testing and results of severe hail exposure

Testing and Resultsof Severe Hail Exposure

Daniel E Brown and Daniel A Boardman PEFM Approvals

1151 Boston-Providence Turnpike Norwood Massachusetts 02062 Phone 781-255-4852 bull E-mail danielbrownfmapprovalscom danielboardmanfmapprovalscom

3 1 s t R C I I n t e R n a t I o n a l C o n v e n t I o n a n d t R a d e s h o w bull M a R C h 1 0 - 1 5 2 0 1 6 b R o w n a n d b o a R d M a n bull 2 4 3

Abstract

increased property damage from hail impact has become more common in recent years with the majority of the damage occurring to roofs To help address this concern a very Severe Hail (VSH) rating for low-slope roofing is being developed using a modified version of the test method described in AnSiFM 4473 Testing was completed using ice balls to impact single-ply modified-bitumen and built-up roof covers over insulations and cover boards to determine which factors contribute to roof system failure when exposed to ice balls with increased impact energies The effects of ultraviolet (Uv) aging and sample surface temperashyture on the performance of the samples were also studied

Speakers

Daniel E Brown mdash FM Approvals

DAniEL BroWn is a graduate of northeastern University with a Bachelor of Science degree in chemical engineering Since 2011 Brown has been an engineer with FM Approvals LLC where he has worked on a variety of research activities in the areas of fire testing and natural hazards testing He works in the Materials Division with a specialization in roofing and hail damage resistance

Daniel A Boardman PE mdash FM Approvals

DAniEL BoArDMAn PE has a BS in mechanical engineering from the University of Massachusetts Dartmouth and an MS in fire protection engineering from Worcester Polytechnic institute Since 2006 he has been an engineer with FM Approvals LLC and FM Global working on a variety of research activities in the areas of fire testing and natural hazshyards testing he is a member of the national Fire Protection Association (nFPA) the Society of Fire Protection Engineers (SFPE) and ASTM Committees D08 and E05

2 4 4 bull b R o w n a n d b o a R d M a n 3 1 s t R C I I n t e R n a t I o n a l C o n v e n t I o n a n d t R a d e s h o w bull M a R C h 1 0 - 1 5 2 0 1 6


ABSTR AC T increased property damage from hail

impact has become more common in recent years with a majority of the damshyage occurring to roofs To help address this concern a very Severe hail (vSh) rating for low-slope roofing is being develshyoped using a modified version of the test method described in AnSiFM 4473 Test Standard for Impact Resistance Testing of Rigid Roofing Materials by Impacting With Freezer Ice Balls Testing was comshypleted using ice balls to impact single-ply modified-bitumen and built-up roof covers over insulations and cover boards to determine which factors contribute to roof system failure when exposed to ice balls with increased impact energies

Test samples were initially subjected to 20-in (51-mm) freezer ice balls with impact energies between 2375 and 2613 ft-lbs (322 and 355 J) Based on the results of these initial tests selected samples were subjected to ice balls with impact energies between 5300 and 5830 ft-lbs (719 and 790 J) The effect of ultraviolet (Uv) aging and sample surface temperature on the pershyformance of the samples was also studied The study shows that ice ball impact testshying can provide a more severe test than the industry currently has access to and allows for options in markets that are at increased risk for hail damage

KE y LE ARNING OB JEC TIvES 1 Identify the requirements and test

method for a new vSh rating for low-slope roofing

2 Assess the viability of using freezer ice balls with the less-rigid materials more commonly used in low-slope roofing

3 Demonstrate that sample conditionshying such as Uv aging and surface temperature can directly impact hail damage testing results

4 Show through testing results that a few currently available low-slope roofing assemblies are capable of meeting the pass criteria for the newly developed vSh rating

INTRODuC TION The insurance industry in the United

States has seen an increase in losses from hail in recent years both in cost per claim and number of claims with the majority of damage occurring to roofs1 According to FM global Property Loss Prevention Data Sheet 1-34 a vSh region has been identishyfied encompassing Oklahoma Kansas and several northern counties in Texas2 The identification of this area as a VSH region is further supported by data from the noAA nWSnCEPStorm Prediction Center that shows an increased concentration of severe hail reports (hail diameter ge2 in (51 mm)) from 1955 to 2002 in this same geographishycal region3 With the identification of the vSh region and increased hail damage to roofs a need for a vSh rating for low-slope roofing has been identified An ANSIFM 4473 Class 4 rating with impact energies between 2375 and 2613 ft-lbs (322 and 355 J) is already recommended in this area for steep-slope roof covers and a simishylar rating for low-slope roofing is needed

