Reducing Urban Heat Islands
Compendium of Strategies
Cool Roofs
m
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Acknowledgements
Reducing Urban Heat Islands: Compendiu m of Strategies describes the
causes and impacts of summertime urban heat islands and promotes
strategies for lowering temperatures in U.S. communities. This compendium
was developed by the Climate Protection Partnership Division in the U.S.
Environmental Protection Agency's Office of Atmospheric Programs. Eva
Wong managed its overall development. Kathleen Hogan, Julie Rosenberg,
and Andrea Denny provided editorial support. Numerous EPA staff in
offices throughout the Agency contributed content and provided reviews.
Subject area experts from other organizations around the United States and
Canada also committed their time to provide technical feedback.
Under contracts 68-W-02-029 and EP-C-06-003, Perrin Quarles Associates,
Inc. provided technical and administrative support for the entire
compendium, and Eastern Research Group, Inc. provided graphics and
production services.
PositvEnergy provided support in preparing the Trees and Vegetation, Cool
Roofs, and UHI Activities chapters under contract PO #2W-036 l-SATX.
Experts who helped shape this chapter include:
Gregory Chin, Andre Desjarlais, Maury Estes, David Hitchcock, Megan
Lewis, Danny Parker, Joyce Rosenthal, Lorraine Ross, Steve Ryan, Rachel
Schmeltz, Peter Turnbull, and Barry Zalph.
Suggested Citation: U.S. Environmental Protection Agency. 2008. "Cool
Roofs." In: Reducing Urban Heat Islands: Compendium of Strategies.
Draft, https://www.epa.gov/heat-islands/heat-island-compendium.
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Contents
Cool Roofs 1
1. How It Works 2
1.1 Solar Energy 2
1.2 Solar Reflectance 3
1.3 Thermal Emittance 3
1.4 Temperature Effects 4
2. Cool RoofTypes 5
2.1 Low-Sloped Cool Roofs 5
2.2 Steep-Sloped Cool Roofs 6
3. Benefits and Costs 8
3.1 Benefits 8
3.2 Potential Adverse Impacts 12
3.3 Costs 12
3.4 Benefit-Cost Considerations 14
4. Other Factors to Consider 16
4.1 Product Measurement 16
4.2 Product Labeling 17
4.3 Installation and Maintenance 19
4.4 Cool Roofing and Insulation 19
5. Cool Roof Initiatives 20
6. Resources 22
6.1 Cool Roof Energy Savings Calculators 22
6.2 Roofing Programs and Organizations 24
Endnotes 26
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Cool Roofs
Cool roofing can help address the
problem of heat islands, which re-
sults in part from the combined heat
of numerous individual hot roofs in a city
or suburb. Cool roofing products are made
of highly reflective and emissive materials
that can remain approximately 50 to 60°F
(28-33°C) cooler than traditional materials
during peak summer weather. Building own-
ers and roofing contractors have used these
types of cool roofing products for more than
20 years. Traditional roofs in the United
States, in contrast, can reach summer peak
temperatures of 150 to 185°F (66-85°C),2
thus creating a series of hot surfaces as well
as warmer air temperatures nearby.
This chapter provides detailed information
that mitigation program organizers can use
to understand, plan, and implement cool
roofing projects and programs. The chapter
discusses:
• Key cool roof properties and how they
help to mitigate urban heat
• Types of cool roofing
• Specific benefits and costs of cool roofing
• Measurement and certification of cool
roof products
• Installation and maintenance of cool roofs
• Tools and resources to further explore
this technology.
Opportunities to Expand Use of Cool
Roofs in Urban Areas
Most U.S. cities have significant opportunities to
increase the use of cool roofs. As part of the U.S.
Environmental Protection Agency's (EPA's) Urban
Heat Island Pilot Project, the Lawrence Berkeley
National Laboratory conducted a series of analyses
to estimate baseline land use and tree cover infor-
mation for the pilot program cities.1
Figure 1 shows the percent of roof cover in four of
these urban areas. The data are from 1998 through
2002. With roofs accounting for 20 to 25 percent of
land cover, there is a large opportunity to use cool
roofs for heat island mitigation.
Figure 1: Roof Cover Statistics for Four U.S. Cities
(BelowTree Canopy)
Salt Lake City
Sacramento
Houston
Chicago
0 5 10 15 20 25 30
Percent Coverage
COOL ROOFS - DRAFT
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1. How It Works
Understanding how cool roofing works
requires knowing how solar energy heats
roofing materials and how the proper-
ties of roofing materials can contribute
to warming. This section explains solar
energy, the properties of solar reflectance
and thermal emittance, and the combined
temperature effect of these two properties
working together.
1.1 Solar Energy
Figure 2 shows the typical solar energy that
reaches the Earth's surface on a clear sum-
mer day. Solar energy is composed of ultra-
violet (UV) rays, visible light, and infrared
energy, each reaching the Earth in different
percentages: 5 percent of solar energy is
in the UV spectrum, including the type of
rays responsible for sunburn; 43 percent of
solar energy is visible light, in colors rang-
ing from violet to red; and the remaining
52 percent of solar energy is infrared, felt
as heat.
Cool Roof Market
The number of ENERGY STAR® Cool
Roof Partners has grown from 60 at
the program's inception to nearly 200
by the end of 2007; the number of
products has grown even faster, from
about 100 to almost 1,600. Based
on 2006 data from more than 150
ENERGY STAR Partners, shipments
of ENERGY STAR products constitute
about 25 percent of the commercial
roofing market and about 10 percent
of the residential market. The overall
market share for these products
is rising over time, especially
with initiatives such as cool roof
requirements in California.
"Cool roofing" refers to the use
of highly reflective and emissive
materials. "Green roofs" refer to
rooftop gardens.
Figure 2: Solar Energy versus Wavelength Reaching Earth's Surface
1.00
0.90
•S 0.80
c
S 0.70
C
S 0.60
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Figure 3: Effect of Albedo on Surface
Temperature
1.2 Solar Reflectance
Solar reflectance, or albedo, is the percent-
age of solar energy reflected by a surface.
Researchers have developed methods to
determine solar reflectance by measuring
how well a material reflects energy at each
solar energy wavelength, then calculating
the weighted average of these values (see
Section 4,1). Traditional roofing materi-
als have low solar reflectance of 5 to 15
percent, which means they absorb 85 to
95 percent of the energy reaching them
instead of reflecting the energy back out to
the atmosphere. The coolest roof materi-
als have a high solar reflectance of more
than 65 percent, absorbing and transferring
to the building 35 percent or less of the
energy that reaches them. These materi-
als reflect radiation across the entire solar
spectrum, especially in the visible and
infrared (heat) wavelengths.
1.3 Thermal Emittance
Although solar reflectance is the most im-
portant property in determining a material's
contribution to urban heat islands, thermal
emittance is also a part of the equation. Any
surface exposed to radiant energy will get
O
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c
156
B i
101
°F
Albedo alone can significantly influence surface
temperature, with the white stripe on the brick wall about
5 to 10°F (3-5 C) cooler than the surrounding, darker areas.
COOL ROOFS - DRAFT
3
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Figure 4:Temperature of Conventional
Roofing
The left half of this traditional bitumen roof in Arizona
is shown in visible wavelengths and the right in
infrared. The roof's temperature reaches almost
175°F (80°C).
1.4 Temperature Effects
Solar reflectance and thermal emittance
have noticeable effects on surface tempera-
ture, Figure 5 illustrates these differences us-
ing three different roof types. Conventional
roof surfaces have low reflectance but high
thermal emittance; standard black asphalt
roofs can reach 165 to 185°F (74 - 85°C)
at midday during the summer. Bare metal
or metallic surfaced roofs have high reflec-
tance and low thermal emittance and can
warm to 150 to 165°F (66 - 77°C). Research
has shown that cool roofs with both high
reflectance and high emittance reach peak
temperatures of only 110 to 115 'F (43-46°C)
in the summer sun. These peak values vary
by local conditions. Nonetheless, research
reveals that conventional roofs can be 55
to 85°F (31-47°C) hotter than the air on
any given day, while cool roofs tend to stay
within 10 to 20°F (6-ll°C) of the back-
ground temperature.^
Figure 5: Example of Combined Effects of Solar Reflectance and
Thermal Emittance on Roof Surface Temperature4
92%
92%
75%
60%
5%
180°F
black roof
low solar reflectance
high emittance
25%
/
160°F
metal roof
high solar reflectance
low emittance
120°F
white roof
very high reflectance
high emittance
solar reflectance
emittance
On a hot, sunny, summer day, a black roof that reflects 5 percent of the sun's
energy and emits more than 90 percent of the heat it absorbs can reach
180°F (82°C). A metal roof will reflect the majority of the sun's energy while
releasing about a fourth of the heat that it absorbs and can warm to 160°F
(71°C). A cool roof will reflect and emit the majority of the sun's energy and
reach a peak temperature of 120°F (49°C).
