The Effect Of Reflective Roof Coatings On The Durability Of Roofing Systems

Editor’s Note: this paper was originally
presented at the RCI Foundation’s “Cool
Roofing…Cutting Through the Glare”
symposium in Atlanta, Georgia, on May 12,
2005.
BACKGROUND
In 1997, the Roof Coating Manufacturers
Association (RCMA) initiated a research
program in cooperation with Oak Ridge
National Laboratory (ORNL) to determine
the effect of reflective coatings on heat
transfer through a small-scale roofing system
over time, using both aluminum-pigmented,
asphalt-based coatings and white,
elastomeric roof coatings. The solar reflectance
and infrared emittance of these coatings
were monitored, along with resulting
roofing membrane temperatures. These
measured properties impact the energy consumption
used for heating and cooling, depending
on geographic location, as has been
clearly documented in Department of Energy,
Lawrence Berkeley Laboratory, and Oak
Ridge National Laboratory publications and
energy calculators.
The roofing membrane chosen by ORNL
and RCMA was a 4-ply, built-up roof
assembly consisting of a nailed glass fiber
base sheet, ASTM D-4601, Type II, and
three plies of ASTM D-2178, Type IV
asphalt glass felt adhered with ASTM D-
312, Type IV asphalt. The assemblies were
applied to the test deck as in a typical roofing
system. The base sheet was nailed to
the plywood, and then three plies of glass
felt were applied in shingle fashion to the
base sheet.
Each membrane was coated with the
reflective coatings mentioned above and
then weathered at ORNL for three years
with reflectance and emittance measurements
taken periodically. As originally conceived,
the primary purpose of this program
for the RCMA was to determine how well the
various types of coatings maintained reflective
properties over time. It was then decided,
after the program had begun, to determine
some simple properties of the roof
cores before and after three years of weathering
at ORNL. The objective was to determine
if there was an effect on the performance
of primarily the asphalt component
in the roof membrane, related to the
reflectance of the coatings. It had been postulated
that the aging rate of asphalt in a
roofing membrane is related to the temperature
history of the membrane.
It was evident from the results of this
study that the use of reflective coatings had
a measurable effect on the rate of change of
the properties measured. The differences in
asphalt original and aged properties
between the aluminum-coated BUR samples
were relatively small and clustered.
There was a significant and measurable difference
in the rate of change in asphalt
properties between the aluminum and
white-coated BUR samples and the uncoated
control. The white-coated membranes
resulted in a significantly lower rate of
change in asphalt properties as compared
to the aluminum-coated membranes. The
asphalt in the uncoated control exhibited
the greatest rate of change. The results of
the reflectance and emittance were previously
reported by ORNL (Wilkes et al., 2000;
Petrie et al., 2000) and the results of the
change in asphalt properties were reported
by RCMA (Mellot and Portfolio, 2003).
RCMA STUDY DESCRIPTION AND OBJECTIVES
RCMA began a second study in 2003 to
determine the change in reflective properties
of coatings over time at three different
locations in the U.S. The study also noted
changes in properties of roofing membranes,
including BUR, modified bituminous
SBS and APP membranes, and EPDM
related to the changes in reflectance of the
coatings. A second objective of the study
was to determine if there was any relationship
between accelerated aging using the
Xenon Arc accelerated weathering tester
(ASTM D-4798, Cycle A), as well as the
Fluorescent UV-condensation accelerated
weathering tester (ASTM D-4799, Cycle A).