Several published standards utilize steel balls to impact roof covering materials FM Approvals Standard 4470 currently has a maximum Severe Hail rating that requires a roofing sample to withstand impacts from 20-in- (51-mm-) diameter steel balls which impart a kinetic energy of 1495 ftshylbs (19 J) to the sample surface4 The UL 2218 impact test procedure contains a maxshyimum Class 4 rating that requires a roofing sample to withstand impacts from 20-in-(51-mm-) diameter steel balls which impart a kinetic energy of 2371 ft-lb (32 J) to the sample surface5 ASTM D3746 requires a roofing sample to withstand impacts from 20-in- (51-mm-) diameter steel balls which impart a kinetic energy of 22 ft-lbs (30 J) to the sample surface6 These test methods require the roofing samples to be subjected to multiple impacts at different locations across the sample area

Unlike the test methods described above which utilize steel balls AnSiFM 4473 utilizes freezer ice balls to impact the roofing sample However this standard was specifically developed for steep-slope

roofing The maximum rating available in this standard is Class 4 which requires a roofing sample to withstand impacts from 20-in- (51-mm-) diameter ice balls which impart a kinetic energy of 2375 to 2613 ftshylbs (322 to 255 J) to the sample surface7

While specifically developed for steep-slope roofing the test method described in AnSiFM 4473 and similar test methods utilizing freezer ice balls have been used on low-slope roofing materials Crenshaw and Koontz documented a series of tests that compared the performance of multiple roofing materials when impacted with both steel balls and freezer ice balls showing that the performance of the test materials varies depending on whether the material is impacted by a steel ball or an ice ball8

Materials tested included thermoplastic ole-fin (TPO) styrene butadiene styrene (SBS) modified bitumen built-up roofing (BUR) atactic polypropylene (APP) modified bitushymen ethylene propylene diene monomer (EPDM) polyvinyl chloride (PvC) clay tile concrete tile and asphalt shingles Koontz and hutchinson later studied the perforshymance of 60-mil (15-mm) EPDM membrane when subjected to impacts from 15- 20- 25- and 30-in- (38- 51- 64- and 76-mm-) diameter ice balls showing that 76 of the 81 EPDM samples tested over various subshystrates did not have a split or cut in the EPDM surface after a single impact9

Based on the current available test methods and the work previously done with freezer ice balls the objective of this project is to determine if the AnSiFM 4473 test method can be adapted to low-slope roofshying materials and used to create a vSh rating The initial phase of this work was used to determine if the AnSiFM 4473 test method when used to test new low-slope roofing assemblies with a known FM Approval Standard 4470 Severe hail rating is capable of distinguishing exceptional performance This initial phase of work was completed and documented in a paper entishytled ldquoDeveloping a very Severe hail rating for Low-Slope Roofingrdquo and was submitted to ASTM for publication The secondary phase of this work as detailed in this paper


involved taking other factors into considshyeration including higher impact energies above the AnSiFM 4473 Class 4 rating performance of samples after being exposed to Uv light and the effects of lowering the surface temperature of the samples directly prior to impact This will be discussed at length below These variables aim to detershymine the most critical scenario for testing as it is relevant to real-world exposure and will aid in development of the testing protocol it is important to note that this study is being done to determine the appropriateness of using freezer ice balls on low-slope roofing materials and will be used to develop a final test protocol for the vSh rating

TEST SETuP Samples of single-ply built-up and

modified-bitumen low-slope roof assemblies were subjected to impacts from 20-in-(51-mm-) diameter freezer ice balls with two different levels of impact energy The different impact energies were achieved by varying the velocity of the freezer ice ball used in testing The first range of impact energies was between 2375 and 2613 ft-lbs (322 and 355 J) whereas the secshyond range was between 5300 and 5830 ft-lbs (719 and 790 J) These impact energies are nearly double and quadruple respectively the 1495 ft-lb (19 J) kinetic energy delivered by the 20-in- (51-mm-) diameter steel balls used in the Severe hail rating test in FM Approvals Standard 4470 These two ranges of impact energies will be referred to as Class 4 and Class 5 respecshytively for the duration of this paper

The freezer ice ball preparation and test procedures in AnSiFM 4473 were followed in order to conduct the tests The impact locations number of impacts and accepshytance criteria found in AnSiFM 4473 were

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not used in this study as they are not applishycable to low-slope roof covers The intent is to develop a new test method that is applishycable to low-slope roofing constructions

