Robin Anderson, Technical and Strategy Development Manager, Westlake Royal Roofing Solutions
Many regions of the United States, including Florida and the Southeast, are subject to high-wind conditions that can damage homes and buildings. The roof is highly susceptible to the wind damage due to its location on top of a home or building. Therefore, it is imperative when choosing roofing materials to select ones that can withstand severe wind events. Concrete roof tile is an option that provides substantial defense against the powerful forces of wind and helps prevent weather-related property damage. Wind can be complex. It is affected by temperature and pressure differences in the Earth’s atmosphere, as well as by variations in terrain and topography. However, when wind meets a home or building structure, it will typically perform in predictable ways. For example, wind meeting the side of the structure will travel up and over the roof edge causing varying degrees of uplift pressure.
As an integral part of the U.S. building codes, ASCE 7-16, or Minimum Design Loads and Associated Criteria for Buildings and Other Structures, outlines key wind uplift pressure considerations including:
• The uplift pressures that affect a roof are highest at the corners of the roof (i.e., eave/rake corner, peak of the ridge at the rake edge)
• The edges: rake and eave, are a close second in uplift pressures
• As wind moves across a roof’s surface, negative pressure (suction) is created.
There are many factors that influence how wind may affect a roof, such as its speed and direction when it encounters the structure. Factors include:
• The design of the roof. Steep slope gable roofs are more susceptible to wind uplift than low slope hipped roofs
• Fastening methods. The number, style and frequency of fasteners such as nails, screws or foam adhesives can significantly change the overall wind resistance of the tile’s installation.
• Local weather. The High Velocity Hurricane Zone region receives higher frequency of high winds.
• Incorrect Installation. Mis-aligned tiles, improper fastening devices or improperly installed underlayment can reduce the roof’s performance in high wind events.
The Tile Roofing Industry Alliance (TRI) also provides guidance and information on tile roofing – both concrete and clay – including wind resistance, stating:
“In regions prone to tornadoes, hurricanes or extreme winds, roof tile provides one of the best defenses against wind-related property damage.”
• Concrete and clay tile roofing helps to resist hurricane-force winds
• Natural air ventilation under the tile, created by its high porosity and installation techniques, helps relieve wind stress
• Independent testing sponsored by TRI Alliance shows that, with proper attachment, clay and concrete roof tiles can sustain winds in excess of 125 miles per hour.
To address wind concerns, concrete roof tiles are subjected to various wind testing in accordance with performance standards to determine the resistance that a given installation method meets for the design requirements in each region. Tests include:
• ASTM C1568 – 08(2020) Standard Test Method for Wind Resistance of Concrete and Clay Roof Tiles (Mechanical Uplift Resistance Method)
• ASTM C1569 – 03(2016) Standard Test Method for Wind Resistance of Concrete and Clay Roof Tiles (Wind Tunnel Method)
• ASTM C1570 – 03(2016) Standard Test Method for Wind Resistance of Concrete and Clay Roof Tiles (Air Permeability Method)
• TAS 100, 101, 102, 102A, 108, 110 and 112 are all standards of procedures for testing the performance of tile roof systems.
Additionally, the Southern Building Code Congress International (SBCCI) in 1990 commissioned Redland Technology to investigate wind loads on roofing tile and to develop a code methodology. Redland performed two experiments to develop their design method. These include:
1. Wind loads were estimated from wind tunnel tests where surface pressures on medium and high-profile roofing tiles were measured as wind was blown across a tile array and,
2. Wind uplift resistance was estimated from constant displacement rate uplift tests that quantified the uplift resistance of roofing tiles either loose laid or with a mechanical fastener (nail).
One recommendation from the Redlands study was to recognize the principal of the differences between roof wind loads and tile wind loads resulting from the air permeability of laid roof tiles and the presence of a pressure resisting underlay or solid deck.
The resulting method was incorporated into the Standard Building Code, and later the Florida Building Code and International Building Code as well.
Some concrete roof tile applications are allowed in wind speeds zones of up to 180 miles per hour when installed to industry and manufacturer guidelines. When combined with a pressure resisting underlayment, their true advantage in wind resistance is due to their shape and construction, which allows wind to freely travel and to greatly reduce stress.
A roof option providing design aesthetics and curb appeal, concrete tile roofs are also extremely functional in the face of a subtropical climates and high wind regions. No roof is completely windproof; however, tile roofs perform very well when compared to many other roofing materials. Concrete tiles are sturdy, durable, long lasting and can manage sustained winds, as well as greater wind gusts.
The above article was featured in April 2022 issue of Florida Roofing Magazine.