REDUCING URBAN HEAT ISLANDS - DRAFT
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These reduced surface temperatures from
cool roofs can lower air temperature.
For example, a New York City simulation
predicted near-surface air temperature
reductions for various cool roof mitigation
scenarios. The study assumed 50-percent
adoption of cool roofs on available roof
space and ran models to evaluate the
resulting temperature changes. Averaged
over all times of day, the model predicted
a city-wide temperature reduction of 0.3°F
(0.2°C). The city-wide, 3:00 p.m. average
reduction was 0.6°F (0.3°C) and ranged
from 0.7 to 1 /r F (0,4 - 0.8 C) in six spe-
cific study areas within the city.5
2. Cool Roof Types
There are generally two categories of roofs:
low-sloped and steep-sloped. A low-sloped
roof is essentially flat, with only enough
incline to provide drainage. It is usually
defined as having no more than 2 inches (5
cm) of vertical rise over 12 inches (30 cm)
of horizontal run, or a 2:12 pitch. These
roofs are found on the majority of com-
mercial, industrial, warehouse, office, retail,
and multi-family buildings, as well as some
single-family homes.
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When purchasing cool roof elasto-
meric coatings, building owners can
require that products meet the
ASTM international standard,
ASTM D 6083-05el, "Standard Spec-
ification for Liquid Applied Acrylic
Coating Used in Roofing," to ensure
the product achieves certain specifi-
cations. There is currently no similar
standard for cementitious coatings.
There are two main types of cool roof
coatings: cementitious and elastomeric.
Cementitious coatings contain cement
particles. Elastomeric coatings include
polymers to reduce brittleness and im-
prove adhesion. Some coatings contain
both cement particles and polymers. Both
types have a solar reflectance of 65 per-
cent or higher when new and have a ther-
mal emittance of 80 to 90 percent or more.
The important distinction is that elasto-
meric coatings provide a waterproofing
membrane, while cementitious coatings
are pervious and rely on the underlying
roofing material for waterproofing.
Single-Ply Membranes. Single-ply mem-
branes come in a pre-fabricated sheet that
is applied in a single layer to a low-sloped
roof. The materials are generally glued or
mechanically fastened in place over the en-
tire roof surface, with the seams sealed by
taping, gluing, or heat-welding. A number
of manufacturers formulate these products
with cool surfaces.
Building owners generally consider cool
roof options when their roof begins to
fail. They typically use a cool roof coat-
ing if an existing roof needs only moder-
ate repair, and a single-ply membrane for
more extensive repairs. The cut-off point
between moderate and extensive repairs is
not easily determined. In making a choice
between these options, however, build-
ing owners can gather input from many
sources, including roofing consultants and
contractors, product manufacturers, and
contacts at other facilities that have had
cool roofing installed.
2.2 Steep-Sloped Cool Roofs
Most cool roof programs focus on the low-
sloped roofing sector, but cool roof options
are becoming available for the steep-sloped
sector as well. Asphalt shingles are the
Figure 8: Conventional and Cool
Colored Tiles
Common Cool
Single-Ply Materials
• EPDM (ethylene propylene
diene monomer), a synthetic
rubber material, with seams that
must be glued or taped together.
• CSPE (chlorosulfonated poly-
ethylene), a polymer material,
with seams that can be heat-
welded together.
• PVC (polyvinyl chloride) and
TPO (thermoplastic olefins),
thermoplastic materials, with seams
that can be heat-welded together.
red tiles
Conventionally
pigmented tiles on
battens \
Cool colored tiles
mounted directly
on deck*
B
\ \ 'V l VTjJi
Coo! roof products can be indistinguishable from
their conventional counterparts. The rightmost
row of curved tiles uses conventional colored
pigments, whereas the other two rows use cool
pigments.
6
REDUCING URBAN HEAT ISLANDS - DRAFT
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most common roofing materials used on
steep-sloped roofs. Other products include
metal roofing, tiles, and shakes.
The market for steep-sloped cool roofing
materials is growing, although the solar
reflectance for these products is generally
lower than for low-sloped cool roofs. A
number of products are available for tiles
and painted metal roofing.
The solar reflectance of traditional tiles,
typically made of clay or concrete, ranges
from 10 to 30 percent. Manufacturers have
begun producing "cool colored" tiles that
contain pigments that reflect solar energy
in the infrared spectrum. The ENERGY
STAR Roof Products List as of April 2008
Cool Colors
The California Energy Commission
has sponsored the "Cool Colors
Project," under which LBNL and Oak
Ridge National Laboratory (ORNL)
are collaborating with roofing indus-
try partners to research and develop
cool colored roof products that could
expand significantly the use of cool
roofing in the residential sector. See
for more
information.
has approved tiles for steep-sloped roofs
with initial solar reflectances ranging from
25 to almost 70 percent, depending on
color. These tiles come in traditional col-
ors, such as brown, green, and terra cotta.
They are durable and long-lasting, but not
widely used. Where tiles are used, the cool
tile alternatives can be available at little or
no incremental cost over traditional tiles.6
Figure 9: Cool Metal Roofing
vXy.
Cool colored metal roofs lend themselves
readily to the steep-sloped market, as this house
demonstrates.
Cool colored metal roofing products also
use infrared-reflecting pigments and have
high durability and long life. About one-
half of the products on the ENERGY STAR
Roof Products List as of April 2008 were
metal roofing products for steep-sloped
roofs, with initial solar reflectances ranging
from about 20 to 90 percent.
Asphalt shingles are the most commonly
used material for steep-sloped roofs, with a
market share of about 50 percent, depending
on the region,7 and a low initial cost of just
over $1.00 per square foot (0.930 m2). As of
April 2008, several manufacturers offered a
line of asphalt shingles on the ENERGY STAR
Roof Products List, with initial solar reflec-
tances ranging from about 25 to 65 percent.
Other shingle products on the list are metal.
Manufacturers, researchers, and other stake-
holders are working together to develop
additional, cool-colored shingle products that
use infrared-reflecting pigments.8
COOL ROOFS - DRAFT
7
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3. Benefits and Costs
The use of cool roofs as a mitigation strat-
egy brings many benefits, including lower
energy use, reduced air pollution and
greenhouse gas emissions, and improved
human health and comfort. At the same
time, there can be a cost premium for some
cool roof applications versus traditional
roofing materials. This section highlights
some of the key benefits and costs of cool
roof programs and individual projects.
Section 6 also introduces cool roof energy
savings calculators that community plan-
ners or individual building owners can use
to help determine whether to pursue cool
roofs as a mitigation option.
3.1 Benefits
Reduced Energy Use. A cool roof trans-
fers less heat to the building below, so the
building stays cooler and more comfortable
and uses less energy for cooling. Every
building responds differently to the effects
of a cool roof. For example, Table 1 lists
examples of the general characteristics and
cooling energy savings of different one-
story buildings in California, Florida, and
Texas. The measured savings varied from
10 to almost 70 percent of each build-
ing's total cooling energy use. In addition,
a 2004 report summarized more than 25
articles about the cooling energy used by
buildings with cool roofs and identified
energy savings ranging from 2 to over 40
percent, with average savings of about 20
percent.9
Local climate and site-specific factors, such
as insulation levels, duct placement, and
attic configuration, play an important role
in the amount of savings achieved (see
the range in Table 1). Other site-specific
variables also can strongly influence the
amount of energy a particular building
will save. For example, a study of a San
Jose, California, drug store documented
cooling energy savings of only 2 percent.
The cooling demands in this store were
driven by the design of the building, in-
cluding a radiant barrier under the roof
and a well ventilated plenum space, so that
heat transfer through the roof contributed
little to the store's cooling demand.10 Thus,
in gauging potential energy savings for a
particular building, the building owners
will need to consider a range of factors to
make cool roofing work for them.
Another benefit of cool roofing is that it
saves energy when most needed—during
peak electrical demand periods that gen-
erally occur on hot, summer weekday
afternoons, when offices and homes are
running cooling systems, lights, and appli-
ances. By reducing cooling system needs, a
cool roof can help building owners reduce
peak electricity demand. The last column in
Table 1 lists reductions in the peak demand
for cooling energy that range from 14 to 38
percent after installation of a cool roof.
