U.S. Department of Energy Building Technologies Program fact sheet about cool roofs, including how they work, the energy-saving benefits, and how to buy and select cool roofs.

1. Cool roofs are ready to save energy, cool urban heat islands, and
help slow global warming.
Cool roofing is the fastest growing sector
of the building industry, as building owners
and facility managers realize the immediate
and long-term benefits of roofs that stay
cool in the sun. Studies exploring the
energy efficiency, cost-effectiveness, and
sustainability of cool roofs show that in
warm or hot climates, substituting a cool roof
for a conventional roof can:
• Reduce by up to 15% the annual air- A white roof saves energy by strongly reflecting sunlight
conditioning energy use of a single- (high solar reflectance) and efficiently emitting thermal
radiation (high thermal emittance).
story building
• Cool interior spaces in buildings that How Cool Roofs Work
do not have air conditioning, making Traditional dark-colored roofing materials
occupants more comfortable strongly absorb sunlight, making them
• Reduce carbon emissions by lowering warm in the sun and heating the building.
the need for fossil-fuel generated White or special “cool color” roofs absorb
electricity to run air conditioners less sunlight, staying cooler in the sun and
• Potentially slow global warming by transmitting less heat into the building. This
cooling the atmosphere reduces the need for cooling energy if the
If you are installing a new roof or reroofing building is air conditioned, or lowers the
an existing building, a systems approach to inside air temperature if the building is not
providing an energy efficient roof should be cooled.
taken with a cool roof considered as one of The “coolness” of a roof is determined by
the options available. two properties and their combined effects on
temperature:
• Solar reflectance — the fraction of
sunlight that is reflected
• Thermal emittance — the efficiency
with which a surface cools itself by
emitting thermal radiation
Both properties are measured on a scale of 0
to 1 — the higher the values, the cooler the
roof.

2. Cool Roofs Save Energy and Money in • It is rarely economical to replace a
Many Settings mechanically sound roof just to increase
Cool choices now exist for most traditional its solar reflectance.
roofing materials. Cool roofing should be • Cool versions of some roofing materials,
considered whenever construction or an including thermoplastic membranes,
energy retrofit is being planned. coated metal products, and clay tiles are
available at little or no additional cost.
• For low-slope roofs (pitch ≤ 2:12), cool
Cool asphalt shingles currently sell for
thermoplastic membranes, elastomeric
up to $0.50/ft2 more than conventional
coatings, and metal products are
asphalt shingles. Cool versions of
available.
some other roofing materials, such
• For steep roofs, cool asphalt shingle,
as modified bitumen, may require a
clay tile, concrete tile, and metal
reflective surface coating that adds
products are available.
Urban Heat Islands • Lower the local air and ground
(Adapted from EPA Urban Heat Island temperatures
Basics Compendium) • Improve human comfort and health
in uncooled buildings and outdoors
http://www.epa.gov/heatisland/resources/
• Reduce the need for electricity to
pdf/BasicsCompendium.pdf
cool buildings
Air temperatures in many urban and • Decrease emissions of nitrogen
suburban areas are higher than those in oxides (NOx), sulfur dioxide (SO2),
their rural surroundings; this regional carbon dioxide (CO2), and/or
elevation in air temperature is called mercury (Hg) from electrical power
an “urban heat island.” Many factors plants
contribute to urban heat islands. In rural
areas, trees and other vegetation provide
shade and also reduce air temperatures
by releasing water to the surrounding air.
Vegetative surfaces are also moderately
solar reflective. In contrast, urban areas
are characterized by dry and impervious
surfaces that strongly absorb light, such
as conventional roofs, sidewalks, roads,
and parking lots. As these urban surfaces
are warmed by the sun, they heat both the
interiors of buildings and the outside air. Philadelphia, PA reduced temperatures in row houses
by installing cool roofs, which improves comfort
Choosing solar-reflective roofing cools
for occupants and may help reduce deaths from heat
the buildings and the outside air. Cool waves. Baltimore, MD took similar steps following
roofs in an urban area can therefore: the success in Philadelphia.

