RICOWI Hailstorm Investigation Program: Dallas/Fort Worth, May 2011

Excerpted with permission from the Roofing Industry Committee on Weather Issues, Inc. T he Roofing Industry Committee on Weather Issues Inc. (RICOWI) has completed its second Hailstorm Investigation Program (HIP). Seven inspection teams examined more than 100 roof systems during a four-day period to evaluate the effects of a signif- icant hailstorm that passed through portions of the Dallas/Fort Worth metropolitan area on May 24, 2011. The purpose of the project was to document the effects of hail impact on a variety of roofing products and describe roof assembly performance and modes of damage for substantiated hailstone sizes. The Dallas/Fort Worth metropolitan area had been targeted because of its concentration of impact-resistant, steep-slope roofing products. Meteorological Info On May 24, 2011, three rounds of thunderstorms containing large hail and tornadoes passed through portions of north Texas, including the Dallas/Fort Worth metropolitan area. Several of the thunderstorms were super-cell variety containing very large hail. The National Climatic Data Center publication Storm Data listed 32 reports of hail in Tarrant County (nine reports stated hail sizes of 2-in. diameter or larger) and ten reports of hail in Dallas County (three reports of 2-in. diameter or larger). See Figure 1. Dallas and Tarrant County are the most populous counties in the Dallas/Fort Worth area, and most of RICOWI’s inspections were made in these counties. Extremely large hail greater than 4 inches in diameter was reported in a portion of northern Tarrant County (cities of Avondale and Keller) and at a separate location Figure 1 – HailTrax report showed inspection locations along a portion in western Dallas County (city of Irving). The hailstorms damaged of the storm path with radar-estimated hailstone sizes provided by planes at DFW Airport and Love Field, Dallas. There were large Weather Decisions Technologies, Inc. (WDT). The area shown covers areas of the two counties where hailstones from 1 to 2 inches in portions of the cities of Irving, Coppell, Dallas, and Carrollton, where diameter were reported (Photo 1). the greatest concentration of inspections was made. November 2012 I n t e r f a c e • 3 3 ed. On each roof, several random test areas were selected for counting the locations that exhibited hailstone impact effects. Other building or surrounding elements were also used to establish the size of the hail at the specific site being investigated. FIELD RESULTS low-Slope Systems The focus of the 2011 HIP investigation was the performance of impact-resistant roofing products as compared to those materials that were not rated for impact resistance. Although the testing for impact resistance applies to low- and steep-slope roof systems, it was difficult to determine if the low-slope roofing systems were rated. Limited low-slope roofing was inspected; however, roof membranes that were solidly supported and/or protected with gravel or stone ballast performed well. Photo 1 – Hailstones saved by a homeowner in Irving, TX. Built-Up Roofing (BUR) BUR roofs appeared to perform well. Five of the six roofs inspected were impacted by Investigation hail sizes and to include a variety of roof hail of 2¼ in. or larger, and one roof was A data form was developed to record system types. Sites primarily were obtained impacted with 1¾-in. hail. All were rated pertinent information from each site. Data through contacts of HIP or RICOWI mem- with damage levels 1 or 2. Observations included location, roof construction details, ber organizations and through local roof- included scuffing and some gravel displacegeneric roof material descriptions, roof ing contractors and government agencies. ment by hail impact. pitch, estimated maximum hailstone size Typical inspections consisted of a complete at the site, and the type(s) and severity of visual survey of the roof surface, followed by Modified Bitumen hailstone impact damage to the roofing randomly selecting sites where the hail hits A total of seven modified-bitumen memproduct. Impact effects were listed on a were counted and the hail size was estimat- brane roofs were inspected in the study. scale of 0 to 5: 0 — No apparent damage 1 — Surface impact marks without fractures or punctures 2 — Minimal damage (low severity and low quantity) 3 — Moderate amount of fractures, punctures, or spalling 4 — Moderate/severe denting of metal roofing 5 — Severe damage resulting in poten- tial leakage Inspection teams consisted of three members with a balance of manufacturer representatives, trade group representatives, engineers, roof consultants, roofing contractors, and insurance professionals. One team member would record the site data, one would photograph and log captions for the photographs, and one would inspect the property and mark items of interest. The selection of inspection sites was targeted toward areas with moderate-to-large Photo 2 – Hail impact damage to a standard asphalt shingle. 3 4 • I n t e r f a c e November 2012 They were impacted by hail from 1¾ to 5 inches in diameter, with four of the seven being rated at damage level 5. One roof Introducing EagleView ® exposed to 2-in. hail had no damage. Single-Ply Sheet Membranes Three low-slope single-ply membrane roofs were inspected.