GreenYour.com

Cool roofs, much like green roofs, reduce the amount of heat energy transferred from hot summer air into a building. Installing a cool roof over your existing roof can reduce cooling and maintenance costs dramatically.

How to install a cool roof

Common roofing materials absorb and transfer heat from the sun’s rays into a building’s interior, which ultimately raise the need for cooling systems like air conditioners. Cool roofs, on the other hand, reduce cooling costs by blocking heat absorption and transfer.

1. Calculate the savings: If you’re having trouble convincing yourself of a cool roof’s effectiveness, go to the US Department of Energy’s (DOE) Cool Roof Calculator. It’ll quantify your building’s potential energy savings with a cool roof.
2. New or used? Sloped or flat?: Doesn’t matter. Whether you’re building for the first time or retrofitting an old structure, and regardless of the slope of your building’s roof, cool surfaces can be applied in almost any situation.
3. Compare options: Check out this breakdown of various roof types to see how differently each reacts in the hot summer sun. You’ll want to know that a bright white roof will raise roof temperature by only 15°F above air temperature. By contrast, black materials boost roof temperature by 90°F. Following is a list of cool roof options available:
   • Coatings: Designed for low-sloped roofs, these liquid white coatings are applied like paint over existing roofing materials. These coatings last from 10 to 20 years and cost between 75 cents and $1.50 per square foot.
   • Single-ply membranes: Intended for low-slopes, these pre-fabricated rubber or plastic sheets are applied in a single layer, usually by heat sealing the seams over existing roof materials. They can last up to 30 years and cost between $1.50 and $3 per square foot.
   • Reflective tiles: Made of clay or concrete, these tiles contain reflective pigments and replace existing roofing materials. They reflect up to 70 percent of the sun’s energy and can be made in a variety of colors (not just white) while maintaining their solar reflectance. Long lasting, this option costs about $3 per square foot.
   • Metal: Some metal roofing materials are available for residential applications. They can contain reflective pigments and other reflective qualities that make them more efficient than traditional roofs. They run about $2 per square foot.
4. Features to look for: When shopping for your cool roof products, look for these features: high solar reflectance, high solar emittance, and excellent endurance of reflectance properties over time.
5. Go for ENERGY STAR: Ensure that your new cool roof is the most efficient it can be by opting for ENERGY STAR labeled products. Reflecting even more of the sun’s rays, they reduce cooling demands by 10-15 percent more than other cool roof materials.
6. Find a contractor: There are several online listings of roofing contractors. For instance, check out: National Roofing Contractors Association and Lawrence Berkeley National Laboratory Cool Roof Supplier list.
7. Keep it clean: After your cool roof has been installed, be sure to maintain it properly so that it continues to benefit your bottom line. Wash your roof on a regular basis to maintain an unobstructed reflective coating.

Find it! Cool roof products and services

Installing a cool roof helps you go green because…

• Cool roofs reflect the sun’s energy, thus keeping temperatures low and reducing cooling energy needs.
• Cool roofs protect existing roof materials, prolonging roof life and requiring fewer infusions of new materials.

Cool roofs keep solar heat out of buildings by reflecting the sun’s radiant heat energy back into the atmosphere.[1] Since dark roofing surfaces absorb more heat (sometimes raising roof temperature by 100°F), they transfer more heat into the building than lighter colored roofs.[2] Smooth, bright white roofing materials are the coolest option for building construction, raising roof temperature by only 15°F compared to 72°F to 90°F of common asphalt shingles.[3] After testing both residential and commercial buildings in 11 US cities, the Heat Island Group estimates that if cool roofs were comprehensively installed, the US national energy savings would be about $750 million per year.[2]

Cool roofs reduce energy consumption and also mitigate the effects of the urban heat island effect. Cool roofs can help to reduce resource waste associated with decaying roofs by protecting existing materials. Over the past 40 years, approximately seven to 10 percent of US landfill space has been used up by 11 million tons of annual asphalt roofing waste.[4] They provide a shield against damaging UV rays, help prevent leaks, and prevent expansion and contraction stress caused by significant temperature fluctuations.[5]

Tax breaks and subsidies

Some energy providers now offer incentives for building owners willing to install cool roofs. First, check out the Database of State Incentives for Renewables & Efficiency (search under “Roofing”). Then check out:

• Progress Energy (Carolinas, Florida): Ten cents per square foot of roof up to a max of $5,000 per building.
• Sacremento Municipal Utility District: Residential Cool Roof program offers between 10 and 20 cents per square foot.
• Salt River Project (Phoenix): Five cents per square foot of cool roof installed up to a maximum of $5,000 per project.

Glossary

• solar emittance: Emittance is the ability of a surface to emit solar energy in the form of heat. High emittance roofs increase the release of heat by thermal radiation, which further lowers roof temperature.
• solar reflectance: Also known as albedo, solar reflectance refers to the direct and diffuse solar radiation reflected by a surface. High solar reflectance means the surface absorbs less solar energy, thus staying cooler.
• reflectance endurance: Reflectance of most roofing materials will decrease over time as it is exposed to the sun, dirt, and microbial influence. It is recommended that reflective materials be tested upon installation and then again after three years to determine reflectance.[6]
• urban heat island effect: A phenomenon where urban temperatures are 2°F to 10°F (1°C to 6 °C) hotter than temperatures in nearby rural regions. This often causes increased energy demands (for air conditioning), air pollution, and heat-related illnesses.[7]

External links

• Cool Roof Rating Council
• Cool Roof Solutions
• ENERGY STAR - Roofing: Cool Roofs
• Heat Island Group - Cool Roofs
• Lawrence Berkeley National Laboratory - Cool Roofing Materials Database
• Pacific Gas and Electric Company - Cool Roof Design Brief
• US Department of Energy - How to Buy Energy-Efficient 'Cool' Roof Products
• US Environmental Protection Agency - Cool Roofs