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.

Shingle marring occurs when people walk acrossthe roof on a day when the shingles are hot, soft, andpliable. The asphalt in the shingle surface softens tothe point where it is pushed aside along with thegranules and typically forms a ridge on the outsideedge of the mark. Persons walking on the roof canalso remove granules along the bottom edges of theshingles.Elevated fasteners can occur during theinstallation of the shingles and can protrude throughor buckle the overlying shingles. The fasteners areeither not driven flush to the shingle or are driven intojoints between the roof decking. Elevated fastenersare not caused by hail striking the roof.Adhesive can drip off the shingles onto the othershingles leaving a round, dark spot that can bemistaken by some as hail damage. If the adhesivefrom one shingle contacts another shingle and bondsto it, a portion of the shingle surface can be removedwhen the shingles are separated leaving a roundedarea of missing granules that can also be mistakenby some as hail damage.6.INTENTIONAL MECHANICAL DAMAGEOn occasion, some people have utilized varioustools or other objects in an attempt to simulate haildamage on a roof. Popular items have included: 1)ball peen hammers, 2) claw hammers, 3) coins, and4) screwdrivers. The authors have recognized anumber of factors that distinguish intentional damagefrom hail damage. For example, intentional damageis not randomly distributed on the roof but usuallyoccurs in groups or lines concentrated in upperportions of the roof, away from roof edges. Impactangles of the tool or object are nearly perpendicularto the affected roof slope, therefore indicating multipleimpact directions (Figure 10). In contrast, hail wouldleave a random distribution of damage on the roof.The windward slope typically sustains the mostconcentrated and direct hail impacts whereas theleeward slopes have fewer, glancing hail impacts.5. ASSESSING HAIL DAMAGEAccurate assessment of hail damage is a step bystep process that involves an examination of the roofshingles as well as other objects on and around theroof.Marshall and Herzog (1999) presented amethodology on how to quantify hail damage to a roofthrough the use of test squares. The number of haildamaged shingles are counted in each test square oneach directional roof slope and that numberdetermines whether the roof slope is repaired orreplaced through the use of the DURA formula.Shingles are particularly susceptible to haildamage if they have little or no underlying support,especially along ridges, rakes, eaves, and valleys.Shingle edges also are vulnerable to being chippedor broken. Therefore, the entire roof must beexamined. Recently exposed asphalt appears blackor unweathered, whereas asphalt exposed for severalmonths oxidizes forming a surface film that is a greycolor. This color difference is one way to tell new haildamage from old hail damage (Figure 9).Figure 9. An example of 9-year-old hail damage to aglass-fiber mat asphalt shingle.Figure 10. Intentional roof damage examples: a) lineof impact marks, b) circular arrangement of impactmarks, and c) impact marks perpendicular to eachaffected slope with no marks on the ridge.Intentional damage is concentrated frequently inthe interior or center portions of the shingles, awayfrom shingle edges, as it is human nature to hit thecenter of an object. Such centered impacts usuallyare found on each affected slope, regardless of slopedirection (Figure 11). The impacts tend to be singular,Figure 11. Attempts to simulate hail damage with aball peen hammer.

