Here is an article I wrote that was published in the June 2010 edition of Professional Roofing magazine.

1. A
fter 18 years of exposure to extreme desert heat, The new roof system was installed by Starkweather
the roof system on the Nationwide® Scottsdale Roofing Inc., Phoenix, in December 2008 and consists
Insurance Co. headquarters building in Scotts- of 3 inches of polyisocyanurate board insulation set in
dale, Ariz., began to deteriorate. The maintenance staff roof adhesive over the concrete roof deck and a self-
had been chasing leaks for nearly five years when Nation- adhering base sheet and self-adhering white laminated
wide Scottsdale Insurance decided to hire Alan Stevens polymer-modified bitumen roof membrane over the
Associates Inc., Cedar Rapids, Iowa, to solve the prob- top. The membrane’s surface is a reflective white film
lem and replace the roof system. laminate with a solar reflectance index (SRI) value of
The building’s original roof system was a ballasted 84.
EPDM membrane over 4 inches of polyisocyanurate In July 2009, the Arizona Cool Roof Council asked
insulation on a concrete roof deck blanketed with a Starkweather Roofing to conduct a case study to deter-
2-inch-thick layer of river rock. The roof system was mine whether white roofs truly are cooler and more
becoming a liability with regard to structural integrity energy-efficient than nonwhite roofs. The Nationwide
(from water damage), maintenance costs and energy Scottsdale Insurance building’s roof was an ideal choice
consumption. for the in-depth study.
40 June 2010 www.professionalroofing.net

2. by Chris Walker
A cool roof case study investigates white roofs’ energy ef ciency

3. on the same building where many vari-
ables could affect the results. The two
buildings are almost identical in height
and construction.
Photos courtesy of Starkweather Roofing Inc., Phoenix.
The temperature sensors on the roof sur-
faces were secured under the new materials
used in each of the current roof systems to
prevent direct sunlight from affecting the
readings and provide an accurate surface
temperature for each building. The tem-
perature sensors placed in the stairwells
were secured 3 feet from the roof hatches
and directly to the underside of the concrete
roof decks to measure the roof systems’ en-
ergy efficiencies; in other words, they meas-
ured how much heat was being transferred
through the concrete deck into the build-
ings’ interiors.
The sensors measured the roof surface
(the top of the membrane) and stairwell
temperatures for both buildings once per
hour, 24 hours per day from Aug. 6, 2009,
to Sept. 4, 2009. Official temperature data
for Scottsdale during the same time period
and at the same time intervals also were
obtained. During the data collection
period, Scottsdale primarily had hot,
sunny days—with a few monsoon storms
sprinkled in—allowing for excellent test
conditions.
The study’s conditions were near-
perfect for various reasons. First, we had
virtually identical buildings that are side
by side. Second, the Wells Fargo Financial
The Nationwide Scottsdale Insurance building before (top) and after (bottom) Starkweather Roofing Services building had an old roof system
installed the cool roof system and the Nationwide Scottsdale Insurance
building had a new roof system—we
could do a before-and-after analysis at the
Energy efficiency Financial Services building in the same same time and under the same conditions.
corporate plaza (which still has its original Finally, concrete decks are not typical in
On the morning of Aug. 6, 2009, Sherm ballasted EPDM roof system in place, in- Arizona (plywood decks are more com-
Robison, lead estimator for Starkweather cluding the same amount of insulation mon), so if the data proved any signifi-
Roofing, and I installed HOBO® tempera- that was on the Nationwide Scottsdale In- cant increase in energy efficiency in a
ture data loggers from Onset Computer surance building’s original roof system). building of this construction (with a con-
Corp., Bourne, Mass., directly onto the Obtaining rooftop and interior temper- crete deck), we would know even better
roof surfaces and in the low-traffic, non- ature data from two different buildings results could be gained in a building that
air-conditioned and nonvented stairwells was beneficial because the results would has a plywood deck because heat transfers
of the Nationwide Scottsdale Insurance be based on identical weather conditions through plywood at a faster, more intense
building and the neighboring Wells Fargo instead of data from one year to the next rate than it does through concrete.
42 June 2010 www.professionalroofing.net

