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Hail Impact Resistance of Building Materials: Testing, Evaluation, and Classification

May 15, 2009

INTRODUCTION
In Switzerland each year, hailstorms
cause substantial damage to building
envelopes, and, over time, total losses show
an upward trend. The use of a plastic ball to
simulate hail impact started in Switzerland
in 1970 when roofing membranes were
competing against traditional roofing materials
such as roof tiles. Standards such as
SN 564 2801 and the recommendations of
building authorities and insurance companies
referred to such procedures. In determining
hail impact resistance (HIR), a 40-
mm plastic ball is shot at a specified speed
at the test specimen. Temperature-sensitive
materials are cooled at the surface to 5˚C
(41˚F) and positioned on a rigid and/or flexible
support. Façade elements are fastened
at an angle of 45˚ or 90˚ with regular fasteners
and jointed to each other. The resultant
damage is assessed for leakage and/or
visual deficiencies.
Constant projectile properties, reproducibility,
instant damage assessment, and
time and costs savings are the advantages
of the current test procedures. There are,
however, various
disadvantages in
this procedure in
re gard to natural
weather influences.
In general,
the density of
plastic balls is
higher than that
of natural hailstones,
and the
fracture behavior
is brittle for ice,
elasto-plastic for
plastic balls. This
means that a
plastic ball exerts
higher energy than that occurring with a
natural hailstone.
HIGH MASS – LOW SPEED VS. LOW MASS
– HIGH SPEED
The approach to this problem with reference
to natural environmental conditions
demands knowledge of the impact speed of
a hailstone. It can be calculated from analytical
evaluation or – as in recent times –
from the use of measuring devices during a
hailstorm. If a high-speed camera is available,
the impact speed can be indirectly
established by videotaping the impact.
EVALUATION OF IMPACT VELOCITY
At impact on the ground, hail appears to
be of white color. This fact leads to the conclusion
that the amount of trapped air in
the ice is apparently rather high. With
increasing size, however, sliced hailstones
often show a shell-like structure. Within
this structure, clear ice alternates with
porous ice, resulting from many ups and
downs in the turbulent air circulation within
a storm supercell. Size of hailstone and
aerodynamic drag coefficient (cw) as determined
by the hailstone shape have the
strongest influence on impact velocity. See
Figures 1 and 2.
Figures 1 (above) and 2 (right) – Shapes and
dimensions of collected hailstones that fell
from a supercell near Lugano on June 21,
2007 (left; photo by F. Terrasi), and in the city
area of Zurich on June 24, 2002 (right; photo
by U. Spreiter). The diameter of the 2-franc
Swiss coin is 27 mm (1.06 in).
S E P T E M B E R 2009 I N T E R FA C E • 2 5
These shapes vary between
round, egg-shaped, disk-like,
smooth, warty, bulgy, and even
extremely jagged-surfaced. Re –
cent ly, bulgy, pointed forms were
also detected in smaller-sized hailstones.
There fore, the cw can range
from 0.45 for a smooth surface to 0.80 for a
rough surface. In turn, the density (rice) may
range from 0.60 to 0.91 kg/dm3.
In the past, various scientists have
reported on hail impact velocity and its
destructiveness. As an example, in 1937,
Bilham and Relf2 studied the differences
between small (<10 mm or 0.40 in) and
large hailstones. Motz3, Kawashita/Flüeler4,
and others evaluated the most cited equations
for terminal velocity. Figure 3 shows
the range of the calculated terminal velocity,
vtH, for hailstone diameters ranging from
20 to 100 mm (0.79 to 3.94 in). As a rule,
factors in the calculation include the sphere
diameter, dH; the density of the ice, ρice; the
density of the air, ρair; and the coefficient of
aerodynamic drag in air, cw. The formula
shown in Figure 3 above is most frequently
used.
In this present study, the following constants
are used (Figure 3, curve 3a):
• Ice density at ρice: 875 kg/m3,
• Air density at 20˚C ρair: 1.226 kg/m3,
and
• Coefficient of aerodynamic drag (cw):
0.5 kg/m2.
