Use cool roof technology for home energy efficiency (video)
There's nothing like a bit of shade on a hot summer day. A brief respite from the heat of the sun can make all the difference in how you feel.
The same thing is true for your home. Giving your house a shield against the sun can make your home more energy efficient and comfortable.
That's why more and more homeowners are turning to a cool roof for their home to save money and improve comfort.
There are two main considerations for sunlight's interaction with a roof:
- Reflectivity: The amount of solar radiation immediately reflected from a surface. It is reported as a decimal or percentage.
- Emissivity: Energy not reflected is stored and emitted over a period of time. The heat stored in the roof may be absorbed into the rooms of the house.
A cool roof is one that has the right degree of reflectivity to reflect the sun's rays and keep the home under the roof much cooler, and manages the emission of heat as well.
Cool roof products come in a variety of roof types, including metal, asphalt and built-up roofs.
Often, the roof is the least energy efficient part of a home. In fact R-value, i.e. the insulation measurement, of a roof may be R-5 or 10, compared to R-20 to R-30 or greater for the walls of a home. According to Oak Ridge National Laboratory, about 30 percent of a home's energy is used for heating and cooling, and about half of that is due to heated or cooled air lost through the roof.
Watch this explanation of metal roofing in green building:
There's more to a cool roof than simply a light color. A true cool roof meets theEPA Energy Star Roof Products Program performance criteria. Some roofs can have a reflectivity as high as 90 percent for painted and granular coated-metal roofing. A cool roof does not have to be white or a light color. There are metal cool roof materials on the market in a wide spectrum of colors to complement many architectural and historic styles.
Cool roofs are highly reflective and emissive materials that stay 50 to 60 degrees Fahrenheit cooler, which reduces energy costs, improves occupant comfort, cuts maintenance costs, increases the life of the roof, and contributes to the reduction of urban heat islands and associated smog.
According to the U.S. Department of Energy's Energy Star Program, qualified cool roof products can lower roof surface temperature by up to 100F, decreasing the amount of heat transferred into a building.
That can help reduce the amount of air conditioning needed in buildings, and can reduce peak cooling demand by 10 to 15 percent.
According to Energy Star, during the summer a typical dark roof is 150 to 190 degrees F at the hottest, while cool roofs peak at 100 to 120 degrees. A cool roof helps keep that heat from getting into the home.
A reflective roof can save up to 40 percent of heating and cooling costs, according to tests by the Oak Ridge National Laboratory.
Depending on your climate, cool metal roofing may be painted or unpainted. Painted surfaces can include oven-baked paint finished and granular coated surfaces.
In a cooling-dominated climate, a highly reflective painted or granular-coated roof is the best option, the Metal Roof Alliance says. This type of roof will reflect heat away from the house. In a heating-dominated climate, an unpainted metal roof is often desired because it will absorb heat and help heat the home during colder weather.
The Florida Solar Energy Center found that metal roofing saved a Florida homeowner about 23 percent per year in cooling costs, compared to a dark gray asphalt shingle roof.
Metal roofing helps the environment in other ways. It's durable and low maintenance. That means once it's installed it will last a long time – in many cases 30 years or more – and won't need maintenance.
Cedar shake roofs for instance, require regular maintenance. In the life span of a single metal roof, an asphalt shingle roof may have to be replaced at least once or twice. A painted metal roof will retain about 95 percent of its initial reflectance and emittance quality throughout its life, according to the Metal Roof Alliance.
Metal roofs also withstand the weather better. They are documented to resist wind, hail, fired and earthquakes.
There are long-term environmental benefits from making a metal roof part of your home remodeling project or new home construction.
Start with the metal itself. It often contains a high percentage of recycled content and it is usually 100 percent recyclable when its useful life is over. Often a metal roof can be installed over existing asphalt shingles, which saving the shingles from going to a landfill.
By lowering energy use, a home with cool roof uses less fossil fuel for heating and cooling, which cuts greenhouse gas emissions.
Cool roofs with the Energy Star label are eligible for federal tax credits, subject to the latest IRS regulations. Also, many metal cool roof products can earn points for LEED certification through the U.S. Green Building Council as well as other green building programs.
To reduce the impact of the sun on your home, improve comfort and reduce home maintenance, look for a metal cool roof. It's like putting your home in the shade.
Click for a downloadable version of this white paper on cool roofs.
Read more about roofing.
Companies: Classic Metal Roofing Systems