An Historical Perspective on The Wind Resistance of Clay and Concrete Roofing Tiles

INTRODUCTION
Asphalt shingle materials and attachment
methods have changed significantly
since the development of the first asphalt
shingle product in 1893. This paper presents
an historical overview of asphalt shingle
roof systems and the advancements in
design, composition, and research that
have improved shingles’ resistance to wind
loading. This document is organized
chronologically into four time periods.
Perfor mance issues are addressed throughout,
with emphasis on the behavior of inservice
systems during windstorms. This
document provides the relevant background
for ongoing research led by the University of
Florida regarding the wind resistance of
aged shingle systems.
THE EARLY YEARS (1893-1950)
The first steep-slope asphalt roofing system
was introduced in 1893. Known as
asphalt-prepared roofing, it consisted of a
thin, reinforcing cotton rag felt impregnated
with asphalt (Abraham, 1920). Installation
was similar to today’s asphalt roll roofing.
In 1897, top-surface mineral granules were
added to improve the durability of the product
(Cullen, 1992). It was later discovered
that the mineral granules served an important
function in absorbing the ultraviolet
(UV) light from the sun. UV oxidizes the top
surface of asphalt coating and leads to
accelerated degradation of the asphalt coating
(Berdahl et al., 2008).
Asphalt shingles were introduced in the
beginning of the 20th century. Shingles
were manufactured by cutting asphaltprepared
roofing into smaller sections in
order to create a discontinuous roof covering
resembling wood shakes or slate.
Similar to today’s three-tab style, single-tab
shingles (typically 9 in. by 16 in.) and multitab
shingles (typically 10 in. by 32¹⁄₈ in.)
were produced. The individual tab shingles
had exposed leading edges that were often
designed with interlocking mechanisms to
hold the shingles down during windstorms.
The multitab styles had unrestrained leading
edges, allowing the shingle tab to lift in
the wind (Abraham, 1920; Cash, 1995).
By the late 1920s, the cotton-reinforcing
felts were replaced with substitute materials
due to a price increase in cotton rags. In
1926, the Asphalt Shingle and Research
Institute and the National Bureau of
Standards (NBS; now the National Institute
of Standards and Technology) jointly investigated
the effects of weathering on the
newer substitute felts. Results of the threeyear
weathering study showed no adverse
aging effects on the shingles containing the
substitute materials (cf. Cullen, 1993). The
use of asphalt shingles increased as a result
of World War II construction demands,
prompting another change of reinforcing felt
to a less expensive wood-based organic
material. Greenfeld (1969) would later show
that the new “organic”-reinforced asphalt
shingles performed as well as their predecessors.
Blake (1925) developed one of the earliest
known shingle-attachment schedules
for a four-tab strip shingle that called for
five ¾-in.-long galvanized clout nails to be
placed ½ in. above each cutout. As shown
in Figures 1 and 2, the specified fasteners
are similar to earlier prepared asphalt rollroofing
products. Single-tab and multitab
shingles were installed on the roof in a
stair-step pattern that mimics today’s standards
(Abraham, 1920). By 1941, three-tab
strip shingles came onto the market with
fastening requirements of four 11- or 12-
gauge galvanized nails per shingle. Snoke
(1941) notes that three-tab shingles with six
nails would be more resistant in high windprone
areas, a statement that is echoed in
today’s shingle specifications. The 1947
standard for shingle attachment called for
six galvanized roofing nails with a minimum
3/8-in.-diameter head 1 in. from the shingle
edge and 1.5 in. on either side of each
tab cutout’s centerline (Strahan, 1947). The
most likely premature shingle failure during
this era was due to wind, signaling that
attachment requirements were inadequate.
During moderate wind, continued flexing of
the unrestrained exposed shingle tabs
weakened the nailed connection, increasing
the vulnerability of the shingle to blow-off in
strong wind gusts (Cullen, 1992).
DEVELOPMENT OF THE FIRST TEST STANDARDS
FOR WIND RESISTANCE (1950-1980)
The 1950s saw the introduction of twotab
sealing methods in order to improve
performance under wind loading (Cullen,
1960). The first method consisted of a thermally
activated “self-seal” adhesive strip
that was applied on the asphalt shingle dur-
4 • IN T E R FA C E MAY / J U N E 2012
ing the manufacturing process. Early tab
seals were typically resin-based materials,
which are asphalt byproducts that have a
sudden softening point that adheres the
leading edge of the shingle tab to the shingle
below. Early formulations of resin-based
tab seals were susceptible to brittle fracture
failures as a result of thermal fluctuations.
Today, tab sealants consist of either limestone
or fly-ash-modified resins, or polymer-
modified bitumen (Nichols, 2010). The
second method consisted of a field application
of asphalt roof cement dollops along
the underside of each shingle tab (Cullen,
1960). This method is still recommended for
roofs with slopes greater than 60 degrees
and for repairs to shingle tabs that have lost
adherence of their self-seal systems.
In the early 1950s, a letter survey was
sent to military installations along the east
coast of the U.S. to ascertain the performance
of asphalt shingles installed on their
buildings. The results were poor: 67% of
those surveyed noted that wind damage had
occurred with their shingles. The survey
results, coupled with increasing insurance
claims on wind-damaged shingles, prompted
the first investigation of asphalt shingle
wind performance in 1955, led by NBS. The
goal of the investigation was to assess the
wind resistance of organic- reinforced
asphalt shingles through laboratory,
simulated-service, and field-performance
evaluations (Cullen, 1960).
There is some evidence that manufacturers
were already testing asphalt shingle
wind performance prior to the NBS study
(Cullen, 1960). However, this was the first
published study of this kind. The major
component of the investigation was the
laboratory-simulated wind testing of
asphalt shingle test decks. There were two
goals to this test:
1. Evaluation of the performance of
free-tab shingles (i.e., unrestrained
shingle tabs) and its correlation to
the weight of the strip shingle.
2. Evaluation of the performance of
restrained shingle tabs by either
self-seal or asphalt roof-cement
methods.
At the time, free-tab systems were losing
popularity to restrained-tab systems. Given
the amount of building stock still using the
free-tab products, however, it was important
to understand how the weight of the
shingle affected performance. This would
also be useful for later studies on restrained
tabs that have lost their adhesive bonds.