Lower peak demand not only saves on total
electrical use but also can reduce demand
fees that some utilities charge commercial
and industrial building owners. Unlike
residential customers, who pay for only the
amount of electricity they use, commercial
and industrial customers often pay an ad-
ditional fee based on the amount of peak
power they demand. Because cool roofing
helps reduce their peak demand, it lowers
these costs.
Insulation and R-Values
The "R-value" of building insulation
indicates its ability to impede heat
flow. Higher R-values are correlated
with greater insulating properties.
8
REDUCING URBAN HEAT ISLANDS - DRAFT
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Researchers have conducted in-depth mod-
eling to assess how building-level energy
savings can affect city-wide energy usage.
The Lawrence Berkeley National Labora-
tory (LBNL) ran simulations to evaluate
the net energy impacts of applying cool
roofing in 11 U.S. cities.11 The original
study was based on 1993 energy prices and
buildings that use electrical cooling sys-
tems and gas furnaces. Figure 10 uses 2003
state-level prices for electricity and natural
gas, based on Energy Information Adminis-
tration data for the commercial sector.
Cool roofs reflect solar energy year round,
which can be a disadvantage in the win-
ter as they reflect away desirable winter-
time heat gain. The net effect is generally
positive, though, because most U.S. cities
have high cooling and peak cooling de-
mand, and electricity is expensive. Figure
10 presents the total anticipated cooling
energy savings and the net savings af-
ter considering increased heating costs.
Although northern and mid-Atlantic cities
with relatively long heating seasons, such
as Chicago, Philadelphia, and Washington
D.C., still reap net savings, the net benefits
for New York City remain particularly high
because of the high price of electricity in
that area. (See Section 3.2 for further dis-
cussion of the heating penalty.)
This same LBNL study extrapolated the
results to the entire United States and es-
timated that widespread use of cool roofs
Table 1: Reported Cooling Energy Savings from Buildings with Cool Roofs12
Size
Building
Location
Citation
(ft2)
Annual
Peak
Roof
Roof
Cooling
Demand
Insulation*
Space
Saved
Savings
Residence
Merritt
Island, FL
(Parker, D., S. Barkaszi,
etal. 1994)
1,800
R-25
Attic
10%
23%
Convenience
Retail
Austin.TX
(Konopacki, S. and H.
Akbari 2001)
100,000
R-12
Plenum
11%
14%
Residence
Cocoa
Beach, FL
(Parker, D., J. Cu(Ti-
mings, etal. 1994)
1,795
R-11
Attic
25%
28%
Residence
Nobleton,
FL
(Parker, D., S. Barkaszi,
etal. 1994)
900
R-3
Attic
25%
30%
School
Trailer
Volusia
County, FL
(Callahan, M., D.
Parker, etal. 2000)
1,440
R-11
None
33%
37%
School
Trailer
Sacramento,
CA
(Akbari, H„ S. Bretz, et
al. 1993)
960
R-19
None
34%
17%
Our Savior's
School
Cocoa
Beach, FL
(Parker, D., J. Sherwin,
etal. 1996)
10,000
R-19
Attic
10%
35%
Residence
Cocoa
Beach, FL
(Parker, D., J. Cum-
mings, etal. 1994)
1,809
None
Attic
43%
38%
Residence
Sacramento,
CA
(Akbari, H.,S. Bretz, et
al. 1993)
1,825
R-11
None
69%
32%
* Note: These insulation levels are lower than the energy efficiency levels recommended by ENERGY STAR. If insulation
levels were higher, the cooling savings likely would be less.
COOL ROOFS - DRAFT
9
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could reduce the national peak demand for
electricity by 6.2 to 7.2 gigawatts (GW),13
or the equivalent of eliminating the need to
build 12 to 14 large power plants that have
an energy capacity of 500 megawatts each.
Reduced Air Pollution and Greenhouse
Gas Emissions. The widespread adop-
tion of heat island mitigation efforts such
as cool roofs can reduce energy use dur-
ing the summer months. To the extent that
reduced energy demand leads to reduced
burning of fossil fuels, cool roofs contrib-
ute to fewer emissions of air pollutants,
such as nitrogen oxides (NOx), as well as
greenhouse gases, primarily carbon dioxide
(CO2). The C02 reductions can be sub-
stantial. For example, one study estimated
potential C02 reductions of 6 to 7 percent
in Baton Rouge and Houston from reduced
building energy use.14 Reductions in air
pollutant emissions such as NOx gener-
ally provide benefits in terms of improved
air quality, particularly ground-level ozone
Case Examples of Building Comfort Improvements
• "Big-box" retailer Home Base, Vacaville, California.15 Installing a cool roof at
this store helped solve the problem created by an incorrectly sized cooling sys-
tem. This store used an undersized evaporative cooling system that was unable to
meet the building's cooling loads. Indoor temperatures above 90°F (32°C) were
recorded, even with the building coolers working around the clock. After adding
a cool roof, peak indoor temperatures were reduced to 85°F (29°C) or lower, and
10 more shopping hours a week were deemed comfortable (below 79°F (26°C)
and 60 percent humidity) inside the store. Although the evaporative coolers were
still not powerful enough to meet the hottest conditions, the cool roof helped
reduce temperatures inside the store.
• Apartment complex, Sacramento, California.16 Adding cool roofs at these
residences lowered indoor air temperatures, improving resident comfort. These
non-air conditioned buildings were composed of two stories and an attic, with an
R-38 level of insulation above the second story and below the attic space. Adding
a cool roof lowered peak air temperatures in the attic by 30 to 40°F (17-22°C).
Generally, the higher the insulation level, the less effect a cool roof will have on
the space beneath it; however, in this case, even with high insulation levels, the
cool roof reduced second-story air temperatures by 4°F (2°C) and first floor tem-
peratures by 2°F (1°C).
• Private elementary school, Cocoa Beach, Florida.17 Cool roof coatings at this
school improved comfort and saved energy. This 10,000-square foot (930 m2)
facility had an asphalt-based roof, gray modified bitumen, over plywood decking
with a measured solar reflectance of 23 percent. The dropped ceiling was insu-
lated to R-19 levels, and insulated chiller lines were used in the hot roof plenum
space. Once the roof was covered by an acrylic white elastomeric coating, the so-
lar reflectance rose to 68 percent. The classrooms became cooler and the chiller
electric use was reduced by 10 percent. School staff noticed improved comfort
levels due to the new roof.
10
REDUCING URBAN HEAT ISLANDS - DRAFT
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Figure 10: Modeled Net Energy Cost Savings* ($/1,000 ft2) in Various U.S. Cities from Widespread Use
of Cool Roofing18
Cooling Savings (2003S/1000 ft2)
Net Savings (2003S/1000 ft2)
H $25
Costs are based on state-specific data applied to each city, using 2003 Energy Information Administration reported
prices for the commercial sector.19
(smog). The relationships between pollut-
ant reductions and improved air quality are
complex, however, and require air quality
modeling to demonstrate the benefits in
specific urban areas.
Improved Human Health and Comfort.
Ceilings directly under hot roofs can be
very warm. A cool roof can reduce air tem-
peratures inside buildings with and with-
out air conditioning.
For residential buildings without air condi-
tioning, cool roofs can provide an important
public health benefit during heat waves. For
example, Philadelphia operates a program
to add cool roofs and insulation to residen-
tial buildings that lack air conditioning to
prevent heat-related illnesses and deaths. A
study measured significant cooling benefits
from this program.20 The study controlled
for differences in outside temperature be-
fore and after the installing the cool roofs
and insulation; these treatments lowered the
daily maximum ceiling surface temperature
by about 4.7°F (2.6°C), while daily maximum
Figure 11: Cool Roofing on Urban Row
Homes
Philadelphia reduced temperatures in row houses
by installing cool roofs, which improves the
comfort for occupants and may help reduce deaths
from excessive heat events. Baltimore, with similar
building stock, took similar steps following the
success in Philadelphia.
room air temperatures dropped by about
2.1 F (1.3°C). The study noted that on a 95°F
(35°C) day, these types of reductions rep-
resent large reductions in heat gain to the
room and significantly improve perceived
human comfort.