TEST PRACTICES OF COMMON STANDARDS
Since the beginning of recorded history,
Australia, South America, the United
States, and central Europe have known the
effects of hailstorms. To toughen materials
against hail impact, test procedures were
first established in South Africa in the
1950s and in the United States at NIST in
the 1960s. In Switzerland, the plastics
industry provided evidence in the early
1970s that polymer roofing membranes are
equal or even superior to classic roofing
Figure 3 – Calculated terminal
velocity for round hailstones from
different authors. 1: Bohm; 2:
ASTM 1038-05; 3a: EMPA with cw
0.5; 3b: EMPA cw 0.6; 4: Motz ρair
0.9 kg/m3; 5: Motz ρair 1.23 kg/m3;
6: Heymsfield; 7: Pflaum; 8 and 9:
Matson; 10: Lozowski, Guastala,
and Flüeler.
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26 • I N T E R FA C E S E P T E M B E R 2009
materials such as clay tiles in their resistance to hail impact. Initial impact testing
was conducted using ice spheres.
Nevertheless, for practical and economic reasons, a 40-mm polyamide (PA)
sphere was chosen. Comparisons of in-service hailstone damage on polymer
roofing membranes to that obtained with the PA spheres showed similar damage
patterns. Due to this fact, SIA established a test protocol in 19775 requiring
a velocity of 17 m/s when shooting at a chilled waterproofing membrane supported
by a steel plate and soft thermal insulation board (EPS). This velocity
equates to a kinetic energy of 5.6 J. In comparison, good classic clay tiles
become damaged at a velocity of 9 m/s, which is equal to 1.6 J.
TEST PROGRAM
To simulate the conditions of natural hail and its impact on the building
envelope, an extensive experimental investigation was performed. A comparative
study was carried out on 50 types of materials originating from 11 fields of application
using laboratory-made ice spheres and plastic balls.
TEST APPARATUS AND PARAMETERS
The test apparatus consisted of a pneumatic gun positioned vertically (Figure
4). This apparatus was originally designed for use with plastic balls only. In the
course of expanding our technical investi gations, the apparatus was modified to
launch 15- to 50-mm ice spheres. By using a light beam, the projectile velocity
is instantaneously measured at the end of the gun barrel at a distance of 30 cm.
Target and distance are aimed exactly by two focusing lasers. The velocity is set
by the pneumatic pressure corresponding to calibration values enabling a
repeatability of <1 m/s. See Figures 5 and 6.
Figure 4 – Test apparatus and tilted steel frame
with mounting for a wood-framed window glass.
S E P T E M B E R 2009 I N T E R FA C E • 2 7
For the project, the following parameters
were chosen:
1. Set-up of test specimen: Condition
new, as installed in building, custom-
designed.
2. Size of test specimen: 0.8 to 1.1 m2
with jointing, possible overlaps, and
original fasteners.
3. Surface treatment: Temperaturesensitive
materials chilled with ice
granules for three minutes.
4. Test temperature: Room temperature
and humidity, approximately
23˚C/50% r.h.
5. Impact angle: Roofing, 90˚, and
façade, 45˚; both applications 45˚ +
90˚.
6. Type of impact: Single-shot mode.
7. Impact speed: Appropriate speed for
size of projectile.
PROJECTILES AND PROPERTIES
For projectiles, precision balls made
from PA 66 (density of 1.16 kg/dm3) and
laboratory ice spheres (density 0.875 g/cm3)
were used. The ice spheres were made in
silicon molds using demineralized water.
The production of crack-free and essentially
pore-free ice spheres re quired approximately
17 hours at -20˚C in a freezer.
Freezing of the water was induced by a
f r e e z e r
plate at the
bottom of
the mold,
thus facilitating
slow growth of the ice core from bottom
to top. Due to time-dependent changes
of ice, a shelf time of less than three weeks
was observed for the newly made ice
spheres. The important properties of both
types of projectiles are listed in Table 1.
PROCEDURE
To investigate the damage mechanism
and weak points, test specimens were first
impacted using PA balls fired within the
velocity range observed for real hailstones
at impact. At a damage velocity considerably
higher or lower than natural velocities,
test specimens were impacted by sphere
sizes 10 mm higher or lower. Then, the procedure
was applied by using ice spheres.
DAMAGE
ASSESSMENT AND
EVALUATION
Assessment
of damage in
regard to insurance
codes of
practice was the
most challenging
task. The diversity
of materials,
supports, substrates,
and fastenings,
along
with the wideranging
damage
characteristics at
impact, demanded
very close
examination of
each application.
Therefore, the
damage characteristics
due to
impact were
grouped within
the following general
categories:
1. Loss of a
main function:
such as
watertight–
ness, breakdown
of mechanical/electrical properties,
loss of load-bearing property,
etc.
