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Cool Color Roofing Materials

Authors:

Hashem Akbari

Concordia University

Paul Berdahl

University of California, Berkeley

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Peak-normalized solar spectral power; over half of all solar power arrives as invisible, “near- infrared” radiation

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. Project residential roofing market in the U.S. western region surveyed by

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. PinwheelTM screen shot.

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Solar spectral reflectance of a PinwheelTM-formulated cool coating (“solution”) designed to match the visible spectral reflectance of a particular shade of green (“target”).

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Description of an iron oxide red pigment in the Lawrence Berkeley National Lab pigment database

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LBNL-XXXXX

Cool Color Roofing Materials

Hashem Akbari, Paul Berdahl, Ronnen Levinson, Steve Wiel

Heat Island Group

Lawrence Berkeley National Laboratory

Berkeley, CA 94720

and

Bill Miller and Andre Desjarlais

Oak Ridge National Laboratory

Oak Ridge, TN 37831

Draft Final Report Prepared for:

California Energy Commission PIER Program

Program Manager: Nancy Jenkins

Project Manager: Chris Scruton

February 2006

This study was supported by funding from the California Energy Commission (CEC)

through the U.S. Department of Energy under contract DE-AC02-05CH11231.

Disclaimer

This document was prepared as an account of work sponsored by the United States Government.

While this document is believed to contain correct information, neither the United States

Government nor any agency thereof, nor The Regents of the University of California, nor any of

their employees, makes any warranty, express or implied, or assumes any legal responsibility for

the accuracy, completeness, or usefulness of any information, apparatus, product, or process

disclosed, or represents that its use would not infringe privately owned rights. Reference herein

to any specific commercial product, process, or service by its trade name, trademark,

manufacturer, or otherwise, does not necessarily constitute or imply its endorsement,

recommendation, or favoring by the United States Government or any agency thereof, or The

Regents of the University of California. The views and opinions of authors expressed herein do

not necessarily state or reflect those of the United States Government or any agency thereof or

The Regents of the University of California.

Cool Color Roofing Materials

A Collaboration of Industry, Lawrence Berkeley National Laboratory (LBNL), and Oak Ridge

National Laboratory (ORNL)

Hashem Akbari, Paul Berdahl, Ronnen Levinson, and Steve Wiel (LBNL)

William Miller and Andre Desjarlais (ORNL)

February 24, 2006

Abstract

Raising roof reflectivity from an existing 10-20% to about 60% can reduce cooling-energy use in

buildings in excess of 20%. Cool roofs also result in a lower ambient temperature that further

decreases the need for air conditioning and retards smog formation. In 2002, suitable cool white

materials were available for most roof products, with the notable exception of asphalt shingles;

cooler colored materials are needed for all types of roofing. To help to fill this gap, the

California Energy Commission (Energy Commission) engaged Lawrence Berkeley National

Laboratory (LBNL) and Oak Ridge National Laboratory (ORNL) to work on a three-year project

with the roofing industry to develop and produce reflective, colored roofing products. The

intended outcome of this project was to make cool-colored roofing materials a market reality

within three to five years. For residential shingles, we have developed prototype light-colored

shingles with solar reflectances of up to 35%. One manufacturer currently markets colored

shingles with the ENERGY STAR qualifying solar reflectance of 0.25. Colored metal and clay

tile roofing materials with solar reflectances of 0.30 to 0.60 are currently available in the

California market.

LBNL and ORNL performed research & development in conjunction with pigment

manufacturers, and worked with roofing materials manufacturers to reduce the sunlit

temperatures of nonwhite asphalt shingles, clay tiles, concrete tiles, metal products, and wood

shakes. A significant portion of the effort was devoted to identification and characterization of

pigments to include and exclude in cool coating systems, and to the development of engineering

methods for effective and economic incorporation of cool pigments in roofing materials. The

project also measured and documented the laboratory and in-situ performances of roofing

products. We also established and monitored three pairs of demonstration homes to measure and

showcase the energy-saving benefits of cool roofs. The following activities were carried out.

In collaboration with the Energy Commission, we convened a Project Advisory Committee

(PAC), composed of 15 to 20 diverse professionals, to provide strategic guidance to the project.

In order to determine how to optimize the solar reflectance of a pigmented coating matching a

particular color, and how the performance of cool-colored roofing products compares to that of a

standard material, we (1) measured and characterized the optical properties of many standard and

innovative pigmentation materials; (2) developed a computer model to maximize the solar

reflectance of roofing materials for a choice of visible colors; and (3) created a database of

characteristics of cool pigments.

In order to help manufacturers design innovative methods to produce cool-colored roofing

materials, we (1) compiled information on roofing materials manufacturing methods; (2) worked

with roofing manufacturers to design innovative production methods for cool-colored materials;

and (3) tested the performance of materials in weather-testing facilities.

One of the project objectives was to demonstrate, measure and document the building energy

savings, improved durability and sustainability attained by use of cool-colored roof materials to

key stakeholders (consumers, roofing manufacturers, roofing contractors, and retail home

improvement centers). In order to do this, we (1) monitored buildings at California

demonstration sites to measure and document the energy savings of cool-colored roof materials;

(2) conducted materials testing at weathering farms in California; (3) conducted thermal testing

at the ORNL Steep-slope Assembly Testing Facility; and (4) performed a detailed study to

investigate the effect of solar reflectance on product useful life.

We developed partnerships with various members of the roofing industry. We worked through

the trade associations to communicate and advertise to their membership new cool color roof

technology and products. This collaboration induced the manufacturers to develop a market plan

for California and to provide technical input and support for this activity. Through the industry

partners, many California housing developers and contractors have been convinced to install the

new cool-colored roofing products.

Acknowledgement

This work was supported by the California Energy Commission (CEC) through its Public

Interest Energy Research Program (PIER), by the Laboratory Directed Research and

Development (LDRD) program at Lawrence Berkeley National Laboratory (LBNL), and by the

Assistant Secretary for Renewable Energy under Contract No. DE-AC02-05CH11231. The

authors wish to thank CEC Commissioner Arthur Rosenfeld and PIER managers Nancy Jenkins

and Chris Scruton for their support and advice. Special thanks go also to Mark Levine, director

of the Environmental Energy Technologies Division at LBNL for their encouragement and

support in the initiation of this project.

This work has been a collaborative research between ORNL, LBNL, and the industry. We

acknowledge the contribution of Tony Chiovare (Custom-Bilt Metals), Lou Hahn (Elk

Corporation), Ingo Joedicke (ISP Minerals), Frank Klink (3M Industrial Minerals), Scott Kriner

(Akzo Nobel Coatings), Kenneth Loye (Ferro), David Mirth (Owens Corning), Jeffrey Nixon

(Shepherd Color Company), Joe Reilly (American Rooftile Coating), Robert Scichili (then

BASF Industrial Coatings, currently a consultant to coated metal industry), Ming L. Shiao

(CertainTeed), Krishna Srinivas (GAF), Yoshihiro Suzuki (MCA Clay Tile), Jerry Vandewater

(Monier Lifetile), Michelle Vondran (Steelscape), Lou R. Zumpano (Hanson Roof Tile).

We also acknowledge the guidance, support, and the directives of the Project Advisory

Committee (PAC) members: Gregg Ander (Southern California Edison Company), Aaron J.

Becker (Dupont Titanium Technologies), Carl Blumstein (California Institute for Energy and

Environment),Tom Bollnow (National Roofing Contractors Association), Jack Colbourn (US

EPA SF Office), Kathy Diehl (US EPA SF Office), Steven Harris (Quality Auditing Institute),

Noah Horowitz (Cool Roof Rating Council and National Resource Defense Council), Scott

Kriner (Cool Metal Roofing Coalition), Scott Kriner (Cool Metal Roofing Coalition), Shari

Litow (DuPont Titanium Technologies ), Archie Mulligan (Habitat for Humanity), Mike Evans

(Evans Construction), Jerry Wager (Ochoa & Shehan), Rick Olson (Roof Tile Institute), Mike

Rothenberg (Bay Area Air Quality Management District), Steven Ryan (US EPA), Thomas A.

Shallow (Asphalt Roofing Manufacturers Association), Peter Turnbull (Pacific Gas and Electric

Company, Jessica C Yen (DuPont Titanium Technologies).

Executive Summary

The world is facing disruptive global climate change from greenhouse gas emissions and

increasingly expensive and scarce energy supplies. Energy efficiency reduces those emissions

and mitigates the rising cost of energy. Energy-Efficient Cool Color Roofing is a new technology

for the roofs of homes that provides a significant leap in energy efficiency. The application of

this technology for developing cool-colored roofing materials has been the focus of this

collaborative study between the scientists at the Lawrence Berkeley National Laboratory

(LBNL), scientists at Oak Ridge National Laboratory (ORNL), and industry.

