New ASCE-7-16 Codes For Steep-Slope Roofing
by Richard K. Olson, president & technical director, Tile Roofing Industry Alliance
(Editor’s Note: Richard K. Olson is president and technical director for the Tile Roofing Industry Alliance. The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the United States and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems. Olson can be reached at firstname.lastname@example.org.)
With the upcoming adoption of the new International Code Council® International Building Code® and International Residential Code®, roofing professionals and designers will need to revisit the wind requirements for future projects. For many steep-slope products, this will mean different uplift requirements for high-wind areas moving forward. The Tile Roofing Industry Alliance has created new wind-design tables and fastening charts that provide information to design professionals for easy reference for the new American Society of Civil Engineers (ASCE) code requirements. So, what are the major changes we will be seeing for steep-slope designs?
The previous ASCE-7-10 codes utilized three roof zones for all roof types, which included hip, gable, and monoslope. For the new ASCE-7-16, there will now be six roof zones for gable roofs and four roof zones for hip roofs. Although we will have additional roof zones, most roofing contractors will, if possible, install a roof to one fastening method, being the most restrictive roof zone. This will reduce the complexity for installation. As with previous codes, there will be the determination of the roof exposure for A, B, C, or D as defined by the codes.
There are wind-speed resources that can help identify wind speeds, as the ASCE-7-16 wind maps have changed slightly. One resource is the ASCE’s Hazard Tool at https://asce7hazardtool.online/. The local building official should also be contacted to determine the official code-design wind speed that has been formally adopted in that jurisdiction. In some areas, it may be different from what the wind maps show.
The wind-design calculations will incorporate the mean roof height for a building design. The new ASCE-7-16 code changes are centered on the increase to the roof zone pressure coefficient GCp. The ASCE-7 committee indicated there is not enough of a safety factor in the previous values and thus increased the GCp for a portion of the roof slopes in ASCE-7-16.
For steep-slope applications there are two main design considerations. The first is the ability to design the underlayment to be attached to the required uplift pressures. All of roof claddings depend upon the underlayment staying in place and not adding any additional uplift to the cladding. The second is the uplift resistance for the roof cladding.
The required fastening can be met using a fastener selection that would meet or exceed the design uplift for all roof zones. Where higher requirements come into play, two methods could be used where the lower-pressure areas are met with one fastening option and the high-pressure zones are a different fastening option. In most cases, this will be the corner zones of the roof.
The new Tile Roofing Industry Alliance installation manuals will have the complete set of tables that will help design professionals determine the applicable uplift resistance based upon roof type, exposure, wind speed, mean roof height, and roof slope. The guides will also have mechanical fastening tables that provide the various options for meeting these new code requirements. In addition, there are foam adhesive manufacturers that have tile-specific uplift resistance values for using their products to meet the ASCE-7-16 codes.
The Tile Roofing Industry Alliance is creating wind-design educational training programs that will be held on a virtual platform for our contractors, code officials and design professionals. While there are changes to ASCE-7-16, as an industry we have developed the necessary resources and options to easily meet the new requirements.