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How Modified Asphalt Tackles Extreme Weather Challenges

May 15, 2015

Of the challenges a roof faces,
hail is, in many ways, the
most devastating. Storms
bring in cold rains that thermally
shock the roof; then,
in this heightened state of
stress, hail slams into the shingles. Each
year, the National Weather Service’s (NWS’s)
Annual Severe Weather Report records locations
of hail with a diameter of one inch or
greater. Preliminary reports from the NWS
show 7,065 instances of large hail throughout
the United States in 2013 (Figure 1),
with preliminary reports for 2014 showing a
similar story.1 It is no surprise that property
damage due to hail reaches an estimated
$1.25 billion annually.2 The stress imparted
by hail can devastate roof coverings. For
asphalt shingles, there are three primary
modes of failure: fracturing of the shingle,
bruising of asphalt, and removal of surface
granules.
The impact energy of hail imparts stress
on the shingle, causing it to flex downward.
The top surface is subjected to vertical compression
while the bottom is subjected to
horizontal tension. To absorb the impact,
the bottom of the shingle will expand. This
expansion can lead to cracking, which is
referred to as fracturing. If the fracture does
not extend through the entire shingle, it is
considered a bruise. Bruising is still considered
functional damage because it leaves a
soft spot in the shingle that is vulnerable
to further damage. The impact to the shingle
may also dislodge granules from the
asphalt, leaving the asphalt exposed to the
aging effects of ultraviolet (UV) rays.3
When the Texas Department of
Insurance created the impact test that has
evolved into UL 2218, the focus was on the
fracturing of the shingle. For this reason,
failure in the UL 2218 test is defined by
the Acceptance Criteria (7.2), which reads:
“For asphalt shingles, a visible crack of the
asphalt on the back of the shingle shall be
determined to be a failure.” The current testing
method accounts for functional damage
due to cracking on the bottom of a shingle,
but does not address the issue of dislodged
granules, asphalt compression, or openings
visible only on the top of the shingle, all of
which lead to premature degradation of the
asphalt material.4
The Insurance
Institute for Business
& Home
Safety (IBHS)
found that homes
with roof coverings
classified as
impact-resistant
were 40% less likely
to have claims—
and even less likely
to have claims
resulting in insurance
payments—
than those without.
5 While many
asphalt shingles pass UL 2218 Class 4
impact resistance testing, they do not all perform
equally. Independent testing by IBHS
has also shown that even among UL-rated,
impact-resistant shingles, polymermodified,
impact-resistant shingles performed
20% to 50% better than traditional
oxidized impact-resistant shingles for all
four steel ball impact classes.6
MODIFICATION OF ASPHALT
All roof coverings are comprised of systems
of components that work together to
create a protective barrier, and shingles
themselves are no different. Asphalt shingles
are a system built primarily of mat,
asphalt, filler, and granules. Each component
serves a function and is critical to the
Ma r c h 2 0 1 5 I n t e r f a c e • 2 1
Figure 1 – National Weather Service preliminary severe
weather report of large hail events in 2013.
success of the product. In the search for
innovation, modified asphalts are ushering
in a new era of more resilient asphalt
products.
The asphalt used in traditional manufacturing
of shingles is known as coating
asphalt. Raw asphalt, also known as flux, is
the base stock for roof coating asphalt and
has a softening point around 80°F to 120°F
(27°C to 49°C). Asphalt shingle roofs have
been measured at temperatures exceeding
180°F (82°C). To function as roof coating
asphalt, flux must be altered to stiffen the
asphalt to withstand the normal operational
temperatures experienced on a roof. The
traditional process, known as the oxidative
aging of asphalt, or oxidation, involves
bubbling air through liquid asphalt flux at
500°F (260°C) for one to 10 hours.7 Once
flux has been oxidized, the common softening
point is raised to temperatures between
200°F and 225°F (93°C and 107°C).
The natural aging process of asphalt is
affected by three components: heat, oxygen,
and UV rays. The process of oxidizing
asphalt artificially expedites the natural
aging effects through heat and oxygen exposure.
This chemically alters the asphalt
from low-molecular-weight compounds (aromatics,
resins, and saturates) in the flux,
forming it into longer chain asphaltenes
and hardening the asphalt. As a result,
the oxidized asphalt is limited in its ability
to respond to strain. To resist strain energy,
traditional asphalt shingles must have
enough mass to resist damage from the
impact energy imparted by hailstones.8
An alternative method to adjust the
asphalt’s physical characteristics is by polymer
modification. Asphalts have physical
properties similar to polymers, but they
differ dramatically at the molecular level.
A simple polymeric material is composed
of large molecules of similar chemical composition
that do not change in molecular
weight with environmental temperature
changes. Unlike polymeric materials,
asphalt is composed of a complex mixture
of smaller molecules whose bonding forces
are highly dependent upon temperature.9
Blending polymers with the asphalt stabilizes
the bonds, making the mixture flow less
temperature-dependent than what is normally
observed in flux and oxidized asphalt.