COOL ROOFS - DRAFT
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3.2 Potential Adverse Impacts
Cool roofs can have a wintertime heating
penalty because they reflect solar heat that
would help warm the building. Although
building owners must account for this pen-
alty in assessing the overall benefits of cool
roofing strategies, in most U.S. climates this
penalty is not large enough to negate the
summertime cooling savings because:
• The amount of useful energy reflected
by a cool roof in the winter tends to be
less than the unwanted energy reflected
in the summer. This difference oc-
curs primarily because winter days are
shorter, and the sun is lower in the sky.
The sunlight strikes the Earth at a lower
angle, spreading the energy out over a
larger area and making it less intense.
In mid-Atlantic and northern states with
higher heating requirements, there also
are more cloudy days during winter,
which reduces the amount of sun re-
flected by a cool roof. Snow cover on
roofs in these climates also can reduce
the difference in solar reflectivity be-
tween cool and non-cool roofs.
• Many buildings use electricity for cool-
ing and natural gas for heating. Electrici-
ty has traditionally been more expensive
than natural gas per unit of energy, so
the net annual energy savings translate
into overall annual utility bill savings.
Note, however, that natural gas and elec-
tricity prices have been volatile in some
parts of the country, particularly since
2000. As shown in Figure 10, with el-
evated natural gas prices in recent years,
the net benefit in terms of cost savings
might be small in certain northern cities
with high heating demands.
California-based research indicates a
cost premium ranging from zero
to 20 cents per square foot for cool
roof products.
3.3 Costs
A 2006 report (see Table 2) investigated the
likely initial cost ranges for various cool
roof products.21 The comparisons in Table
2 are indicative of the trade-offs in cost and
reflectance and emittance factors between
traditional and cool roof options. For low-
sloped roofs, the report noted that:
• Cool roof coatings might cost be-
tween $0.75 and $1.50 per square
foot for materials and labor, which
includes routine surface preparation
like pressure-washing, but which does
not include repair of leaks, cracks, or
bubbling of the existing roof surface.
• Single-ply membrane costs vary from
$1.50 to $3.00 per square foot, including
materials, installation, and reasonable
preparation work. This cost does not in-
clude extensive repair work or removal
and disposal of existing roof layers.
• For either type of cool roof, there can
be a cost premium compared to other
roofing products. In terms of dollars
per square foot, the premium ranges
from zero to 5 or 10 cents for most
products, or from 10 to 20 cents for a
built-up roof with a cool coating used
in place of smooth asphalt or alumi-
num coating.
• As with any roofing job, costs depend
on the local market and factors such as
the size of the job, the number of roof
penetrations or obstacles, and the ease
of access to the roof. These variables
often outweigh significantly the differ-
ence in costs between various roofing
material options.22
12
REDUCING URBAN HEAT ISLANDS - DRAFT
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Table 2: Comparison of Traditional and Cool Roof Options23
Warmer Roof Options Cooler Roof Options
RoofType
Reflectance
Emittance
m
RoofType
Reflectance
Emittance
m
Built-up Roof
With dark gravel
With smooth asphalt
surface
0.08-0.15
0.04-0.05
0.80-0.90
0.85-0.95
1.2-2.1
Built-up Roof
With white gravel
With gravel and
cementitious coating
0.30-0.50
0.50-0.70
0.80-0.90
0.80-0.90
1.2-2.15
With aluminum coating
0.25-0.60
0.20-0.50
Smooth surface with
white roof coating
0.75-0.85
0.80-0.90
Single-Ply Membrane
Black (PVC)
0.04-0.05
0.80-0.90
1.0-2.0
Single-Ply Membrane
White (PVC)
Color with cool
pigments
0.70-0.78
0.40-0.60
0.80-0.90
0.80-0.90
1.0-2.05
Modified Bitumen
With mineral surface
capsheet (SBS, APP)
0.10-0.20
0.80-0.90
1.5-1.9
Modified Bitumen
White coating over a
mineral surface (SBS,
APP)
0.60-0.75
0.80-0.90
1.5-1.95
Metal Roof
Unpainted, corrugated
Dark-painted,
corrugated
0.30-0.50
0.05-0.08
0.05-0.30
0.80-0.90
1.8-3.7
Metal Roof
White painted
Color with cool
pigments
0.60-0.70
0.40-0.70
0.80-0.90
0.80-0.90
1.8-3.75
Asphalt Shingle
Black or dark brown
with conventional
pigments
0.04-0.15
0.80-0.90
0.5-2.0
Asphalt Shingle
"White" (light gray)
Medium gray or brown
with cool pigments
0.25-0.27
0.25-0.27
0.80-0.90
0.80-0.90
0.6-2.1
Liquid Applied
Coating
Smooth black
0.04-0.05
0.80-0.90
0.5-0.7
Liquid Applied Coating
Smooth white
Smooth, off-white
Rough white
0.70-0.85
0.40-0.60
0.50-0.60
0.80-0.90
0.80-0.90
0.80-0.90
0.6-0.8
Concrete Tile
Dark color with
conventional pigments
0.05-0.35
0.80-0.90
1.0-6.0
Concrete Tile
White
Color with cool
pigments
0.70
0.40-0.50
0.80-0.90
0.80-0.90
1.0-6.0
Clay Tile
Dark color with
conventional pigments
0.20
0.80-0.90
3.0-5.0
Clay Tile
White
Terra cotta (unglazed
red tile)
Color with cool pigments
0.70
0.40
0.40-0.60
0.80-0.90
0.80-0.90
0.80-0.90
3.0-5.0
Wood Shake
Painted dark color with
conventional pigment
0.05-0.35
0.80-0.90
0.5-2.0
Wood Shake
Bare
0.40-0.55
0.80-0.90
0.5-2.0
COOL ROOFS - DRAFT
13
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3.4 Benefit-Cost Considerations
Based on the benefits of cool roofs and the
cost premiums noted in Table 2, a commu-
nity can develop a benefit-cost analysis to
determine whether a cool roof project or
program will provide overall net benefits
in a given area. For example, the cost study
referenced in Table 2 also evaluated the
cost effectiveness of low-sloped cool roofs
for commercial buildings in California by
quantifying five parameters (see summary
results in Table 3):2t
• Annual decrease in cooling electricity
consumption
• Annual increase in heating electricity
and/or gas
• Net present value (NPY) of net
energy savings
• Cost savings from downsizing cooling
equipment
• Cost premium for a cool roof
The study recognized that other parameters
can provide benefits or reduce costs that
were not part of the analysis. These include:
• Reduced peak electric demand
for cooling
• Financial value of rebates or energy
saving incentives that can offset the cost
premiums for cool roofing materials
• Reduced material and labor costs over
time resulting from the extended life
of the cool roof compared to a tradi-
tional roof
climate zones studied (see Table 3). Cali-
fornia relied in part on this benefit-cost
analysis to establish mandatory statewide
low-sloped cool roof requirements.
In 2006, California began evaluating wheth-
er to extend the state's mandatory cool roof
requirements to the steep-sloped market.
One analysis in support of this approach
anticipated positive cost effectiveness in
many but not all California climate zones.25
The state will consider that analysis, as
well as public comments on benefits and
costs in deciding what final action to take
on steep-sloped roof requirements. A final
rule is expected in 2008.
Although the results of Table 3 are specific
to California in terms of electricity rates
and typical cooling and heating energy use,
the cost effectiveness approach can be rep-
licated by other communities considering
cool roof projects or programs.
Figure 12: Cool Roof on a Condominium
4
1
Homeowners can also reap the benefits of cool roofs.
Given the information at hand, the study
found that expected total net benefits, after
considering heating penalty costs, should
range from $0.16 to $0.66/square foot
(average $0.-17/ft2) based on the California
14
REDUCING URBAN HEAT ISLANDS - DRAFT
-------
Table 3: Example Cool Roof Cost/Benefit Summary for California26
California
Annuc
al Energy/
1000 ft2
Peak Power/1000 ft2
Net PresentValue (NPV)/1000ft2
Climate
Roof
Source
Zone
R-Value
kWh
kW
$equip
$kWh
$therm
$energy
$total
1
19
115
-8.3
0.3
0.13
67
157
-62
95
162
2
19
295
-5.9
2.4
0.20
100
405
-43
362
462
3
19
184
-4.9
1.4
0.15
76
253
-35
218
294
4
19
246
-4.2
2.1
0.18
90
337
-31
306
396
5
19
193
-4.7
1.5
0.17
83
265
-35
230
313
6
11
388
-4.1
3.6
0.22
111
532
-29
503
614
7
11
313
-2.6
2.9
0.25
125
428
-20
408
533
8
11
413
-3.7
3.9
0.25
125
565
-28
537
662
9
11
402
-4.5
3.7
0.20
101
552
-33
519
620
10
19
340
-3.6
3.1
0.18
89
467
-26
441
530
11
19
268
-4.9
2.3
0.15
75
368
-37
331
406
12
19
286
-5.3
2.4
0.19
95
392
-39
353
448
13
19
351
-5.1
3.1
0.19
96
480
-37
443
539
14
19
352
-4.7
3.1
0.21
105
483
-33
450
555
15
19
380
-1.7
3.7
0.16
82
520
-13
507
589
16
19
233
-10.6
1.3
0.18
90
319
-78
242
332
min
115
-10.6
0.3
0.13
67
157
-78
95
162
max
413
-1.7
3.9
0.25
125
565
-13
537
662
avg
297
-4.9
2.6
0.19
94
408
-36
372
466
* This table presents dollar savings from reduced air conditioning use (in kWh) and reduced air conditioning equipment
sizing ($equip), offset by natural gas heating penalty costs (measured in therms).The"Net PresentValue (NPV)/1000 ft2"
column uses the kWh and therm information to project savings for energy only and in total (energy plus equipment).
