President Obama’s Nobel prize-winning green guru and U.S. Secretary of Energy, Dr. Steven Chu, says that painting your roof white can help reduce global warming while saving money. Speaking at a climate conference last year, Chu demonstrated that one of the most significant ways we can mitigate global warming is also one of the simplest to understand and offers significant cost savings.
How Does a White Roof Work?
It’s true that a simple coat of specialty white paint can achieve both lowered carbon emissions and lowered costs. The concept is simple: as sunlight beams through the atmosphere, roughly half of the energy shines as light. Among other things, the light hits our rooftops.
In the case of a typical dark-colored roof, the sunlight converts directly to heat. The building absorbs the heat causing its internal and external temperature to rise. It’s the same reason black clothes feel hot more than white clothes. If a roof is white, the sunlight will reflect back instead of heating the surface, resulting in lower building temperatures and thus, less cooling requirements.
Greece, famous for its distinctive white architecture, caught on to the “cool roof” idea hundreds of years ago. Using simple limestone pigments, the light coloring reflects hot sunlight away from dwellings, producing a natural cooling effect in an otherwise steamy climate.
In most areas of the world, however, there’s a different kind of island living. The black roads and dark pavements that blanket our cities have helped create the phenomenon known as the urban heat island. The term refers to the fact that cities are significantly hotter than outlying suburban and rural areas receiving the same amount of sunshine, due to their high concentration of dark roads and roofs, and lack of absorbing vegetation.
One element of urban heat island mitigation efforts involves making residential and commercial roofs white. By increasing the earth’s reflectivity, local temperatures in hot cities are reduced, lessening overall cooling needs. This, in turn, results in reduced carbon emissions and improved public health. It is estimated that simply painting a 1,000 square foot rooftop white could save 10 tons of CO2 emissions annually, thereby slowing global warming.
In July, Steven Chu mandated that all Department of Energy buildings have white roofs. He has touted the benefits of white roofs, frequently citing a calculation finding that if the world’s 100 largest and hottest cities switched to white roofs and light-colored cement pavement, the net environmental effect would be the equivalent of taking all the world’s automobiles off the streets for 11 years.
Saving Green with White
Not only do white roofs cut carbon emissions, they save on energy costs as well. A 2009 study by the Lawrence Berkeley National Laboratory’s Heat Island Group found that retrofitting 80% of air-conditioned buildings in the United States with white roofs would save $735 million annually in reduced energy bills. Today, households that opt for a white roof could reduce their residential air conditioning bills by an estimated 20%. In all, with roughly 90% of U.S. roofs painted black, that’s a savings of $1 billion per year in the U.S. alone.
Making the switch to a reflective rooftop is also cost-effective and one of the easier green modifications you can make to your house. If you’re thinking of putting up new roofing, go with white material from the start. It costs no more than black roofing, so if you choose white roofing materials the money you won’t spend on air conditioning your house will be 100% savings. If you’re not in the market for a new roof, yet are still interested in cooling your home, consider buying white roof coating. In addition to cutting down on your energy bills, these specialized coatings extend your roof’s life. Numerous companies are now sprouting up, specializing in white roofs.
Don’t forget go check your local bylaws and building suppliers for cool roof green rebates and tax breaks. Just for starters, the Stimulus Package signed in February 2009 states that homeowners who make energy efficient updates to their home — including the installation of a painted or coated Energy Star(R) labeled metal roof – between January 1, 2009 and December 21, 2010, may be eligible for a tax credit worth 30% of the installation costs (materials only) up to $1,500 per home.
White is the New Green
The cool roof movement is already gaining momentum in the U.S., with Georgia and Florida offering incentives to homeowners who install white or light-colored roofs. Considering the potential energy and cost savings, California now requires most flat-roofed buildings to be white. As a testament to the potential cash savings, Walmart has installed white roofs on 75% of its stores in the United States.
Over 50% of the world population now lives in urban areas, and by 2040 that fraction is expected to reach 70%. Roofs comprise over 20% of urban surface. Hashem Akbari, a scientist at the Lawrence Berkeley National Laboratory estimates that permanently retrofitting urban roofs and pavements in the tropical and temperate regions of the world with solar-reflective materials would offset 44 billion tons of emitted CO2.
While white roofs reflect solar energy, they do not minimize the underlying cause of global climate change – greenhouse gas emissions. Still, the concept demonstrates that not all green engineering projects have to be as difficult to understand as a lecture on advanced organic chemistry. Cooling our roofs and streets by switching to shades of white shows that sometimes simple solutions have the greatest green effect.