The laboratory tests consisted of bond
strength tests on the tab sealants and windstorm
simulation tests. In his report of the
wind tests, Cullen (1960) notes that laboratory
wind tests fell short of completely sim-
MAY / J U N E 2012 I N T E R FA C E • 5
Figure 1 Figure 2
ulating in-service wind behavior, but that
these tests may serve as a useful tool when
combined with other methods. The simulation
was conducted by using an open-jet
configuration. No mention of the flow characteristics
of the jet (i.e., magnitude of turbulence)
is provided in Cullen’s report. A 4-
by 3-ft. test deck with a slope of 2 in. on 12
in. was placed in front of the jet.
The free-tab test decks—nine in total—
were subjected to a mean wind speed of 30
mph for an unknown amount of time, with
the rise of the leading edge measured to
describe performance. Good-performing
free-tab shingles were defined as having
smaller lifts during wind testing. Not surprisingly,
heavier shingles performed the
best, and a near-linear relationship
between performance and weight was identified
for a given uniform shingle thickness.
The goal of the wind investigation was to
assess the sealing characteristics of several
manufacturers’ self-sealing three-tab
organic-reinforced shingles. Therefore, the
test decks containing self-sealing shingles—
twelve in total—were subjected to three different
curing temperatures (120ºF, 140ºF,
and 160ºF) for 16 hours each. The test consisted
of four step-and-hold mean wind
velocities of 30, 40, 50, and 60 mph. The
time held at the first three wind velocities
was not reported. The time for the 60-mph
test was two hours. Failure during these
tests was defined as failure of the adhesion
on one shingle tab. The tests revealed that
nine of the 12 shingle deck specimens could
withstand 60 mph for two hours when they
were conditioned at 140ºF for two hours.
The remaining three required a 160ºF cure.
Bond strength tests correlated well with
the wind tests’ findings. Twelve asphalt
shingle products were subjected to the
same variation in cure temperature for five
and 16 hours and then tested for uplift
resistance of their tab seals (Cullen, 1993).
From these two tests, it was reported that a
cure temperature of 140ºF and time of 16
hours were adequate to evaluate the wind
performance of self-sealing shingle systems.
To validate the findings of the laboratory
tests, Cullen investigated the performance
of self-sealing shingle systems in the natural
environment. Twenty-two test decks were
exposed for a period of one year in
Washington, DC, starting in the spring. The
tab seals were periodically inspected for
adherence, and results showed that all
decks had full adhesion within 50 days.
When the tab seal bonds were broken the
following December, all shingles had
resealed by the following spring.
At the time of the Cullen (1960) report,
no standard wind performance tests existed
for asphalt shingles, but as a result of this
investigation, the Underwriters Lab oratory’s
(UL) 997, Wind Resist ance of Prepared Roof
Covering Ma te rials (1995), was developed.
The test is similar to Cullen’s 1960 work in
both test setup and conditioning. When first
drafted in 1960, 60 mph was near the limit
of fan controllability;
therefore, the
test decks were
subjected to a
maximum of 60
mph despite the
likelihood of higher in-service wind speeds.
The American Society for Testing and
Materials’ (ASTM) D3161, Standard Test
Method for Wind-Resistance of Asphalt
Shingles (2005), was first published in 1972
with an identical test procedure. These
standards are based on data from shingles
that were developed and manufactured
using 1950s technology.
Following up on Cullen’s experiments,
UL conducted a study of self-seal organicreinforced
asphalt shingle response to higher
wind speeds and wind speed fluctuations
(Benjamin and Bono, 1967). This research
was conducted using a larger fan system
capable of wind speeds up to 100 mph.
Additional tests were conducted on shingles
that passed the UL 997 60-mph wind test.
All of the 225 shingle test decks passed a
15-minute, 75-mph mean wind-speed test,
and 95% of the test decks passed a 5-
minute, 100-mph mean wind-speed test. To
replicate the fluctuating component of the
wind speed, the speed was varied between
30 mph and 100 mph. Each wind speed
was held for 60 seconds for some decks and
30 seconds for others before a series of
“practically instantaneous” (from Benjamin
and Bono, 1967) wind-speed changes
cycling from 30 mph to 100 mph for a total
of 20 oscillations were applied. All test
decks passed the wind fluctuation tests.
While results of higher wind-speed research
showed good asphalt shingle wind performance
in simulated hurricane-strength
wind speeds, concerns surrounding the
validity of the ASTM D3161/UL 997 test
methods soon followed.
With the advent of the asphalt shingle
self-seal tab system and its improved wind
resistance, the weight of the asphalt shingle
6 • IN T E R FA C E MAY / J U N E 2012
Figure 3
was no longer the main source of wind
resistance. This allowed the use of lighterweight
and cheaper-shingle mats (Cash,
1995). In 1960, glass fiber strand-based
mats were introduced as a replacement for
the organic material-based mat (Cullen,
1992). The drawback to the fiberglass mat
is an increase in flexibility of the shingle;
that is, if a self-seal were to fail, the shingle
would be more likely to lift in the wind compared
to a heavier and stiffer organicreinforced
shingle. Beyond their lighter
weight and lower manufacturing costs, the
new “fiberglass” shingles contain a chemical
saturant that gave the fiberglass-reinforced
shingles a Class A fire rating. Organic-reinforced
asphalt shingles typically have a
lower-class (Class C) rating due to the combustibility
of the organic material. The
growth of the fiberglass-reinforced asphalt
shingle market can be partly attributed to
the increase in condominium and commercial
construction that required Class A fire
ratings. By 1982, production of fiberglassreinforced
asphalt shingles overtook organicreinforced
asphalt shingle production—a
trend that has continued (Cash, 1995).
DEVELOPMENT OF THE ASPHALT SHINGLE WIND
UPLIFT MODEL (1980-1997)
The goal of the UL 997 test was to provide
a predictive method for in-service
asphalt shingle wind performance.
However, during in-house product testing
in the early 1980s using the UL 997 wind
test standard, Owens-Corning Fiberglas™
observed no appreciable shingle performance
differences between products that
should have produced significantly different
results. Following this, Drs. Jon Peterka
and Jack Cermak of Colorado State
University (CSU) were contracted by
Owens-Corning to reevaluate UL 997 and
develop a more refined test method that
would more accurately simulate in-service
wind loading conditions. This work (Peterka
and Cermak, 1983) led to today’s asphalt
shingle wind uplift model.
Dr. Peterka’s experiments concentrated
on modifying the UL 997 procedure to
include more realistic wind effects. The
standard 3- by 4-ft. test deck was placed
inside CSU’s Meteorological Boundary-
Layer Wind Tunnel to conduct tests using
turbulent boundary-layer wind that simulated
natural wind behavior (Figure 3).