The following roofing systems were constructed
in triplicate for aging studies to be
conducted in Akron, Ohio; Phoenix,
Arizona; and Tampa, Florida:
J U LY 2006 I N T E R FA C E • 1 5
Membrane Type: BUR
Deck: Plywood
Insulation: 2-in. isocyanurate/1/2-
in. fiberboard (mechanically
attached)
Ply: G2 base (hot mopped in
Type IV asphalt, 25
lb./100 ft2)
2 – G1 felts (hot mopped
in Type IV asphalt,
25 lb./100 ft2)
Surface
membrane: Type IV asphalt glaze
coat (15 lb./100 ft2)
Membrane Type: SBS
Deck: Plywood
Insulation: 2-in. isocyanurate/1/2-
in. fiberboard (mechanically
attached)
Ply: G2 base (hot mopped in
Type IV asphalt, 25
lb./100 ft2)
Surface
membrane: Granule SBS membrane
(hot mopped in Type IV
asphalt)
Membrane Type: APP
Deck: Plywood
Insulation: 2-in. isocyanurate/1/2-
in. fiberboard (mechanically
attached)
Ply: G2 base (hot mopped in
Type IV asphalt, 25
lb./100 ft2)
Surface
membrane: Smooth APP membrane
(torched)
Membrane Type: EPDM
Deck: Plywood
Insulation: 2-in. isocyanurate/1/2-
in. fiberboard (mechanically
attached)
Surface
membrane: Black unreinforced
EPDM (fully adhered with
adhesive)
Along with the large decks, one smaller
deck of identical construction was built to
determine the initial physical properties of
each of the membranes and relevant materials
to be characterized.
The systems were constructed for subsequent
destructive testing. Ply sheets were
applied in one-over-one fashion so that the
removal of cores for testing (to be made
throughout the aging cycle) would result in
an equivalent number of plies at each sampling.
Each of the decks was divided into
equivalent areas and the following coatings
applied to each of the membranes:
1. Asphalt/solvent-based aluminum
pigmented roof coating
a. High-softening-point asphalt
(ASTM D-2824)
b. Low-softening-point asphalt
(ASTM D-2824)
2. Asphalt/water-based, aluminum,
pigmented roof coating (ASTM D-
6848)
3. White water-based elastomeric roof
coating (ASTM D-6083)
16 • I N T E R FA C E J U LY 2006
a. Acrylic
b. Styrene-acrylic
4. White styrene-ethylene-butylenestyrene
elastomeric solvent-based
roof coating (no ASTM specification)
5. Asphalt emulsion (ASTM D-1227)
Several samples of each coating type
were obtained from different manufacturers,
and then one of the coatings was blindly
chosen to be used in the study. The coatings
were applied in a fashion and at the
application rate suggested by the manufacturer.
The decks were shipped to each of the
weathering locations in the summer of 2003
and were put out for exposure, at 1/2-inch
slope facing south, within a couple of
months of each other at the three locations.
In most cases, it was necessary to recoat
the samples due to minor scuffing that
occurred during shipment.
PRELIMINARY PHYSICAL PROPERTY DATA
To date, original and limited first-phase
properties have been determined for the
exposure decks, as well as from accelerated
aging studies.
Original Physical Property Data
The objective of this part of the project is
to establish the base-line physical properties
of the roofing systems. These properties
will be used to determine the effect of the
coatings on the rate of change of the baseline
properties as related to time, weather,
and the reflectance of the coatings used in
the study. Throughout the exposure
process, the reflectance of the field decks
will be determined to monitor the changes
in reflectance of the coatings. It is expected
that the reflectance will change for any
number of reasons throughout the exposure
process. It is suspected that dirt pickup
will be a major contributor. To relate to
real-world conditions, the coatings will not
be cleaned throughout the aging process.
However, when cores are periodically
removed for destructive analysis, the
reflectance will be determined before and
after cleaning to establish data relating to
cleaned and uncleaned surfaces.
As described above, for each roofing system,
a small-scale deck was constructed to
be used to establish initial data. The small
decks were used, realizing that the physical
property analysis was destructive in nature.
The roofing systems were analyzed for a
variety of physical performance properties
to established base-line properties. The procedures
for the bitumen-based systems –
APP, SBS, and BUR – were as follows:
• Softening point: ASTM D-36
• Penetration at 77˚F: ASTM D-5
• Tensile strength and elongation at
73˚F: ASTM D-2523
• Chemical composition using Iatroscan
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• Rheological properties using Dynamic
Shear Rheometer (DSR)
The samples were cut from the small
deck and the BUR and modified bituminous
samples were chilled to approximately 40ºF
and split apart. The bituminous portions
were then removed from the samples using
a heated spatula.
For each property, ASTM procedures,
where applicable, were followed. The results
for each of the systems are listed in Table 1.
To determine the initial EPDM properties,
the small deck was used, as in the case
of the asphalt-based systems. The physical
property testing on the EPDM system was
different. The procedures used to determine
each of the properties were as follows:
• Thickness by ASTM D-412
• Tensile strength and elongation at
73°F by ASTM D-412
• Tear strength at 73°F by ASTM D-
624
The results are listed in Table 2.