Cool Color Roofing uses solar-reflective pigments to reduce a home’s solar heat gain and air-

conditioning energy consumption in a warm climate by about 10 to 20%. These roofs also lower

a home’s peak-hour cooling power demand by about 10 to 20%, helping prevent blackouts and

brownouts on hot summer afternoons. We used pigment spectroscopy to identify solar-reflective

pigments of different colors and developed software for the design of cool color coatings. We

collaborated with a consortium of U.S. pigment, coating and roofing manufacturers to develop

novel methods to manufacture asphalt shingle, clay tile, concrete tile, and metal roofing products

in a wide palette of cool colors. We estimate that applying cool-colored roofs to houses could

achieve a net energy savings in the U.S. worth over $400 million per year (Konopacki et al.

1997). The estimated savings in California (in 2005 $) is about $100 million per year (see Figure

EX-1).

Figure EX-1. Potential annual cool roof net energy savings in U.S. cities.

The Need for Cool Color Roofing

Cool nonwhite roofing technology is intended not to replace light-colored roofing, but to

improve the solar reflectance of dark-colored products, which dominate the residential roofing

market. (White residential roofing products stay cool in the sun, but sell poorly in California

where homeowners prefer the aesthetics of dark-colored roofs.) Cool Color Roofing technology

makes solar-reflective roofing available in any color (dark or light) by selectively reflecting the

invisible component of sunlight in the “near-infrared” (NIR) spectrum (see Figure EX-2).

(a) (b)

Figure EX-2. (a) Spectral solar power distribution, and (b) solar spectral reflectance of cool

and standard brown surfaces.

On a summer day, the peak daily surface temperature of a cool dark roof of solar reflectance 0.35

is about 14 °C lower than that of a conventional dark roof of solar reflectance 0.10. Compared to

the conventional dark roof, the cool dark roof conducts about 20 to 40 percent less heat into a

home’s conditioned space, reducing the home’s demand for cooling power by about 7 to 15

percent in the late afternoon. These are the same hours during which demand for air conditioning

strains the electrical grid and requires utilities to produce additional power using less efficient,

more expensive, and more polluting “peak” generators. The cool dark roof yields a net annual

energy savings (decrease in cooling energy minus increase in heating energy) of about 6 to 11

percent. . Our findings for sub-tile venting shows the heating penalty is lessened, which will

make annual energy savings for cool roofs even more appealing.

Figure EX-3 depicts examples of cool metal panel, concrete tile, asphalt shingle, and clay tile

roofing products.

Figure EX-3. Cool metal panel, concrete tile, asphalt shingle, and clay tile roofing products.

Development of Cool Color Roofs

This multi-year research project is funded by the California Energy Commission’s Public Interest

Energy Research program, with an initial grant from the U.S. Department of Energy. The

California Energy Commission’s (the Commission) cool-color program at LBNL has three

elements: (1) measuring the rates at which many common pigmented coatings absorb (convert to

heat) and backscatter (reflect) light at wavelengths in the UV, visible, and NIR spectra; (2) using

these rates in a LBNL software tool for the design of color-matched coatings with high solar

reflectance; and (3) working with the roofing industry to develop novel manufacturing methods.

Our industrial partners manufactured the prototypes and products. ORNL performed the

demonstration work, measuring both the residential energy savings achieved by use of cool

colored roofing, and the extent to which exposure changes the appearance and performance of

cool colored roofing. ORNL also tested several cool roofing products at their facilities at Oak

Ridge. Hereafter, we refer to this national labs partnership as the “Cool Team.”

Pigment characterization begins with measuring the reflectance (r) and transmittance (t) of a thin

coating (e.g., a paint film) colored by single pigment, such as iron oxide red. These "spectral," or

wavelength-dependent, properties of the pigmented coating are measured at 441 evenly spaced

wavelengths spanning the solar spectrum (300 to 2500 nanometers (nm), where 1 nm = 10

-9

meter.) Inspection of the film's spectral absorptance (calculated as 1-r-t) reveals whether a

pigmented coating is "cool" (has low NIR absorptance) or "hot" (has high NIR absorptance).

The spectral reflectance and transmittance measurements are used to compute spectral rates of

light absorption and backscattering (reflection) per unit depth of film. These calculations employ

a variant of the Kubelka-Munk two-flux continuum model of light propagation through a

pigmented coating that Berkeley Lab has adapted to account for the reflectance of incompletely

diffused light at the air-coating interface. Such “interface reflectances” can significantly alter the

reflectance and transmittance of the optically thin pigmented coatings applied to roofing

materials.

To help the roofing industry identify cool pigments to use and hot pigments to avoid in their

coatings, the LBNL researchers have produced a browsable HTML database describing the solar

spectral optical properties of more than 80 single-colorant pigmented coatings (see Figure EX-4).

The database charts the solar spectral reflectance, transmittance, absorptance, backscattering

coefficient, and absorption coefficient of each pigmented coating, and also presents images,

commentary, and a chemical description of each pigment. Machine-readable datafiles are also

included.

Figure EX-4. A screen image of the cool coatings database.

The radiative properties of these pigmented coatings serve as inputs to Pinwheel™, a software

tool for the design of color-matched cool coatings that the LBNL team has developed and shared

with its industrial partners (see Figure EX-5).

Figure EX-5. Pinwheel™ screen shot.

Pinwheel™ formulates color-matched coatings with high solar reflectance. It models a coated

surface with two or three layers: an opaque substrate, an optional basecoat, and a topcoat. The

solar spectral reflectance of the substrate; the thickness and colorant composition of the optional

basecoat; and the thickness of the topcoat are specified by the coating designer. Pinwheel™ then

seeks the topcoat colorant composition that maximizes the solar reflectance of the coated surface

while acceptably matching a target visible spectral reflectance. The solar spectral reflectance of a

coated surface, and hence its solar reflectance and visible spectral reflectance, are computed by

applying to the solar spectral absorption and backscattering coefficients of colorants (a) a two-

flux, two-constant model of light propagation through a film and (b) a colorant mixture model.

Pinwheel™ has a large library of over 80 colorants whose solar spectral properties have been

characterized by LBNL.

This tool differs in three major respects from conventional coating formulation software. First, it

predicts solar spectral reflectance (300 to 2500 nm), rather than just visible spectral reflectance

(400 to 700 nm). Second, it does not require that coatings be opaque. This permits design of thin

coatings that transmit both visible and near-infrared light, as well as thicker coatings that stop

visible light but transmit near-infrared light. Third, it contains the solar (and not just visible)

spectral properties of the 80+ colorants.

Production of Cool Colored Roofing

Asphalt shingles are the dominant residential roofing product in the western United States,

covering about 54% of the total residential roof area. The other major residential roofing

products are concrete tiles (10%), clay tiles (10%), metal panels (9%), and wood shake (4%).

The Cool Team and their industrial partners have developed methods for creating cool colored

surfaces and applied them to create a wide variety of residential roofing materials, including

metal, clay tile, concrete tile, and asphalt shingle. The basic technique is to maximize NIR

reflectance by coloring a topcoat with pigments that weakly absorb and (optionally) strongly

backscatter NIR radiation, and adding an NIR-reflective basecoat (e.g., titanium dioxide white) if

both the topcoat and the substrate weakly reflect NIR radiation. Use of NIR-absorbing pigments

(e.g., carbon black) commonly used to adjust colors must be minimized. LBNL’s coating design

software guides the formulation of the topcoat and optional basecoat.

The Cool Team collaborated with pigment manufacturers and roofing materials manufacturers.

The materials companies are:

• 3M Industrial Minerals (St. Paul, MN);

• Akzo Nobel (Macungie, PA);

• American Rooftile Coatings (Fullerton, CA);

• BASF Industrial Coatings (Southfield, MI);

• CertainTeed Corporation (Valley Forge, PA);

• Custom-Bilt Metals (Chino, CA);

• Elk Corporation (Ennis, TX);

• GAF Materials (Wayne, NJ);

• Hanson Roof Tile (Fontana, CA);

• ISP Minerals (Hagerstown, MD);

• MCA Clay Tile (Corona, CA);

• Monier Lifetile (Thousand Oaks, CA);

• Owens Corning (Granville, OH);

• Steelscape Inc. (Kalama, WA).

The pigment manufacturers are Ferro Corporation (Cleveland, OH) and Shepherd Color

Company (Cincinnati, OH).

All of these companies have introduced, or plan to introduce, cool color roof products or

components (e.g., pigments, coatings, or colored granules). This consortium includes most of the

major roofing manufacturers in the United States. Therefore, the appropriate product comparison

is between a manufacturer’s conventional roofing product, and its corresponding Cool Color

Roofing product.

Metal panels and clay tiles were the first types of roofing to be produced in cool colors. BASF

Industrial Coatings (Southfield, MI) has launched “Superl SP II™ ULTRA-Cool®,” a line of

cool colored Kynar coatings that is quickly replacing the more conventional silicone-modified

polyester coatings. Steelscape Inc. (Kalama, WA) has recently introduced Spectrascape MBM, a

cool Kynar coating for the metal building industry. Custom-Bilt Metals (Chino, CA) has

switched over 250 of its metal roofing products to cool colors.

Clay tiles are colored with a pigmented glaze that is fired at high temperature. MCA Clay Tile

(Corona, CA) is currently selling 11 products with solar reflectances exceeding the ENERGY

STAR requirement of 0.25. The Berkeley Lab team is working with MCA tile to further increase

the solar reflectance of its products by adding a white basecoat.

