Mike Silvers, CPRC, Owner of Silvers Systems Inc. and FRSA Technical Director
During the FRSA-TRI Florida High Wind Concrete and Clay Tile Manual Review Committee meetings that started in 2018 and ran into 2020, an issue that was widely discussed concerned the load path required for roof coverings to resist uplift pressures and the
increases in those pressures that ASCE 7-16 would create. This topic applied to almost all roof systems, not just tile roofs which were our primary focus.
Meeting the requirements for uplift resistance is more complex for tile than most other systems. There are many reasons for this, but among those are the need to resist both uplift pressures for underlayment, as well as for hip and ridge or trim tile in pounds per square foot while meeting the aerodynamic uplift moment resistance required for the tile itself. This is further complicated as many of the components are manufactured by different companies. In many cases, the tile is adhered with foam adhesive or, in rare instances, with mortar to the underlayment which must be adhered or fastened to the roof deck to complete the roof system load path.
Many of the prescriptive methods previously used to adhere tile were based on information obtained for what is commonly referred to as a 30/90 hot mop. Much of this information was adopted and transferred when self-adhering membranes came on the scene.
But as self-adhering membranes’ popularity grew, it became obvious that the adhesives performed differently than hot asphalt.
One difference was demonstrated as self-adhering membranes were introduced for low slope roofs, where meeting uplift pressure resistance requirements were more universally understood and expected. Installing self-adhering membranes to standard #30 felt or other standard base sheets would yield very low uplift resistance when tested. That led to the introduction of specially designed base sheets that allowed for better adhesion as well as improved nail pull through test results. For some of us, it seemed
counterintuitive that we needed special base sheet for adhesion of mid ply and cap sheets on low slope roofs but didn’t need them when we were adhering tile to those same materials on steep slope roofs.
The information available from several manufacturers who had tested for product approval using an ASTM D226 #30 with self-adhering underlayments resulted in very low resistance numbers that were not equal to those required for most roofs in Florida.
An important decision was eventually made by the FRSA-TRI Manual Review Committee that in order for the manual to comply with ASCE 7, tile underlayments had to meet the uplift pressures and this would be the approach reflected in the manual. It led to separating how the manual dealt with the hot mopped and self-adhered underlayments. Hot mopped systems have prescriptive methods included in the manual. Self-adhering membranes use the manufacturer’s product approvals – a conservative approach arrived at with an abundance of caution.
This left Florida’s roofing contractors and tile manufacturers concerned about the possible afore mentioned flaw. The Test Protocols for High-Velocity Hurricane Zones (HVHZ) included in the Florida Building Code, and in particular, Roofing Application
Standards (RAS) 118, 119 or 120 do not take the same approach. This would concern us if it were just acceptable in the HVHZ where it is the only option, but the RAS are also referenced in the Florida Building Code (FBC) for use in all other areas of Florida as well. Direct-to-deck application of self-adhered membranes is not allowed in the HVHZ or the RAS. Unfortunately, HVHZ is also where self-adhered membranes have their best uplift resistance. The RAS instead have prescriptive methods that fail to recognize some of the differences between hot mopped and self-adhered systems. They also use nailing patterns that may fail to resist nail pull through at design pressures. FRSA wants to know what uplift resistance these prescriptive methods will produce. The FRSA Codes Committee approved and the Educational & Research Foundation Trustees funded a research project to test the combination of a nailed #30 and self-adhering tile underlayment to determine the resistance to uplift pressure using several different attachment patterns and products. Our goal is to determine if a nailed #30 is a suitable base (anchor) sheet for these particular
underlayment systems and just how much uplift resistance they provide. A task group was assigned to work on this project. It includes Greg Keeler of Owens Corning, Manny Oyola of Eagle Roofing Products and me.
We began testing at the PRI facility in Tampa in April. Four different ASTM D226 felts and four different self-adhering membranes were tested using TAS 117B for pull through and ASTM D1876 for adhesion peel test. The best performing of each were then installed on five test decks and are currently undergoing weathering. The #30 with best pull through resistance and the one offering the best surface for adhesion were nailed using tin tabs and ring shank nails on two decks using the standard pattern of 6” o.c. at the laps and two rows at 12” o.c. staggered in the field (per RAS) with three others using 6” o.c. at the laps and three rows at 8” o.c. staggered in the field. The best performing self-adhering membrane was then applied to the #30 on all five test decks. Approximately thirty days later we will be testing them to failure in a bell chamber test. Stay tuned for the results.
I want to thank Greg and Manny for their dedication to this project. That also goes for Jason Simmons and the crew at PRI, their consideration, direction, help and hospitality is certainly appreciated. Thanks also to Maury Alpert of Polyglass and Daniel Cuevas of APOC who kindly volunteered their help in preparing the test decks.
Mike Silvers, CPRC, is owner of Silvers Systems Inc. and is consulting with FRSA as Director of Technical Services. Mike is an FRSA Past President, Life Member and Campanella Award recipient and brings over 45 years of industry knowledge and experience to
FRSA’s team.
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