Accelerated Weathering
The accelerated weathering part of the
project involved 2,000 hours of exposure for
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Table 2: EPDM initial physical properties.
Table 1: Bituminous materials and membrane initial physical properties.
PROPERTY RESULTS
Membrane Identification APP SBS BUR
Softening point, °F 306 249 231
Penetration, dmm 16 22 10
Tensile strength, peak load, MD, lbf. 123 123 271
Elongation at peak load, MD, % 51 34 3.2
Iatroscan composition
Saturates, % 16.2 13.9 TBD
Aromatics, % 39.7 24.2 TBD
Resins, % 36.5 52.7 TBD
Asphaltenes, % 7.6 9.2 TBD
DSR TBD TBD TBD
TBD – To be determined
PROPERTY RESULTS
Membrane Identification EPDM
Thickness, in. 0.435
Tensile Strength, psi 1389
Ultimate Elongation, % 893
Tear Resistance, lbf. 10
samples of each of the coatings on aluminum
panels in two different types of
weatherometers:
1. Xenon-arc type: ASTM D-4798:
Cycle A: 51 minutes light, 9 minutes
light and water spray.
2. Fluorescent UV condensation type
(QUV): ASTM D-4799: Cycle A: 4
hours UV light at 60°C alternating
with 4 hours condensation at 50°C.
The effect of accelerated weathering
time on the reflectance of the coating on
aluminum panels was measured. These
changes in reflectance versus exposure time
will be used to determine if there is a correlation
between accelerated and natural
weathering.
Comparison of Accelerated Weathering
to Real-time Weathering:
To date, reflectance data have been collected
on initial and short-term exposed (9
to 10 months and 12 or 16 months in some
cases) for all of the systems at two of the
three locations: Florida and Northeast Ohio.
The Arizona data will be collected when
cores are extracted for analysis in the
future. Each figure represents a different
coating. The reflectance data are compiled
to include the following conditions of exposure:
1. Florida exposed
2. Northeast Ohio exposed
3. Fluorescent UV-condensation (QUV)
weatherometer: Laboratories 1 and 2.
4. Xenon-Arc: Laboratories 1 and 2.
Each figure compares the original
reflectance versus periodic reflectance measurements
taken throughout the exposure
of the decks. These results are the colored
bars on each of the graphs. The figures also
show results of reflectance values taken
from in-laboratory accelerated weathering
samples. These samples were applied at
manufacturers’ suggested thicknesses,
without primer, to standard aluminum
exposure panels. Note that in all cases, the
in-laboratory original reflectance results
were greater than the applied samples. We
will continue to investigate this observation
and how it relates to the field exposure
samples.
PRELIMINARY REFLECTANCE RESULTS
The systems are only a short period into
their long-term aging cycle, and it is difficult
to draw any conclusions from the data
compiled thus far. Although trends may
change, there are some obvious tendencies
in the initial solar reflectance data. It can be
seen that the substrate that is coated has
an observable and measurable effect on the
initial and aged reflectance of the coating.
The reflectance result can be as much as a
ten percent difference for some of the coat-
J U LY 2006 I N T E R FA C E • 1 9
ing types.
It is also evident, in many cases, that
the measured reflectance on the laboratory-
prepared samples is higher than the
measured reflectance recorded for the
larger-scale deck systems. This has been
an assumption, but the initial data supports
this hypothesis. This difference may
be confounded by the fact that the field
samples are not being cleaned prior to performing
the reflectance measurements.
However, the study will attempt to address
these phenomena by analyzing the periodically
removed system cores for reflectance
before and after cleaning. This data may
shed some light on the need for field versus
in-laboratory aging data on coatings.
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of the various coatings and substrates as a
result of accelerated weather testing using
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the two different devices is also evident. It
can be seen that the two methods generally
result in different changes in reflectance values
after 2,000 hours of exposure. It will be
interesting to see if the change in reflectance
as a result of accelerated weathering shows
any correlation to natural weathering on any
of the substrates. As was already indicated,
the short-term change in reflectance measured
in the natural weathering studies
appears to be substrate-specific. The accelerated
weathering samples were applied to
aluminum panels.