Unsealed organic-reinforced and fiberglassreinforced
shingles from several manufacturers
were subjected to wind speeds up to INDEPENDENT STANDARD FOR AERIAL ROOF MEASUREMENT REPORTS
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MAY / J U N E 2012 I N T E R FA C E • 7
80 mph. To evaluate the effects of temperature
on shingle performance, the shingles
were tested at two temperatures: 75ºF and
35ºF. At the time, it was thought that lower
temperatures would increase the brittleness
of the shingles, thereby exacerbating shingles
pulling out over the fasteners during
wind events. The goal of the test was to
observe how the shingles behave during
this new test method and to discern if performance
differences could be extrapolated.
It was observed that organic-reinforced
shingles sustained less damage than fiberglass-
reinforced shingles, likely due to a
higher shingle mass, resulting in a greater
resistance to uplift. Greater shingle damage
was observed in tests on the colder (35ºF)
shingles. The overall outcome from the testing
was that performance of the shingles in
the new test correlated to the predicted
quality of the shingle.
From wind-flow visualization tests, a
wind uplift mechanism was proposed. It
states that as wind flow encounters the
leading edge of a shingle’s tab, the flow separates
above the shingle surface, causing a
negative pressure relative to the ambient
pressure in this separated region. A positive
pressure relative to ambient is produced at
the leading edge and is forced under the
shingle. The effect of the positive pressure
below the shingle and the negative pressure
above the shingle produce a net uplift force
on the shingle (Figure 4). Future experiments
by Dr. Peterka’s group would attempt
to validate this model (Peterka et al., 1983).
Following the initial shingle uplift experiments,
Peterka et al. (1983) experimentally
investigated the proposed wind uplift model
as well as shingle permeability and the distribution
of wind-induced uplift pressures
on asphalt shingles. Relatively air-impermeable
roofing materials such as membranes
are susceptible to uplift pressures
developed by the separation of wind flow
over the building. The pressure in this separated
re gion is lower than the internal
pressure of the
building, producing
wind uplift pressure
distributions
and magnitudes
found in building
standards such as
ASCE-7 for impermeable
systems. A
permeable roofing
system will allow
for partial equalization
of pressure between the upper and
lower surfaces of the system. If the permeability
is high enough, the loads developed
within the separation region will be of a
small magnitude due to rapid venting of
pressure through the system surface.
To examine the permeability of shingles,
a box was sealed to an asphalt shingle deck
with a vacuum attached to rapidly reduce
the pressure within the sealed volume. Two
different tests were conducted: one with
shingles installed in accordance with installation
and the other with all shingle tab and
deck joints sealed with silicone.
Pressure measurements above and
below the asphalt shingle revealed that
asphalt shingles rapidly vent air between
their upper and lower surface. The results
suggested that, given a high permeability in
asphalt shingles, a significant uplift load
will not be generated by the larger-scale
flow separation region. Rather, the proposed
mechanism of localized flow separation
at the shingle tab leading edge may be
the genesis of asphalt shingle uplift.
Pressure measurements taken simultaneously
above and below shingles during
wind testing showed that wind flow near the
roof surface was correlated to uplift pressure,
further validating the new uplift
model. Expected uplift pressures for
asphalt shingles subjected to 80-mph wind
testing varied from 1 to 3 psf, significantly
lower than pressures found on impermeable
roofing systems.
The results of these two studies (Peterka
and Cermak, 1983; Peterka et al., 1983)
provided three major conclusions about
asphalt shingle wind loading:
1. For wind flowing up the roof slope,
localized flow separation at the leading
edge of the shingle tab may be
the largest contributor to asphalt
shingle wind uplift. Asphalt shingles
are a relatively air-permeable
assembly and may not be significantly
affected by the larger-scale
flow separation bubble.
2. Near-roof-surface wind speed may
be used as a prediction for asphalt
shingle uplift pressures.
3. Near-freezing temperatures may
increase the brittleness of fiberglassreinforced
asphalt shingles, which
in turn may increase the vulnerability
of the wind-related damage.
Seeking to develop a more refined predictive
method for asphalt shingle wind
resistance than the current UL 997/ASTM
D3161 test standards, the Asphalt Roofing
Manufacturers Association (ARMA) formed
the High Wind Task Force in 1990. The goal
of the task force was to determine the relationship
between wind speeds and asphalt
shingle tab uplift resistance (Shaw, 1991). A
two-phase program was developed: 1) create
a standardized test method that would
determine the uplift resistance of a shingle
tab’s self-seal adhesive strip (described in
the next section), and 2) define the physics
of shingle wind uplift and resulting loads on
the tab’s adhesive strip (described below).
Dr. Peterka and his colleagues were contracted
to perform the wind-tunnel and outdoor
studies that validated the asphaltshingle-
load model previously developed
(Peterka and Cermak et al., 1983; Peterka et
al., 1983). He proposed the asphalt shingle
uplift equation. See Equation 1.
With this equation, the peak uplift pressure
exerted on a shingle can be predicted
8 • IN T E R FA C E MAY / J U N E 2012
Figure 4
Equation 1 (Peterka et al., (1997)
Where: DP = peak uplift pressure that the shingle must resist
ρ = density of air
Uref = mean approach wind velocity at the eave height of the building
Uroof = peak gust wind speed on the roof
DCp = uplift differential pressure coefficient, unique for each shingle design
( Uroof )
Uref
2
U 2 ref
1
2
DP = ρ DCp ˆ
ˆ
ˆ
¯
¯ ¯
¯
ˆ
by knowing the approach flow characteristics,
the near-roof-surface wind flow characteristics,
and the uplift pressure coefficient
that will be unique to each shingle
design. Building standards such as ASCE 7
represent uplift loads as pressure coefficients,
a dimensionless number that
defines the relative pressure for a given flow
field independent of the flow velocity. For
asphalt shingles, a differential pressure
coefficient is used to describe the net uplift
pressure on asphalt shingles. The wind
experiments conducted in the early 1990s
by Peterka et al. (1997) investigated parameters
of the components in this uplift
equation by three methods:
1. Magnitude and distribution of nearroof-
surface wind flow on modelscale
residential buildings in a
boundary-layer wind tunnel.
2. Correlation between near-surface
roof flow and uplift pressures generated
on a full-scale asphalt shingle
test deck in a boundary-layer wind
tunnel.