occurring once per shingle. In contrast, hail does notprefer the centers of the shingles nor strike shinglesonce consistently.In our inspections of suspicious roof damage, weutilize a series of magnification rings to closelyphotograph the impact marks. Typically, shinglesstruck by metal objects will have broken or shatteredthe ceramic coating on the granules. This will leave a"powder" residue containing shattered ceramicmaterial within the impact mark. Any side-to-side or"rounding out" motions will tend to leave swirl markswithin the powder residue and/or leave smudges inthe exposed asphalt surface (Figure 12).When claw hammers are utilized, the metal peenfrequently does not strike the roof slopes exactlyperpendicular but tends to tilt forward slightly leavinga characteristic curving fracture in the shingles thatopens towards the direction of impact. The concavefracture in the shingle resembles a "frowny" facewhen looking upslope. Granules closest to theconcave side of the fracture are frequentlycompressed uniformly into the shingle mat.Sometimes coins are utilized to leave small divotsin the shingle surface. Quarter coins have smallridges around their perimeters that can leave a seriesof ridges in the asphalt under magnification.the size and direction of any alleged hail damage tothe roof shingles.After a general examination of the buildingsurroundings is performed, a roof plan diagram isdrawn and shingle marks are plotted. Any pattern orgrouping of shingle marks quickly becomes apparentin the diagram (Figure 13). The diagram will indicatethose roof slopes or ridges that are notably withoutshingle marks as well as any grouping of marks.Usually, large areas of the affected roof slopes arewithout shingle marks as are other, perhaps smaller,roof slopes that face the same direction. Shinglemarks closest to the roof edge are measured.Figure 13. Roof plan diagram showing thedistribution of mechanically-caused impact marks inan alleged hail damage claim.8. SUMMARYFigure 12. Close-up views of mechanically causedimpacts to shingles using: a) a ball-peen hammer, b)claw hammer, c) screwdriver, and d) quarter coin.7. DOCUMENTING INTENTIONAL DAMAGEThe authors have developed a methodology tobetter document intentional damage to a roof. Theprocedure involves examining objects around and onthe house similar to the hail damage inspectionprotocol as explained by Marshall and Herzog (1999).Hail-caused "spatter" marks are usually found onfaded metal surfaces such as air conditioners,electrical junction boxes, and metal window frames.Hail-caused "scuff" marks are recorded on woodenfences and dents occur in aluminum fins on airconditioners. Such items provide good estimates ofhail size and direction of hailfall. The same can besaid with the examination of metal items on the roof.Thus, items on and around the house can provideevidence of hail size and direction that should matchIn this paper, we have explored certain issues withregard to hail damage on asphalt roof shingles. Theresults of our ten-year granule loss study werepresented where it was found that there was no lossof life or reduction of water shedding ability even with70% of the granules removed from the glass-fibermat shingles. The shingle with 100% of the granulesremoved did exhibit more erosion than the othershingles. Therefore, asphalt roof shingles that losesome granules during a hailstorm are not considereddamaged as long as the shingles remain coveredwith granules. Functional damage to asphalt roofshingles includes punctures, tears, or fractures(bruises) in the shingle mats.We also have shown there are a number ofanomalies on asphalt shingles that occur duringmanufacturing, installation, and weathering. Some ofthese anomalies take on rounded forms that can bemistaken by some as hail damage. We also havediscussed how to recognize intentional damage toasphalt roof shingles where someone attempts tosimulate hail-caused damage. A methodology waspresented to better document intentional damage to aroof.

9. ACKNOWLEDGEMENTSThe authors would like to thank our reviewers: C. S.Kirkpatrick, P. Lawler, J. Stewart, and D. Teasdale.10. REFERENCESGreenfeld, S.H., 1969: Hail resistance of roofingproducts, Building Science Series #23, NationalBureau of Standards, 9 pp.Koontz, J.D., 1991: The effects of hail on residentialroofing products, Proc. of the Third InternationalSymposium on Roofing Technology, NRCA/NIST,206-215.Marshall, T. P., and R. F. Herzog, 1999: Protocol forAssessment of Hail-Damaged Roofing, Proc. of theNorth American Conf. on Roofing Technology,Toronto, Canada, p. 40-46.Marshall, T.P, R.F. Herzog, S.J. Morrison, and S.R.stSmith, 2002. Preprints, 21 Conf. on Severe LocalStorms, San Antonio, TX, Amer. Met. Soc., 95-98.Morrison, S.J., 1999: Long-Term Effects of Hail onAsphalt Composition Shingles Proc. of the NorthAmerican Conf. on Roofing Technology, Toronto,Canada, 30-39.Ribble, R., D. Summers, R. Olson, and J. Goodman:From generation to generation: issues and problemsfacing the steep-slope roofing industry. Proc. of theth10 Conf. on Roofing Technology, 1-5.

definition of hail damage to asphalt shingles and explain the characteristics of such damage. We also will present the results of our ten-year study on granule loss to asphalt shingles as well as review the methodology to assess hail damage to an asphalt shingle roof