The process of polymer modification
allows control of the softening point, while
adding benefits such as improved adhesive
qualities. The addition of styrene-butadiene-
styrene (SBS) polymers to asphalt
increases the softening point without changing
the chemical makeup
of the asphalt and better
maintains the flexibility
that would be lost during
oxidation.10 By using
this alternative to the
oxidation process, manufacturers
are able to
engineer strain-response
properties in the asphalt.
This creates asphalts
able to function under
substantially greater
strain energy, such as
the energy imparted from
a hailstone striking the
shingle.
The incorporation
and application of polymer
modification during
the manufacturing process
will also influence
the durability of the
shingle. There are three
common methods for
incorporating polymermodified
asphalts into
the production of shingles.
The first method
is to fully impregnate the mat base with
polymer-modified asphalt. This method may
slow production due to the added viscosity
of the polymer-modified asphalt requiring
more time to fully saturate the mat.
Shingles that are fully impregnated with
SBS polymer-modified asphalt ensure that
the SBS flexibility and strain resistance
are fully incorporated. The second common
method impregnates the mat with oxidized
asphalt and then adds a layer of polymermodified
asphalt on top. This allows manufacturing
to maintain faster production due
to the lower viscosity of oxidized asphalt
but loses some of the flexibility and associated
benefits seen in the fully incorporated
method. The third method adds a polymer
oil mixture, or a rosin or resin additive, to
the oxidized asphalt. This method slightly
softens the oxidized asphalt, but does not
provide the full range of polymer characteristics
due to incorporation with the artificially
aged, oxidized asphalt rather than the
raw asphalt.
INTRODUCTION OF POLYMERMODIFIED
SHINGLES
The first SBS polymer-modified commercial
base sheet was introduced to North
America by Malarkey Roofing Products in
2 2 • I n t e r f a c e Ma r c h 2 0 1 5
Photo 1 – A roof with Legacy® SBS polymer-modified shingles after a hailstorm in El Dora, Iowa, in
August of 2008. The only shingle damage was to the ridge vents, due to the unsupported ridge area.
1977. Building upon this technology, the
company introduced the first SBS polymer-
modified shingle in 1986. The SBS
shingles were developed to allow for
low-temperature installation in Alaska,
which effectively extended the roofing season
and reduced cracking seen from the
oxidized shingles in cold-weather application.
Upon installation, observations in the
field showed polymer-modified asphalt had
another unexpected trait: wind resistance.
In 1992, further testing began for resistance
to strain energy generated by wind.
The test was performed in a testing lab by
applying the SBS polymer-modified shingles
to a deck, ensuring they were fully sealed,
and subjecting them to 110-mph winds for
two hours. After passing the initial test, a
second test was run with unsealed shingles,
again blown at 110 mph for two hours. In
the second test, the shingles curled up in
the wind, and then lay down to their original
position when the test ended. Neither deck
experienced shingle blow-off.
2 4 • I n t e r f a c e Ma r c h 2 0 1 5
Photos 2 and 3 –
Alternate views show
destruction of siding
and a bronze steeple
on the same building
during the same hail
event.
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Asphalt shingles rely primarily on the
effectiveness of the top shingles sealing
to the shingles below to prevent blow-offs
during high-wind conditions. SBS polymermodified
shingles provide an added level
of protection through their ability to flex in
the wind and then return to a flat position
on the roof, reducing the likelihood of blowoffs
and complete roof failure. In concurring
2014 testing, IBHS has seen indications
through its research that the increased
toughness and flexibility of polymermodified
shingles may allow the shingle to
survive a storm, even if the seal is broken.11
During the aftermath of Hurricane Andrew
in 1993, Miami-Dade County amended the
building code and instituted the 110-mph
requirement for roofing materials. The SBS
polymer-modified shingle was shipped to
Florida and became the first code-approved
shingle in Miami-Dade County.
Throughout the late 1990s, increased
installations in elevated wind areas, such as
the Midwest, brought with them the strain
of hail. Again, the polymer-modified shingles
were observed to resist the strain energy
imparted on them from the impacts seen
in these storms. In 1996, UL introduced UL
2218, the first standard test developed to
assess the impact resistance of flexible roof
covers.12 In 1997, the SBS polymer-modified
shingle passed the UL 2218 impact resistance
test at a Class 4 rating. Since that
time, SBS polymer-modified shingles have
gained traction throughout the Midwest as
the preferred shingle for impact resistance.13
Shingle performance is about more than
resistance to impacts; it is also about recovery.
In ASTM D412, asphalt is tested to
withstand tensile forces.14 During this test,
oxidized asphalt may elongate up to 50% of
its original size, but will not recover to the
original size. In the same test, SBS polymermodified
asphalt may elongate 300% or
more, then recover substantially to its original
size. The elastic recovery of SBS polymer-
modified asphalt allows for better strain
response. Elastic recovery also contributes
to improved granule adhesion. Granules
naturally swell and contract as they heat
and cool with the weather. The ability of the
SBS polymer-modified asphalt to expand
and recover allows the asphalt to maintain
better granule adhesion, which, in turn,
protects the asphalt from UV degradation.
