Do Code Changes Mean New Design Needs?
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.)
Later this year, the ASCE-7-22 recommendations for new code language will be debated in the next round of formal building code cycles. For the design professional, this might be a great time to review what and how these recommendations will affect your future projects. While the ICC code cycle will not be completed until 2023, there are local code jurisdictions around the country that will look to implement certain changes in this year’s code hearing process. That will make some of the changes implemented as early as January 2023.
The Tile Roofing Industry (TRI) Alliance has begun review and will focus on the wind-based changes that will impact the roofing assembly designs for steep-slope in both residential and commercial applications. With almost all roof cladding materials following wind-uplift pressure design criteria, it will require the design professional to review and recalculate future projects for steep slope applications on both commercial and residential buildings.
So, what will be the changes we might need to consider? For the roofing envelope there will be significant changes from the current ASCE-7-16 design requirements. One of the first noticeable changes will be the reduction from six roof zones back to three zones for gable roof designs. While it will appear like the previous ASCE-7-10 designations, it unfortunately does not reduce the wind velocity pressures to those previous levels. For hip roof designs it will reduce from four to three roof zones, which will help simplify the design process from the current versions. The ASCE-7-22 will have both the hip and gable tables for roof design needs, but the various design coefficients found within the calculation may change depending upon roof slope, roof height, and designated wind speed.
For both gable and hip roofs, the notable change is the deletion of the directional factor Kd, used in the calculation of the velocity pressure qh. Our industry initial analysis shows that, in some applications, this will increase the velocity pressures by 5-15% that will equate to a similar increase in our required aerodynamic overturning moment resistance for fastener designs on certain slopes. In other applications, it will have a similar decrease. As there is no consistent number, we will be doing a complete review to better understand the impact. For a hip roof, the revised code design for the external pressure coefficient, GCp, has been simplified to now be based the ratio of the building h/B. In other areas, it will have a similar decrease.
Like other industry associations, we are currently performing a full design analysis on every roof slope, wind speed, and building height up to 60’ to determine what changes, if any, that we will need to make to our industry-based installation fastening guides. The outcome will be the issuance of a new installation manual for the roofing and design professional to use moving forward.
The TRI Alliance has tried to create design guides that provide conservative design uplift resistance by utilizing the perimeter areas of the roof designs. For those with a larger project, there will be the opportunity to do job-specific designs that might reduce these values based upon actual building construction. Design professionals can capture the actual roof slope, wind speed, building height, tile dimensions, and tile weight that can generate custom fastening options. Our conservative approach will allow the roofing professional the ability to easily identify a fastening option that meets the code requirements without the need for calculations.
We will be releasing our 2022 version of our regular Concrete and Clay Tile Installation Guide, replacing the current July 2015 version. The revised manual will include the new ASCE-7-22 wind design data in addition to upgraded drawings and best practices that have been identified by our contractor members since our last release.
Looking forward, the TRI Alliance will be developing short design training program opportunities that we will conduct on a virtual platform once the new code tables have been generated. For most projects, our easy-to-read tables will cover the required fastening options that you will need to use. For those that wish to have a deeper understanding, we will be developing a similar course on wind design for concrete and clay roofing tiles that will walk through the various coefficients and factors for custom designers to utilize.