The samples consisted of either a piece of 15-in- (38-mm-) thick glass-reinforced organic felt-faced polyisocyanurate insulashytion or a 025-in- (64-mm-) thick fiber-glass-faced gypsum board representing a range of substrate densities The substrate was mechanically fastened to a 075-in-(19-mm-) thick plywood board with metal insulation plates and fasteners The various roof covers were either fastened or adhered over the entire substrate area The samples were 15 by 21 in (381 by 533 mm) in order to allow enough area for several impacts A general diagram of the sample construcshytion with the roof cover cut away to show the substrate and fastener arrangement is shown in Figure 1

Each sample was subjected to impacts at three different locations 1) over the lap seam 2) over a fastener and metal plate and 3) in the field of the roof cover Each location was impacted two times at the same spot unless a failure was observed after the initial impact

The initial testing was conducted in a laboratory maintained at a temperature of 734plusmn36degF (23plusmn2degC) with the samples allowed to equilibrate to the ambient temshyperature of the room before testing A second series of tests was run in the same laborashytory conditions with test samples that were subjected to 1000 hours of Uv light condishytioning using the ASTM g154 test method10

A third series of tests was conducted with samples that had been cooled within a freezer maintained at -7degF (-22degC) until they reached a surface temperature of below 40degF (44degC) at which point they were removed from the freezer and immediately placed under

a direct spray of chilled water within the testshying apparatus The water was maintained at 45degF (72degC) in order to keep the samples in a temperature-c o n d i t i o n e d state These samples were brought to 45 to 55degF (72 to

3 1 s t R C I I n t e R n a t I o n a l C o n v e n t I o n

128degC) immediately prior to impact by allowshying them to begin to equilibrate to the temshyperature within the chamber underneath the water spray Temperature readings were taken using an infrared thermometer prior to each impact The first and second series of tests were subjected to both Class 4 and Class 5 impacts whereas the third series was subjected only to Class 4 impacts

observations of damage were taken after each impact Damage to the roof cover was noted for all samples Damage to the substrate and fasteners was noted only on samples with a mechanically fastened roof cover since peeling back an adhered roof cover is not always possible and may have caused more damage to the substrate on some assemblies All samplesmdashboth adhered and mechanically fastenedmdashconshytained insulation plates below the roof cover A sample was considered to have failed when a through-opening (tear) or crack was observed in the roof cover For the purposes of this study denting or impressions in the roof cover and damage to the substrate and fasteners were not conshysidered failures but were noted in the test observations when possible

SAMPLE SELECTION AND IDENTIFICATION

Samples of low-slope roofing assem shyblies were selected from wwwroofnavcom All have an FM Approvals Standard 4470 Severe hail rating The samples were selectshyed to represent a variety of common fully adhered and mechanically fastened roofshying assemblies As previously stated the assemblies were limited to those with polyshyisocyanurate insulation or gypsum board directly below the roof cover in order to include representative samples with a low-and high-density substrate respectively

Two different polyisocyanurate insulashytion boards were used in this study and are referenced as Polyiso 1 and Polyiso 2 Likewise two fiberglass-faced gypsum boards were used and are referenced as gypsum Board 1 and gypsum Board 2 The same-type fasteners and 3-in- (762-mm-) diameter metal insulation plates were used for all samples in order to remove the variability of different fasteners and plate profiles from the test program and are referenced as fasteners The roof covers analyzed included EPDM PvC TPo SBS modified bitumen APP modified bitumen and asphaltic BUr membranes roof cover

a n d t R a d e s h o w bull M a R C h 1 0 - 1 5 2 0 1 6

Figure 1 ndash Sample construction

samples from three different manufacturers were used The manufacturers are refershyenced as Manufacturer 1 Manufacturer 2 and Manufacturer 3 in order to distinguish among the samples The samples along with the composition are shown in Tables 1 through 3

R E S u LT S AND DI S C u S S I O N roof cover tears cracks and punctures

were observed in 36 of the samples that were tested The samples along with the failure location and a description of the failshyure are shown in Table 4

Test results were evaluated in several difshyferent ways in order to gain a better undershystanding of how the freezer ice balls impact the more flexible materials (in comparison to steep-slope roofing shingles and tiles) found in low-slope roofing assemblies and to assist in establishing acceptance criteria for the