3. about $1/ft2 to the installed cost. • DOE’s Building Energy Software Tools
• Installing a white roof on a commercial Directory provides information on 370
building yields annual energy savings building software tools for evaluating
worth up to $0.20/ft2 and installing a energy efficiency, renewable energy,
cool color roof on a home yields annual and sustainability in buildings.
energy savings worth up to $0.05/ft2. http://apps1.eere.energy.gov/buildings/
Savings vary, and are greatest in hot tools_directory
and warm climates. Use the DOE or • The DOE and the U.S. Environmental
EPA calculator referred to later in this Protection Agency (EPA) each offer
document to estimate your savings. online calculators that estimate the
• A cool roof may increase the need for cooling energy savings and heating
heating energy in winter by reflecting energy penalties attained by installing a
sunlight that would otherwise warm cool roof.
the building. However, winter penalties DOE calculator:
can be smaller than summer savings http://www.ornl.gov/sci/roofs+walls/
even in mixed climates (locations facts/CoolCalcEnergy.htm
with comparable heating and cooling EPA calculator:
requirements). http://roofcalc.com
• The EPA lists thousands of ENERGY
How to Select and Buy Cool Roofing
STAR approved cool roofing materials.
Materials
http://www.energystar.gov/index.
The energy and cost savings that can be cfm?c=roof_prods.pr_roof_products
achieved by using cool roofing technologies • The Cool Roof Rating Council (CRRC)
depend on many factors, such as climate and maintains a program for measuring
building characteristics. and reporting the solar reflectances and
Three aspects of cool roofing technologies thermal emittances of roofing materials.
also affect their cost-effectiveness: Their Rated Products Directory lists
• The aged solar reflectance and thermal over 1000 materials.
emittance of the roof (since many roofs http://coolroofs.org
become less reflective over time, energy
savings should be based on long-term For more information, contact:
values of solar reflectance and thermal Marc LaFrance, DOE Technology
emittance). Development Manager for Cool Roofs
• The incremental initial cost of the cool 202-586-9142, marc.lafrance@ee.doe.gov
roof (if any). Andre Desjarlais, Oak Ridge National
• The incremental cost of keeping a cool Laboratory Building Envelopes Group Leader
roof clean and reflective (if any). 865-574-0022, desjarlaisa@ornl.gov
Ronnen Levinson, Lawrence Berkeley
Several tools are available to help consumers
National Laboratory Heat Island Group,
and professionals choose appropriate cool 510-486-7494, rmlevinson@lbl.gov
roofing materials and estimate their benefits.

4. The Emergence of Cool Roofs Twenty years after DOE initiated its work
Cool roofing is not a new concept. In the on cool roofs, these products dominate the
mid-1980s, researchers at DOE national commercial roofing marketplace in warm
laboratories in Tennessee and California and hot climates, partly because the State
were measuring the energy-saving benefits of California changed its energy code to
of “solar radiation control coatings” on prescribe cool roofing for most commercial
test roofs. Although energy savings were buildings with low-sloped roofs.
confirmed in these early studies, they were Today
not sufficient to lead roofing designers and
Today both white and “cool color” products
installers to switch away from traditional
are available for low-slope and steep-slope
dark-colored roofing systems.
roofs.
A parallel effort was launched to determine
• Cool products are generally economical
the influence of light-colored roofing
on low-slope roofs for commercial or
products on summer urban heat islands.
industrial buildings.
This research demonstrated that solar
• Cool options are available for most
reflective roofs, solar reflective pavements,
traditional roofing materials.
and vegetation could lower urban air
• White roofs are coolest, but cool colors
temperatures, saving additional energy and
are a popular alternative for roofs that
improving air quality.
can be seen by neighbors.
Rolling blackouts during the summer of • The U.S. EPA lists about 3,000
2001 motivated California’s public utilities ENERGY STAR® compliant cool-
to expand the scope of their peak load roofing materials.
management programs. They found that cool • Federal tax credits are available for
roofing reduces peak demand for electricity, some cool materials, including asphalt
helping to lower costs and avoid power shingles and metal products.
outages. • Many state agencies and
utility programs offer
incentives for installing
cool roofs.
• Cool roof credits are
offered in sustainable
building programs such as
the U.S. Green Building
Council’s Leadership in
Energy and Environmental
Design (LEED).
Cool roofing for residential buildings need not be white; cool colors are
available for a number of roofing materials.