Concrete tiles can be colored either by mixing pigments into the wet concrete (cement +

aggregate + water), or by adding a pigmented coating to the tile’s surface. American Rooftile

Coatings (Fullerton, CA) is currently selling polymeric coatings systems for concrete tiles that

offer solar reflectances of at least 0.35.

Berkeley Lab has collaborated with a manufacturer of roofing granules (ISP Mineral Products;

Hagerstown, MD) to develop about 100 prototype shingles. Figure EX-6 shows the iterative

development of a cool black shingle prototype. A conventional black roof shingle has a

reflectance of about 0.04. Replacing the granule's standard black pigment with a cool NIR-

scattering black pigment (prototype 1) increases the solar reflectance of the shingle to 0.12.

Incorporating a thin white sublayer (prototype 2) raises the shingle's solar reflectance to 0.16;

using a thicker white sublayer (prototype 3) increases the shingle's reflectance to 0.18. The figure

also shows an approximate performance limit (solar reflectance 0.25) obtained by applying 25-

nm NIR-reflective black topcoat over an opaque white background. Roughness and limits to the

thicknesses of the basecoat and topcoat are expected to make the reflectance of any granule-

surfaced shingle pigmented with this cool inorganic black less than that achieved by the white-

backed smooth film.

Figure EX-6. Development of a cool black shingle.

In 2005, one of the industrial partners, Elk Corporation (Ennis, TX) introduced its Prestique Cool

Colors Series, a small line of light-gray and light-brown asphalt shingles with solar reflectances

that meet or exceed the Energy Star requirement of 0.25. The cool color shingles are advertised

on Elk’s web site

as the “first energy-efficient cool asphalt shingles offered in a palette of rich,

organic colors.” Elk offers a 40-year limited warranty with a limited wind warranty of up to 90

mph, and a UL Class “A” fire-rating. The prototype shingles were developed in conjunction with

3M™ to meet initial ENERGY STAR performance.

Field-Testing and Demonstration of Cool Colored Roofing

ORNL has set up a residential demonstration site in Fair Oaks, CA (near Sacramento) consisting

of two pairs of single-family, detached houses roofed with metal and concrete tile. We have also

set up two houses in Redding, CA to demonstrate asphalt shingles. The demonstration pairs each

include one building roofed with a cool-pigmented product and a second building roofed with a

conventionally (warmer) pigmented product of nearly the same color. The paired homes are

adjacent, and share the same floor plan, roof orientation, level of blown ceiling insulation of 3.4

K/W (R-19 insulation), and all have air-handlers and air-delivery duct work in the attic.

Demonstration homes in Fair Oaks have soffit and gable vents, while the homes in Redding are

equipped with soffit and ridge vents. Each home will be monitored through at least the summer

of 2006.

Temperatures at the roof surface, on the underside of the roof deck, in the mid-attic air, at the top

of the insulation, on the surface of the sheet rock facing the attic, and inside the building are

logged continuously by a data acquisition system. Relative humidity in the attic air and the

residence are also measured. Heat flux transducers are embedded in the sloped roofs and the attic

floor to measure the roof heat flows and the building heat leakage. We have instrumented the

building to measure the total house and air-conditioner electrical energy use. A fully

instrumented meteorological weather station is set up to collect the ambient dry bulb

temperature, the relative humidity, the solar irradiance, and the wind speed and wind direction.

One of the Fair Oaks homes roofed with low-profile concrete tile was colored with a

conventional chocolate brown coating (solar reflectance 0.10), while the other was colored with

a matching cool chocolate brown with solar reflectance 0.41. The attic air temperature beneath

the cool brown tile roof has been measured to be 3 to 5 K cooler than that below the

conventional brown tile roof during a typical hot summer afternoon. The results for the pair of

homes roofed with painted metal shakes are just as promising. There the attic air temperature

beneath the cool brown metal shake roof (solar reflectance 0.31) was measured to be 5 to 7 K

cooler than that below the conventional brown metal shake roof. Attic air temperature below the

cool shingle (solar reflectance 0.26) was about 3 K cooler than the temperature below the

conventional pigmented shingle roof.

The application of cool colored coatings reduced the surface temperature of the roofs, which in

turn reduced the average daylight heat flows crossing the roof deck by 20% for cool pigmented

tile, by 32% for cool pigmented painted metal shakes and by 30% for cool pigmented asphalt

shingle roofs as compared to each roof type’s conventional counterpart. A day selected from

August 2004 depicts a consistent and sustained reduction in heat flow during the daylight hours

for the painted metal roof shakes (see Figure EX-7).

Cool color materials appeared to provide more thermal benefit for the pair of homes with metal

roofs then the pair of homes with tile roofs. We believe the difference is attributable to sub-tile

http://www.elkcorp.com/homeowners/products/shingles_prestique_ccs.cfm

venting of the concrete tile roofs as compared to the metal shake roofs which were direct nailed

to the roof deck. Sub-tile venting is more efficient on hotter roofs so it diminishes the effect of

the solar reflectance of the cool tiles.

Figure EX-7. Heat flows through the roof decks of an adjacent pair of homes over the

course of a hot summer day. The total daily heat influx through the cool brown metal shake

roof (solar reflectance 0.31) between the solar hours of 8AM and 5PM is 31% lower than

that through the conventional brown metal shake roof (solar reflectance 0.08).

Materials Testing at Weathering Farms in California

The long-term benefits of cool pigmented roofing systems (Akbari et al. 2004) can be

compromised if a significant loss in solar reflectance occurs during the first few years of service

life. Ultraviolet radiation, atmospheric pollution, microbial growths, acid rain, temperature

cycling caused by sunlight and sudden thunderstorms, moisture penetration, condensation, wind,

hail, freezing, and thawing are all thought to contribute to the loss of a roof’s solar reflectance.

Understanding the effect of climatic soiling is essential for developing defensible claims about

energy savings for cool roofs. Miller et al. (2002) discovered that aerosol deposition introduced

biomass of complex microbial consortia onto the test roofs and the combination of contaminants

and biomass accelerated the loss of solar reflectance for the thermoplastic membranes and the

roof coatings. Results published by Berdahl et al. (2002) indicate that the “the long-term change

of solar reflectance appears to be determined by the ability of elemental carbon (deposited soot)

to adhere to the roof, resisting washout by rain”.

To document the effect of airborne contaminants and biomass we completed the following

objectives (1) set up seven weathering sites in six climatic zones of California; (2) measured the

drop in solar reflectance and the change in thermal emittance of roof products with and without

cool pigmented colors; (3) characterized the particulate matter deposited on the roof samples; (4)

established the relationship between deposited contaminants and the loss of solar reflectance; (5)

determined the contribution of particulate matter on the enhancement or loss of solar reflectance;

(6) identified the biomass existing on roof samples; and (7) determined the effect of biomass on

the loss of solar reflectance.

The long-term loss of reflectance appears driven by the ability of the particulate matter to cling

to the roof and resist being washed off by wind and or rain. The chemical composition of

particles deposited on the roof samples was very similar across the state of CA; there was no

clear distinction from one region to another. Organic and elemental carbon was detected;

however, the elemental carbon did not contribute significantly to the loss of solar reflectance.

Dust particles (characterized by Ca and Fe) and organic carbon compensated for the loss of solar

reflectance due to elemental carbon possibly because some crystalline forms of these elements

were light reflecting and contributed to the solar reflectance. Polar lipid fatty acid and quinone

analyses showed diverse microbial communities with cyanobacteria or fungi being the dominant

players.

Climatic soiling did not cause the cool pigmented roof coupons to lose any more solar

reflectance than their conventional pigmented counterparts. The loss in solar reflectance for

painted metal and clay and concrete tile coupons was of the order 6% of the initial reflectance for

this 2½ year time limited study. As and example, the solar reflectance of a cool brick-red colored

metal dropped from 0.37 to 0.36; only a 0.02 drop over 2 ½ years. Results show that elemental or

black carbon did not contribute significantly to the degradation of reflectance, but dust particles

(characterized by Al) and organic carbon had a statistically significant effect on balancing the

degradation over the course of the study.

Steep-slope Assembly Testing at ORNL

An assembly of steep-slope attics having shed-type roofs was installed on top of the ESRA for

field-testing clay and concrete tile roofs. The attics are adjacent to one another, and their shed

roofs face directly south. The footprint for each attic is about 16 ft long by 5 ft wide. Roof slope

was set at 4 in. of rise for every 12 in. of run (18.4° pitch). Soffit and ridge venting are provided

with vent openings of 1:300. The steep-slope assembly was field-tested for a summer with the

ridge vent closed to simulate conventional construction in the western states and with the ridge

vent open the following summer to observe whether an unimpeded airflow under the tile (sub-tile

venting) and attic ventilation would further improve the thermal performance of the tile roofs.

