With tile roofs popular across Florida, and with questionable claims about roof damage raising concerns in insurance and engineering circles, two Florida consulting engineers have offered this guide to aid engineers, attorneys, ad
justers and property owners in examining wind damage to concrete tile roofs. This can be used to help understand the dynamics of wind and its effects. Key points have been highlighted in boldface type.
Introductiona
Buildings are obstacles to wind currents and will cause changes in the direction of airflow. Redirection of the airflow results in varying magnitudes of negative and positive wind pressure over building surfaces. In general, inward-acting (positive) pressures are produced on windward surfaces, and ou
tward-acting (negative) pressures are produced throughout the building surfaces (Dalgliesh, 1965). Further, since the flow of air cannot negotiate sharp discon
tinuities in building surfaces such as wall corners, eaves, roof ridges, and roof corners, the flow will separate from building surfaces, resulting in outward-acting pressures. Failure of cladding in these areas typicall
y will occur first, followed by damage to unsupported components or loosely fastened structural elements. The evaluation of wind effects on structures is outlined in the American Society of Civil Engineers (ASCE) Minimum Design Loads for
Buildings and Other Structures, with the 2010, 2016, and 2022 editions (referred to as ASCE 7-10, 7-16, or 7-22; respectively) being the ones most often utilized.
Evaluating concrete roof tiles in accordance with ASCE 7 and knowing the areas of the highest pressures
is important. A proper analysis cannot be done without basic knowledge of wind dynamics. The formulas used for any calculations must be from approved sources and should be true and accurate.
The shielding effects of nearby buildings, trees, and other ground-level obstructions are well documented. It has been shown that in all but the most devastating windstorms (e.g., hurricanes and tornadoes), most conventionally built structu
res will not suffer major wind damage to the primary structural system. Broad differences in the performances of buildings exposed to wind forces often are observed durin
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a storm event, even between structures in proximity to each other. Structural performance also depends on variations in location, orientation to the wind direction, and the quality of the original construction or subsequent repairs.
Since the flow of air is redirected at sharp discontinuities in building surfaces, such as wall corners, roof eaves, and ridges, higher wind forces are typically experie
nced at these locations during a strong wind event. On a systemic level, initial roof tile failures (displacement) will normally occur first along the edges, corners, and ridges of the roof and can progress inward to the field tiles as p
ressure forces increase (Florida Roofing and Sheet Metal Contractors, December 31, 2020). This behavior of wind forces is recognized by applicable building codes that require these areas to be designed and constructed to resist higher forces for a given wind speed than other parts of the building. Greater
resistance to uplift at the eaves and ridges/hips is usually achieved with a stronger method of attachment, e.g., via mechanical