2. Deformation: indentation, dent formation,
deformation of defined
depth.
3. Cracking and fracture: visible
cracks, spontaneous fracture,
delamination.
4. Aesthetics: change of appearance,
loss of light transmission, view in
back light from a distance of 5 m.
5. Damage affecting aging: inherent
cracking, face separation, debonding,
and damage of surface layers.
After impact, the damage category was
assigned based on the lowest velocity (i.e.,
kinetic energy according to Equation 2) that
Figure 5 – To condition the clay tile probe before
testing, it is moistened three times with a wet
sponge.
Figure 6 – Impacting a 50-mm ice sphere on a
framed 7-mm-thick wire glass window.
TABLE 1 – MASS OF ICE SPHERES AND PLASTIC BALLS FOR VARIOUS DIAMETERS
28 • I N T E R FA C E S E P T E M B E R 2009
TYPE OF SPHERE UNIT DIAMETER (MM) FAILURE BEHAVIOR
20 30 40 50
Mass of ice (g) 3.8 12.3 30.2 58.3 brittle
Mass of Polyamide (g) 4.8 16.1 38.8 74.9 tough
resulted in damage. For ductile materials such as metallic sheets,
the formation of a dent was judged to be aesthetic damage. In general,
aesthetic damage was not observable until the depth of the
indent reached about 0.5 mm.
RESULTS
The diversity of the investigated materials and their uses generated
a wide range of results. Nevertheless, these results could be
classified into three material categories according to load-bearing
behavior, i.e., stiffness (Tables 2.1 – 2.3). A condensed report is
provided by the Swiss Association of Fire Insurance Companies
VKF6, also in French.
Figure 7 is a plot relating depth of indentation to projectile
kinetic energy for the case of a 0.7-mm zinc-plated, corrugated
MATERIAL/ ELEMENT E·I ANGLE EKIN (J) HIR LOWEST VALUES FOR
COMPONENT STIFFNESS (KN•MM2/MM) (°) CLASS
PRODUCT Ø (MM) EKIN (J)
Tiles high 2330 – 2635 90 13.7 – 27.3 4 clay tiles 50 13.75
Glass high 370 – 3000 45 5.5 – 46.7 3 – 5 wire glass 7 40 5.5
Fiber cement high 140 – 252 45/90 17.6 – 38.2 4 – 5 corrug. plate 5.5 40 17.6
Polymer plates high 0.3 – 9.6 90 6.4 – 38.8 3 – 5 PMMA 4 30 6.4
Skylights high 5.3 – 7.4 90 0.8 – 3.1 2 – 5 PMMA 2.5 30 0.8
GRP boards high 6 – 88 45 1.4 – 20.5 2 – 3 GRP-UP struct. 30 1.4
MATERIAL/ ELEMENT E·I ANGLE EKIN (J) HIR LOWEST VALUES FOR
COMPONENT STIFFNESS (KN•MM2/MM) (°) CLASS
PRODUCT Ø (MM) EKIN (J)
Shutters very low 0.1 – 4.2 45/90 0.05 – 1.75 1 – 2 profile, foam 0.25 20 0.05
Roller blinds very low 0.5 – 1.2 45/90 0.2 – 0.7 1 – 2 folded 0.45 20 0.2
GRP: corrug., trapez. low 1.95 90 0.4 – 0.5 1 GRP-UP trp. 1.4 20 0.4
Metal sheets, façade low 1.9 – 2.6 45 0.6 – 1.7 1 – 2 alu 0.7 30 0.6
Membrane: stiff* medium 0.001 – 0.6 90 39 – 90 5 SBS 3.7 sand coat 50 > 80
Membrane: soft* medium 0.001 – 0.6 90 12.9 – 53.3 4 – 5 SBS 3.7 sand coat 40 12.9
MATERIAL/ ELEMENT E·I ANGLE EKIN (J) HIR LOWEST VALUES FOR
COMPONENT STIFFNESS (KN•MM2/MM) (°) CLASS
PRODUCT Ø (MM) EKIN (J)
Larch wood medium 1.7 45 0.6 – 1.8 1 – 2 coated 30 0.6
Spruce wood medium 1.5 45 0.8 – 3.1 2 planed 30 0.8
EIFS** medium 1.7 – 2.8 45 5.7 – 17.0 3 – 4 EPS 20, 4 30 5.7
Metal sheets, roof medium 2.1 – 6.0 90 0.6 – 2.0 1 – 2 cupper, 0.6 30 0.6
Figure 7 – Indentation versus kinetic energy (J) of a corrugated 0.7-
mm steel sheet tested using 40-mm PA balls and 40-mm ice spheres.