COOL ROOFS - DRAFT 15
-------
4. Other Factors to Consider
4.1 Product Measurement
To evaluate how "cool" a specific prod-
uct is, ASTM International has validated
test methods to measure solar reflectance
and thermal emittance (see Table 4). The
Cool Roof Rating Council (CRRC) also has
developed a test method for variegated
roof products such as composite shingles,
including laboratory and field tests. Labo-
ratory measurements help determine the
properties of new material samples, while
field measurements are useful for evaluat-
ing how well a roof material has withstood
the test of time, weather, and dirt.
The final method listed in Table 4 is not an
actual test but a way to calculate the "solar
reflectance index" or SRI. The SRI is a value
that incorporates both solar reflectance and
thermal emittance in a single value to rep-
resent a material's temperature in the sun.
This index compares how hot a surface
would get compared to a standard black
and a standard white surface. In physical
terms, this scenario is like laying a roof ma-
terial next to a black surface and a white
surface and measuring the temperatures of
all three surfaces in the sun. The SRI is a
value between zero (as hot as a black sur-
face) and 100 (as cool as a white surface)
and calculated as follows:
(Tblack - Tsurface)
SRI= x 100
(Tblack - Twhite)
Table 4: Test Methods to Evaluate Coolness of Roofing Materials
Property
Test Method
Equipment Used
Test Location
Solar
reflectance
ASTM E 903 - Standard Test Method for Solar Absorp-
tance. Reflectance, and Transmittance of Materials
Using Integrating Spheres
Integrating sphere
spectrophotometer
Laboratory
Solar
reflectance
ASTM C 1549 - Standard Test Method for Determina-
tion of Solar Reflectance Near Ambient Temperature
Using a Portable Solar Reflectometer
Portable solar
reflectometer
Laboratory or
field
Solar
reflectance
ASTM E 1918 - Standard Test Method for Measuring
Solar Reflectance of Horizontal and Low-Sloped Sur-
faces in the Field
Pyranometer
Field
Solar
reflectance
CRRCTest Method #1 (for variegated roof products,
[i.e. products with discrete markings of different col-
ors]); used in conjunction with ASTM CI 549
Portable solar
reflectometer
Laboratory or
field
Thermal
emittance
ASTM E 408-71 - Standard Test Method forTotal
Normal Emittance of Surfaces Using Inspection-Meter
Techniques
Reflectometer or
emissometer
Laboratory
Thermal
emittance
ASTM C 1371 - Standard Test Method for
Determination of Emittance of Materials Near Room
Temperature Using Portable Emissometers
Emissometer
Field
Solar
reflectance
index
ASTM E 1980 - Standard Practice for Calculating Solar
Reflectance Index of Horizontal and Low-Sloped
Opaque Surfaces
None (calculation)
16
REDUCING URBAN HEAT ISLANDS - DRAFT
-------
The U.S. Green Building Council, as
part of its Leadership in Energy
and Environmental Design (LEED)
Rating System, has developed an
SRI Calculator to assist project spon-
sors in calculating a roofs SRI under
"LEED-NC, Version 2.2, Sustainable
Site Credit 7.2: Heat Island Effect:
Roof." See .
4.2 Product Labeling
ENERGY STAR for Roof Products and the
Cool Roof Rating Council (CRRC) both
operate voluntary labeling programs for
manufacturers. Many building codes and
energy efficiency rebate programs require
that cool roofing materials meet recognized
specifications and standards, and that a
vendor's product be listed with either or
both of these voluntary labeling programs.
u
_c
fl5
c
rt5
CO
in
ENERGY STAR for Roof Products. Manu-
facturers can participate voluntarily in the
ENERGY STAR for Roof Products program.
A product qualifies for ENERGY STAR if
it meets the solar reflectance criteria ex-
pressed in Table 5. The program uses sig-
nificantly different criteria for low-sloped
versus steep-sloped roof products. Highly
reflective products, which are currently
bright white for the most part, are available
for low-sloped roofs. For aesthetic reasons,
bright white options are generally not
marketable for steep-sloped roofs. Instead,
steep-sloped cool roof products generally
use moderately reflective, colored options.
Version 2.0 of the program guidelines be-
came effective in January 2008. The guide-
lines require manufacturers to test their
products' initial solar reflectance and main-
tenance of solar reflectance after at least
three years of service. For the initial testing,
manufacturers can rely on tests conducted
for purposes of certifying a product under
the Cool Roof Rating Council's Product Rat-
ing Program, if applicable. To ensure the
long-term integrity of reflective products,
ENERGY STAR also requires products to
maintain warranties comparable to those
offered for non-reflective roof products. Fi-
nally, the Version 2.0 guidelines also require
manufacturers to report a product's initial
emissivity as part of the application process.
There is no emissivity level required, but
this information can provide valuable infor-
mation on the potential savings and benefits
Figure 13: Olympic Oval, Salt Lake City, Utah
The Olympic Oval features a cool roof covering
almost 205,000 square feet (19,000 m2). ENERGY
STAR partners, who helped build the oval's roof,
have played key roles in advancing cool roofing
technology.
The most up-to-date list of ENERGY
STAR qualified roof products,
and current, proposed, and prior
specifications, can be found on the
ENERGY STAR Web site at .
COOL ROOFS - DRAFT
17
-------
Table 5: ENERGY STAR for Roof Products (Version 2.0) Qualifying Criteria
* Maintenance of solar reflectance is measured on a roof that has been in service for three years or more.
** Manufacturers can also use CRRCTest Method #1 for variegated roof products and can use results from tests
conducted as part of CRRC Product Rating Program certification.
Type of Roof Product
Initial Solar Reflectance
Standard Test Methods
Maintenance of Solar Reflectance*
Standard Test Methods
Low-sloped
65% or higher
ASTM E 903 or
ASTM C 1549**
50% or higher
ASTM E 1918 or
ASTM C1549
Steep-sloped
25% or higher
ASTM E 903 or
ASTM CI 549**
15% or higher
ASTM C1549
of a specific product in the region where it
will be used.
Based on data from almost 90 percent of
the ENERGY STAR Partners, the market
share of cool roof products from these
manufacturers has grown in recent years.
In 2004, cool roof products represented 8
percent of these manufacturers' shipments
in the commercial roofing sector and 6
percent in the residential. In 2006, their
shipments of commercial cool roof product
tripled to represent more than 25 percent
of their commercial roof products, and the
residential share almost doubled, reaching
10 percent.
Cool Roof Rating Council. CRRC is a non-
profit organization with members from the
business, consulting, and research fields.
The CRRC was formed in 1998 and applied
to join the American National Standards
Institute (ANSI) ten years later. In Septem-
ber 2002, CRRC launched its product rating
program with a list of solar reflectance and
thermal emittance values of roofing materi-
als. As of February 2007, this list included
only initial or new values of roofing mate-
rial properties, but work is underway to
add three-year weathered values to the list.
The weathered values of solar reflectance
and thermal emittance will come from
test farms located in different areas of the
country, where roof materials are exposed
to the elements for three years.
See the CRRC Rated Product
Directory at .
Manufacturer participation in the CRRC
program is entirely voluntary. Participat-
ing manufacturers must adhere to stringent
requirements; however, to ensure accurate
reported values, only agencies or laborato-
ries accredited by CRRC can perform tests,
and their test programs must use the ASTM
and CRRC standards listed in Table 4.