3. Evaluation of uplift pressures and
near-roof-surface wind flow generated
on a full-scale residential building
located outdoors and subjected
to natural wind.
For component one, three 1:25-scale Tshape
model buildings were constructed
(Figure 5A) with roof slopes of 2:12, 5:12,
and 9:12. Also tested was a 1:25-scale
model gable-roofed building that matched a
full-scale building constructed for validation
of the model-scale data (Figure 5B). Each
building was placed inside the boundarylayer
wind tunnel at CSU and subjected to a
wind flow corresponding to open country
exposure (i.e., ASCE 7, Exposure C).
Because the flow near the roof surface was
of greatest interest for asphalt shingle wind
loading, flow measurements were taken over
each building’s roof surfaces at a height of
0.04 in. (1 in. at full scale) above the roof
surface. The ratio between the peak
observed near-roof-surface wind speed and
the mean wind speed of the upwind air flow
is needed for Equation 1. An upper-bound
ratio of 2.5 was observed in the scaled model
wind-tunnel tests. The highest observed
near-roof-surface wind speeds for all four
buildings were located near the intersection
of the roof ridge and gable end (Cochran et
al., 1999).
The design of the leading edge of the
asphalt shingle plays an important role in
the aerodynamics of asphalt shingle uplift.
These design factors may include the location
of the self-seal adhesive, the installed
pattern (or distribution) of the self-seal
adhesive (i.e., a discontinuous pattern may
allow airflow behind the seal, increasing the
pressure on the underside and thereby
increasing the net uplift on the shingle),
and the profile of the leading edge of the
shingle tab (i.e., thick butt, sharp edge,
etc.). The second component of the Peterka
et al. (1997) investigation utilized the same
elevated 4- by 3-ft. asphalt shingle test deck
developed during the 1983 experiments
(Peterka and Cermak, 1983). The deck was
subjected to a boundary layer flow in the
CSU wind tunnel with two different turbulence
intensity levels of 4% and 17%. The
CSU wind tunnel was unable to replicate
full-scale turbulence intensities found in
natural wind; therefore, it was necessary to
determine the effect of the magnitude of
turbulence intensity on the developed shingle
uplift pressure coefficients.
The shingle tab located in the middle of
each deck was instrumented with pressure
taps above and below the shingle surface,
and wind flow measurements were obtained
1 in. above the instrumented shingle using
either a hot-film anemometer or a pitotstatic
probe. Mean pressure coefficients
captured during this test showed that the
uplift force is higher in front of the tab
sealant compared to behind (up-slope of)
the tab sealant (Table 1). This likely occurs
for three reasons: 1) a separated flow region
is generated above the leading edge of the
shingle with reattachment occurring a few
inches upwind, 2) the tab seal
reduces/prevents the positive pressure
behind the tab sealant (depending on the
sealant design), and 3) tab cutouts assist in
MAY / J U N E 2012 I N T E R FA C E • 9
Figure 5A
Figure 5B
Table 1 – Wind-tunnel-measured DCp three-tab shingle with cutouts (Peterka et al., 1997).
SHINGLE PART SHINGLE THICKNESS
SINGLE, ~0.11 IN. DOUBLE, ~0.22 IN.
Seal strip to front edge -0.4 -0.8
Top of cutout to seal strip -0.1 -0.1
Top of cutout to front edge for unsealed shingle -0.4 -0.8
pressure equalization behind the seal strip.
Therefore, the location of the tab sealant
will play a large role in the loading mechanism
generated on the tab adhesive.
Differences also exist in pressure coefficients
between the three-tab and doublethickness
shingles (Table 1). To investigate
the role of near-surface wind flow on uplift
pressures, the middle shingle tab from a
test deck was replaced with a thin, rectangular
piece of brass that would mimic a
shingle tab—both in dimension and location
on the deck—with a seal located where
one would be on an asphalt shingle. Fiftyfour
pressure taps were installed on the
brass shingle (half on the top surface, half
on the bottom surface), as this would allow
for larger area averages to be determined.
The deck was placed on the floor, oriented
such that the generated wind flow would
travel up the 4:12 sloped test deck with a
smooth, curved transition between the
wind-tunnel floor and the test deck. As with
the previous pressure measurements, nearsurface
roof flow at 1 in. above the brass
shingle was captured. From these data, it
was observed that asphalt shingle uplift
pressures correlate with near-roof-surface
flow in flow fluctuations up to 12 Hz for a
wind flow of 22.5 mph.
The final component of the Peterka et al.
(1997) investigation was the validation of
wind tunnel test data using a full-scale,
gable-roofed building constructed outside
in a windy location near Fort Collins, CO.
The house consisted of a 23- by 34.5-ft.
one-story building with a 5:12 gable roof.
Three-tab fiberglass-reinforced asphalt
shingles were installed on the roof with
pressure taps installed above and below the
shingles at several locations on the roof. To
capture simultaneous velocity and pressure
data, unidirectional velocity sensors were
installed above the tapped shingles and oriented
down the roof slope. The house could
be rotated 360 degrees to provide uplift/
velocity data for all wind azimuths. To capture
the approach flow conditions, a 197-ft.
instrumented meteorological tower was
located near the house, and a 33-ft. meteorological
tower was installed upwind of the
house. Data from the observation towers,
shingle-pressure transducers, and roof surface
velocity sensors were captured during
strong windstorms with peak wind gusts
ranging from 30 to 60-plus mph. Several
observations were made from the comparison
of the full-scale outdoor tests and the
wind tunnel experiments:
1. The full-scale data appeared to validate
the wind tunnel data, and the
highest pressures observed were
within the prediction of the uplift
model.
2. For wind flow up the roof slope,
asphalt shingle uplift pressures correlated
well with near-surface roof
flow.
3. The highest observed shingle uplift
pressures corresponded to a 50-
degree wind azimuth relative to the
ridgeline of the building (Figure 6).
Due to the unidirectional nature of
the velocity sensors, only the up –
slope component of the wind velocity
vector could be obtained for this
azimuth.
4. Significant shingle uplift pressures
were observed for wind flow ap –
proaching the leeward side of the roof
(with respect to the instrumented
shingles). While the wind uplift
model only describes wind flow up
the roof slope, it may correctly model
the local flow at other wind azimuths.