A high-profile S-Mission clay tile with cool pigmented colors, two different styles of high-

profile terra-cotta concrete tiles, a medium-profile concrete (the same as that tested in California

demonstrations), and a flat concrete slate tile were installed on the attic assemblies by the Tile

Roofing Institute. The clay S-Mission tile and the medium-profile concrete tile were direct-

nailed to the roof deck, a high-profile S-Mission concrete tile was spot-adhered with foam to the

roof deck, the flat concrete slate tile was fastened to a batten and counter-batten system, and

another concrete S-Mission tile was fastened to battens. A sixth attic assembly has a

conventional asphalt shingle roof for comparing roof and ceiling heat flows.

Cool color pigments and sub-tile venting of clay and concrete tile roofs significantly impacted

the heat flow crossing the roof deck. Field measures for the tile roofs revealed a 70% drop in the

peak heat flow crossing the deck as compared to a direct-nailed asphalt shingle roof. The slate

and medium-profile concrete roofs, having nearly the same surface properties as the asphalt

shingle, reduced the deck heat flow by ~45% of that crossing the shingle roof because of sub-tile

venting. The results imply that sub-tile venting is just as important as is the boost in solar

reflectance for reducing the heat gain into the conditioned space.

In winter, the air gap on the tile’s underside adds an additional radiation heat transfer resistance

which causes the heat escaping the roof decks to be about the same as that observed for the direct

nailed asphalt shingles in East Tennessee’s climate. Sub-tile venting therefore lessens the heating

penalty associated with cool roof products. The improved summer performance coupled with the

reduced heat losses during the winter as compared to a dark heat absorbing shingle roof show

that offset-mounting roofs can provide the roof industry the opportunity to market cool

pigmented roofs in climates that are predominated more by heating loads. Sub-tile venting and

cool pigments provide the best of both worlds; reduced cooling loads in summer and reduced

heat loads in winter.

Accelerated Weathering and Product Useful Life

The Cool Team studied several aspects of the weathering of roofing materials. Xenon-arc and

fluorescent light exposures were conducted to judge the effectiveness of cool pigments used in

painted metal, clay tile, concrete tile and asphalt shingle roof products. Test results were very

promising and showed that new cool pigmented concrete, clay, painted metal and asphalt shingle

roofs maintain their solar reflectance as well as their standard production counterparts. Total

color change is reduced or at least similar and the new cool pigmented products have similar if

not improved fade resistance and gloss retention.

Degradation of materials initiated by ultraviolet radiation was investigated for plastics used in

roofing, as well as wood and asphalt. Elevated temperatures accelerate many deleterious

chemical reactions and hasten diffusion of material components. Effects of moisture include

decay of wood, acceleration of corrosion of metals, staining of clay, and freeze-thaw damage.

Soiling of roofing materials causes objectionable stains and reduces the solar reflectance of

reflective materials. (Soiling of non-reflective materials can also increase solar reflectance.)

Soiling can be attributed to biological growth (e.g., cyanobacteria, fungi, algae); deposits of

organic and mineral particles; and to the accumulation of fly ash, hydrocarbons and soot from

combustion.

Technology transfer

The objective of this task was to make cool-colored roofing materials available for the residential

market within three to five years. LBNL, ORNL, color pigment manufacturers and granule

manufacturers worked and supported the efforts of roofing manufacturers to penetrate the

roofing market with new, more reflective cool-pigmented colored roofing materials. The Cool

Team worked with roofing component manufacturers and color pigment manufacturers to

introduce prototype cool-colored asphalt shingles, clay and concrete tiles, metal roofing, and

wood shake roof products. Both laboratories in conjunction with their respective industry

partners presented research results at appropriate trade shows, and published their results in each

industry’s appropriate trade magazine. The following is a list of articles presented in various

trade magazines, conferences, and academic journals.

Akbari, H. and André Desjarlais. 2005. “Cooling down the house: Residential roofing products

soon will boast "cool" surfaces.” Professional Roofing, March.

Akbari, H. R. Levinson, and P. Berdahl. 2005. “A review of methods for the manufacture of

residential roofing materials, Part I.” Western Roofing, Jan/Feb, page 54.

Akbari, H. R. Levinson, and P. Berdahl. 2005. “A review of methods for the manufacture of

residential roofing materials, Part II.” Western Roofing, Mar/Apr, page 52.

Akbari, H., R. Levinson, W. Miller, and P. Berdahl. 2005. “Cool Colored Roofs to Save Energy

and Improve Air Quality.” Proceedings of the 1

International Passive and Low Energy Cooling

for the Built Environment, Palenc 2005, Vol 1, Page 89, 19-21 May, Santorini, Greece.

Akbari, H. 2005. “Potentials of Urban Heat Island Mitigation.” Proceedings of the 1

International Passive and Low Energy Cooling for the Built Environment, Palenc 2005, Vol 1,

Page 11, 19-21 May, Santorini, Greece.

Akbari, H., A. Berhe, and R. Levinson, S. Graveline, K. Foley, A. Delgado, and R. Paroli. 2005.

“Aging and Weathering of Cool Roofing Membranes.” Proceedings of Cool Roofing … Cutting

through the Glare, Atlanta GA, May 12-13, RCI Foundation.

Akbari, H. P. Berdahl, R. Levinson, S. Wiel, A. Desjarlais, W. Miller, N. Jenkins, A. Rosenfeld,

and C. Scruton. 2004. “Cool Colored Materials for Roofs.” Proceedings of the 2004 ACEEE

Summer Study on Energy Efficiency in Buildings, Vol. 1, p. 1, Pacific Grove, CA.

Akbari, H., P. Berdahl, R. Levinson, S. Wiel, A. Desjarlais, W. Miller, N. Jenkins, A. Rosenfeld,

C. Scruton. 2004. “Cool Colors: A Roofing Study is Developing Cool Products for Residential

Roofs,” Eco-Structure, Sep/Oct, pp. 50-56.

Levinson, R., P. Berdahl, A. Berhe, and H. Akbari. 2005. “Effects of soiling and cleaning on the

reflectance and solar heat gain of a light-colored roofing membrane.” Atmospheric Environment,

Vol 39, pp, 7807-7824.

Levinson, R. P. Berdahl, H. Akbari, W. Miller, I. Joedicke, J. Reilly, Y. Suzuki, M. Vondran.

2005. “Methods of Creating Solar-Reflective Nonwhite Surfaces and their Application to

Residential Roofing Materials.” Solar Energy Materials & Solar Cells (in press).

Levinson, R., P. Berdahl and H. Akbari. 2005. “Solar spectral optical properties of pigments, part

I: Model for deriving scattering and absorption coefficients from transmittance and reflectance

measurements.” Solar Energy Materials & Solar Cells, Vol 89/4 pp, 319-349.

Levinson, R., P. Berdahl and H. Akbari. 2005. “Solar spectral optical properties of pigments, part

II: Survey of common colorants.” Solar Energy Materials & Solar Cells, Vol 89/4 pp 351-389,

2005.

Levinson, R., P. Berdahl, and H. Akbari. 2005. “Solar Spectral Optical Properties of Pigments.”

Proceedings of Cool Roofing … Cutting through the Glare, Atlanta GA, May 12-13, RCI

Foundation.

Levinson, R., H. Akbari and J. Reilly. 2004. Cooler tile-roofed buildings with near-infrared-

reflective nonwhite coatings. Accepted by Building & Environment.

Miller, W.A., MacDonald, W.M., Desjarlais, A.O., Atchley, J.A., Keyhani, M., Olson, R.,

Vandewater, J. 2005. “Experimental analysis of the natural convection effects observed within

the closed cavity of tile roofs.” Proceedings of Cool Roofing … Cutting through the Glare,

Atlanta GA, May 12-13, RCI Foundation.

Miller, W. A., Kriner, S., Parker, D.S. 2005. “Cool Metal Roofing Is Topping The Building

Envelope With Energy Efficiency And Sustainability.” Proceedings of Cool Roofing … Cutting

through the Glare, Atlanta GA, May 12-13, RCI Foundation.

Miller, W. A., Desjarlais, A.O., Akbari, H., Levenson, R., Berdahl, P. and Scichille, R.G. 2004.

“Special IR Reflective Pigments Make a Dark Roof Reflect Almost Like a White Roof.” in

Thermal Performance of the Exterior Envelopes of Buildings, IX, proceedings of ASHRAE

THERM IX, Clearwater, FL., Dec.

Miller, W. A., Desjarlais A.O., Parker, D.S. and Kriner. S. 2004. "Cool Metal Roofing Tested for

Energy Efficiency and Sustainability," International Conference on Building Envelope Systems

and Technologies (ICBEST), proceedings of National Research Council Canada, Toronto

Canada, May 2-7.

Miller, W.A., Loye, K. T., Desjarlais, A. O., and Blonski, R.P. 2003. “PVDF Coatings with

Special IR Reflective Pigments,” in Fluorine in Coatings V, proceedings of Paint Research

Association, Orlando, FL., Jan.

Miller, W.A., Loye, K. T., Desjarlais, A. O., and Blonski, R.P. 2002. “Cool Color Roofs with

Complex Inorganic Color Pigments,” in ACEEE Summer Study on Energy Efficiency in

Buildings, proceedings of American Council for an Energy Efficient Economy, Asilomar

Conference Center in Pacific Grove, CA., Aug.