4. Internal temperatures versus external temperatures
105.00
Degrees Fahrenheit 100.00
95.00
90.00
85.00
80.00
75.00
12:02 10:02 11:02 12:02 10:02 11:02
1:02 AM 2:02 AM 3:02 AM 4:02 AM 5:02 AM 6:02 AM 7:02 AM 8:02 AM 9:02 AM 1:02 PM 2:02 PM 3:02 PM 4:02 PM 5:02 PM 6:02 PM 7:02 PM 8:02 PM 9:02 PM
AM AM AM PM PM PM
Avg Outside Temp 88.28 86.78 85.45 84.61 82.61 81.65 81.03 81.73 84.85 88.77 91.71 94.15 96.66 98.67 100.44 101.46 102.21 102.17 101.19 99.55 96.13 93.98 91.99 90.04
Avg PolyKool Stairwell Temp 84.24 84.11 84.01 83.93 83.79 83.72 83.67 83.68 84.01 84.15 84.28 84.50 84.69 84.92 84.98 85.06 85.13 85.61 85.47 85.40 85.09 84.69 84.44 84.33
Avg EPDM Stairwell Temp 85.81 85.60 85.29 84.97 84.94 84.86 85.22 85.60 86.61 88.14 89.66 90.51 91.60 92.23 92.78 92.94 92.96 92.88 92.13 89.97 87.44 86.92 86.44 86.05
Time
Figure 1: Average internal stairwell temperatures versus average external temperatures
Analysis and conclusions while the Nationwide Scottsdale Insurance average range of only 2 degrees in internal
building remains virtually unchanged. Fig- temperature from the hottest to the coolest
The first thing that caught our attention
ure 2 shows between 5 p.m. and 8 p.m., parts of the day inside the Nationwide
when observing the study’s results was the
the Wells Fargo Financial Services build- Scottsdale Insurance building. Conversely,
significant reduction of internal thermal
ing cools down faster than it heated up the Wells Fargo Financial Services building
variation, which is caused directly by the
and the Nationwide Scottsdale Insurance typically has an 8-degree range of internal
cool roof system’s consistent temperature
building’s internal temperature again re- temperature during a 24-hour period. For
range.
mains constant. buildings as large as these two, a nearly
In Figure 1, notice that between 10
p.m. and 6 a.m., the buildings have simi- Figure 1 also demonstrates how internal 8-degree range means a lot in terms of the
lar internal temperatures but the Wells temperatures change as a result of outside additional energy required to maintain a
Fargo Financial Services building always temperatures. Notice how the Nationwide consistent temperature for the buildings’
is hotter than the Nationwide Scottsdale Scottsdale Insurance building’s tempera- tenants.
Insurance building during the day. At 8 ture holds steady all day while the Wells During August 2008, the Nationwide
a.m., the Wells Fargo Financial Services Fargo Financial Services building’s tem- Scottsdale Insurance building consumed
building begins to heat up dramatically perature fluctuates rapidly. There is an 719,000 kilowatts (kW) of electricity.
Comparison of internal temperature change
2.00
Temperature change
1.50
1.00
0.50
-
(0.50)
(1.00)
(1.50)
(2.00)
(2.50)
(3.00)
12:02 10:02 11:02 12:02 10:02 11:02
1:02 AM 2:02 AM 3:02 AM 4:02 AM 5:02 AM 6:02 AM 7:02 AM 8:02 AM 9:02 AM 1:02 PM 2:02 PM 3:02 PM 4:02 PM 5:02 PM 6:02 PM 7:02 PM 8:02 PM 9:02 PM
AM AM AM PM PM PM
Avg PK SW Temp Rate of Change (0.12) (0.10) (0.08) (0.14) (0.07) (0.05) 0.02 0.33 0.14 0.13 0.22 0.18 0.23 0.06 0.08 0.07 0.48 (0.14) (0.07) (0.32) (0.40) (0.25) (0.11)
Avg EPDM SW Temp Rate of Change (0.21) (0.31) (0.32) (0.03) (0.08) 0.36 0.39 1.00 1.53 1.51 0.86 1.09 0.62 0.55 0.16 0.02 (0.08) (0.75) (2.16) (2.53) (0.52) (0.48) (0.38)
Time
Figure 2: Average rates of change of internal stairwell temperature
ProfessionalRoofing June 2010 43