Following Peterka et al.’s (1997) tests,
ARMA and UL drafted a standard test
method to determine
the loads
generated on a
shingle’s tab
seal. UL 2390,
Test Methods for
Wind-Resistant
Asphalt Shingles
With Sealed Tabs
(2003), was published
in May
2003. The identical
ASTM D7381,
Wind Resistance
of Asphalt Shin –
gles (Uplift Force/Uplift Resistance Method)
(2008d) was published in 2005. These standards
are based on a standards development
report (Peterka and Esterday, 2000)
that is not publicly available, since the provisions
are published in the standard.
These methods can be separated into three
parts:
1. Determine uplift rigidity of the
shingle through mechanical uplift
testing. Shingles will lift in the wind,
and the magnitude of this lift will
depend on the stiffness of the shingles.
The aerodynamics of asphalt
shingles change as the shingle lifts;
therefore, the resulting pressures
exerted on the shingle can change.
The stiffer the shingle, the lower the
resulting loads. A conservatively low
stiffness (EI) of 2.5 lbs-in2 may be
used as a default. This shingle stiffness
value is used for Part 2 to determine
pressure coefficients.
2. Determine the wind uplift pressure
coefficients on the asphalt
shingle. Shingles are installed on a
4- by 3-ft. test deck with one shingle
tab in the middle of the deck containing
four pressure taps above and
four taps below the shingle. Similar
to ASTM D3161, these decks are
conditioned and placed in front of a
fan system. However, fan speeds are
limited to 35 mph, and a small
amount of turbulence is introduced
into air flow. Mean uplift pressures
are captured for shingles lying flat
on the deck surface and for shingles
that have their edges raised with
shims at the leading edge to simulate
shingle uplift during strong
wind events. The pressure coefficients
are used in combination with
the Peterka wind uplift equation to
determine the uplift loading of
asphalt shingles at various peak 3-
second gust wind speeds.
3. Determine the uplift resistance of
the asphalt shingle tab sealant
through mechanical uplift testing
(outlined in the next section).
Results of this test are compared to
the predicted uplift loads determined
in Part 2.
From ASTM D7158, asphalt shingles
are classified and labeled on their packaging
according to their predicted resistance
to peak 3-second gust (basic) wind speeds
10 • I N T E R FA C E MAY / J U N E 2012
Figure 6
at 33 ft. in Exposure C (open country), following
ASCE 7-05. Adjustment factors are
required for various environmental/
building factors such as buildings higher
than 60 ft. and if the user is using the ASCE
7-10 design standard. The shingle classification
is thus:
• Class D – Passed at basic wind
speeds up to and including 90 mph
• Class G – Passed at basic wind
speeds up to and including 120 mph
• Class H – Passed at basic wind
speeds up to and including 150 mph
Most United States residential building
codes refer to ASCE 7-05 as their wind load
standard; therefore, this classification system
provides a direct comparison between
shingle requirements and shingle performance.
A 2011 survey of asphalt shingle
products offered by seven major manufacturers
shows that 91% of their shingle products
have been wind-tested by ASTM
D7158, and all of those tested were classified
with Class H ratings (Inspections,
2011). The same survey noted that all products
listed have a Class F (110 mph) ASTM
D3161 classification as well.
ASTM D6381, STANDARD TEST METHOD FOR
MEASUREMENT OF ASPHALT SHINGLE TAB
MECHANICAL UPLIFT RESISTANCE
Prior to the initiation of the Peterka wind
load studies, the ARMA task force began
development of a test method that would
determine the uplift resistance of a shingle’s
tab sealant (Shaw, 1991). From the initial
Peterka et al. report (1983), it was evident
that the greatest uplift loads would occur
nearest the leading edge of the shingle. At
the time, shingles were typically produced
with ¾- to 1-in. distances between the leading
edge of the tab sealant and the leading
edge of the shingle tab (Hahn et al., 2004).
The resultant wind loading on this cantilever
span would produce a peel-type uplift force
on the tab sealant. The mechanical uplift
test was developed to simulate this loading
condition. The test specimen consisted of a
3.5-in.-wide by 7-in.-long asphalt shingle
lower piece with a 3.5-in.-wide by 4-in.-long
upper tab piece. The tab was installed over
the lower piece’s sealant such that the inservice
tab bond is replicated.
Prior to uplift testing, the bond between
the lower and upper shingles was conditioned
at 140ºF for 16 hours, the same as
the ASTM D3161/UL 997 conditioning procedure.
Mechanical uplift testing consisted
of the specimen attachment to a clamp
assembly along the 3.5-in. edges. The uplift
load was generated from a clamp affixed
along the leading edge of the shingle specimen.
This clamp was connected to a universal
testing machine, which provided a
constant velocity uplift of 5 in./min. and
simultaneous measurement of uplift load
on the shingle tab. Seven testing labs were
utilized for round-robin testing of this draft
standard to confirm repeatability of test
methods and results (Shaw, 1991). After
confirmation, the standard was published
in 1999 and designated as ASTM D6381,
Standard Test Method for Measurement of
Asphalt Shingle Mechanical Uplift Resist –
ance.
As described below, recent modifications
to the mechanical uplift test have been
made in response to changes in the tab
sealant design and market trends. Many
shingles now have tabs seals located closer
to the shingle tab’s leading edge. A decrease
in distance between the tab sealant and the
leading edge will reduce the total uplift
loading generated ahead of the sealant.
Therefore, this loading mechanism can
change from a peel-type to a direct tensiontype
loading (Hahn et al., 2004). The way an
adhesive is loaded (i.e., peeling, direct tension,
etc.) is known to have a significant
effect on its strength (Shiao et al., 2004).
Results of asphalt shingle tab sealant
mechanical uplift resistance tests comparing
peel, direct tension, and combined
showed that direct tension produced over
double the resistance of the D6381 peeltype
resistance (Shiao et al., 2004). The
combined test consisted of an attachment
that mimicked the Peterka wind load model,
with forces being generated on shingle specimens
ahead and behind the tab sealant.
The sealant strength for this loading fell
between the low peel strength and high
direct-tension strength, suggesting that the
actual loading of a tab seal is a combination
of peel and direct tension. As a result, the
2008 edition of the ASTM D6381 test
requires direct-tension testing be conducted
along with the original peel test. Depending
upon the magnitude of the pressure coefficients
obtained from ASTM D7158/UL 2390
testing, the results of each test may be used
separately or in combination to determine
total uplift resistance of a shingle’s tab seal
(Hahn et al., 2004).