The Energy Commission through this project has dramatically advanced the technology of non-

white “Cool Roofs” that exploit complex inorganic paint pigments to boost the solar reflectance

of clay and concrete tile, painted metal, and asphalt shingle roofing. The project has successfully

developed several non-white cool-colored roof products for sloped roofs over the past three years

and has shown positive energy savings in residential field tests demonstrating pairs of homes

roofed in concrete tile, painted metal and asphalt shingles with and without cool pigmented

materials. Without further efforts, the accomplishments achieved by the Energy Commission in

its “Cool Roofs” Public Interest Energy Research (PIER) project will creep into the marketplace

over the next several decades, slowly bringing the significant energy, cost, smog and carbon

savings that the technology promises.

Near the end of this project, the project's 16 industrial partners discussed their needs to further

develop and successfully market their residential cool roofing products. The opportunity exists to

rapidly accelerate the uptake of cool roofing materials. First and foremost, residential cool roofs

need to be credited and recommended in the state’s Title 24 standards that primarily determine

what products are used in the construction of new houses and major remodels. Second, more

cool materials for all residential (and commercial) sloped roofing systems must be available and

appropriately labeled. Third, the application of appropriate labels on roofing products must

become universal. Fourth, architects, designers, builders, roofing material distributors and

retailers, and consumers need to learn of the availability and benefits of using cool roofing

materials. Fourth, California utilities and the state government can further influence the selection

of cool roofs through innovative incentive and rebate programs to accelerate their market

penetration. Finally, market penetration can also be accelerated by enhancing the credibility of

retailer and utility marketing claims through large-scale demonstrations of cool roofs to

consumers, developer, designers, and roofing contractors.

In collaboration with the roofing industry partners, we prepared a market plan for

industry/national labs collaborative efforts to help the Energy Commission in deploying cool-

colored roofing. The plan focuses on six parallel initiatives: 1) regulate; 2) increase product

selection; 3) label, 4) educate; 5) provide incentives; and 6) demonstrate performance.

The Cool Team prepared a preliminary document of energy and peak demand savings for

installing cool roofs in various California climates. This data can be further developed to prepare

a proposal for updating the Title 24 to include cool colored roofing materials.

To estimate the energy-savings of cool-colored roofing materials, we calculated the annual

cooling energy use of a prototypical house for most cooling dominant cities around the world.

We used a simplified model that correlates the cool energy savings to annual cooling degree days

(base 18°C) (CDD18). The model is developed by regression of simulated cooling energy use

against CDD18. We performed parametric analysis and simulated the cooling- and heating-

energy use of a prototypical house with varying level of roof insulation (R-0 to R-49) and roof

reflectance (0.05 to 0.80) in more than 250 climate regions, using the DOE-2 building energy use

simulation program.

We estimated of savings for a prototypical house for an increase in roof solar reflectance from a

typical dark roof of 0.10 to a cool-colored roof of 0.40. The savings ranged from approximately

250 kWh per year for mild climates to over 1000 kWh per year for very hot climates. For houses

that are not air conditioned, cool-colored roofing materials offer comfort, typically at very

reasonable costs.

Performance Comparison of Cool Colored and Standard Roofs:

Energy Savings and Environmental Benefits

For illustration purposes, we compared the attributes of cool-colored and standard roofing

products. In the following matrix (Table EX-1), a conventional roof product is paired with a cool

roof product from the same company. Four types of roof products are depicted in the matrix. The

cool roof product is in light blue, the conventional product in red. Only the solar reflectance of

the cool and conventional products are compared; all other rows enumerate the energy, power or

money saved by the cool roof as compared to a conventional roof.

Table EX-1. A comparison of the attributes of cool-colored and standard roofing products.

Feature Glazed clay tile

roofing

Polymer-coated

concrete tile roofing

Polymer-coated

metal roofing

Asphalt shingle

roofing with ceramic-

coated granules

Competitive Advantage of

Energy-Efficient

Cool Color Roofing

Example of conventional roofing

product

(manufacturer/model/color name)

MCA Clay

Tile/Corona

Tapered

Mission/Burnt

Sienna

American Rooftile

Coatings/ Wearm

Earthtone Rooftile

Coating / Onyx

Custom-Bilt

Metals/Titan Select

Vail Shingle/

Musket Brown

Elk/ Prestique Plus

High Definition/

Weatherwood

Example of cool roofing product

(manufacturer/model/color)

MCA Clay

Tile/Corona

Tapered

Mission/Tobacco

American Rooftile

Coatings/

COOLTILE IR

COATING™/ IR

Onyx topcoat over

Plaster White

basecoat

Custom-Bilt

Metals/Titan Cool

Roof Vail Shingle

/Musket Brown

Elk/ Prestique Cool

Color Series/Cool

Weatherwood

Solar reflectance of conventional

roofing product sample

0.18 0.04 0.08 0.09

Solar reflectance of cool roofing

product sample

0.37 0.38 0.27 0.25

Solar reflectance increase (cool

product reflectance –

conventional product reflectance)

for dark colors

0.18-0.25 0.18-0.34 0.17-0.25 0.10-0.16 Cool roofs absorb less solar

heat

Reduction in peak surface

temperature on a summer

afternoon of the cool roof (K)

10-12 10-12 10-12 7-8 Cool roofs stay cooler in the

sun, reducing urban air

temperatures and slowing

smog formation

Peak power demand savings of

the cool roof (W)

300-400 300-400 400-600 300-350 Cool roofs help stabilize the

electrical grid

Annual cooling energy savings of

the cool roof (kWh)

150-400 150-400 250 - 650 190 - 490 Cool roofs save energy

Annual cooling energy savings at

$0.15/kWh of the cool roof ($)

22 - 60 22 - 60 37 - 97 28 - 73 Cool roofs save money on air

conditioning bills

Annual heating energy penalty of

the cool roof (therms)

1 - 4 1 - 4 2 - 8 1 - 5 Heat lost in the winter from

reflected incident solar gain is

small compared to energy

savings in the summer

Annual heating energy penalty at 2 - 6 2 - 6 3 - 12 2 - 7 Cost of heat lost in the winter

$1.5/therm of the cool roof($) from reflected incident solar

gain is less than 30% of the

cooling savings

Net savings provided by the cool

roof($)

20 -54 20 – 54 35 - 85 26 - 66 Cool roofs reduce annual

energy bill

Cost premium of the cool roof

compared with conventional roof

($)

nil 100 - 500 nil 500 Cost premium of cool roofs is

small or nonexistent for most

materials.

15-year net present value of net

energy savings at 3% discount ($)

240 - 650 240 - 650 420 - 1020 310 - 790 The energy savings of a cool

roof is about 20 to 30 percent

of the material cost of the

cool roof.

Simple payback time of the cool

roof (years)

0 2 - 10 0 8-19 Most cool roofs achieve

payback quickly. New

product introductions will

reduce cool shingle roof

payback.

* A dark-colored surface is defined here to mean one that reflects no more than 20% of visible sunlight. Smooth, flat surfaces reflect

about 5% of visible sunlight when black; about 10% when dark brown; and about 10 to 20 % when dark red, dark green, or dark blue

surfaces.

The cool color pigment database, Pinwheel™ coating design software, and engineering methods

for producing cool surfaces help roofing material manufacturers develop cool color roofing

products similar in appearance to their conventional products. The major selling point of cool

products is that they keep roofs cooler, and therefore save customers money on air conditioning

bills. In large areas of the United States with hot summertime climates, the energy savings from

these cool roofs can be substantial (10 to 20 percent). Cool roofs also improve the comfort of the

indoor environment by helping to maintain thermal comfort with less mechanical cooling. For

some people, air conditioners are difficult to regulate to produce a comfortable temperature. Cool

roofs also offer the added societal benefit of lowering peak power demand (relieving strain on

the electricity grid) and reducing emissions of greenhouse gases and airborne pollutants from

power plants (mitigating climate change and improving air quality).

Regional climate modeling suggests that the widespread application of cool roofs can reduce

urban air temperatures, decreasing cooling peak power demand and smog production. For

example, on a warm afternoon in Los Angeles, each 1°C decrease in the daily maximum

temperature lowers peak demand for electric power by about 2 to 4 percent, and each 1°C

decrease down to 21ºC (70ºF) reduces smog (specifically, the probability that the maximum

concentration of ozone will exceed the California standard of 90 parts per billion) by 5 percent.

A 3°C reduction in the air temperature of the Los Angeles basin could reduce peak power

demand by 200 MW, offer cooling energy savings worth $21 M/year, and yield a 12 percent

reduction in ozone worth $104 M/year [Rosenfeld et al. 1998]. More than 450 U.S. counties

(including some of the most heavily populated areas of California) had ozone levels that

exceeded federal 8-hour standards as of 2004. Widespread adoption of cool roofs could help

cities in many of these areas reduce the magnitude of their air quality problem.

