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American Meteorological Society, Annual Meeting, 2004P 9.4HAIL DAMAGE TO ASPHALT ROOF SHINGLESTimothy P. Marshall*, Richard F. Herzog, and Scott J. MorrisonHaag Engineering Co.Dallas, Texas1. INTRODUCTIONControversies can arise with regard to how asphaltshingles are damaged by hail, and what hail damageactually looks like. More specifically, questions havebeen raised as to whether granules removed fromasphalt shingles during a hailstorm will reduce theexpected life or water shedding ability of the roofshingles. In this paper, the authors will review thedefinition of hail damage to asphalt shingles andexplain the characteristics of such damage. We alsowill present the results of our ten-year study ongranule loss to asphalt shingles as well as review themethodology to assess hail damage to an asphaltshingle roof.The authors have inspected thousands of asphaltshingle roofs and found that damage inspectorsfrequently mistake various shingle anomalies such asfoot scuffs, adhesive spots, etc., as hail damage. Wehave also inspected numerous roofs where peoplehave tried to simulate hail damage by using a varietyof tools or other objects in order to defraud aninsurance carrier. Therefore, the last part of thispaper will focus on various shingle anomalies that arefrequently misidentified as hail damage and explainhow to differentiate between intentional andunintentional roof damage.2. ASPHALT ROOF SHINGLE COMPONENTSAsphalt roof shingles are one of the most commonand affordable roof coverings on the market today.Base mat materials are either paper (organic) orglass-fiber (inorganic). The mats are coated with anasphaltic mixture composed of asphalt, limestonepowders, and other mineral stabilizers (fillers).Granules are applied to the shingle surfaces to givethem color, add weight, and to block the underlyingasphalt from deleterious effects of the sun. Mostgranules are crushed stone coated with a ceramicmaterial. The ceramic gives color to the granules.Generally, one third of the shingle weight is granules,one-third asphalt, and one-third filler. The mat is asmall fraction of the total weight.Asphalt roof shingles come in various sizes,shapes, and thicknesses. Generally, the thicker orheavier the asphalt shingle, the more it costs. Themost common asphalt shingles are three-tab andlaminated varieties.*Corresponding author address: Timothy P. Marshall,2455 McIver Ln., Carrollton, TX 75006. Email:[email protected] tab shingles contain slots or joints that givethe appearance of a common brick pattern wheninstalled on the roof. Laminated type shingles arecomprised of one full shingle and half a shinglebonded together with asphalt to give them thickerlook, similar to that of wood shingles or slate.2. HAIL DAMAGE DEFINITIONMorrison (1999) defined damage to roofing as adiminution of water-shedding capability or a reductionin the expected long-term life of the roofing material.Marshall and Herzog (1999) more specifically definedfunctional hail-caused damage to asphalt shingles aspunctures, tears, or fractures (bruises) in the shinglemats (Figure 1). Shingle bruises are an indentationwith fracture in the mat that feels soft like that of anapple bruise. The bruise is usually obvious asgranules are also dislodged from the impact areaexposing the asphaltic mat.Marshall et al. (2002) presented their ice impacttest results that employed a mechanical launchingdevice.Ice stones were launched at standardvelocities against roofing products that includedvarious 11-year-old, naturally aged, asphalt shingles.Impacts were oriented perpendicular to the shingles.The study concluded that aged organic mat-basedasphalt shingles were damaged half of the time byone-inch diameter ice stones, whereas it took 1.25 in.(3.1 cm) diameter ice stones to damage the agedglass-fiber mat asphalt shingles.Thicker, agedlaminated type shingles were damaged by 1.5 in. (3.8cm) ice stones. Greenfeld (1969) and Koontz (1991)had presented similar results in conducting ice ballimpact tests on asphalt shingles.Figure 1: Hail damage to asphalt shingles: a) brokenedges, b) bruise, c) puncture, d) torn edge.

