Cool-Color Roofing Material
Publication Number: CEC-500-2006-067
Publication Date: Auguust 2006
PIER Program Area: Buildings End-Use Energy Effciency Research
The executive summary, abstract and table of contents for this report are available below. This publication is available as an Adobe Acrobat Portable Document Format File. In order to download, read and print PDF files, you will need a copy of the free Acrobat Reader software installed in and configured for your computer. The software can be downloaded from Adobe Systems Incorporated's website.
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|Attachment 1||Task 2.4.1 Reports: : Identify and Characterize Pigments with High Solar Reflectance||6.5 MB|
|Attachment 2||Task 2.4.2 Reports: Develop a Computer Program for Optimal Design of Cool Coatings||456 kb|
|Attachment 3||Task 2.4.3 Reports: Develop a Database of Cool-Colored Pigments||252 kb|
|Attachment 4||Task 2.5.1 Reports: Review of Roofing Materials Manufacturing Methods||4.5 MB|
|Attachment 5||Task 2.5.2 Reports: Design Innovative Methods for Application of Cool Coatings to Roofing Materials||648 kb|
|Attachment 6||Task 2.5.3 Reports: Accelerated Weathering Testing||364 kb|
|Attachment 7||Task 2.6.1 Reports: Building Energy-Use Measurements at California Demonstration Sites||2.5 MB|
|Attachment 8||Task 2.6.2 Reports: Materials Testing at Weathering Farms in California||1.8 MB|
|Attachment 9||Task 2.6.3 Reports: Steep-slope Assembly Testing at ORNL||1.8 MB|
|Attachment 10||Task 2.6.4 Reports: Product Useful Life Testing||916 kb|
|Attachment 11||Task 2.7.1 Reports: Technology Transfer||9.6 MB|
|Attachment 12||Task 2.7.2 Reports: Market Plan||1.2 MB|
|Attachment 13||Task 2.7.3 Reports: Title 24 Code Revisions||304 kb|
|Entire Report with All Attachments (675 pages)||27.8 MB
Solar reflective, thermally emissive (cool) roofs decrease demand for building air conditioning power, lower the ambient air temperature, and, by promoting lower ambient air temperatures, retard the formation of smog. For example, raising the solar reflectance of a roof from 0.10 (typical of a conventional dark roof) to 0.35 (typical of a cool dark roof) can reduce building cooling energy use by more than 10 percent. In 2002, suitable cool white materials were available for most products, with the notable exception of asphalt shingles, the most widely used roofing material. However, cooler colored (nonwhite) materials were needed for all types of roofing, especially in the residential market. The California Energy Commission engaged Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory to work with the roofing industry to develop cool-colored roofing products, with the goal of bringing to market within three to five years roofs that meet the ENERGY STAR® qualifying solar reflectance of 0.25. This project led to the development of prototype colored asphalt shingles with solar reflectances of up to 0.35. One manufacturer currently markets colored asphalt shingles with solar reflectance of 0.25. Colored metal, clay tile, and concrete tile roofing materials with solar reflectances of 0.30 to 0.60 are currently sold in California.
Keywords: cool roof, reflectance, building energy, cool-color, energy efficiency, albedo, roofing material manufacture, pigment
Coatings colored with conventional pigments tend to absorb the invisible near-infrared (NIR) radiation that bears more than half of the power in sunlight. Replacing conventional pigments with "cool" pigments that absorb less NIR radiation can yield roofing coatings similar in color to those used in conventional roofs 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. For example, raising the solar reflectance of a residential roof from 0.10 (the typical reflectance of a conventional dark color, to 0.35 (the reflectance of cool dark color) can decrease building cooling-energy use by 7 percent to 15 percent.
In 2002, suitable cool white materials were available for most roofing products, with the notable exception of asphalt shingles . To respond to the consumer preference for colored roofs, cool nonwhite materials are needed for all types of roofing—and especially for asphalt shingles, which account for about 54 percent of the total residential roof market in the western United States.
The California Energy Commission engaged Lawrence Berkeley National Laboratory (LBNL) and Oak Ridge National Laboratory (ORNL)—hereafter called the Cool Team—to work with the roofing industry to develop cool-colored roofing products, with the goal of bringing cool roofing products that meet the ENERGY STAR qualifying solar reflectance of 0.25 to market with within three to five years.