The principal application of Cool Color Roofing is to provide roofing manufacturers with the

tools they need to develop energy-efficient products which (a) benefit their customers and (b)

improve the competitive advantage of these U.S roofing products in the marketplace. Cool color

roofing materials provide clear, measured advantages and dollar savings compared to

conventional roofing materials at a small cost premium that is paid back within a few years

through reduced energy bills.

The cool color technologies have other applications:

Automobiles. The Berkeley team is now working with the automobile industry to apply cool

colored coatings to the exterior metal and plastic surfaces of cars. Such coatings reduce the

amount of solar heat absorbed by the car’s body, lowering the air temperature in the cabin of a

car that has been parked in the sun. This allows car manufacturers to install lighter, lower

capacity air conditioning units that operate with greater efficiency. The reduced weight and

power consumption of these AC units could increase the fuel efficiency of cars, potentially

saving U.S. drivers billions of dollars in gasoline costs. This is a significant development given

the current high cost of gasoline, and the security issues raised by dependence on foreign

petroleum. Any inexpensive, easy-to-use technology that has the potential to save gasoline has a

tremendous market potential.

Cool colors can also be applied to the interior surfaces of cars, such as seats and steering wheels,

to lower their temperatures and make it more comfortable to enter and occupy a vehicle parked

in the sun.

Buildings. Cool color pigments can be used in building paints to reduce solar heat gain by

interior and exterior walls.

Clothing. Cool color pigments can be used in clothing to produce dark uniforms (such as those

worn by police officers) that stay cool in the sun.

Miscellaneous. Cool color pigments can be used to reduce the sunlit temperature of a wide

variety of coatings, including those applied to furniture, machinery, tools, or camping gear.

Concluding Comments

If we could develop technology to reduce every type of energy use by 10 to 20 percent, we

would be taking a huge step towards reducing dependence on oil imports, and emissions of

greenhouse gases. Energy-Efficient Cool Color Roofing accomplishes does just this, while also

strengthening the economy and improving air quality.

Re-roofing houses with cool products when roofs are due for replacement and specifying cool

roofs in new construction are economically sensible ways to significantly increase energy

efficiency. The price premium of cool roofs compared to conventional ones is small, and is paid

back in air conditioning savings within a few years. When a sufficiently large number of home

and commercial building owners adopt cool roofs regionally, urban air temperatures decrease,

slowing the rate of smog formation. This improves public health, and helps cities meet federally

mandated clean air requirements. Finally, cool roofs reduce peak electrical demand on hot

summer afternoons, reducing strain on the electrical grid and helping to avoid blackouts and

brownouts.

If applied to cars, cool color technology could improve fuel economy by allowing manufacturers

to downsize air conditioning units. These savings could help further reduce greenhouse gas

emissions and increase U.S. energy security by reducing reliance on imported petroleum. For all

of these reasons Cool Colors, on roofs and in other applications, have a tremendous potential to

contribute to the solution of major global problems within a short time, at a reasonable cost.

Recommendations

The California Energy Commission (CEC) has dramatically advanced the technology of non-

white “Cool Roofs” that exploit complex inorganic paint pigments to boost the solar reflectance

of clay and concrete tile, painted metal, and asphalt shingle roofing. The project has successfully

developed several non-white cool-colored roof products for sloped roofs over the past three and a

half years and has shown positive energy savings in residential field tests demonstrating pairs of

homes roofed in concrete tile, painted metal and asphalt shingles with and without cool

pigmented materials. Without further efforts, the accomplishments achieved by the CEC in its

“Cool Roofs” Public Interest Energy Research (PIER) project will creep into the marketplace

over the next several decades, slowly bringing the significant energy, cost, smog and carbon

savings that the technology promises.

Near the end of the CEC project, the project's 16 industrial partners discussed their needs to

further develop and successfully market their residential cool roofing products. Their

recommendations and requests are summarized in Table EX-2.

The opportunity exists to rapidly accelerate the uptake of cool roofing materials. First and

foremost, residential cool roofs need to be credited and recommended in the state’s Title 24

standards that primarily determine what products are used in the construction of new houses and

major remodels. Second, more cool materials for all residential (and commercial) sloped roofing

systems must be available and appropriately labeled. Third, the cool roofing pigment database

should be maintained and expanded with new materials in order to assist the industry to develop

new and advanced materials at competitive prices. Fourth, the aging and weathering of cool

roofing materials and their effects on the useful life of roofs need to be further studied. Fifth, the

application of appropriate labels on roofing products must become universal. Sixth, architects,

designers, builders, roofing material distributors and retailers, and consumers need to learn of the

availability and benefits of using cool roofing materials. Seventh, California utilities and the state

government can further influence the selection of cool roofs through innovative incentive and

rebate programs to accelerate their market penetration. Eighth, for utilities to develop incentive

programs and for manufacturers to coordinate their materials development with their marketing

efforts, they need to have an industry-consensus calculator to accurately estimate energy and

peak demand of cool colored roofs. The calculator should account for both the cooling energy

savings and potential heating energy penalties of cool roofs. Finally, market penetration can be

accelerated by enhancing the credibility of retailer and utility marketing claims through large-

scale demonstrations of cool roofs to consumers, developer, designers, and roofing contractors.

Table EX-2. Industry needs to successfully market their cool roof product

Assistance requested in marketing cool roofs Industry partner

requesting assistance

Continuing education for design-build firms, architects, utility

consumers, construction professionals and homeowners

integrated into seminars offered by the California Association

of Building Energy Consultants (CABEC).

Steelscape, BASF, Custom-

Bilt, Shepherd

Software to estimate the cooling energy savings and peak

demand reduction achieved by installing cool roofs on specific

buildings

Steelscape, BASF, Custom-

Bilt, Ferro, Elk, ARC

Monitoring solar reflectance and color change of the materials

installed at the California weathering sites

Steelscape, BASF, Custom-

Bilt, ISP, Ferro, Elk, ARC

Monitoring solar reflectance, color change, and thermal

performance of materials at ORNL test facilities and the

Sacramento test homes

Steelscape, BASF, Custom-

Bilt, ISP, Elk, Ferro, ARC

Expanding the cool coating database Steelscape, BASF, Custom-

Bilt, ISP, Ferro, Shepherd, 3M

Large-scale demonstration of cool roofs Steelscape, BASF, Custom-

Bilt, ISP, Ferro, Elk, ARC

Predictive software for design of cool coatings Steelscape, BASF, Custom-

Bilt, ISP, Ferro, 3M

Research to increase reflectivity and reduce costs ISP, Ferro, Elk, 3M,

Shepherd, ARC

Tools to accurately measure solar reflectance ISP, Elk, 3M, ARC

Calculations of weathering benefits of cool roofing ISP

Identification of new materials and techniques ISP, Ferro, 3M

Determination of the relationship between granule and ultimate

shingle reflectances

Acceleration of cool roof rating criteria by CRRC and Energy

Star

Table of Contents

Disclaimer...............................................................................................................................................2

Abstract...................................................................................................................................................3

Acknowledgement ..................................................................................................................................5

Executive Summary ................................................................................................................................6

The Need for Cool Color Roofing....................................................................................................6

Development of Cool Color Roofs...................................................................................................8

Production of Cool Colored Roofing .............................................................................................11

Field-Testing and Demonstration of Cool Colored Roofing..........................................................13

Materials Testing at Weathering Farms in California ....................................................................14

Steep-slope Assembly Testing at ORNL........................................................................................15

Accelerated Weathering and Product Useful Life..........................................................................16

Technology transfer........................................................................................................................16

Performance Comparison of Cool Colored and Standard Roofs: Energy Savings and Environmental

Benefits...........................................................................................................................................19

Concluding Comments ...................................................................................................................23

Recommendations ..........................................................................................................................23

Table of Contents..................................................................................................................................26

List of Figures.......................................................................................................................................27

List of Tables ........................................................................................................................................28

Introduction...........................................................................................................................................29

Technical Tasks ....................................................................................................................................34

Task 2.4: Development of Cool Colored Coatings.........................................................................34

Task 2.4.1: Identify and Characterize Pigments with High Solar Reflectance.....................34

Task 2.4.2: Develop a Computer Program for Optimal Design of Cool Coatings ...............37

Task 2.4.3: Develop a Database of Cool-Colored Pigments ................................................40

Task 2.5: Development of Prototype Cool-Colored Roofing Materials.........................................44

Task 2.5.1: Review of Roofing Materials Manufacturing Methods .....................................44

Task 2.5.2: Design Innovative Methods for Application of Cool Coatings to

Roofing Materials .................................................................................................................44

Shingles ............................................................................................................................45

Tiles and Tile Coatings.....................................................................................................49

Metal Panels .....................................................................................................................51

Task 2.5.3: Accelerated Weathering Testing (Durability of Cool Nonwhite Coatings).......53

Task 2.6: Field-Testing and Product Useful Life Testing ..............................................................55

Task 2.6.1: Building Energy-Use Measurements at California Demonstration Sites...........55

Task 2.6.2: Materials Testing at Weathering Farms in California........................................57

Task 2.6.3: Steep-slope Assembly Testing at ORNL ...........................................................59

