How Underlayment & Flashings Can Increase Long-Term Performance
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.)
Roof architecture is a continuously changing, and sometimes challenging, part of the design industry. Long-term performance and low maintenance costs are prime considerations of building owners, consumers, and homeowners associations when it comes to new building construction and reroofing projects. In order to ensure that a new or upgraded roofing system uses top-performing products, industry professionals must monitor and review the market. It is through continuous product research that industry professionals learn of the performance of various roofing systems, as well as the appropriate installation requirements.
While the existing building codes reference the minimum requirements of roofing performance needs, there is always the question of when upgrades might be considered in the selection of products or the installation techniques used. The cost for the upgrades in certain areas of roof designs, particularly the underlayment and flashings, can help reduce the overall life cycle costs.
With the growth of so many new underlayment options, it is important to check with the manufacturer for installation requirements and long-term performance. With roofing tiles having such a long service life, the performance of the underlayment is a critical component of the system. With the entrance of the synthetic underlayments comes the question of equivalency to not only the minimum, but what will be an upgrade. Because there are so many different synthetic products, the codes and industry have not been able to provide guidance for them. The Synthetic Roofing Underlayment Institute (SRUI) was created in 2014 in response to the building industry’s need for clarity, standards, and best practices regarding mechanically fastened synthetic roofing underlayment. Since their introduction to the building trade, synthetic roofing underlayments have provided the industry with a superior solution to conventional saturated roofing felt.
In addition, there are self-adhering underlayments that allow for upgraded performance in areas that have more extreme weather climates such as cold, wind-driven rain and high wind. The manufacturers of these products have formal code-issued approvals that provide the roofing professionals with the information for selection and benefits to upgrades for various steep-slope applications.
When it comes to flashings, while the codes will reference No. 26-gauge minimums, the long-term performance of certain roof claddings such as tile might benefit from an upgrade in flashing details to a No. 24-gauge flashing or the use of copper flashings, in certain applications. The use of drip flashing at the roof edge and proper flashing at all roof penetrations will increase the performance over time for the full assembly. Roofing tile installations require both a deck and top flashing for penetrations to help provide greater protection. Where profile flashings are used, soft lead that is not less than 3 lbs./sq.ft, dead soft aluminum not less than 0.019”, or soft copper not less than 16.0 oz./sq.ft. must be used.
In valley areas, the consideration of increased underlayments under the flashing can help improve the overall performance. These are areas where the flow of water is the greatest. Selection of proper valley metal designs that will help reduce and properly direct the tributary water are important to the system performance. The installation of flashing at areas around chimneys, skylights, and roof-mounted accessories is critical to the to the long-term performance. Step flashings, wider crickets, and the use of upgraded underlayments in these areas might be considered as an upgrade. Mastics, caulkings, or other sealants should be used as directed by the manufacturers of these products and designed to be compatible with the materials they will come in contact with.
While upgrades will increase the costs of the new installation or reroof process, they can help provide an improved overall performance for the life cycle of the roofing assembly. The roofing professional should contact the material manufacturer for proper code approvals, installation instructions, and any restriction for use. Understanding the merits of the upgrades will help to communicate the benefits when selling the upgrades to the building owner.