A material does not need to meet a solar
reflectance or thermal emittance value to
appear on the CRRC Rated Product Direc-
tory roofing products list. Because any
product can be listed, regardless of how
cool it might be, it is up to the consumer
to check the values on the CRRC list and
decide which products meet their own
criteria for cool materials. Building own-
ers and heat island mitigation groups can
use the CRRC ratings in conjunction with
the ENERGY STAR guidelines to help to
identify cool materials on the basis of solar
reflectance.
18
REDUCING URBAN HEAT ISLANDS - DRAFT
-------
4.3 Installation and Maintenance
A coating or single-ply membrane on a
low-sloped roof can serve as the top sur-
face of a roofing assembly and can be
applied directly over a roof deck or on top
of other existing materials. Proper installa-
tion is important to the long-term success
of a cool roof project. For example, when
applied properly, many cool roof coatings
have been shown to last more than 20
years. When applied poorly, cool roof coat-
ings can peel or flake off the roof within
a couple of years. To ensure good product
performance, building owners can seek ap-
propriate warranties for both the product
and the installation service.
On steep-sloped roofs, profession-
als do not recommend using cool
coatings over existing shingles. This
technique can cause moisture prob-
lems and water damage because the
coating can inhibit normal shingle
drying after rain or dew accumula-
tion, allowing water to condense and
collect under the shingles.
A key concern for cool roofs is maintain-
ing their high solar reflectance over time.
If a building's roof tends to collect large
amounts of dirt or particulate matter, wash-
ing the roof according to the manufactur-
er's recommended maintenance procedures
can help retain solar reflectance. Also,
smoother surfaces and higher sloped sur-
faces tend to withstand weathering better.
With proper maintenance, coatings are able
to retain most of their solar reflectance,
with decreases of only about 20 percent,
usually in the first year after application of
the coating.27
Figure 14: Installation of a Cool Single-
Ply Membrane
Cool roofs can be applied to existing buildings or
designed into new ones.
4.4 Cool Roofing and Insulation
Cool roofing and roof insulation are not
comparable options for saving building
energy—they work very differently. Build-
ing owners must make separate decisions
to upgrade roof insulation levels or install
cool roofing.
Some studies have evaluated the insula-
tion levels needed to produce the same
summertime energy savings as a cool
roof.28-29-30 These studies have been used
to support building codes that allow
less roof insulation if cool roofing is in-
iUlfedJftP The conditions for choosing
levels of roof insulation or cool roofing
vary based on climate, utility prices, build-
ing use, building and fire code consider-
ations, and preference. Thus, the following
factors for choosing insulation or cool
roofing are general approximations. Build-
ing owners might consider adding roof or
ceiling insulation if:
• There is less roof insulation than
called for in the latest state or local
building codes
COOL ROOFS - DRAFT
19
-------
• The building is in a climate with signifi-
cant cold weather or heating needs
• The roof accounts for much of the
building's envelope (i.e., the roof area
equals or exceeds one-fourth of the
building's exterior surface area, calcu-
lated as the walls plus the roof).
Cool roofing can be used on any building,
but is especially useful if:
• The building is in a climate with hot
and sunny weather during at least part
of the year (80°F or hotter weather with
clear skies for at least three months of
the year)
• Significant cooling energy is used
(three or more months of cooling use)
• The duct system is in the attic or ple-
num space
• There are problems maintaining indoor
comfort in the summer (if air condi-
tioning equipment cannot maintain
the desired temperature, or without air
conditioning, if indoor temperatures
exceed 80°F)
• The roof accounts for much of the
building's envelope (i.e., the roof area
equals or exceeds one-fourth of the
building's exterior surface area, calcu-
lated as the walls plus the roof)
• The roof materials tend to crack and
age prematurely from sun damage (if
damage begins before the warranty
period or the roof life ends).
Generally, adding roof insulation means
adding insulation under the roof or above
the ceiling, which can be disruptive to
building occupants. Another option on
the market is to spray insulating foam or
affix rigid insulation onto the top of the
roof surface. Each of these products adds
approximately an R-6 level of long-term
thermal resistance for each inch (2.5 cm)
of thickness added. These technologies by
themselves are not cool roofing materials;
however, they are often applied as part
of a complete roofing system, where the
top surface is a cool coating or single-ply
membrane.
5. Cool Roof Initiatives
Communities have developed cool roof
programs by taking action in their own
buildings, often called leading by example;
through voluntary incentives; and through
mandatory requirements.
Local governments have frequently started
by installing cool roofs in public build-
ings. Their efforts have included launching
demonstration projects and adapting public
building procurement practices to require
cool roofs for new public buildings and
roofing renovation projects. Beginning with
the public sector allows a community to
demonstrate the technology, make contrac-
tors aware of the products available, and
promote the use of cool roof materials in
other building sectors.
In many communities, voluntary cool roof
incentives have been provided by local
energy companies as part of their demand-
side management programs. A few local
government agencies also offer incentives
to assist low-income or other households
with installing cool roofs.
Some governments have mandated imple-
mentation of cool roofs in certain areas.
These actions generally require adopting
specific energy code provisions that require
cool roofs or include cool roofs in the
calculation of how much insulation is re-
quired to meet minimum energy efficiency
requirements.
20
REDUCING URBAN HEAT ISLANDS - DRAFT
-------
Mandatory requirements for cool roofs
have played an increasingly significant role
in implementation. Before 1995, the only
regulations affecting cool roofing mandated
that roof color not cause undue glare. The
American Society of Heating, Refrigerating,
and Air-conditioning Engineers (ASHRAE)
has since developed energy-efficient design
standards that provide minimum require-
ments for both commercial and residential
buildings. ANSI/ASHRAE/IESNA Standard
90.1-1999, Energy Standards for Build-
ings Except Low-Rise Residential Buildings
and ANSI/ASHRAE Standard 90.2-2001,
Energy-Efficient Design of Low-Rise Resi-
dential Buildings provide guidelines for
new equipment, systems, and buildings.
These standards were originally developed
in response to the 1970s energy crisis and
now serve as the generally accepted basis
for many state building and energy codes.
Both ASHRAE standards include credits
pertaining to cool roofing. An example
of a cool roofing credit is Addendum f to
90.2-2001, which allows the use of high-
albedo roofs in hot and humid climates as
part of the energy efficiency ceiling calcula-
tion for a residential building.33
A number of states and localities now have
developed specific energy code require-
ments to encourage or require cool roofing.
For example:
• In 1995, Georgia was the first state
to add cool roofs to its energy code.
The code allowed building owners to
reduce roof insulation if they installed
a cool roof that had a minimum solar
reflectance of 75 percent and a mini-
mum thermal emittance of 75 percent.34
Note that if a building owner uses less
insulation when installing a cool roof,
he may not accrue net energy savings.
• Florida is using a similar approach to
Georgia in its energy code.35 Because
of the energy efficiency gains from cool
roofs, the Florida code allows com-
mercial and multi-family residential
buildings using a roof with at least 70
percent solar reflectance and 75 percent
thermal emittance to reduce the amount
of insulation required to meet building
energy efficiency standards. The ad-
justment does not apply for roofs with
ventilated attics or semi-heated spaces.
• In January 2003, Chicago amended
its energy code requirements for low-
sloped roofs.36 This code applies to all
buildings except separated buildings
that have minimal peak rates of en-
ergy use and buildings that are neither
heated nor cooled. Low-sloped roofs
installed on or before December 31,
2008, must achieve a minimum solar
reflectance (both initial and weathered)
of 0.25 when tested in accordance with
ASTM standards E 903 and E 1918 or
by testing with a portable reflectometer
at near ambient conditions. For low-
sloped roofs installed after that date,
roofing products must meet or exceed
the minimum criteria to qualify for the
ENERGY STAR Roof Products label.
• In 2001, in response to electrical power
shortages, California updated its build-
ing energy code (Title 24), adding cool
roofing as an energy efficiency op-
tion.37 A cool roof is defined as having
minimum solar reflectance of 70 per-
cent and minimum thermal emittance
of 75 percent, unless it is a concrete
or clay tile, in which case it can have
a minimum solar reflectance of 40
percent. This 40 percent rating incor-
porates new cool colored residential
products. Owners must use specific
methods to verify building energy use
to account for cool roofing as an energy
efficiency option. In this case, the heat
COOL ROOFS - DRAFT
21
-------
gain of the roof is reduced to account
for use of a cool roof. In 2005, these
cool roof provisions became mandatory
for all new non-residential construc-
tion and re-roofing projects that involve
more than 2,000 square feet (190 m2)
or 50 percent replacement. The code
also provides alternatives to the stan-
dard criteria as additional compliance
options. In 2006, California began con-
sidering planned 2008 updates to Title
24 and is studying the possibility of
extending cool roof requirements to the
steep-sloped market.38
For further information on California
Title 24, see
-------
Table 6: Examples of Cool Roof Initiatives
Type of Initiative
Description
Links to Examples
Research
National
laboratories
- The Heat Island Group at Lawrence
Berkeley National Laboratory provides research and information about
cool roofing and other heat island mitigation measures. The Cool Roofing
Materials Database lists the solar reflectance and thermal emittance of
numerous roof products, including cool colored roofing.