Sample Roof Cover Fastening Type Substrate

1 45-mil-thick TPo Manufacturer 1

Mechanically fastened Polyiso 1


Mechanically fastened Gypsum board 1

3 45-mil-thick fleece-backed TPO Manufacturer 1




5 50-mil-thick PVC Manufacturer 2












Table 1 ndash Mechanically fastened single-ply sample constructions


7 45-mil-thick reinforced EPDM Manufacturer 2

Fully adhered with solvent-based adhesive Polyiso 2

8 45-mil-thick EPDM Manufacturer 2




10 80-mil-thick TPO Manufacturer 1

Fully adhered with water-based adhesive Polyiso 1

11 45-mil-thick fleece-backed EPDM Manufacturer 2

Fully adhered with low-rise foam adhesive Polyiso 2




Fully adhered with solvent-based adhesive Gypsum Board 1






Fully adhered with low-rise foam adhesive Gypsum Board 1





Table 2 ndash Adhered single-ply sample constructions








Fully adhered with water-based adhesive Gypsum Board 1




Ribbon-adhered with low-rise foam adhesive Polyiso 1














Fully adhered with solvent based adhesive Polyiso 2

































Table 2 (continued) ndash Adhered single-ply sample constructions



23 4-ply Type IV glass felt BUR with hot asphalt flood coat Manufacturer 1

Adhered in hot asphalt to substrate Gypsum Board 1


Adhered in hot asphalt to substrate Polyiso 1

25 2-ply aPP Manufacturer 1

Torched to substrate Gypsum board 1

26 3-ply sbs Manufacturer 1

adhered in hot asphalt to mechanically fastened base sheet Polyiso 1


adhered in hot asphalt to substrate Gypsum board 1


Cap ply torched to ply Ply and base ply adhered in hot asphalt Gypsum board 1










self adhered Gypsum board 2


self adhered Polyiso 1


Torched to mechanically fastened base sheet Gypsum board 1


Torched to mechanically fastened base sheet Polyiso 1


adhered to mechanically fastened base sheet Gypsum board 1


adhered to mechanically fastened base sheet Polyiso 1

Table 3 ndash Modified-bitumen and built-up roof sample constructions

final VSH rating test protocol The results were evaluated based on performance of the entire assembly after being subject to

1 Class 4 impacts 2 Class 5 impacts 3 Ultraviolet conditioning and Class 4

impacts 4 Ultraviolet conditioning and Class 5

impacts 5 reduced sample temperature and

Class 4 impacts

Samples from each of these different categories were examined for performance as a whole sample with performance at each impact location and performance based on damage observations taken after each impact The results were further broshyken down to show the efficacy of each type of membrane when subjected to Class 4 and Class 5 impacts

P E R F OR M A N C E OF T H E E N T I R E A S S E MB Ly ndash C L A S S 4 IMPAC T S

A total of 35 samples were tested for Class 4 impact evaluation at room temperashyture with no Uv conditioning Evaluation of each samplersquos performance as an entire assembly indicated that 16 out of the 35 tested samples met the acceptance criteria and did not develop any through-openings or cracks in the roof membrane As shown in Figure 2 this translates into an overall acceptance rate of 46 of the tested samples

The results are further broken down in Figure 2 to indishycate the performance

Figure 2 ndash Percentage of samples meeting the pass criteria (Class 4)

of each type of roof cover tested The fully adhered single-ply samples have the highest success rate at 48 whereas the mechanishycally attached single-ply samples come in lower with 33 of the samples passing This indicates that the freezer ice ball test method used in this study is a more severe


Sample Failure Location Description

1 ndash 45-mil TPO over polyiso Fastener Roof cover torn after second impact 2 ndash 45-mil TPO over gypsum board Fastener Roof cover torn after first impact 3 ndash 45-mil fleece-backed TPO over polyiso Fastener Roof cover torn after second impact 5 ndash 50-mil PVC over polyiso Fastener Roof cover torn after first impact 7 ndash 45-mil reinforced EPDM over polyiso Fastener Roof cover torn after first impact 8 ndash 45-mil EPDM over polyiso Fastener Roof cover torn after first impact 12 ndash 45-mil fleece-backed TPO over polyiso Fastener Roof cover torn after first impact 13 ndash 45-mil TPO over gypsum board Fastener Roof cover torn after second impact 17 ndash 90-mil fleece-backed EPDM over polyiso Fastener Roof cover torn after second impact 18 ndash 45-mil fleece-backed EPDM over gypsum board Fastener Roof cover torn after first impact 20 ndash 50-mil PVC over gypsum board Fastener Roof cover torn after second impact 23 ndash 4 Ply BUR over gypsum board Fastener Top ply cracked after second impact 24 ndash 4 Ply BUR over polyiso Field Top ply cracked after second impact 29 ndash 45-mil fleece-backed TPO over polyiso Fastener Roof cover torn after first impact 32 ndash 80-mil fleece-backed TPO over polyiso Fastener Roof cover torn after second impact 33 ndash 45-mil reinforced EPDM over gypsum board Fastener Roof cover cracked after first impact 34 ndash 90-mil fleece-backed EPDM over polyiso Fastener Roof cover torn after first impact 36 ndash 50-mil PVC over gypsum board Fastener Roof cover torn after second impact 37 ndash 45-mil EPDM over gypsum board Fastener Roof cover cracked after first impact 38 ndash 45-mil TPO over polyiso Fastener Roof cover torn after first impact 40 ndash 50-mil PVC over gypsum board Fastener Roof cover torn after first impact 43 ndash 90-mil fleece-backed EPDM over polyiso Fastener Roof cover torn after second impact 47 ndash 45-mil TPO over polyiso Field Roof cover torn after first impact