No observations can be made concerning
the physical performance of the systems
to date. Only original properties have been
captured and, once aged samples are analyzed,
the data can begin to be compiled and
analyzed.
PLAN FOR THE CONTINUATION OF THE STUDY
The roof systems will continue to be
exposed until three years have elapsed. At
the three-year point, one-foot square cores
will be removed from each of the coating
and membrane types, as well as controls
from each of the systems. The physical
properties of these samples will be determined
and compared to the original data
collected from the small decks. The systems
will also be assessed and the plan for subsequent
sample core collection will be
determined. Based on the design of the
decks, one-foot square cores can be
removed up to four times, including the
three-year sampling.
Throughout the exposure, reflectance
data will be periodically determined – typically
every six months. The data will continue
to be compiled in an effort to determine
if there is a correlation between field
exposure and accelerated weathering. As
mentioned above, as each deck is sampled
by removing a core, the reflectance will be
determined for both cleaned and uncleaned
coatings in an effort to validate the effect of
cleaning on enhancing coating performance.
The industry will be updated as additional
data become available.
ACKNOWLEDGEMENTS
Thanks to SR Products, Inc., Cleveland,
Ohio for materials and construction of the
exposure decks; Momentum Technologies
for assistance with the construction of the
decks, selection of samples to be used for
study, preparation of the weatherometer
panels’ exposure, membrane testing, exposure
of decks, and reflectance measurements;
Tamko Roofing Products with assistance
in coating the decks; PRI Asphalt
Technologies for exposure of decks, membrane
and asphalt testing, and reflectance
measurements; and Henry Company for
exposure of decks and weatherometer exposure.
REFERENCES
Mellot II, Joseph. W. and Donald C.
Portfolio. “The Effect of Reflective
Roof Coatings on the Durability of
Roofing Systems.” Roofing Research
and Standard Development Volume,
STP 1451. 2003.
Petrie, T.W., A.O. Dejarlais, R.H. Robertson,
and D.S. Parker. “Comparison
of Techniques for in-situ, Non-
Damaging Measurements of Solar
Reflectance of Low-slope Roof
Membranes,” International Journal
of Thermophysics. 2000.
Wilkes, K.E., T.W. Petrie, J.A. Atchley,
and P.W. Childes. “Roof Heating and
Cooling Loads in Various Climates
for the Range of Solar Reflectances
and Infrared Emittances Observed
for Weathered Coatings,” Proceedings
2000 ACEEE Summer Study on
Energy Efficiency in Buildings:
Efficiency and Sustainability, American
Council for an Energy-efficient
Economy, Washington D.C. 2000.
J U LY 2006 I N T E R FA C E • 2 1
Donald C. Portfolio received a bachelor of science degree in
chemistry from the University of Massachusetts and a master
of science degree in organic chemistry from the University of
South Florida. He has been involved in the roofing industry
for more than 35 years in capacities ranging from product
development to fundamental polymer research. He has had
product development responsibility for materials, including
asphalt shingles, conventional BUR, modified bituminous
membranes, polyisocyanurate and glass fiber, insulations,
and conventional and polymer-modified asphalt cements, coatings, and adhesives. He
served as technical chair of the Roof Coatings Manufacturers Association from 1996 –
2000 and was a faculty member of the Roofing Industry Educational Institute for many
years. He has published numerous papers in the area of roofing technology. Portfolio is
currently vice president of PRI Asphalt Technologies, Tampa, Florida.
Donald C. Portfolio
Joseph W. Mellott II has a bachelor’s degree in macromolecular
engineering from Case Western Reserve University. He has
served the roofing industry for the past 15 years in a variety
of capacities, including product formulation, material testing,
failure forensics, and raw material development. He specializes
in the area of development and testing of polymeric modified
bitumen systems, adhesives, sealants, and coatings. He
most recently served as technical chair of the Roof Coatings
Manufacturers Association from 2000 – 2004. He has written
several published papers in the area of roof system testing and coatings science and
technology. Mellot is currently vice president of technology for Momentum Technologies,
Uniontown, Ohio.
Joseph W. Mellott II
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in 2006 stated up to 40% of the average roofing contractor’s workforce was Hispanic.
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Roofing and Undocumented Immigrants