5. Roof surface temperatures versus external temperatures
180.00
Degrees Fahrenheit
160.00
140.00
120.00
100.00
80.00
60.00
40.00
20.00
-
12:02 10:02 11:02
1:02 AM 2:02 AM 3:02 AM 4:02 AM 5:02 AM 6:02 AM 7:02 AM 8:02 AM 9:02 AM 12:02 PM 1:02 PM 2:02 PM 3:02 PM 4:02 PM 5:02 PM 6:02 PM 7:02 PM 8:02 PM 9:02 PM 10:02 PM 11:02 PM
AM AM AM
Avg Outside Temp 88.28 86.78 85.45 84.61 82.61 81.65 81.03 81.73 84.85 88.77 91.71 94.15 96.66 98.67 100.44 101.46 102.21 102.17 101.19 99.55 96.13 93.98 91.99 90.04
Avg PolyKool Roof Temp 66.46 65.44 64.36 62.76 61.69 60.45 59.80 65.65 82.32 99.77 113.09 122.21 128.59 130.59 129.15 124.86 117.84 108.06 97.16 84.57 74.47 70.35 68.27 66.92
Avg EPDM Roof Temp 70.86 69.45 68.15 66.66 65.37 64.14 63.21 66.99 89.05 114.86 135.36 148.47 156.28 156.91 152.75 145.61 135.06 122.80 110.14 97.22 86.22 79.42 75.50 72.66
Time
Figure 3: Average roof surface temperatures versus average external temperatures
According to Chris Peterson, lead facilities sunlight isn’t increasing the roof ’s surface cooler now that you can place your
technician for the Nationwide Scottsdale temperature. hand on it midday without discomfort.
Insurance building, all other items remained Figure 3 shows that during the study, Sunglasses now are mandatory for all
virtually unchanged when compared with the largest difference in roof surface workers because the reflectivity is like
2008, and the self-adhering white laminated temperature occurred at noon when the sunshine on snow.
polymer-modified bitumen roof membrane average outside temperature was 97 F. The “Our utility bill has shown a consistent
installation was the only substantial differ- Wells Fargo Financial Services roof system monthly drop in kilowatt-hour (kWh) use
ence in 2009. During August 2009, the on average was 156 F at that time, but the since the roofing project’s completion,”
kilowatt consumption was 663,000 kW— Nationwide Scottsdale Insurance roof sys- he continues. “A conservative estimate of
a nearly 8 percent decrease (or $5,450 tem was only 129 F. That’s a difference of power reduction is around 50,000 kWh
saved) in electricity required to cool 27 degrees. Between 9 a.m. and 5 p.m. per month during midsummer. The build-
the building, deeming it more energy- (maximum sunlight hours), there is an av- ing’s air-conditioning demand has dropped
efficient. erage 22-degree difference in roof surface tremendously. The cooling tower load has
Again, this is on a building with a con- temperature, which is quite significant re- decreased so much I rarely have all four
crete roof deck. Also, note that the cool garding the long-term survival of rooftop towers online. With the old roof sys-
roof cap sheet has an SRI value of 84. If equipment (most rooftop equipment isn’t tem, we used all four towers from June
the building had a plywood roof deck and constructed or warranted to last as long to October to satisfy the building
if the materials’ SRI value used was higher in such extreme temperatures), as well demand.”
(100 is typical of most high-quality roof as the health of the building’s facilities So the answer to the Arizona Cool Roof
coatings), the energy savings would be workers who have to perform work on Council’s question is clear: By obtaining
the roof. rooftop and temperature data from an
even greater. Starkweather Roofing has
begun performing similar analyses using EPDM roof system and a self-adhering
buildings with plywood roof decks and
Benefits white laminated polymer-modified bitu-
higher SRI value roof coatings to com- Peterson says the new roof system has given men roof membrane and comparing the
pare the results. Nationwide Scottsdale Insurance, as well results, we now know without a doubt
On average, the Nationwide Scottsdale as the building’s maintenance staff, peace that white roof systems truly are cooler
Insurance roof system is 12 degrees cooler of mind. and more energy-efficient than nonwhite
than the Wells Fargo Financial Services roof “The cool roof does not leak and is easy roof systems.
system—but that includes overnight when to clean and keep free of debris,” Peterson
Chris Walker is a senior technologies project
there is no solar gain from direct sunlight. says. “We used to try to clean up the old
manager contracted by American Express,
Therefore, the study results include temper- roof, but the rock ballast made this task New York. He is a former employee of
ature readings from during the night when next to impossible. The surface is so much Starkweather Roofing Inc., Phoenix.
44 June 2010 www.professionalroofing.net