Fastener Roof cover torn after second impact 48 ndash 45-mil fleece-backed EPDM over polyiso Fastener Roof cover torn after second impact 49 ndash 45-mil fleece-backed TPO over gypsum board Fastener Roof cover torn after second impact 51 ndash 45-mil-thick EPDM over gypsum board Fastener Roof cover torn after first impact 53 ndash 3-ply SBS over polyiso Fastener Top ply cracked after second impact 54 ndash 2-ply APP over gypsum board Field Top ply cracked after first impact 58 ndash 45-mil-thick TPO over polyiso Fastener Roof cover torn after first impact 59 ndash 45-mil-thick EPDM over gypsum board Fastener Roof cover torn after second impact 62 ndash 45-mil-thick reinforced EPDM over gypsum board Fastener Roof cover cracked after second impact 64 ndash 2-ply SBS over polyiso Field Top ply cracked after second impact 65 ndash 2-ply APP over gypsum board Lap Top ply cracked after second impact 66 ndash 2-ply APP over polyiso Lap Top ply cracked after second impact 67 ndash 2-ply SBS over gypsum board Field Top ply cracked after second impact 68 ndash 2-ply SBS over polyiso Lap Top ply cracked after second impact

Table 4 ndash Failed samples


test than that used to grant the Severe hail rating as all of the samples tested have an FM Approvals 4470 Severe Hail rating In addition the 4470 rating requires the roof covers to be tested after 1000 hours of Uv light exposure The effect of Uv exposure is addressed in the conclusions

P E R F O R M A N C E O F T H E E N T I R E A S S E M B Ly ndashC L A S S 5 IMPAC T S

A total of 19 samples that had passed the Class 4 impact evaluation were tested for Class 5 impact evaluation at room temperature with no Uv conditioning Evaluation of each samplersquos performance as an entire assembly indicated that six out of the 19 tested samples met the acceptance criteria and did not develop any through openings or cracks in the roof membrane As shown in Figure 3 this translates into an overall acceptance rate of 38 of the tested samshyples Figure 3 indicates that there were no successful tests


Figure 4 ndash Percentage of total samples tested meeting the Figure 5 ndash Percentage of UV-conditioned samples tested pass criteria (Class 4 vs Class 5)

of mechanically attached single-ply memshybranes when tested for Class 5 impact resisshytance Samples tested for Class 5 impact resistance composed of adhered single-ply membranes and modified-bitumen and BUR membranes show higher passing rates than the respective results for Class 4 impact resistance over these membranes in Figure 2 This could be due to the sample set for Class 5 impacts being comprised of samples that have passed Class 4 impact resistance and thus a smaller subset of samples

We have assumed that any sample that fails to pass the criteria of acceptance after being tested for Class 4 will not pass the criteria of acceptance after being subjected to Class 5 impacts The data presented in Figure 4 gives us an indication of total samshyple pass rates for both Class 4 and Class 5 if we include all of the data points that did not pass the Class 4 criteria as data points that would also not pass Class 5 The data shows that the Class 5 impact testing has a pass rate of approximately 17 This establishes it as a much more severe testing procedure than the current FM Approvals Standard 4470 Severe hail rating while also demonshystrating that there are still a fair amount of materials in current production that can meet the acceptance criteria for this test

PERFORMANCE OF THE ENTIRE ASSEMBLy ndashuv-CONDITIONED SAMPLES

A selection of samples was constructshyed to be tested after 1000 hours of Uv light exposure using the ASTM g154 Test Method10 These samples had already demshyonstrated the ability to meet the acceptance criteria of AnSiFM 4473 Class 4 impact testing at room temperature These samples were tested for Class 4 impact resistance

meeting the pass criteria (Class 4 and Class 5)

and some were tested for Class 5 The samshyples did not all initially pass Class 5 testing but the tests were carried out to determine if there would be additional modes of failure after Uv conditioning results will be anashylyzed by areas of failure in a later section of the conclusions Figure 5 shows that the Uv conditioned samples had a pass rate of approximately 88 This leads to the conclusion that the Uv conditioning being performed on the samples has a small but noticeable effect on the outcome Further examination may include longer periods of conditioning for samples