Questions remain on the applicability of
this test method in predicting in-service
shingle wind resistance. Foremost among
them is the loading protocol, which specifies
a constant displacement velocity of 5
in./min. Near-roof-surface wind flow is turbulent
in nature; therefore, the uplift loading
from wind will also contain fluctuations
(Peterka et al., 1997). Shiao et al. (2004)
have shown that an increase in loading rate
correlates to a higher shingle-tab-seal resistance
(i.e., the current ASTM D6381 loading
rate produces conservative resistance
results). However, shingles are potentially
subjected to thousands of wind gusts
throughout their lifetimes, and the longterm
performance of shingle tab seal to
these fluctuations (i.e., fatigue resistance)
has not been quantified. Thus, with the current
ASTM D6381, it is difficult to predict
how the tab’s seal will respond to gusts later
in the shingle’s service life. See Table 2.
IN-SERVICE WIND PERFORMANCE
OF ASPHALT SHINGLES
Laboratory wind testing of asphalt shingles
provides a relatively simple method for
predicting in-service wind performance.
However, these methods cannot completely
replicate the conditions that shingles are
subjected to once they are installed. A key
component in understanding shingle wind
resistance is observations that are made following
shingle damage caused by wind
events. Since 1989, damage assessments
made by organizations and federal agencies
such as FEMA and RICOWI have provided
“ground truth” on asphalt shingle performance.
The observations made in these
reports provide an opportunity to evaluate
deficiencies in products, design, and installation.
An overview of selected damage
report observations is provided below.
Hurricane Hugo made landfall on the
east coast of South Carolina in 1989 as a
Category 4 hurricane on the Saffir-Simpson
scale. Damage observations of asphalt shingle
roofing by Smith and McDonald (1990)
noted highly variable wind uplift performance
of shingles, with some houses sustaining
no damage, while others nearby
sustained complete shingle loss. The damage
was primarily attributed to weak tab
seals. Improperly located fasteners were
also often observed at damaged roofs.
Failure of the roof covering did not just
impact the covering itself. Rather, in financial
terms, the resulting interior losses
caused by roofing failure were often greater
than loss from the roof covering. Smith concluded
that standardized wind testing of
roof coverings, including ASTM D3161 for
MAY / J U N E 2012 I N T E R FA C E • 1 1
12 • I N T E R FA C E MAY / J U N E 2012
asphalt shingles, appeared deficient in predicting
wind performance. This observation
would be repeated after Hurricane Andrew
made landfall in South Florida in 1992, also
causing damage to asphalt roofing systems
on houses (Smith, 1995).
Improperly located shingle fasteners
have often been observed at damaged shingles
(FEMA, 2005a; Smith, 1995; Smith and
McDonald, 1990). However, the extent to
which the installation affects the wind
resistance of the shingle has not yet been
quantified. Pull-through of the shingle over
the fasteners is often attributed to improper
fastener placement. Smith and Millen
(1999) note that it is “unrealistic to expect
fasteners to be located exactly in the specified
locations.” Furthermore, wind tunnel
tests on unsealed asphalt shingles with
misplaced fasteners showed a decrease in
wind performance, but no definitive conclusions
could be made regarding variations in
placement (Smith and Millen, 1999).
A common observation throughout poststorm
reports is the failure of roof details
such as hip, ridge, eave, and rake shingle
conditions (FEMA, 2005a; FEMA, 2005b;
FEMA, 2006; FEMA, 2009; IBHS, 2009).
These failures appear to be independent of
the age of the roof and more closely tied to
the design and installation of these edge conditions.
Bonding of the hip and ridge caps
appears to be an ongoing issue, and starter
courses along the eave are often improperly
installed. The implications of failures to
these areas of the roof range from a minor
exposure of the hip and ridge deck joints to
a more widespread failure propagating from
eave and rake-edge failures. While damage
reports continue to be a valuable source of
information, more work is necessary to
understand the role of installation variability
in asphalt shingle wind performance.
Throughout the 2000s, hurricanes
impacted the Southeast and U.S. Gulf
Coast, causing extensive shingle damage.
Shingle performance was variable (RICOWI,
2006). An Insurance Institute of Business &
Home Safety (IIBHS, 2009) study of shingle
damage in Hurricane Ike showed variable
performance amongst products with the
same ASTM D7158 Class H (150-mph) rating.
Wind speeds at the investigated site
were 110 mph (peak 3-second gust at 33 ft.,
Exposure C), below design level. Based on
their findings, IIBHS “suggests that there
remain significant differences between roof
cover products with the same nominal
design.”
Liu et al. (2010) conducted an asphalt
shingle damage survey in Texas after hurricanes
Ike and Gustav in 2008 and found
that homes with newer (less than five years
old) shingle installations performed significantly
better than older shingle roofs
(greater than five years old), although it was
not certain if age or changes to the building
code around 2002 were the cause. This performance
gap was also noted by RICOWI
(2006) after Hurricane Charley struck
Florida in 2004 and by Gurley and Masters
(2011) in a post-2004 hurricane season
building performance survey. All three
studies postulated that while product
improvement could be attributed to the better
performance of newer roofs, the effects
of aging could not be discounted. Exper i –
ments by Terrenzio et al. (1997) and Shiao
et al. (2003) have noted that the greatest
cause of asphalt shingle aging is thermal
loading. Over time, the asphalt within the
shingle becomes oxidized, causing embrittlement
of the shingle. Currently, no studies
have quantified the effects of aging on
asphalt shingle wind performance. Con sid –
ering that a shingle’s tab adhesive is based
upon an asphaltic formulation, what effects
would this potential oxidation reaction have
on the tab seal’s adhesive strength? The
current ASTM D7158/D6381 and UL 2390
standard test methods only provide information
on the performance of new, laboratoryprepared
asphalt shingles, making estimation
of the long-term performance of the tab
adhesive difficult.
LOOKING FORWARD
During the last century, asphalt shingles
have evolved partially in response to
developments in the understanding of
asphalt shingle wind resistance. Despite the
advancements made through research and
damage observations, questions still remain
with regard to asphalt shingle performance.
Topics include the following:
1. Effects of aging on asphalt shingle
wind resistance.
2. Effects of long-term wind gusts on
the fatigue resistance of asphalt
shingle tab self-seals.
3. Quantification of installation errors
Table 2 – Summary of standardized test methods to evaluate asphalt shingle wind
performance.