Task 2.6.4: Product Useful Life Testing...............................................................................61

Task 2.7: Technology transfer and market plan .............................................................................64

Task 2.7.1: Technology Transfer..........................................................................................64

Task 2.7.2: Market Plan........................................................................................................64

Task 2.7.3: Title 24 Code Revisions.....................................................................................66

Conclusions and Recommendations .....................................................................................................69

Recommendations ..........................................................................................................................70

References.............................................................................................................................................72

List of Figures

Figure 1. Peak-normalized solar spectral power; over half of all solar power arrives as invisible,

“near-infrared” radiation...........................................................................................................29

Figure 2. Illustration of our pigment characterization activities. .....................................................36

Figure 3. Pinwheel™ screen shot.....................................................................................................38

Figure 4. Solar spectral reflectance of a Pinwheel™-formulated cool coating (“solution”)

designed to match the visible spectral reflectance of a particular shade of green (“target”)....39

Figure 5. Description of an iron oxide red pigment in the Lawrence Berkeley National Lab

pigment database ......................................................................................................................41

Figure 6. First index page of the LBNL Pigment database, including links to the detail pages

of 4 white pigment and 21 black/brown pigments....................................................................42

Figure 7. Application of the two-layered technique to manufacture cool colored materials ...........45

Figure 8. Development of super white shingles...............................................................................46

Figure 9. White roofs and walls are used in Bermuda and Santorini (Greece)................................46

Figure 10. Development of a cool black shingle by industrial partner ISP Minerals.. ....................47

Figure 11. Examples of prototype cool shingles..............................................................................48

Figure 12. Application of cool colored roofing shingles on two houses advertised by Elk Corp....48

Figure 13. Palette of color-matched cool (top row) and conventional (bottom row) rooftile

coatings developed by industrial partner American Rooftile Coatings. ...................................49

Figure 14. Simulated roofing products made from metal ................................................................52

Figure 15. (a) Solar reflectance (b) and total color change of asphalt shingles exposed to

accelerated direct UV radiation simulating solar’s short-wave irradiance ...............................54

Figure 16. Daily air-conditioning energy consumption and savings, measured during the

daylight hours from June through September 2005..................................................................56

Figure 17. Solar reflectance of a concrete tile coupon (light gray color) exposed to climatic

soiling at each of the seven CA weathering sites......................................................................58

Figure 18. Integrated heat flow measured through the roof deck and the attic floor for all tile

and shingle roofs field tested in East Tennessee during the month of January 2005.. .............60

Figure 19. Oxidation (carbonyl) profiles measured during accelerated UV aging

of polypropylene.......................................................................................................................62

Figure 20. Spectral reflectance of western red cedar roofing shingles.. ..........................................63

List of Tables

Table 1. Project residential roofing market in the U.S. western region surveyed by

Western Roofing (2002). ..........................................................................................................31

Table 2. List of industry partners.....................................................................................................33

Table 3. Industry representation on the Project Advisory Committee.............................................33

Table 4. Pigment properties tabulated in the LBNL pigment database. ..........................................43

Table 5. Sample cool colored clay tiles and their solar reflectances................................................50

Table 6. Industry needs to successfully market their cool roof product ..........................................65

Table 7. Estimates of annual cooling electricity savings (kWh) and heating energy

penalties (therms) from installation of cool-colored roofs on pre-1980 single-family

detached homes with gas furnace heating systems...................................................................67

Table 8. Estimates of annual cooling electricity savings (kWh) and heating energy

penalties (therms) from installation of cool-colored roofs on 1980

single-family

detached homes with gas furnace heating systems...................................................................68

Introduction

Coatings colored with conventional pigments tend to absorb the invisible “near-infrared” (NIR)

radiation that bears more than half of the power in sunlight (Figure 1). Replacing conventional

pigments with “cool” pigments that absorb less NIR radiation can yield similarly colored

coatings with higher solar reflectance. These cool coatings lower roof surface temperature, which

in turn reduces the need for cooling energy in conditioned buildings and makes unconditioned

buildings more comfortable.

Figure 1. Peak-normalized solar spectral power; over half of all solar power arrives as invisible, “near-

infrared” radiation

Field studies in California and Florida have demonstrated cooling-energy savings in excess of

20% upon raising the solar reflectance of a roof to 0.60 from a prior value of 0.10–0.20

(Konopacki and Akbari, 2001; Konopacki et al., 1998; Parker et al., 2002). Energy savings are

particularly pronounced in older houses that have little or no attic insulation, especially if the

attic contains the air distribution ducts. At 8¢/kWh, the value of U.S. potential nationwide net

commercial and residential energy savings (cooling savings minus heating penalties) exceeds

$750 million per year (Akbari et al., 1999). Cool roofs also significantly reduce peak electric

demand in summer (Akbari et al., 1997; Levinson et al., 2005a). The widespread installation of

cool roofs can lower the ambient air temperature in a neighborhood or city, decreasing the need

for air conditioning, retarding smog formation, and improving environmental comfort. These

“indirect” benefits of reduced ambient air temperatures have roughly the same economic value as

the direct energy savings (Rosenfeld et al., 1998). Lower surface temperatures may also increase

the lifetime of roofing products (particularly asphalt shingles), reducing replacement and

disposal costs.

According to Western Roofing Insulation and Siding magazine (2002), the total value of the

2002 projected residential roofing market in 14 western U.S. states (AK, AZ, CA, CO, HI, ID,

MT, NV, NM, OR, TX, UT, WA, and WY) was about $3.6 billion (B). We estimate that 40%

($1.4B) of that amount was spent in California. The lion’s share of residential roofing

expenditure was for fiberglass shingle, which accounted for $1.7B, or 47% of sales. Concrete

and clay roof tiles made up $0.95B (27%), while wood, metal, and slate roofing collectively

represented another $0.55B (15%). The value of all other roofing projects was about $0.41B

(11%). We estimate that the roofing market area distribution was 54–58% fiberglass shingle, 8–

10% concrete tile, 8–10% clay tile, 7% metal, 3% wood shake, and 3% slate (Table 1).

Suitable cool white materials are available for most roofing products, with the notable exception

(prior to March 2005

) of asphalt shingles. Cool nonwhite materials are needed for all types of

roofing. Industry researchers have developed complex inorganic color pigments that are dark in

color but highly reflective in the near infrared (NIR) portion of the solar spectrum. The high

near-infrared reflectance of coatings formulated with these and other “cool” pigments—e.g.,

chromium oxide green, cobalt blue, phthalocyanine blue, Hansa yellow—can be exploited to

manufacture roofing materials that reflect more sunlight than conventionally pigmented roofing

products.

Cool colored roofing materials are expected to penetrate the roofing market within the next few

years. Preliminary analysis suggests that they may cost up to $1/m

more than conventionally

colored roofing materials. However, this would raise the total cost of a new roof (material plus

labor) by only 2 to 5%.

In March 2005, a major manufacturer of roofing shingles in California announced availability of cool colored

shingles in four popular colors.

Market share by $ Estimated market

share by roofing

area

Roofing Type

$B % %

Fiberglass Shingle 1.70 47.2 53.6-57.5

Concrete Tile 0.50 13.8 8.4-10.4

Clay Tile 0.45 12.6 7.7-9.5

Wood Shingle/Shake 0.17 4.7 2.9-3.6

Metal/Architectural 0.21 5.9 6.7-7.2

Slate 0.17 4.7 2.9-3.6

Other 0.13 3.6 4.1-4.4

SBC Modified 0.08 2.1 2.4-2.6

APP Modified 0.07 1.9 2.2-2.3

Metal/Structural 0.07 1.9 2.2-2.3

Cementitious 0.04 1.1 1.2-1.3

Organic Shingles 0.02 0.5 0.6

Total 3.60 100 100

Table 1. Project residential roofing market in the U.S. western region surveyed by Western Roofing

(2002). The 14 states included in the U.S. western region are AK, AZ, CA, CO, HI, ID, MT, NV, NM,

OR, TX, UT, WA, and WY

In May 2002, the California Energy Commission (Energy Commission) sponsored a research

project to develop “cool” nonwhite roofing products that could revolutionize the residential

roofing industry. The technical project tasks included:

Task 2.4: Development of Cool Colored Coatings

Task 2.4.1 Identify and Characterize Pigments with High Solar Reflectance

Task 2.4.2 Develop a Computer Program for Optimal Design of Cool Coatings

Task 2.4.3 Develop a Database of Cool-Colored Pigments

Task 2.5 Development of Prototype Cool-Colored Roofing Materials

Task 2.5.1 Review of Roofing Materials Manufacturing Methods

Task 2.5.2 Design Innovative Methods for Application of Cool Coatings to Roofing

Materials

Task 2.5.3 Accelerated Weathering Testing

Task 2.6 Field-Testing and Product Useful Life Testing

Task 2.6.1 Building Energy-Use Measurements at California Demonstration Sites

Task 2.6.2 Materials Testing at Weathering Farms in California

Task 2.6.3 Steep-slope Assembly Testing at ORNL

Task 2.6.4 Product Useful Life Testing

Task 2.7 Technology transfer and market plan

Task 2.7.1 Technology Transfer

Task 2.7.2 Market Plan

Task 2.7.3 Title 24 Code Revisions

An initial collaboration between Lawrence Berkeley National Laboratory, Oak Ridge National

Laboratory, and eight roofing manufacturers rapidly grew to include 16 industrial partners (see

Table 2). Seven other manufacturers and roofing organizations have joined the project’s advisory

committee (see Table 3).