PERFORMANCE OF THE ENTIRE ASSEMBLy ndash TEMPERATuRE-CONDITIONED SAMPLES

A selection of samples was constructed to be tested for Class 4 impact resistance at a reduced temperature to determine if a decrease in temperature would correlate with a decrease in impact resistance of the flexible membranes These samples had already demonstrated the ability to meet the acceptance criteria of AnSiFM 4473 Class 4 impact testing at room temperature

The temperashyture of each samshyple was lowered to 45 to 55degF (72 to 128degC) in a freezer chamber before testshying Chilled water held at a constant temperature of 45degF was sprayed on top of the sample in order to keep the temperature within the range throughshyout the testing This

process was intended to simulate conditions within a hailstorm of lowered temperatures and water exposure The data in Figure 5 show a pass rate of 50 for the samples that were tested at a reduced temperature This indicates that reduction in temperashyture can have a significant effect on the pershyformance of the flexible roofing membrane to withstand impacts from hailstones

PERFORMANCE OF THE ASSEMBLy MATERIALS

The results can also be separated by the materials within the samples Figure 6 shows the percentages of samples that failed to meet the pass criteria based on the components contained in the assembly

Based on the entire set of 66 samples it would appear that those samples with the higher-density gypsum board substrate beneath the roof covers performed better than those samples with the lower-density polyisocyanurate insulation board subshystrate Based on the 50 single-ply samples it appears that thicker roof covers perform better than thinner materials which is to be expected When the results are sepa-

Figure 6 ndash Percentage of failures by material property


rated out by roof cover type EPDM roof covers appear to have performed slightly better than TPo and PvC This reinforces what was previously done by Koontz and hutchinson9 in their study of EPDM roof covers which indicated their good pershyformance it would appear that PvC roof covers stand out as poor performers in this sample set but it should be noted that only seven PvC assemblies were tested while 22 samples with EPDM and 21 samples with TPo roof covers were tested

PERFORMANCE AT EACH IMPACT LOCATION

The percentage of failures at each of the impact locations is shown in Figure 7 As

Figure 9 ndash Sample 47 failure failed over field of sample

etrated through the roof cover when the freezer ice ball impacted the sample at the fastener location (see Figure 8 for example) of these failures 52 failed after the first impact and 48 failed after the second impact Each failed single-ply sample failed at the fastener location but did not fail at the lap and field locations except for Sample 47 which failed at the fastener and in the field (see Figure 9) The modified-bitumen and built-up roof samples that failed developed cracks and tears at field lap and plate locations These samples only failed

after the second impact except for Sample 54 which developed cracks after the first impact These cracks were exacerbated upon the second impact

DAMAGE OBSERvATIONS visual observations of the

samples were taken after each

Figure 10 ndash Sample 1 substrate damage

2 5 2 bull b R o w n a n d b o a R d M a n 3 1 s t R C I I n t e R n a t I o n a l C o n v e n t I o n

Figure 8 ndash Failure over fastener of sample

impact with a freezer ice ball observations were taken of the roof cover on all of the samples on the mechanically fastened single-ply samples observations were also taken of the substrate and fastener The observations for the samples with mechanishycally fastened roof covers are shown in Table 5

The observations of the mechanically fastened single-ply samples reveal that damage to the substrate and plates can occur without any noticeable damage to the roof cover The polyisocyanurate substrate appears to be susceptible to significant damage that may compromise the integrity of the roof construction Typical damage of the polyisocyanurate substrate that was observed on the samples can be seen in Figure 10

Figure 10 is a post-test picture taken of Sample 1 after all impacts had been

completed The field lap and plate impact areas are noted Failure of the roof cover on Sample 1 was only observed after the second impact at the plate location Similar tearing of the facer and denting of the plate on one sample with a gypsum board substrate (Sample 6) was also observed but to a much lesser extent than the damage to the samshyples with polyisocyanurate insulation

As previously mentioned observations of the adhered samples were limited to dam-


Figure 7 ndash Percentage of failures by impact location

expected the majority of samples that failed (81) developed a crack or tear that penshy

Sample Impact Pass Fail Post-Impact Observations

1 ndash 45-mil TPo over polyiso

field 1 Pass surface dents no cover tear torn substrate facer and broken polyiso field 2 Pass no tear in roof cover increased damage to substrate lap 1 Pass surface dents no cover tear torn substrate facer and broken polyiso lap 2 Pass no tear in roof cover increased damage to substrate fastener 1 Pass Plate dented substrate facer broken dents on roof cover surface fastener 2 fail Roof cover torn further damage to plate and substrate visible