- ORNL conducts research on reflective roofing and solar
radiation control. Its Web site includes fact sheets, a cool roof calculator,
background information about cool roofing, and research publications.
Voluntary efforts
Demonstration
programs
- Tucson,
Arizona, Cool Roof Demonstration Project (city office building).
Incentive
programs
- Pacific Gas & Elec-
tric's utility rebate program for cool roofs.
- Southern California Edison's Cool
Roof Rebate Program.
-
Austin Energy's Reflective Roof Coating and Roof and Ceiling Insulation
rebate information.
- Chicago announced in Fall 2007 that it
was expanding a green roof grant program to include cool roofs, with up to
55 $6,000 grants targeted peryear; see information under Department of
Environment portion of the City's website.
Outreach &
education
- EPA's Heat Island Reduction Initiative pro-
vides information on the temperature, energy, and air quality impacts from
green roofs and other heat island mitigation strategies.
Weatherization
programs
- Philadelphia cool roof
incentive program for low-income housing.
Policy efforts
State and munici-
pal energy codes
that require or
- California building energy
code that requires cool roofs on nonresidential low-sloped roofs; applies to
new and retrofit projects over certain size thresholds.
provide recogni-
tion of cool roofs
- Georgia Energy
Code revision applicable to cool roofs.
- See Energy Code listings under
Chicago Department of Construction and Permits under local government
portion of the website.
COOL ROOFS - DRAFT
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Access these calculators on the Web:
ENERGY STAR Calculator:
,
under "Roof Products."
ORNL Calculator:
.
For information on an effort begun
in 2007 to develop an integrated
EPA/Department of Energy (DOE)
calculator, see: .
The roofing calculator is intended to
estimate the savings that a reflective roof
can offer to a typical building and to aid
in the decision of whether to choose an
ENERGY STAR-qualified roof product. It is
only one of many tools that can be used in
the decision making process. A more de-
tailed building energy simulation would be
needed to estimate savings for a particular
building or calculate specific benefit-cost
ratios for a project.
Note that the ENERGY STAR calculator es-
timates could underpredict the energy sav-
ings from a cool roof in some cases. This
is because the equations used in the EN-
ERGY STAR calculator were derived from
multiple runs of a DOE building energy
analysis model, which does not consider
the effects of widely varying roof tempera-
tures or duct location. These effects in-
clude changes in the thermal conductivity
of the insulation, thermal radiation in the
attic or plenum, and conduction gains to
cooling ducts.
ORNL Cool Roof Calculator. This cool
roof calculator is a Web-based tool that
helps estimate the energy and financial
impacts from installing cool roofs on build-
ings with low-sloped roofs that do not have
ventilated attics or plenums.
To generate the equations used in this
tool, researchers ran a computer model of
a roof and ceiling assembly over a range
of climates for roofs with varying levels of
insulation, solar reflectance, and thermal
emittance. This model was calibrated to
emulate heat transfer measurements made
on a special roof and ceiling test assembly
at ORNL.39
This calculator requires input on build-
ing location (a choice of 235 different U.S.
cities is provided); information about the
insulation, solar reflectance, and thermal
emittance of the proposed roof; and the
cost of energy and efficiency of the heating
and cooling systems. The tool provides the
annual cost savings on a square-foot basis
in comparison to a black roof, as well as
annual heating energy savings or penalty,
also in dollars per square foot.
6.2 Roofing Programs and Organizations
Table 7 lists a number of programs that
actively promote cool roofs or that are cur-
rently involved in cool roof research.
24
REDUCING URBAN HEAT ISLANDS - DRAFT
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Table 7: Cool Roof Programs and Organizations
Program/Organization
Role
Web Address
Cool Metal Roofing Coalition
This industry group educates architects,
building owners, specifiers, code and stan-
dards officials, and other stakeholders about
the sustainable, energy-related impacts of
cool metal roofing.
Cool Roof Rating Council (CRRC)
Created in 1998 as a nonprofit, educational
organization, CRRC's members include
manufacturers, utilities, researchers, and
consultants. CRRC maintains a product rating
program and associated product directory.
ENERGY STAR
ENERGY STAR is a joint EPA and DOE program
that helps consumers save money and pro-
tect the environment through energy-
efficient products and practices. Regarding
cool roofs, the Web site provides informa-
tion on qualified roofing products, industry
partners, and case studies.
< www.e n e rgy sta r.g o v>
National Roofing Contractors
Association (NRCA)
This trade association includes roofing, roof
deck, and waterproofing contractors and
industry-related associate members. It pro-
vides technical and safety information, news,
and calendars of industry events.
Roof Consultants Institute (RCI)
This international, nonprofit association
includes professional roof consultants, archi-
tects, and engineers. It hosts trade conven-
tions and develops standards for professional
qualifications.
Roof Coatings Manufacturers As-
sociation (RCMA)
RCMA is a national trade association repre-
senting the manufacturers of cold-applied
coatings and cements for roofing and wa-
terproofing. It promotes the availability and
adaption of energy-efficient materials.
Single Ply Roofing Industry (SPRI)
SPRI is a trade organization representing
sheet membrane and component suppli-
ers to the commercial roofing industry. It
provides information about and forums to
discuss industry practices, workforce training,
and other concerns.
COOL ROOFS - DRAFT
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Endnotes
1 Rose, L.S., H. Akbari, and H. Taha. 2003. Characterizing the Fabric of the Urban Environment: A
Case Study of Greater Houston, Texas. Paper LBNL-51448. Lawrence Berkeley National Labora-
tory, Berkeley, CA.
2 These temperature ranges are compiled from the following individual reports:
Konopacki, S., L. Gartland, H. Akbari, and I. Rainer. 1998. Demonstration of Energy Savings of
Cool Roofs. Paper LBNL-40673. Lawrence Berkeley National Laboratory, Berkeley, CA.
Gartland, L. n.d. Cool Roof Energy Savings Evaluation for City of Tucson.
Miller, W.A., A. Desjarlais, D.S. Parker, and S. Kriner. 2004. Cool Metal Roofing Tested
for Energy Efficiency and Sustainability. CIB World Building Congress, May 1-7, 2004.
Toronto, Ontario.
Konopacki, S. and H. Akbari. 2001. Measured Energy Savings and Demand Reduction from
a Reflective Roof Membrane on a Large Retail Store in Austin. Paper LBNL-47149. Lawrence
Berkeley National Laboratory, Berkeley, CA.
3 Ibid.
4 Konopacki, S., L. Gartland, H. Akbari, and I. Rainer. 1998. Demonstration of Energy Savings of
Cool Roofs. Paper LBNL-40673. Lawrence Berkeley National Laboratory, Berkeley, CA.
5 Rosenzweig, C., W. Solecki, L. Parshall, S. Gaffin, B. Lynn, R. Goldberg, J. Cox, and S. Hodges.
2006. Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Sur-
faces. Sixth Symposium on the Urban Environment and Forum on Managing our Physical and
Natural Resources, American Meteorological Society. Atlanta, GA.
6 Chen, Allan. Cool Colors, Cool Roofs, part 2. Science Beat Berkeley Lab. 27 August 2004. Re-
trieved 14 April 2008 from .
7 Pacific Gas and Electric Company. 2006. Inclusion of Solar Reflectance and Thermal Emittance
Prescriptive Requirements for Residential Roofs in Title 24. Pacific Gas and Electric Company.
Sacramento, CA.
8 Public Interest Energy Research Program. At Home with Cool-Colored Roofs. Technical Brief,
CEC-500-2005-164-F111005. California Energy Commission. Sacramento, CA.
9 Haberl, J., and S. Cho. 2004. Literature Review of Uncertainty of Analysis Methods (Cool Roofs),
Report to the Texas Commission on Environmental Quality. Energy Systems Laboratory, Texas
A&M University, College Station, TX.
