August, 2007

What’s New in Cool Roofing

New products are “not so hot,” and that’s good news!

By John Wagner

On a hot, sunny day, set a piece of black cloth on the ground next to a piece of white cloth, touch them after a bit, and the black cloth will be hotter. Repeat the experiment but put some wood battens under either cloth, and the air flowing beneath will cool them down.

Believe it or not, that’s about all the physics you’ll need to understand the “cool roofs” movement.

Sure, there are fancy terms to describe the phenomenon described above—such as solar reflectance or thermal emittance—but it all boils down to common sense: Black roofs get hotter than white roofs and air flowing under a roof will cool it down and interrupt heat transfer between the roof and the structure.

The benefits of cooler roofs have long been known, but cool roofs are getting lots of attention these days as green building gains momentum. In fact, the green building movement has not only brought cool roofs to the forefront, but it has also shown the advantage of roofing products that use recycled (or recyclable) components.

Why all the fuss about roof temperatures? A roof with black shingles reflects about 5% of the sun’s heat. (Black roofs have low solar reflectance.) Yet a roof with gray shingles reflects back about 20% of the sun’s heat, while white shingles reflect around 25%. As a result, black roofs get as much as 90ºF hotter than white roofs, and if the shingles have low thermal emittance, the shingles won’t radiate that heat back out to the air. Instead, the heat is transferred into the building. Hotter roofs mean hotter buildings, and there are environmental and financial costs to cooling them. In fact, the EPA has found that just changing the color of a roof can reduce cooling costs by 10-30%. And remember, we’re not just talking about a single black rooftop somewhere but the cumulative total of square miles, even hundreds of square miles, of black roofs across the U.S.

EPA figures show that $40 billion is spent each year in the U.S. to cool buildings. That’s more than 15% of all the electricity generated each year. As such, hot roofs actually drive up the amount of pollution created when electricity is generated to power air conditioning units. Since 90% of the electric energy in the U.S. is generated by fossil fuels, hot roofs contribute directly to unnecessary pollution.

Let’s take a look at some cool roof products and roofing systems that you can recommend to your customers who want to “go green” when selecting roofing. (And by the way, cool roofs shouldn’t be confused with green roofs. Green roofs usually refer to the process of installing living plants on the roof to absorb rain and keep the building cool, an entirely viable technology, especially for flat roofs.)

Cool Roof Technologies

Shingles. Because the physics of hot and cool roofs is so simple, you’d think that creating cool roofs would be easy, right? Wrong. Many people don’t like the look of white or light-colored roofs on their homes. A number of clever roofing manufacturers have come up with lighter-colored shingles and shingle surface treatments that have an advanced ability to reflect sunlight and emit heat. Elk offers a Cool Color series, with its Domain Winslow and Prestique lines. Elk’s shingles are composed of highly reflective granules (with higher solar reflectance) that are also effective at releasing absorbed heat (higher thermal emittance), yet the shingles don’t appear too lightly colored.

Either as traditional “three-tab” or metal shingles and shakes, Owens Corning, CertainTeed, IKO, GAF, and TAMKO all offer roof shingles in this category, as tested and listed by one of three accepted standards and testing agencies:

1. Energy Star, which accepts a roofing material that has an “initial” (upon installation) solar reflectance greater than or equal to 0.25, meaning that 25% of the sun’s heat is reflected.

2. The Cool Roof Rating Council (CRRC), which tests roofing material and rates the solar reflectance and solar emittance to create a CRRC rating of between 0 and 1. For this score, the higher the number, the better. Generally, roofs that are considered cool have ratings in the 0.70 to 0.75 range. (CRRC is the rating system used by California’s Title 24—the mandated green building standard—but CRRC is not strictly a California program.)

3. The Solar Reflectance Index, or SRI, which is expressed as a number from 0 to 100. The SRI uses solar reflectance and thermal emittance, as defined by ASTM.

Any product labeled by CRRC or Energy Star is a safe bet as a cool roof. For SRI, the higher the number, the better.

For shingle products, you’ll also find that several electric utilities offer rebates for the installation of cool roofing materials in new construction and/or roof retrofits, including Pacific Gas and Electric Company (PG&E), Southern California Edison (SCE), Idaho Power, and the City of Austin. Call your local utility to see if they offer one.                                    

Metal and Tile Roofs

Metal Roofs. For homes that don’t use shingles, metal and tile roofs can provide cool roof options. The use of metal roofs opens up a broad opportunity to treat the metal with factory-applied reflective paints that bring strong, enduring reflectivity and high cool-roof ratings to these materials. In fact, Oak Ridge National Laboratory determined that reflective metal roofing can save homeowners up to 40% on summer cooling costs. (If you use the Energy Star product listing to research cool roof options, you’ll find that the overwhelming majority of Energy Star roofs are metal roofs.) Plus, metal roofs are 100% recyclable. BASF Corp.’s Ultra-Cool is a leading reflective coating, as is Kynar 500, Hylar 5000, and Fluropon SR. These aren’t necessarily products that you’ll recommend in lumberyard and dealer settings, but it’s good to know about them.

Tile Roofs.

Tile roofs employ age-old technology to cool the roofs, through the use of lighter colored tiles and by accommodating passive airflow beneath the roofing surface. Today’s tile roofs are generations beyond natural clay tiles, and new tiles are made of composite materials, plastic, rubber, concrete, and fiber cement. These materials are sometimes installed (like MonierLifetile) over barrier-and-batten systems that create airflow under the tiles. These roofs have long warranties (50 years is common) and good fire and wind ratings. But they are also costly to install and some require beefed-up rafters to support the extra weight. In addition to MonierLifetile, Hanson Roof Tile, U.S Tile, and Eagle Roofing are among the many manufacturers of these roof components.

Synthetic slate roofing offers shingles or shakes made of recycled (or recyclable) material, such as rubber or plastic. EcoStar offers Majestic Slate Traditional tiles made of recycled industrial rubber and plastic that is injection molded in the shape of a slate tile. EcoStar also offers Seneca Cedar Shake Tiles and Seneca Plus, which are tiles the replicate the look of thick, hand-split cedar shake. These are made of recycled EPDM rubber and TPO plastic. DaVinci markets a 100% recyclable polyethylene shingle that is factory-crafted to look like slate. Joining the list, Trimline Composite Tile offers a lightweight and long-lasting tile alternative to traditional concrete and clay roof tiles, and it is part of the whole-roof Trimline ventilation system.

The Bottom Line

If a contractor or homeowner comes into your shop looking for a “green roof”—and you determine that they aren’t interested in plant systems—they are looking for a cool roof. And that means you’re in luck because you can up-sell them to the cool roof shingle lines or even the premium synthetic roof tile systems profiled above.