S E P T E M B E R 2009 I N T E R FA C E • 2 9
TABLE 2.1 – HIGH-STIFFNESS, TOUGH MATERIALS
TABLE 2.2 – LOW-STIFFNESS MATERIALS, NON LOAD-BEARING
TABLE 2.3 – MEDIUM-STIFFNESS MATERIALS
*Membrane placed on stiff/soft substrates, respectively **External Insulation and Finishing Systems (EIFS)
steel sheet impacted with 40-mm PA balls
and 40-mm ice spheres. Figure 8 shows a
photo of the indentations at projectile velocities
of 26, 30, and 36 m/s.
At a 90˚ impact angle, both projectile
types caused circular indentations that
increased in size with increasing velocity. At
an angle of 45˚, mainly ellipsoidal indents
resulted. Upon impact, PA balls remained
intact and showed no cracking. In contrast,
ice spheres tended to split – even at a velocity
as low as 10 m/s – depending on the
nature, mass, and surface topology of the
specimen. A clear observation from the testing
was that for heavy mass specimens
such as clay tiles, the ice fragmentation
pattern was distinct and more diverse,
changing with increasing velocity in comparison
to the fragmentation of compliant
specimens. A heavy-mass specimen is one
for which the ratio of the test specimen
mass to the projectile mass is greater than
50. Another observation was that low HIR
values (i.e., <3 J) were, in general, found for
specimens where the damage was categorized
as aesthetic rather than functional.
See Figures 8 and 9.
CORRELATION OF DATA FROM PA AND ICE SPHERES
Test data from two projectile materials –
ice versus PA – allow a correlation of the
tested materials. A ratio can be calculated
between the values of velocity (and also
kinetic energy) of ice spheres and PA ball
spheres. Figure 10 shows the relationship
between the primary kinetic energy data for
various specimens tested using 40-mm PA
balls and 40-mm ice spheres.
This figure clearly confirms that many
specimens experienced damage at very low
kinetic energies. It is noted that hailstones
having diameters less than 30 mm generally
have kinetic energies of less than 3.5 J.
Most importantly, from Figure 10, it is evident
that the data points for many specimens
fell well below or above the correlation
line, indicating for these cases that testing
needs to be conducted with ice spheres and
not with PA balls. This is especially the case
for roofing membranes tested on rigid substrates
and for clay tiles.
CLASSIFICATION AND DESCRIPTION
A classification of building materials
should be understood not only by
material scientists and professionals
in the building business, but also by
users. So, it should be easy to understand
and related to the observed
weather phenomena. In a 1991 publication,
Flüeler7 made an attempt to
define a classification system, including
five levels of HIR. It is now stated
to classify hail impact resistance into
classes 1 to 5 (Table 3), which correspond
to hailstone diameters of 10 to
50 mm where the building materials
remain damage-free. It includes the
corresponding terminal velocity of an
impacting hailstone as calculated
using Equation 1, curve 3a, of the
Figure 9 – Fractured clay tiles
caused by 40-mm ice spheres:
beaver’s tile with center shot at
24.4 J (above); plane tile with
corner shot at a kinetic energy of
25.8 J (right).
Figure 8 – Indentations caused by 40-mm projectiles. Impact using PA balls (left) and ice
spheres (right) at velocities of 26, 30, and 36 m/s.
30 • I N T E R FA C E S E P T E M B E R 2009
plot in Figure 3, and calculated maximum
kinetic energy using Equation 2. An examination
of Table 3 shows that for each HIR
class, the range of kinetic energy corresponding
to that given HIR Class is rather
large, ranging from 11.1 J to <27.0 J for
HIR Class 4, for example. This realization
dictates that for a more precise description,
differences in kinetic energy sustained
without damage must be taken into account
in the proposed classification system.
The classification thus signifies not only
the HIR class designation, but also the
highest kinetic energy achieved without
damage for the given sized ice sphere. Table
4 provides HIR Class designations (without
kinetic energy) for the specimens in this
study.