2 ndash 45-mil TPo over gypsum board

field 1 Pass no visible damage field 2 Pass no visible damage lap 1 Pass no visible damage lap 2 Pass no visible damage Fastener 1 Fail Roof cover torn at location of screw no visible damage to substrate Fastener 2 No second impact required due to failure on first impact

3 ndash 45-mil fleece-backed TPo over polyiso

field 1 Pass surface dents no cover tear torn substrate facer and broken polyiso Field 2 Pass No tear in roof cover increased damage to substrate lap 1 Pass surface dents no cover tear torn substrate facer and broken polyiso lap 2 Pass no tear in roof cover increased damage to substrate fastener 1 Pass Plate dented substrate facer broken dents on roof cover surface fastener 2 fail Roof cover torn further damage to plate and substrate visible


field 1 Pass surface dents no cover tear torn substrate facer and broken polyiso Field 2 Pass No tear in roof cover increased damage to substrate lap 1 Pass no visible roof cover damage torn substrate facer and broken polyiso lap 2 Pass no visible roof cover damage increased damage to substrate fastener 1 Pass Plate dented substrate facer broken dents on roof cover surface fastener 2 Pass no further damage to cover increased damage to plate and substrate

5 ndash 50-mil PVC over polyiso

field 1 Pass surface dents no cover tear torn substrate facer and broken polyiso field 2 Pass no tear in roof cover increased damage to substrate lap 1 Pass no visible roof cover damage torn substrate facer and broken polyiso lap 2 Pass no visible roof cover damage increased damage to substrate fastener 1 fail Roof cover torn plate dented and substrate facer broken Fastener 2 No second impact required due to failure on first impact

6 ndash 50-mil PVC over gypsum board

field 1 Pass no visible damage field 2 Pass no visible damage lap 1 Pass no visible damage lap 2 Pass no visible damage fastener 1 Pass no visible cover damage plate dented and substrate facer torn fastener 2 Pass no visible cover damage or further damage to plate or substrate


field 1 Pass no visible damage field 2 Pass no visible damage lap 1 Pass no visible damage Lap 2 Pass Very slight indentation Fastener 1 Pass Slight denting Visible screw head indent Plate dented Fastener 2 Fail Roof cover torn over the screw head


Field 1 Pass Slight denting torn substrate facer and broken polyiso field 2 Pass no tear in roof cover increased damage to substrate lap 1 Pass no visible roof cover damage torn substrate facer and broken polyiso lap 2 Pass no visible roof cover damage increased damage to substrate fastener 1 Pass Plate dented substrate facer broken dents on roof cover surface fastener 2 Pass slight scratching of cover increased damage to plate and substrate


Field 1 Pass Significant denting torn substrate facer and broken polyiso Field 2 Pass Significant denting increased damage to substrate Lap 1 Pass Significant denting torn substrate facer and broken polyiso Lap 2 Pass Significant denting increased damage to substrate fastener 1 fail Roof cover torn plate dented and substrate facer broken fastener 2 fail Roof cover tear exacerbated increased damage to plate and substrate

The first and second impacts at each location are noted with a 1 and a 2 respectively

Table 5 ndash Mechanically fastened single-ply sample observations



57 ndash 50-mil Field 1 Pass Slight denting torn substrate facer and broken polyiso PVC over field 2 Pass no tear in roof cover increased damage to substrate gypsum lap 1 Pass no visible roof cover damage torn substrate facer and broken polyiso board lap 2 Pass no visible roof cover damage increased damage to substrate

fastener 1 Pass no visible roof cover damage plate dented substrate facer broken fastener 2 Pass slight scratching of cover increased damage to plate and substrate


Table 5 (continued) ndash Mechanically fastened single-ply sample observations

age of the roof cover surface Typical damshyage that did not result in a failure included denting and surface scratches similar to that observed on the mechanically fastened samples it can be assumed based on the observations taken of the mechanically fasshytened samples that significant denting of fastener plates and tearing of the polyisoshycyanurate substrates also occurred on the adhered samples While the extent of the damage cannot be shown it does raise conshycerns about the integrity of the roof system after impact by hail especially on systems relying on the bond between the roof cover and substrate and the pull-through resisshytance of the fastener plate to provide uplift resistance during a windstorm event

C ON C L u S ION S The freezer ice ball test method used

in this study is a more severe test than that used to grant the Severe hail ratshying in FM Approvals 4470 and is capable of distinguishing exceptional performance Impacting low-slope roofing assemblies with 20-in- (51-mm-) diameter freezer ice balls having impact energies between 2375 and 2613 ft-lbs (322 and 355 J) produced results that were reasonable and useful as a test method for identifying roof cover assemshyblies that are able to withstand exposure to very severe hail conditions in addition impacting low-slope roofing assemblies with 20-in- (51-mm-) diameter freezer ice balls having impact energies between 5300 and 5830 ft-lbs (719 and 790 J) produced results that set roof cover assemblies apart as able to withstand extreme impact damshyage Several of the key findings of this study that will be used in developing the final test protocol for the vSh rating are as follows

