Guidelines to Assess Hail Damage to Shingle Roofs

Guidelines to Assess Hail Damage to Shingle Roofs B. East, M.S., P.E., M.ASCE1 T. Lozos, CPE2 S. Verhulst, M.S., P.E., M. ASCE3 M. DeLeon M.E., P.E., M.ASCE4 D. Ahuja M.S., P.E., M.ASCE5 Project Director, Nelson Architectural Engineers, Inc., 9701 Brodie Lane, Suite 201, Austin, Texas 78748; PH (512) 610-2800; Fax (512) 610-2795 email: [email protected] Technical Director, Nelson Architectural Engineers, Inc., 2740 Dallas Parkway, Suite 220, Plano, Texas 75093; PH (469) 429-9000; Fax (469) 326-5000 email: [email protected] Austin Branch Director, Nelson Architectural Engineers, Inc., 9701 Brodie Lane, Suite 201, Austin, Texas 78748; PH (512) 610-2800; Fax (512) 610-2795 email: [email protected] Vice President of Research and Development, Nelson Architectural Engineers, Inc., 2740 Dallas Parkway, Suite 220, Plano, Texas 75093; PH (469) 429-9000; Fax (469) 326-5000 email: [email protected] Executive Vice-president, Nelson Architectural Engineers, Inc., 2740 Dallas Parkway, Suite 220, Plano, Texas 75093; PH (469) 429-9000; Fax (469) 326-5000 email: [email protected] ABSTRACT The severity of hail damage to residential and commercial roofs depends on several parameters including the age and type of roofing material, the roofing assembly, hail size, and roof slope, among others. Asphalt shingled roofs comprise a large percentage of insurance claims submitted for roof-related hail damage. For asphalt shingled roofs, hail damage typically consists of radial/circular areas of granule loss, which constitute latent damage and may affect the future performance and lifespan of the shingles. The severity and extent of hail damage to asphalt shingled roofs is not as visually apparent as compared with some other common high-slope roofing materials, such as metal panels, wood shakes, and clay/concrete tiles. Assessing the extent of hail damage to shingled roofs and developing a scope of repairs can be difficult. Furthermore, guidelines for such assessment are not well established. Based on the authors' experience, we propose guidelines and procedures to assess the extent of hail damage to asphalt shingled roofs from which a scope of repairs can be developed. A cost analysis for the consideration of repair versus replacement is also presented. WEATHER RESEARCH AND DETERMINATION OF HAIL SIZE During an investigation of hail damage to roofing materials, it is important to determine the approximate size of the impacting hail. Hail size will vary not only between different storm events, but also within a particular storm event. Because of the exponential increase in kinetic energy with the increase in hail size (due to increased mass and increased velocity), the size of the largest hailstones from the storm event are of primary interest (Noon 2001). Weather research can be conducted using information freely available from the National Oceanic and Atmospheric Administration (NOAA) or by obtaining a more detailed site specific meteorological report by private companies. Because hail size can vary between locations during a hail event, the distance between the site and the location of reported hail should be considered. Even if an investigator has reported weather information, the conditions at the site are typically the best indicator of hail size and severity. Indentations in metal surfaces and burnish markings on metal or other smooth surfaces can provide valuable information regarding hail size and even the directionality of falling hail during a storm event. Burnish marks occur where impact from hailstones removes the surfacing of an exposed material, such as dirt, fungal discoloration on wood surfaces, or slight oxidation on metal surfaces. This burnishing changes the appearance of the surface, leaving distinct markings which can be useful in determining the approximate size and distribution of hailstones. Burnish marks on vertical surfaces and the splash patterns of burnish marks on horizontal surfaces can also aid in determination of the directionality of hail impacts. Considering typical light gauge metal surfaces (such as 24 or 26 gauge metal panels or parapet wall cap flashing), an indentation from hail impact will usually measure approximately half the diameter of the impacting hailstone (Koontz and Crenshaw 2002). Indentations in softer metal surfaces, such as aluminum coil fins at roof top HVAC units and soft metal covering for pipe insulation, can also give an indication of hail size (Noon 2001). While it is important to evaluate the shingle roofing for evidence of impact damage, the information gained from the weather data and the conditions at other building materials can assist in the overall evaluation of hail occurrence. HAIL DAMAGE TO SHINGLE ROOFING When evaluating shingles for hail damage, two types of damage are considered: latent damage and severe damage. Latent damage may affect the function of the roof materials at a later time. Latent damage to shingles exists when the hailstone impact removes the protective mineral surface granules and exposes the asphaltic matrix to ultraviolet light. This can accelerate the deterioration of a shingle. Severe damage exists when a shingle is punctured/fractured or torn by a hailstone impact. Shingles overlaying a previous shingle roof are more susceptible to impact damage from hail than if the same shingles had been installed directly over a roof deck. Underlying shingles are much more forgiving (or less resistant) than wood decking, which allows impacting hailstones to better penetrate a roof system comprised of two or more layers of shingles.