Our industry partners manufacture roofing materials, including fiberglass shingles, roofing

granules, clay tiles, concrete tiles, tile coatings, metal panels, metal coatings, and pigments. The

development work with our industrial partners has been iterative and has included selection of

cool pigments, choice of base coats for the two-layer applications (discussed later in this report),

and identification of pigments to avoid.

The Energy Commission’s goal is to create dark shingles with solar reflectances of at least 0.25,

and other nonwhite roofing products—including tiles and painted metals—with solar

reflectances not less than 0.40. Raising the solar reflectance of a residential roof from 0.15

(conventional dark color) to 0.40 (cool dark color) can decrease building cooling-energy use by

more than 10%.

The manufacturing partners of the two national labs have raised the solar reflectance of

commercially available concrete tile, clay tile, and metal roofing products to 0.30 – 0.45 from

0.05 – 0.25 by reformulating their pigmented coatings. Bilayer coating technology (a color

topcoat over a white or other highly reflective undercoat) is expected to soon yield several cost-

effective cool-colored shingle products with solar reflectances in excess of the Energy-Star

threshold of 0.25.

1. 3M Industrial Minerals, Pittsboro, NC; www.scotchgard.com/roofinggranules

2. Akzo-Nobel, Macungie, PA; www.akzonobel.com

3. American Rooftile Coatings, Fullerton, CA; www.americanrooftilecoatings.com

4. BASF Industrial Coatings, Mount Olive, NJ; www.ultra-cool.basf.com

5. CertainTeed, Valley Forge, PA; www.certainteed.com

6. Custom-Bilt Metals, South El Monte, CA; www.custombiltmetals.com

7. Elk Corporation, Dallas, TX; www.elkcorp.com

8. Ferro Corporation, Cleveland, OH; www.ferro.com

9. GAF Materials Corporation, Wayne, NJ; www.gaf.com

10. Hanson Roof Tile, Fontana, CA; www.hansonrooftile.com

11. ISP Minerals Incorporated, Hagerstown, MD; Tel. (301) 733-4000

12. MCA Tile, Corona, CA; www.mca-tile.com

13. MonierLifetile LLC, Irvine, CA; www.monierlifetile.com

14. Owens Corning, Granville, OH;

http://www.owenscorning.com/around/roofing/Roofhome.asp

15. Shepherd Color Company, Cincinnati, OH; www.shepherdcolor.com

16. Steelscape Incorporated, Kalama, WA; www.steelscape-inc.com

Table 2. List of industry partners

1. DuPont Titanium Technologies

2. National Roofing Contractors Association

3. Cedar Shake and Shingle Bureau (CSSB)

4. CRRC

5. Cool Metal Roofing Coalition

6. Tile Roofing Institute

7. Asphalt Roofing Manufacturers Association

Table 3. Industry representation on the Project Advisory Committee

Technical Tasks

The following is a summary of the work accomplished under each task.

Task 2.4: Development of Cool Colored Coatings

To determine how to optimize the solar reflectance of a pigmented coating matching a particular

color, and how the performance of cool-colored roofing products compares to those of a standard

materials, we have (a) characterized the optical properties of over 80 single-pigment coatings; (b)

created a database of pigment characteristics; and (c) developed a computer model to maximize

the solar reflectance of roofing materials for a choice of visible color.

Task 2.4.1: Identify and Characterize Pigments with High Solar Reflectance

We examined pigments in widespread use, with particular emphasis on those that may be useful

for formulating non-white materials that can reflect the near-infrared (NIR) portion of sunlight,

such as the complex inorganic color pigments (mixed metal oxides).

Pigment characterization begins with measuring the reflectance r and transmittance t of a thin

coating (e.g., a 25-µm thick paint film) colored by single pigment, such as iron oxide red. These

“spectral,” or wavelength-dependent, properties of the pigmented coating are measured at 441

evenly spaced wavelengths spanning the solar spectrum (300 to 2500 nanometers). Inspection of

the film's spectral absorptance (calculated as 1-r-t) reveals whether a pigmented coating is “cool”

(has low NIR absorptance) or “hot” (has high NIR absorptance).

The spectral reflectance and transmittance measurements are used to compute spectral rates of

light absorption K and backscattering (reflection) S per unit depth of film. A cool color is defined

by a small absorption coefficient K in the near infrared (NIR). For cool colors, the backscattering

coefficient S is small (or large) in the visible spectral range for formulating dark (or light) colors,

and preferably large in the NIR. (Weak backscattering in the NIR is acceptable when a basecoat

or the substrate provide high NIR reflectance.) Calculations of S and K employ a variant of the

Kubelka-Munk two-flux continuum model of light propagation through a pigmented coating that

Berkeley Lab has adapted to account for the reflectance of incompletely diffused light at the air-

coating interface. Such “interface reflectances” can significantly alter the reflectance and

transmittance of the optically thin pigmented coatings applied to roofing materials.

As a check, we found that values of S computed from the Kubelka-Munk model for generic

titanium dioxide (rutile) white pigment were in rough agreement with values computed from the

Mie theory, supplemented by a simple multiple scattering model.

The optical properties of 87 single-pigment films—4 white, 21 black or brown, 14 blue or

purple, 11 green, 9 red or orange, 14 yellow, and 14 pearlescent—were characterized by

computing spectral Kubelka-Munk coefficients from spectral measurements of film reflectance

and transmittance. Twenty-six polyvinylidene fluoride (PVDF) resin paint films were provided

by a manufacturer of coil-coating paints. Another 34 acrylic paints were purchased as artist

colors, and the remaining 27 coatings were acrylic-base letdowns (dilutions) of cool (primarily

metal-oxide) pigment dispersions from pigment manufacturers.

We identified cool pigments in the white, yellow, black/brown, red/orange, blue/purple, and

pearlescent color groupings with NIR thin-film absorptances less than 0.1, as well as other

pigments in the black/brown, blue/purple, green, red/orange, yellow and pearlescent groupings

with NIR absorptances less than 0.2. Most are NIR transmitting and require an NIR-reflecting

background to form a cool coating. Over an opaque white background, some pigments in the

pearlescent, white, yellow, black/brown red/orange, green, and blue/purple families offer NIR

reflectances of at least 0.7, while other pigments in the blue/purple, black/brown, and green color

families have NIR reflectances of at least 0.5. A few members of the white, yellow, black/brown,

pearlescent, red/orange, and green color families have NIR scattering sufficiently strong to yield

NIR reflectances of at least 0.3 (and up to 0.64) over a black background.

Use of pigments with NIR absorptances approaching unity (e.g., nonselective blacks) should be

minimized in cool coatings, as might be the use of certain pearlescent, blue/purple, red/orange,

and brown/black pigments with NIR absorptances exceeding 0.5.

Figure 2 illustrates our pigment characterization activities, showing (a) images over white and

black backgrounds of the 87 single-pigment films; (b) coupons of a pigmented polymer film (an

organic red) over white and black backgrounds; and (c) the measured and computed solar

spectral reflectances of a pigmented polymer film (an inorganic cool black). The three charts

show, from top to bottom, (i) measured reflectance, measured transmittance, and computed

absorptance of a free film; (ii) Kubelka-Munk backscattering and absorption coefficients

computed from the measured reflectance and transmittance of the free film; and (ii) the measured

and computed reflectances of the film over black and white backgrounds, which are used to

validate the accuracy of the backscattering and absorption coefficients computed from the free-

film properties.

We have published two milestone papers published in the academic journal Solar Energy

Materials & Solar Cells (Attachment 1). Feedback from the journal’s referees was extremely

positive. To wit:

REF#1: “Great work with extensive detail, I have not seen such detail on pigments since

work in the 1960's by the aerospace companies. It is nice to see such a seminal work in

one location and with one set of testing methodologies. Please publish.”

REF#2: “...Very nice work, uniform and detailed- the beginnings of a handbook. Very

valuable to my industry (paint formulation). If Elsevier puts together a Materials Property

Handbook, the results of this work should be in it.”

(a) (b) (c)

Figure 2. Illustration of our pigment characterization activities, showing (a) images over white and black

backgrounds of the 87 characterized single-pigment coatings; (b) coupons of a pigmented polymer paint

film (an organic red) over white and black backgrounds; and (c) measured and computed solar spectral

optical properties of a characterized pigmented paint film (an inorganic black).

Task 2.4.2: Develop a Computer Program for Optimal Design of Cool

Coatings

The radiative properties of the pigmented coatings characterized in Task 2.4.1 serve as inputs to

Pinwheel™, a software tool for the design of color-matched cool coatings that the LBNL team

has developed and shared with its industrial partners.