1 When fasteners are present directly below the roof cover in the roofing assembly it is critical to impact the roof cover over the fastener and plate

2 Establishing multiple impact enershy

gy ranges could potentially allow for more levels of hail damage resisshytance thus separating the very good from the best

3 Exposure to Uv light has some negashytive impact on the performance of roof cover assemblies More exploshyration into this variable will be explored in future testing including but not necessarily limited to lonshyger exposure and different materials being conditioned

4 reduction of temperature during the sample testing has a significant negative impact on the performance of the roof cover assemblies

5 Lower-density substrates in the roof assembly are more critical to impact by freezer ice balls than higher-denshysity substrates with the roof covers evaluated

6 As expected thinner roof cover mateshyrials are more susceptible to damage than their thicker counterparts and the thinnest material should be used during testing

7 Two impacts at each location should be required as failure was not evishydent on several of the samples until after the second impact This creates a more stringent requirement for the test method

While we are able to draw many valushyable conclusions from the results of this program it is important to note that there is more work to be done in the area of severe hail impact damage resistance These first and second phases of the testing estabshylished important variables to consider and identified how they can impact performance individually The future stages of this work will include approaching these variables conshycurrently as well as finding an appropriate conditioning amount for both the temperashyture and Uv light exposure of the samples

The impacts of all of these variables should be fully analyzed before issuing a final VSH rating testing protocol once the variables are analyzed in full we will be able to issue a testing protocol that serves the best interests of property owners who find themselves subshyject to potential extreme hail damage

R EF ER EN C E S 1 S Lekas M gannon S Moghul

ldquoProperty hail Claims in the United States 2000-2013rdquo verisk insurance Solutions Jersey City nJ 2014

2 FM global Property Loss Prevention Data Sheet 1-34 ldquohail Damagerdquo Factory Mutual insurance Company Johnston ri october 2014

3 J Schaefer J Levit S Weiss D McCarthy ldquoThe Frequency of Large hail over the Contiguous United Statesrdquo noAAnWSnCEPStorm Prediction Center norman oK

4 FM Approvals Standard 4470 5 UL 2218 UL Standard for Safety for Impact Resistance of Prepared Roof Covering Materials Second Edition Underwriters Laboratories January 25 2010

6 ASTM D3746 Standard Test Method for Impact Resistance of Bituminous Roofing Systems

7 AnSiFM 4473 8 v Crenshaw JD Koontz ldquoSimushy

lated hail Damage and impact resistance Test Procedures for roof Coverings and Membranesrdquo Interface May 2001

9 JD Koontz TW hutchinson ldquohail impact Testing of EPDM roofs Assembliesrdquo Proceedings of the RCI 24th International Convention amp Trade Show Dallas TX March 12 -17 2009

10 ASTM g154 Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials


Abstract

increased property damage from hail impact has become more common in recent years with the majority of the damage occurring to roofs To help address this concern a very Severe Hail (VSH) rating for low-slope roofing is being developed using a modified version of the test method described in AnSiFM 4473 Testing was completed using ice balls to impact single-ply modified-bitumen and built-up roof covers over insulations and cover boards to determine which factors contribute to roof system failure when exposed to ice balls with increased impact energies The effects of ultraviolet (Uv) aging and sample surface temperashyture on the performance of the samples were also studied

Speakers

Daniel E Brown mdash FM Approvals

DAniEL BroWn is a graduate of northeastern University with a Bachelor of Science degree in chemical engineering Since 2011 Brown has been an engineer with FM Approvals LLC where he has worked on a variety of research activities in the areas of fire testing and natural hazards testing He works in the Materials Division with a specialization in roofing and hail damage resistance

Daniel A Boardman PE mdash FM Approvals

DAniEL BoArDMAn PE has a BS in mechanical engineering from the University of Massachusetts Dartmouth and an MS in fire protection engineering from Worcester Polytechnic institute Since 2006 he has been an engineer with FM Approvals LLC and FM Global working on a variety of research activities in the areas of fire testing and natural hazshyards testing he is a member of the national Fire Protection Association (nFPA) the Society of Fire Protection Engineers (SFPE) and ASTM Committees D08 and E05





























































































































































































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Class 4 impacts







































































































testing and results of severe hail exposure

Documents