- Characterize the optical properties of common and innovative pigments
- Develop a software tool to maximize the solar reflectance of color-specified roofing material
- Work with roofing manufacturers to design innovative cool roofing material production methods
- Measure the energy savings of the cool roofs on demonstration houses and test the performance of conventional and cool roofing systems at ORNL's steep-slope assembly testing facility
- Characterize the effects of weathering and aging on the cool roofs
- Estimate the energy and demand savings of the new cool roof materials
- Help bring cool roofing products to market within three to five years
Pigment characterization and manufacturing partnership
The Cool Team developed complex inorganic dark colored pigments that are highly reflective in the near-infrared portion of the solar spectrum. The team also created a software tool for designing high-reflectance coatings that match the colors of conventional colored roofing products. The team then worked with a consortium of 16 industry partners—representing most of the major and several minor U.S. roofing manufacturers—to develop novel manufacturing methods, which industry partners then used to manufacture cool roof prototypes and products.
To date and as the direct result of this collaborative effort, manufacturers of roofing materials have introduced cool shingles, cool concrete tile coatings, and cool concrete tiles and have significantly expanded the production of cool clay tiles and cool metal roofs. 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 (up from 0.05–0.25) by reformulating their pigmented coatings.
Tests of roofs at residential sites that compared the energy performance of cool and conventional roofs yielded these findings:
- The attic air temperature beneath a cool chocolate brown concrete tile roof (solar reflectance 0.41) was 3 to 5 K (5.4 to 9°F) cooler than that below a the same color and type conventional roof (solar reflectance 0.10)
- The attic air temperature beneath the cool brown metal shake roof (solar reflectance 0.31) was 5 to 7 K (9 to 12.6°F) cooler than a similar color and type conventional roof (solar reflectance 0.08).
Material testing showed that long-term change in the solar reflectance of cool roofs—which could compromise the benefits—appears to be driven by particulate matter that sticks to the roofs and resists being washed off by wind or rain.
Steep-slope assembly testing at ORNL suggests that sub-tile venting is just as important as the increase in solar reflectance in reducing the heat flow into the conditioned space of a house. Further, these tests revealed that sub-time venting reduces the small winter heating loss associated with cool-color roofs.
Finally, the accelerated and product useful life testing were promising, showing that novel cool pigmented concrete, clay, painted metal, and asphalt shingle roofs maintain their solar reflectance as well as do their standard production counterparts.
The Cool Team, in conjunction with respective industry partners, presented research results at appropriate trade shows, and published their results in each industry's appropriate trade magazines. More than 20 journal articles have been published by the Cool Team over the course of the project.
In collaboration with the roofing industry partners, the Cool Team prepared a market plan outlining industry/national lab collaborative efforts that would help the Energy Commission deploy cool-colored roofing. The plan focuses on six parallel initiatives: regulate; increase product selection; label; educate; provide incentives; and demonstrate performance.
Cool Team estimates of energy and peak demand savings showed that increasing roof solar reflectance from a conventional dark roof of 0.10 to a cool-colored roof of 0.30 yields net savings in the range of 100–600 kWh per 100 m2 per year. These data can be used to prepare a protocol for updating the state's Title 24 building energy code to include cool-colored roofing materials.
By enlisting the partnership of most of the major roofing manufacturers in the United States, the Cool Team exceeded the initial goal of creating dark asphalt 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 0.35.
Many of the products resulting from this work are already in the marketplace. For example, BASF industrial Coatings has launched a line of cool-colored siliconized-polyester coating, MCA Clay Tile is selling 11 products with solar reluctances about 0.25, and Elk Corporation has introduced its Prestique Cool-color Series, a line of light-gray and light-brown asphalt shingle with solar reflectances at or above 0.25. The Cool Team therefore met its commercialization goal of helping to bring products to market in three to five years.
Near the end of the project, the Cool Team's 16 industrial partners discussed their needs to further develop and successfully market their residential cool roofing products. Their recommendations, summarized below, were used to develop a deployment proposal.
- 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 in major remodels.
- More cool materials for all residential (and commercial) sloped roofing systems must be available and appropriately labeled.
- The cool roofing pigment database should be maintained and expanded with new materials to assist the industry in developing new and advanced materials at competitive prices.
- The aging and weathering of cool roofing materials and their effects on the useful life of roofs need to be further studied.
- Appropriate labels on roofing products must be universally applied.
- Architects, designers, builders, roofing material distributors and retailers, and consumers need to learn of the availability and benefits of using cool roofing materials.
- California's utilities and government can further influence the selection of cool roofs through innovative incentive and rebate programs to accelerate their market penetration.
- 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.
- 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.
Benefits to California
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 K (1.8°F) decrease in the daily maximum temperature lowers peak demand for electric power by about 2 percent to 4 percent and each 1 K (1.8°F) 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%. A 3 K (5.4°F) 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%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 eight-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. Table ES1 summarizes many of the benefits of cool roofing, based on findings from a single-family home.
The principal application of cool-color roofing is to provide roofing manufacturers with the tools they need to develop energy-efficient products that benefit their customers and 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.
Table of Contents
Please see report.