CONCLUSIONS
This study confirmed field observations
– particularly from insurance companies –
that indicate that considerable hail damage
payment (>80%) is made for the materials
that fall within HIR classes 1 and 2. They
experience damage at kinetic energies of 0.7
J or less.
Impact of stiff, high-mass construction
materials by a PA ball provokes considerably
higher kinetic energy than that of an
ice sphere of the same size. The fragmentation
energy is not available for the damage
process. For very stiff and high-mass materials,
an ice sphere must have a kinetic
energy up to 15 to 20 times greater than
that of a PA ball to inflict damage.
With the exception of mass difference,
lightweight elastic materials behave almost
similarly with the two types of projectiles
because of low fracture/deformation energy
absorption.
For materials with structured cross sections
with thin faces (e.g., double face plate,
<1 mm), a smaller projectile diameter might
provoke damage, while a larger diameter
causes no damage.
Due to the diversity of materials and
systems used for building envelopes, HIR
evaluations have to be performed using ice
spheres impacting at natural terminal
velocity. Moreover, the kinetic energy sustained
during these evaluations has to be
taken into account in an HIR classification
system.
HIR ICE SPHERE MASS (G) TERMINAL KINETIC
CLASS DIAMETER (MM) VELOCITY (M/S) ENERGY (J)
1 10 0.5 13.8 0.04
2 20 3.6 19.5 0.7
3 30 12.3 23.9 3.5
4 40 29.2 27.5 11.1
5 50 56.9 30.8 27.0
Figure 10 – Kinetic energy in J for ice
spheres and PA balls causing damage.
Actual requirement (red) for roofing
membranes in Switzerland and new
requirement for HIR Class 4 materials.
􀁳􀀀􀀷􀁁􀁔􀁅􀁒􀁔􀁉􀁇􀁈􀁔􀀀􀁒􀁏􀁏􀁆􀀀􀁁􀁔􀁔􀁁􀁃􀁈􀁍􀁅􀁎􀁔􀁓􀀌􀀀􀁏􀁖􀁅􀁒􀀀􀀒􀀑􀀌􀀐􀀐􀀐􀀀
􀁉􀁎􀁓􀁔􀁁􀁌􀁌􀁅􀁄􀀀􀁎􀁁􀁔􀁉􀁏􀁎􀁗􀁉􀁄􀁅􀀀􀁗􀁉􀁔􀁈􀁏􀁕􀁔􀀀􀁁􀀀􀁓􀁉􀁎􀁇􀁌􀁅􀀀􀁌􀁅􀁁􀁋
􀁳􀀀􀀰􀁒􀁏􀁊􀁅􀁃􀁔􀀀􀁓􀁐􀁅􀁃􀁉􀁬􀀀􀁃􀀀􀁅􀁎􀁇􀁉􀁎􀁅􀁅􀁒􀁉􀁎􀁇􀀀􀁉􀁎􀁃􀁌􀁕􀁄􀁅􀁄
􀁳􀀀􀀭􀁏􀁄􀁕􀁌􀁁􀁒􀀌􀀀􀁂􀁏􀁌􀁔􀀍􀁔􀁏􀁇􀁅􀁔􀁈􀁅􀁒􀀀􀁄􀁅􀁓􀁉􀁇􀁎 􀀣􀁁􀁌􀁌􀀀􀁕􀁓􀀀􀁔􀁏􀁌􀁌􀀀􀁆􀁒􀁅􀁅􀀀􀁁􀁔
􀀘􀀖􀀖􀀍􀀲􀀯􀀯􀀦􀀳􀀣􀀲􀀥􀀥􀀮
􀀘 􀀖 􀀖 􀀍 􀀗 􀀖 􀀖 􀀍 􀀓 􀀗 􀀒 􀀗
􀁒􀁏􀁏􀁆􀁓􀁃􀁒􀁅􀁅􀁎􀀎􀁃􀁏􀁍
When you really need your
equipment covered,
call RoofScreen!
S E P T E M B E R 2009 I N T E R FA C E • 3 1
TABLE 3 – CLASSIFICATION OF HAIL IMPACT RESISTANCE (HIR)
AND CALCULATED MAXIMUM KINETIC ENERGY
Very often, hail damage resulting in loss
of function or other physical characteristics
is not as disconcerting as aesthetic damage.
As an example, car bodies dented by hail
are still roadworthy.
The effect of hail impact on aging behavior
must be sufficiently taken into consideration.