However, there remains a controversy whethergranules removed by hail, without visible asphaltexposure, constitutes hail damage. Many asphaltshingle manufacturers have issued "technicalbulletins" about hail and granule loss, stating that ifgranules are lost from the shingle due to hail, theshingle has lost life. However, there are no publishedscientific studies to validate this statement.3. GRANULE LOSS STUDYIn order to determine how many granules, if any,must be removed in order to affect the service life orwater shedding ability of the shingle, the authors' firmconducted a granule loss study on asphalt shingles.Varying quantities of granules were removed with awire brush from new, three-tab, glass-fiber matshingles. The shingles then were exposed naturallyto the weather in Dallas, Texas for a period of tenyears. The quantities of granules removed werenone (control), and approximately 6, 15, 45, and 70percent of the total granules on the shingles. Anothershingle was installed upside down such that theasphaltic mat was exposed to the weather. Theshingles were installed conventionally over a plywooddeck on a 4:12 pitch that faced south. The shingleswere examined at intervals throughout the ten yearperiod as well as at the conclusion of the study(Figures 2 and 3).Figure 2. Test panel at the beginning of the studyshowing percentage of granules removed. "C" is thecontrol.In one year, the exposed asphalt had oxidizedgrey but there was no visible evidence of surfacecracks or erosion. After five years, areas of exposedasphalt had oxidized but this did not affect thefunction of the shingles to shed water. Surfaceerosion was visible on the shingle without granules,and some of the glass fibers had become exposed.After ten years, no significant change was noted inthe shingles except for the shingle without granules.More glass fibers were exposed on this shingle due toerosion; but, the shingle continued to shed water(Figure 4).Figure 4. Close up views of new shingle and tenyear weathering with both 70 percent of the granulesremoved and no granules, respectively.The quantity of granules lost from the roof shinglesduring a hailstorm is a relatively small amount.Generally, about one-third the weight of an asphaltshingle is granules such that a 25 square roofcovered with three-tab shingles would have aboutone ton of granules. Granule loss is expected fromthe moment shingles are manufactured, shipped,installed, and during the weathering process.Granules are part of the wearing surface on theshingle and exposure to hail is part of the wearingprocess that is actually built into the design. Thus,more granules are initially placed on the shinglesthan needed to cover the mat.In our study, we found between 12 to 15 percentof the surface granules had to be removed from newshingles before the asphaltic mat was exposed. Theamount of "excess" granules on new shingles variedby plus or minus ten percent. We would expect thatthe quantity of granules lost during a hailstormgenerally would fall within the normal variation ofgranules placed on a shingle.Therefore, it seems logical to conclude that thesmall quantities of granules removed from shinglesduring a hailstorm does not shorten the life of the roofor adversely affect its water shedding ability as longas the impacted areas are not bruised or punctured,and remain covered with granules. This conclusionagrees with the work done by Morrison (1999).4. ASPHALT SHINGLE ANOMALIESFigure 3. Same view as Figure 2 only at theconclusion of the ten-year study.There are usually a number of anomalies on anasphalt shingle roof not related to hailstone impact.Some of these anomalies may take rounded forms

that can be mistaken as hail damage. Understandinghow shingles are manufactured, installed, andweather is important when properly differentiatingbetween non-hail conditions and hail damage.Asphalt shingles are manufactured in a highspeed, fully automated process.Occasionally,certain defects involve insufficient granule or asphaltcoverage, or the use of poor quality asphalt. Shinglemanufacturers should "cull" or remove such defectsbefore the shingles are shipped. However, the levelof quality control of shingle products varies. Thus, itis not unusual to find shingle defects on a roof thatinvolves bands or spots of missing asphalt and/orgranules (Figure 5).Figure 5. Various shingle manufacturing defects: a)lack of granule adhesion on a three-tab, b) blotchyappliques, c) asphalt exposed in lower laminate, andd) lines of missing asphalt and granules.As asphalt shingles age, their components breakdown. The extent of aging depends upon manyfactors including the quality of the asphalt, shinglecolor, roof pitch, slope direction, and attic ventilation.Common deficiencies inherent with aged asphaltshingles are blistering, splitting, cupping, clawing,crazing, and flaking. In many instances, theseanomalies are not discovered until after a hailstorm;however, this does not mean they were created oraggravated by the storm (Figures 6 and 7).Figure 6. Various shingle anomalies not caused byhail: a) closed blisters, b) open blisters includingclose-up view in the inset photograph, c) diagonalsplitting, and d) horizontal splitting.Shingle blisters occur from a combination of poorquality asphalt combined with heat. They appear assmall bubbles in the shingle surfaces where a portionof the granule surface is raised. Eventually, theshingle bubbles rupture exposing steep-sided voids inthe shingle surfaces that frequently extends down tothe shingle mat. Shingle blisters are usually 1/4 in.(.6 cm) in diameter or less and are not caused byhailstone impact.Diagonal and horizontal splitting of asphaltshingles involves a combination of asphalt shrinkage,deck movement, and low tensile strength in the mat.Ribble et al. (1993) further explain such problemswith asphalt shingles.Figure 7. Various shingle anomalies not caused byhail: a) cupping, b) clawing, c) crazing, and d) flaking.Cupping and clawing results from asphaltshrinkage on the top and bottom surfaces of theshingles, respectively. The corners and edges of theshingles are prone to curling or cupping as the matshrinks. Crazing of the shingle surfaces also resultsfrom asphalt shrinkage.Eventually, chunks ofgranules flake away from the mat leaving the asphaltcoated mat exposed to the weather.Additional shingle anomalies can be createdduring installation.The most common shingleinstallation deficiencies are marring, edge scuffing,elevated staples, and adhesive spots (Figure 8).Figure 8.Shingle installation deficiencies: a)marring, b) edge scuffing, c) elevated fasteners, andd) adhesive spots.