wind speed design of 105 mph; general commercial buildings (Risk Category II), are assigned a wind speed design of 115 mph; and high occupancy buildings (Risk Category III) and emergency – critical buildings (Risk Category IV) are assigned a wind speed design of 120 mph. Knowing applicable code changes, such as how, when and why important changes that affect life safety are very important in today’s construction industry. Wind speed design, in part, affects the engineering calculations pertaining to the wind loads for which roofs must be tested to determine whether a particular roof system can be used based on the required design.

 

Low sloped roofs must be tested to any of the following standards: FM 4474, UL 580 or UL 1897. To help navigate through these intricate calculations, the roofing industry has developed a few useful online calculators and reference tables such as RoofNav, NRCA’s Roof Wind Designer, and RCI’s Wind Pressures on Low-Slope Roofs. Using the right calculation method and proper wind speed helps identify and qualify the appropriate roof system to meet applicable code requirements. Thank you Roof-Tec for attending our recent wind uplift education seminar so you are up to speed on these important code changes for your city.

 

Joel King

Director of Technical Services/Product Development

U.S. Ply, Inc.