10 Konopacki, S., L. Gartland, H. Akbari, and L. Rainer. 1998. Demonstration of Energy Savings of
Cool Roofs. Paper LBNL-40673. Lawrence Berkeley National Laboratory, Berkeley, CA.
11 Konopacki, S., H. Akbari, M. Pomerantz, S. Gabersek, and L. Gartland. 1997. Cooling Energy
Savings Potential of Light-Colored Roofs for Residential and Commercial Buildings in 11 U.S.
Metropolitan Areas. Paper LBNL-39433. Lawrence Berkeley National Laboratory, Berkeley, CA.
12 See the following reports for individual results:
H. Akbari, S. Bretz, J. Hanford, D. Kurn, B. Fishman, H. Taha, and W. Bos. 1993. Monitor-
ing Peak Power and Cooling Energy Savings of Shade Trees and White Surfaces in the
Sacramento Municipal Utility District (SMUD) Service Area: Data Analysis, Simulations, and
Results. Paper LBNL-34411. Lawrence Berkeley National Laboratory, Berkeley, CA.
Callahan, M., D. Parker, J. Sherwin, and M. Anello. 2000. Demonstrated Energy Savings of
26
REDUCING URBAN HEAT ISLANDS - DRAFT
-------
Efficiency Improvements to a Portable Classroom. American Council for an Energy Efficient
Economy ACEEE Summer Study on Energy Efficiency in Buildings. Pacific Grove, CA.
Konopacki, S. and H. Akbari. 2001. Measured Energy Savings and Demand Reduction from
a Reflective Roof Membrane on a Large Retail Store in Austin. Paper LBNL-47149. Lawrence
Berkeley National Laboratory Berkeley CA.
Parker, D.S., J.B. Cummings, J.R. Sherwin, T.C. Stedman, andJ.E.R. Mcllvaine. 1994. Mea-
sured Residential Cooling Energy Savings from Reflective Roof Coatings in Florida. ASHRAE
Transactions, Paper 3788. 100(2):36-49.
Parker, D.S., J.R. Sherwin, J.K. Sonne, S.F. Barkaszi. 1996. Demonstration of Cooling Savings
from Light Colored Roof Surfacing in Florida Commercial Buildings: Our Savior's School.
Florida Solar Energy Center, Cocoa, FL.
Parker, D., S.F. Barkaszi, and J.K. Sonne. 1994. Measured Cooling Energy Savings from Re-
flective Roof Coatings in Florida: Phase II Report. Florida Solar Energy Center, Cape Canav-
eral, FL.
Konopacki, S., H. Akbari, M. Pomerantz, S. Gabersek, and L. Gartland. 1997. Cooling Energy
Savings Potential of Light-Colored Roofs for Residential and Commercial Buildings in 11 U.S.
Metropolitan Areas. Paper LBNL-39433. Lawrence Berkeley National Laboratory, Berkeley, CA.
14 Konopacki, S., and H. Akbari 2002. Energy Savings for Heat Island Reduction Strategies in Chi-
cago and Houston (Including Updates for Baton Rouge, Sacramento, and Salt Lake City). Paper
LBNL-49638. Lawrence Berkeley National Laboratory, Berkeley, CA.
15 Gartland, L. 1998. Roof Coating Evaluation for the Home Base Store in Vacaville, California.
PositivEnergy, 27. Oakland, CA.
16 Vincent, B., and J. Huang. 1996. Analysis of the Energy Performances of Cooling Retrofits in
Sacramento Public Housing Using Monitored Data and Computer Simulations. Contract No.
500-93-053. Prepared for the California Energy Commission, Sacramento, CA.
17 Parker, D. 1997. Cool Roofs. FSEC-PF-323-97. Roofer Magazine. 17(7).
18 Konopacki, S., H. Akbari, M. Pomerantz, S. Gabersek, and L. Gartland. 1997. Cooling Energy
Savings Potential of Light-Colored Roofs for Residential and Commercial Buildings in 11 U.S.
Metropolitan Areas. Paper LBNL-39433. Lawrence Berkeley National Laboratory, Berkeley, CA.
19 See Energy Information Administration. 2003. Retrieved February 11, 2008, from . Electricity prices are reported as cents per kilowatt-hour. Natural gas prices
were converted from dollars per 1,000 cubic feet (28,300 liters) of gas to cents per thousand
Btu (1.1 MJ) based on a conversion factor of 1,021 Btu/cubic foot of gas.
20 Blasnik, M. 2004. Impact Evaluation of the Energy Coordinating Agency of Philadelphia's Cool
Homes Pilot Project. M. Blasnik & Associates, Boston, MA.
21 Levinson, R., H. Akbari, S. Konopacki, and S. Bretz. 2002. Inclusion of Cool Roofs in Nonresi-
dential Title 24 Prescriptive Requirements. Paper LBNL-50451. Lawrence Berkeley National
Laboratory, Berkeley, CA.
22 Mattison, K. 1998. Factors Affecting Roof System Costs. Perspectives. 34 (December). Retrieved 9
October 2007 from .
23 Levinson, R., H. Akbari, S. Konopacki, and S. Bretz. 2002. Inclusion of Cool Roofs in Nonresi-
dential Title 24 Prescriptive Requirements. Paper LBNL-50451. Lawrence Berkeley National
Laboratory, Berkeley, CA.
24 Ibid.
COOL ROOFS - DRAFT
27
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25 Pacific Gas and Electric Company. 2006. Inclusion of Solar Reflectance and Thermal Emittance Pre-
scriptive Requirements for Residential Roofs in Title 24. Draft Report, May 17, 2006. Sacramento, CA.
26 See the following study which includes an analysis of annual energy peak demand reductions,
cooling equipment savings, and net present value savings from expanding California cool roof
requirements to portions of the residential sector:
Pacific Gas and Electric Company. 2006. Inclusion of Solar Reflectance and Thermal Emit-
tance Prescriptive Requirements for Residential Roofs in Title 24. Draft Report, May 17,
2006. Sacramento, CA.
27 Bretz, S., and H. Akbari. 1997. Long-Term Performance of High-Albedo Roof Coatings. Energy &
Buildings. 25(2):159-167.
28 Akbari, H., S. Konopacki, C. Eley, B. Wilcox, M. Van Geem and D. Parker. 1998. Calculations in
Support of SSP90.1 for Reflective Roofs. Paper LBNL-40260. Lawrence Berkeley National Labora-
tory, Berkeley, CA.
29 Akbari, H., S. Konopacki, and D. Parker. 2000. Updates on Revision to ASHRAE Standard 90.2:
Including Roof Reflectivity for Residential Buildings. American Council for an Energy Efficient
Economy. ACEEE Summer Study on Energy Efficiency in Buildings. Pacific Grove, CA.
3° Konopacki, S., and H. Akbari. 1998. Trade-off between cool roofs and attic insulation in new
single-family residential buildings. American Council for an Energy Efficient Economy. ACEEE
Summer Study on Energy Efficiency in Buildings, Pacific Grove, CA.
31 California Energy Commission. 2006. 2005 Building Energy Efficiency Standards for Residential
and Non-residential Buildings. Title 24, Publication No. CEC-400-2006-015.
32 Georgia Energy Code. 1995. Georgia Amendment to the 1995 CABO Model Energy Code for
Section 704.
33 ASHRAE. 2003. ANSI/ASHRAE Addendum f to AN SI/ASHRAE Standard 90.2-2001, ASHRAE Stan-
dard: Energy-Efficient Design of Low-Rise Residential Buildings. ISSN 1041-2336. Atlanta, GA.
34 Georgia Energy Code. 1995. Georgia Amendment to the 1995 CABO Model Energy Code for
Section 704.
35 Florida. 2004. Florida Building Code, Chapter 13: Efficiency. Retrieved 13 November 2007 from
.
36 Chicago, Illinois. 2003. Municipal Code, ch. 8-13.
37 California Energy Commission. 2006. 2005 Building Energy Efficiency Standards for Residential
and Nonresidential Buildings. No. CEC-400-2006-015 (replaces P400-03-001F).
38 Pacific Gas and Electric Company. 2006. Inclusion of Solar Reflections and Thermal Emittance
Prescriptive Requirements for Steep-Sloped Nonresidential Roofs in Title 24. Draft Report, May
18, 2006. Sacramento, CA.
39 Wilkes, K. 1991. Thermal Model of Attic Systems with Radiant Barriers. Oak Ridge National
Laboratory, ORNL/CON-262. Oak Ridge, TN.
28
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