TEST METHOD YEAR FIRST TEST METHOD OVERVIEW
DESIGNATION PUBLISHED
UL 997 1960 Asphalt shingles are installed on a 3- by 4-ft. test deck,
cured for 16 hours at 140°F, and then subjected to two hours
of 60-mph winds. Failure is defined as a shingle tab that either
loses its tab adhesion or whose mechanical interlock fails.
ASTM D3161 1972 Essentially identical to UL 997 with the exception of the
maximum allowable wind speed. D3161 has three classification
designations: 1) Class A – passed 60 mph, 2) Class D –
passed 90 mph, 3) Class F – passed 110 mph. Note: These
wind speeds do not directly correlate to ASCE 7 wind speeds.
ASTM D6381 1999 Method to determine a shingle tab sealant’s uplift resistance.
Shingle specimens are subjected to a constant-rate peel and
direct tension testing of the sealant.
UL 2390 2003 Based on the Peterka wind-load model, this test method
determines a shingle’s wind uplift pressure coefficients. The
pressure coefficients can be used to predict the loads that
will be exerted on a shingle at various ASCE 7 wind speeds.
ASTM D7158 2005 Identical to UL 2390 in test procedure. References ASTM
D6381 to determine the uplift resistance of the shingle’s tab
sealant. Comparison between D7158 predicted uplift force
and D6381 measure resistance gives three wind speed
classifications: 1) Class D – up to 90 mph resistance,
2) Class G – up to 120 mph resistance, 3) Class H – up to
150 mph resistance. Note: These wind speeds correlate to
winds defined by ASCE 7-05 for noncritical facilities less than
60 ft. tall in Exposure C.
and their impact on asphalt shingle
wind resistance.
4. In-service performance of asphalt
shingle tab self-seals.
5. Comparative shingle performance
evaluation between ASTM D7158/UL
2390 tests and full-scale simulation
of hurricane wind loads.
6. The mechanics of near-roof-surface
wind flow.
Beginning in July 2010, the University
of Florida commenced a research program
to address the research topics outlined
above. This three-year program will build
upon the previous asphalt shingle wind
research with the goal of improving the
wind performance of shingles throughout
their life cycle. Outcomes of this research
will be presented in a future article.
ACKNOWLEDGEMENTS
This paper was written though the support
of the Southeast Region Research
Initiative (SERRI), which is managed by Oak
Ridge National Laboratory for the U.S.
Department of Homeland Securit; and the
Florida Building Commission. Any opinions,
findings, conclusions, or recommendations
expressed in this paper are those of the
authors and do not necessarily reflect the
views of the sponsors, partners, or contributors.
REFERENCES
H. Abraham, Asphalts and Allied
Substances, D. Van Nostrand
Company, 1920.
ASTM D3161 (2005), Standard Test
Method for Wind Resistance of
Asphalt Shingles (Fan-Induced
Method). ASTM International, West
Conshohocken, PA.
ASTM D7158 (2008d), Standard Test
Method for Wind Resistance of
Asphalt Shingles (Uplift Force/Uplift
Resistance Method). ASTM International,
West Conshohocken, PA.
I.A. Benjamin and J.A. Bono, “Wind-
Resistance Tests of Roof Shingles
and Roof Assemblies,” ASTM Special
Technical Publication 409, 1969.
P. Berdahl, H. Akbari, R. Levinson, and
W.A. Miller, “Weathering of Roofing
Materials – An Overview,” Construc –
tion and Building Materials, pp. 423-
433, 2008.
E.G. Blake, Roof Coverings: Their
Manufacture and Application, Van
Nostrand Co., 1925.
C. Cash, “Asphalt Roofing Shingles,”
11th Conference on Roofing Technol –
ogy, Gaithersburg, MD, 1995.
L. Cochran, J.A. Peterka, and R.
Derickson, “Roof Surface Wind
Speed Distributions on Low-Rise
Buildings,” Architectural Science
Review, 1999.
W. Cullen, “Wind Resistance of Asphalt
Shingle Roofing,” Fall Conferences of
the Building Research Institute,
National Academy of Sciences,
Washington, DC, pp. 33-42, 1960.
W. Cullen, “Research and Performance
Experience of Asphalt Shingles,”
10th Conference on Roofing Technol –
ogy, Gaithersburg, MD, pp. 6-12,
1993.
W. Cullen, “The Evolution of Asphalt
Shingles: Survival of the Fittest?”
Professional Roofing, National Roof –
ing Contractors Association, pp. R4-
R8, 1992.
FEMA (2005a), “Summary Report on
Building Performance: 2004 Hur –
ricane Season,” FEMA 490, Federal
Emergency Management Agency.
FEMA (2005b), “Hurricane Charley in
Florida,” FEMA 488, Federal Emer –
gency Management Agency.
FEMA (2006), “Summary Report on
Building Performance: Hurricane
Ka trina,” FEMA 548, Federal Emer –
gency Management Agency.
FEMA (2009), “Hurricane Ike in Texas
and Louisiana,” FEMA P-757, Fed er –
al Emergency Management Agency.
S.H. Greenfeld, “Performance of Roofing
Felts Made With Asplund Fibers,”
Na tional Bureau of Standards,
1969.
K.R. Gurley and F.J. Masters, “Post-
2004 Hurricane Field Survey of Res –
idential Building Performance,”
ASCE Natural Hazards Review, No –
vember 2011.
L.T. Hahn, D.J. Roodvoets, and K.D.
Rhodes, “New Shingle Wind Re sist –
ance Test Standards.” Interface,
RCI, Inc., August 2004.
Inspections, Texas, “Asphalt Shingle
Products That Conform to the 2008
International Residential Code (IRC)
and 2006 International Building
Code (IBC), as Modified With Texas
MAY / J U N E 2012 I N T E R FA C E • 1 3
Craig R. Dixon, EI, received his undergraduate degree in civil
engineering in the fall of 2008 from the University of Florida,
and in the fall of 2009 he joined Dr. David O. Prevatt’s wind
engineering research group at the University of Florida as a
research assistant. During his undergraduate work, Dixon
spent six summers interning for Gale Associates in Orlando,
FL, performing roof observation and roof assessment studies.
Dixon’s work as a research assistant includes investigations
on the wind resistance of wood roof sheathing, standingseam
metal roofing, and asphalt shingles.
Craig R. Dixon, EI
Dr. Forrest J. Masters, PhD, PE, is an assistant professor of
civil and coastal engineering at the University of Florida. His
research program focuses on improving the resistance of residential
and commercial buildings to extreme winds and rain.