ACKNOWLEDGEMENTS
The research detailed herein was funded
by the prevention fund of the Swiss
Cantonal Building Insurance Association.
The author wishes to acknowledge the various
contributions from the building material
industries and the support of the EMPA
laboratories, mainly polymer and composites.
Thanks to Thomas Egli, the main project
leader, and to Maja Stucki and Fabio
Guastala, coworkers at EMPA. Thanks also
to Walter Rossiter for his English review and
comments.
REFERENCES
1. SIA, Polymer Waterproofing Membranes/
Kunststoff-Dichtungsbah –
nen, Swiss Association of Engineers
and Architects, standard SN 584
280, editions 1977, 1988, 1996.
2. E.G. Bilham and E.F. Relf, “The
Dynamics of Large Hailstones,”
Symon’s Meteorological Magazine,
pp.149-162.
3. H.D. Motz, Hagelrisiko – eine sicherheitswissenschaftliche
Studie von
Kausalität und Effekt, PhD thesis,
Univ. Gesamthochschule Wupper –
tal, D 468, Wuppertal, Germany,
1986.
4. L. Kawashita and P. Flüeler, simulated
hail impact tests with ice and
polyamide spheres, internal research
report Empa no 860’091/2
(not public), August 20, 2002.
5. SIA
6. Swiss Association of Fire Insurance
Companies VKF, Bern, Elementar –
schutzregister Hagel, Synthesebericht,
Untersuchungen zur
Hagelgefahr und zum Widerstand
der Gebäudehülle, July 2007, 32
pages.
7. P. Flüeler and F. Rupp, “The Hail
Impact Resistance of Plastic Com –
ponents of the Building Shell,” Pro –
ceedings, 3rd International Conference
on Durability of Building
Materials, Bournemouth, England,
1988.
This paper was originally published in the
Proceedings of the 11DBMC International
Conference on Durability of Building
Materials and Components, Istanbul,
Turkey, May 11-14, 2008.
32 • I N T E R FA C E S E P T E M B E R 2009
Peter Flüeler is the founder of FPC Flüeler Polymer
Consulting GmbH, Aathal, Switzerland. He received his masters
in civil engineering from the Swiss Federal Institute of
Technology (ETHZ) in Zurich and did postgraduate studies at
MIT, Cambridge, MA, on polymers and composites. In the
early 1970s, he was a structural engineer with Stocker
Engineering, Bern. Later, he worked in the civil and mechanical
engineering department of the Swiss Federal Laboratories
for Materials Testing and Research (EMPA), and he has
served as a lecturer at ETH Zurich. He was engaged as an expert in waterproofing and
drainage of tunneling during construction of the Alptransit. Flüeler has authored and
coauthored over 125 articles and holds two patents. He may be reached at
p.flueler@hispeed.ch.
Peter Flüeler
HIR CLASS MATERIAL/COMPONENT TYPE THICKNESS (MM) PREDOMINANT DAMAGE
CATEGORY
1 roller shutters, roller blinds aluminum, folded < 0.5 deformation, aesthetics
metal sheets copper, tin < 0.6 deformation, aesthetics
GRP panels light, shaped > 2 fiber matrix defect
2 metal sheets, façade and roofing Fe, Cu-Fe, Ti plated > 0.5 – 0.7 deformation, aesthetics
reinforced roller shutters aluminum 0.9 deformation, aesthetics
wood panels planed, coated 25 indent, cracked paint
3 Skylights PMMA 2.5 fracture, leakage, transparency
GRP double-faced panels structural 20 fiber matrix defect
EIFS (EPS and rock wool) reinforced glass web > 3 cracking, debonding
wire glass wire net, 10 mm 7 fracture
4 roofing membranes EPDM, SBS 4 leakage
polymer sheets PMMA modified 4 transparency, defect
roof tiles clay, structured surface 15 internal fissure (sound check)
fiber cement boards/roofing flat, undulated 6 indent, surface crack, fissure
5 roofing membranes TPO, PVC-P > 1.5 leakage
polymer sheets, skylights PC, plain + structured 4 deformation
safety glasses single, laminated 6 splitting, fracture
window glasses insulated, aluminum-framed 4/16/4 splitting, fracture
TABLE 4 – HIR GUIDE VALUES OF TESTED BUILDING MATERIALS AND PREDOMINANT DAMAGE CATEGORY
Note: HIR classes in this table are examples achieved in the study and should not be taken as requirements or guide values.