A FORTIFIED SYSTEM
We cannot change the weather, but we
can fortify the roofing system to better withstand
the increasing demands from forces
of nature. In an effort to advance roofing
solutions, IBHS has developed the Fortified
Roofing System that provides independently
tested guidelines to reduce the potential for
property damage due to natural disasters.15
In the same search for innovative solutions,
research continues on how the integration
of polymers can create a more resilient roofing
material. The ability to blend asphalt
with new modifiers opens the door for
further modification and greater control of
asphalt shingle properties, leading to resilient
roofs and safer homes.
REFERENCES
1. Storm Prediction Center, National
Weather Service, http://www.spc.
noaa.gov/wcm/#data.
2. Hail Fact Statistics, Insurance
Informative Institute, http://www.
iii.org/fact-statistic/hail.
3. “Mastering Roof Inspections: Asphalt
Composition Shingles,” Part 44,
Ma r c h 2 0 1 5 I n t e r f a c e • 2 5
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Interface (RCI)
http://www.nachi.org/asphaltcomp-
shingles-part44-98.htm.
4. “Relative Impact Resistance of
Asphalt Shingles,” Insurance Institute
for Business & Home Safety,
August 2014, https://www.disastersafety.
org/wp-content/uploads/
r e l a t i v e – i m p a c t – r e s i s t a n c e –
asphalt-shingle-testing_IBHS.pdf.
IBHS, www.disastersafety.org/wpc
o n t e n t / u p l o a d s / r e l a t i v e –
impact-resistance-asphalt-shingletesting-
ibhs.pdf.
5. Insurance Claim Hail Study,
IBHS, www.disastersafety.org/wpcontent/
uploads/hail_taxes_es.pdf.
6. IBHS, August 2014.
7. U.S. Environmental Protection
Agency, AP 42, “Chapter 11: Mineral
Products Industry,” fifth edition, Vol.
1, 11.2-1, January 1995.
8. Sidney Greenfield, Hail Resistance of
Roofing Products, 1969.
9. Transportation Research Circular
E-C140, Transportation Research
Board.
10. Asphalt Institute.
11. Timothy Reinhold and Anne Cope,
“Assessing High Wind and Hail
Performance of Asphalt Shingles,”
Asphalt Magazine, Vol. 29, No. 3.
12. Impact Resistant Roof Coverings,
Blueprint for Safety, http://
www.blueprintforsafety.org/doc.
php?d=Hail_Mitigation_Techniques.
13. Terry Binion, “Let it Hail, Let it
Hail, Let it Hail!” 2003, http://www.
insurancejournal.com/magazines/
features/2003/04/07/28144.htm.
14. ASTM D412-06a(2013), Standard
Test Methods for Vulcanized Rubber
and Thermoplastic Elastomers –
Tension, ASTM International, West
Conshohocken, PA, 2013, www.
astm.org.
15. “What Is Fortified?” Insurance
Institute for Business & Home
Safety, http://www.disastersafety.
org/wp-content/uploads/FH-New-
Fact-Sheet_IBHS.pdf.
2 6 • I n t e r f a c e Ma r c h 2 0 1 5
Gregory Malarkey
is the current
president of the
Asphalt Roofing
Manufacturers
A s s o c i a t i o n
(ARMA) and senior
vice president
at Malarkey
Roofing Products.
He has
over 30 years
of multidisciplinary
experience in the asphalt roofing
industry, is co-chairman of the Asphalt
Roofing Environmental Council, and is
active with the Asphalt Institute.
Gregory Malarkey
Traci Shaw is the
communications
coordinator at
Malarkey Roofing
Products.
She grew up in
a family-owned
roofing business
and now writes
educational materials
and external
communications
for Malarkey.
She currently sits on the Communications,
Marketing, and Education
Committee of the Asphalt Roofing
Manufacturers Association (ARMA).
Photo 4 – Untouched photograph of an oxidized asphalt shingle in the same Traci Shaw
neighborhood after the same hail event in El Dora, Iowa.
Insured thunderstorm wind and hail losses topped $27 billion in 2011 and $14 billion in 2012,
whereas in the early 2000s, they hovered around $5 billion. According to Eberhard Faust, head
of climate risk and natural hazards research at MunichRE, inflation-adjusted annual losses due to
severe thunderstorms ($250+ million in damage) have doubled since 1970.
Faust’s study team has found that storm formation seems to be easier now than it was 40 years
ago, though it is not clear whether this is due to natural climate variability or man-made climate change.
At the same time, the median age of a home in the U.S. has increased from 25 years in 1987 to 35
years in 2010. In many parts of the country, the majority of homes still have their original roof, making them
more likely to fail in storms than new roofs, built to stricter codes.
— BuildFax
THUNDERSTORM
DAMAGE RISES