Experiments are conducted in the laboratory with full-scale
simulators and in hurricanes to characterize the behavior of
surface wind and wind-driven rain. He has received support
from more than 20 grants from state, federal, and private
sources, including the NSF Faculty Early Career Development
(CAREER) Program. Dr. Masters is a reviewer for five journals
and a member of ASCE, RICOWI, and ASTM.
Dr. Forrest J. Masters, PhD, PE
Author biographies continued on page 14
Revisions,” Texas Department of
Insurance Windstorm Inspections,
2011.
IIBHS (2009). “Hurricane Ike: Nature’s
Forces vs. Structural Strength,”
Insurance Institute for Business &
Home Safety.
Z. Liu, H. Pogorzelski, F.M. Masters, S.
Tezak, and T.A. Reinhold, “Surviving
Nature’s Fury: Performance of As –
phalt Shingle Roofs in the Real
World,” Interface, RCI, Inc., Novem –
ber 2010.
T. Nichols, “A Stronger Bond,” Pro –
fessional Roofing, National Roofing
Contractors Association, 2010.
J.A. Peterka and J.E. Cermak, “Wind-
Tunnel Study of Wind Resistance of
Roofing Shingles,” Colorado State
University, Fort Collins, Colorado,
1983.
J.A. Peterka, J.E. Cermak, L.S. Coch –
ran, B.C. Cochran, N. Hosoya, R.G.
Derickson, J. Jones, B. Metz, “Wind
Uplift Model for Asphalt Shingles,”
Journal of Architectural Engineering,
pp. 147-155, 1997.
J.A. Peterka, J.E. Cermak, and N. Ho –
soya, “Wind-Tunnel Study of Wind
Pressures on Roofing Shingles,”
Colorado State University, Fort
Collins, CO, 1983.
J.A. Peterka and W.S. Esterday, “De vel –
op ment of a Shingle Uplift
Coefficient Test Standard,” Cermak
Peterka Petersen, Inc., 2000. (Not
publicly available.)
RICOWI, “Hurricanes Charley and Ivan
Investigation Report,” Roofing In –
dus try Committee on Weather
Issues, McDonough, GA, 2006.
D.E. Shaw, “ARMA’s New Approach for
Evaluation of Asphalt Shingle Wind
Resistance,” 1991 International Sym –
posium on Roofing Technology, Na –
tional Roofing Contractors Asso ci a –
tion, 1991.
M.L. Shiao, D.A. Nester, and L.A. Ter –
renzio, “On the Kinetics of Thermal
Loads for Accelerated Aging,” ASTM
Roofing Research and Standards
Development, 2003.
M.L. Shiao, R.A. Snyder, R.D. Livsey,
and H.M. Kalkanoglu, “Measuring
Uplift Resistance of Asphalt
Shingles,” ASTM Special Technical
Publication, pp. 3-18, 2004.
T.L. Smith, “Improving Wind Per for –
mance of Asphalt Shingles: Lessons
Learned From Hurricane Andrew.”
11th Conference on Roofing Tech –
nology, National Roofing Contrac –
tors Association, Gaithersburg, MD,
pp. 39-48, 1995.
T.L. Smith and J. McDonald, “Roof Wind
Damage Mitigation: Lessons From
Hugo,” National Roofing Contractors
Association, Professional Roofing,
1990.
T.L. Smith and M. Millen, “Influence of
Nail Locations on Wind Resistance
of Unsealed Asphalt Shingles,” North
American Conference on Roofing
Technology, 1999.
H.R. Snoke, “Asphalt-Prepared Roll
Roof ings and Shingles,” National
Bureau of Standards, 1941.
Strahan, J.L., Asphalt Roofing and
Accessories: A Discussion Covering
the Manufacture, Selection, and
Appli cation of Asphalt Roofing
Products, Asphalt Roofing Industry
Bureau, 1947.
L.A. Terrenzio, J.W. Harrison, D.A.
Nester and M.L. Shiao, “Natural vs.
Artificial Aging: Use of Diffusion
The ory to Model Asphalt and
Fiberglass-Reinforced Shingle Per –
for mance,” Fourth International Sym –
po sium on Roofing Technology,
NRCA, 1997.
UL 997 (1995), Wind Resistance for Pre –
pared Roof Covering Materials, Un –
der writers Laboratories.
UL 2390 (2003), Test Methods for Wind-
Resistant Asphalt Shingles With
Sealed Tabs, Underwriters Lab or a –
tories.
14 • I N T E R FA C E MAY / J U N E 2012
Dr. Kurtis R. Gurley is an associate professor at the University
of Florida. His primary areas of research are wind effects on
residential structures and stochastic modeling of extreme
winds and structural resistance. Dr. Gurley has largely
focused on in-field measurement and modeling of ground-level
hurricane winds and wind loads on occupied coastal residential
structures. This field data is coupled with post-storm residential
damage assessments, laboratory evaluations of component
capacities, and wind tunnel studies to model the vulnerability
of residential structures to hurricane wind damage. The research output from
Dr. Gurley and his colleagues contributes to a variety of hazard preparation and
response initiatives. Dr. Gurley is an associate editor for ASCE Journal of Structural
Engineering, a member of the Board of Directors for the Applied Technology Council, and
a member of the Technical Advisory Committee for the Federal Alliance for Safe Homes.
Dr. Kurtis R. Gurley
After earning his PhD from Clemson University in 1998, Dr.
David O. Prevatt, PE, worked with the Boston-based ENR500
consulting engineering firm Simpson Gumpertz & Heger, Inc.
in building envelope system design and remediation. He
joined the faculty of Clemson University in 2004 as an assistant
professor and directed the Wind Load Test Facility, conducting
wind tunnel tests on low-rise building models and
investigating of post-hurricane damage to residential buildings.
In May 2007, Dr. Prevatt joined the University of
Florida’s Department of Civil and Coastal Engineering, where his research focuses on
the mitigation of extreme wind damage to low-rise construction. Dr. Prevatt recently led
the damage assessment teams that documented damages caused by the 2011
Tuscaloosa, AL, and Joplin, MO, tornadoes. He was recently awarded an NSF Career
research grant to develop more tornado-resilient homes and communities. Dr. Prevatt
is a professional engineer (registered in Massachusetts and in Trinidad and Tobago). He
is a member of ASCE, the American Association for Wind Engineering, and the UK Wind
Engineering Society.
Dr. David O. Prevatt, PE