Painting Your Rooftop White Makes You Green?
July 22, 2009 5 Comments
“By painting your rooftop white, you can save anywhere from 5, to 15, to 20% on your air conditioning bill” said Steven Chu, Secretary of Energy, on the Daily Show with Jon Stewart (21 July 2009). In a rare moment without a snappy comment, Jon Stewart encouraged Steven Chu to continue. “If we start the transition to white rooftops and white pavement, (we could make) a profound effect on the climate.”
The concept is pretty simple. If we spend less on energy, the requirement to produce energy is reduced, and we create less carbon dioxide.
In addition, Chu mentioned that if we painted the rooftops of our houses and buildings white, and the roadways to white or a lighter color, it would have the (one time) effect of taking 1 billion automobiles off the road for 11 years (from a study by Art Rosenfeld, California Energy Commission).
It really can’t be this easy…, can it?
Here is the idea. Consider when you wear white clothing on a hot day, versus if you wear black clothing on a hot, sunny day. White naturally reflects heat, while black absorbs heat. Same thing applies to a black car on a hot, sunny day. If you take this idea and apply it to a rooftop, sidewalk, roadway – you can start to imagine the potential impact if we are reflecting this heat generated by sunlight back toward the sun.
In fact, Chu continued to explain that white rooftops “reflect sunlight back into space, with no greenhouse effect.” This means we are actually eliminating that source of absorbed heat, without a carbon dioxide by-product, and no negative impact on the planet.
Not an Entirely New Idea
Throughout history we have seen examples of white and light colors being used to help cool buildings – just look at the hillside villages along the Mediterranean Sea. Or the white colors on robes worn by Arabs and Bedouins in the Sahara or Saudi Arabia. White is definitely a “cool” color.
California has required white paint on all new buildings with flat roofs since 2005. This month (July 2009) all new buildings with sloping rooftops will need to use either white or light colored paint on the roof, although it is accepted the more off-white the color gets, the less reflection value we’ll achieve.
Some “Cool” Facts
- A typical urban “heat island” area is 25% rooftop and 35% pavement (Lawrence Berkeley National Laboratory/LBNL)
- A 1000 square foot rooftop rooftop painted white, versus black, cloud save nearly 10 tons of carbon dioxide each year (LBNL)
- An average car emits around 4 tons of carbon dioxide per year. Painting a small roof white could potentially offset more than a year’s worth of CO2 emissions from a car! (What’s with Climate?)
- Dark roofs absorb and hold more than 80 percent of solar energy, while white ones can reflect 75 percent of it away (to space)(Washington Post)
- The urban heat island effect is a relatively newly identified phenomenon that is characterized by a measured increase in the ambient air temperature in cities over their surrounding rural areas. (Construction Continuing Education center)
Urban Heat Islands
Using the above facts related to cities, such as nearly 60% of space within a city is either rooftop or pavement, it is easy to understand the impact of absorbing sunlight in a city such as Phoenix or Las Vegas. The Rosenfeld study shows that temperatures when using black paint can absorb in excess of 50 degrees centigrade, in contrast to white paint absorbing around 10 degrees centigrade(or 5 if using an optical white surface). Other surfaces such as raw steel, red clay tiles, green shingles, and other similar surfaces have varying absorption rates.
If 60% of the city is potentially using an off-white or dark color, then we can assume the heat absorption is high, and in fact may accelerate depending on the size of the city area. The cost in producing air conditioning needed to make the heat island livable or comfortable for human beings is much higher in this environment (obviously), and is transferred into our power grids.
While we may be able to offset a bit of the cost of power using alternative energy such as solar cells and wind, it is minimal, as the energy demand for air conditioning in extreme heat environments will far outstrip the capacity of a normal household or commercial property solar source.
By making an effort to eliminate dark rooftop space and pavement within urban heat islands, we could have a profound impact on the cost of energy, the need to continue building energy infrastructure (don’t forget the human impact of power infrastructure as shown in stories such as Erin Brockovich and her fight with PG&E), and the impact on our planet.
While there are a few groups of “greenhouse effect” naysayers, there are a lot more scientists banded together in a voice that says humans are having a direct impact on global climate change through mass production of carbon dioxide.
And a simple thing like painting our rooftops white, and producing pavement with lighter compounds and colors, can save millions of tons of carbon dioxide which is currently slung freely into the atmosphere, raising global temperatures, and contributing to air pollution.
Urban heat islands represent more than 1% of the world’s land mass (29% of the Earth). The heat radiating force of urban heat islands can raise surface and air temperatures by more than 3 watts per square meter (LBNL), further creating an almost unthinkable human problem in the event an urban heat island suffers a major or prolonged power outage. Without air conditioning and cooling systems within the urban heat island, it is probable those cities would have to be evacuated, as the heat would make the area uninhabitable.
Yes, let’s start painting things white. Let’s use some stimulus money to buy white paint. Maybe we can offer prison inmates an opportunity to complete some community service by painting stuff white. There are a lot of ways we can start paining things white.
Time to Learn More about Getting Green with White
Here are some great resources and links for more information on the topic of reducing our global carbon foot print with the simple idea of painting stuff white.
- Painting Rooftops White Would Slow Global Warming
- Obama’s green guru calls for white roofs (Telegraph)
- White Rooftops May Help Slow Warming (Washington Post)
- Steven Chu: White Roof to Fight Global Warming (Wall Street Journal)
- Painting your roof tops White? (Green Business Alliance)
- Paint Roofs White to Save Money and Delay Global Warming
- FIFTH Annual California Climate Change Research Conference
- The Cool Colors Project
- The Cool Roof Rating Council
- McGraw Hill Construction Continuing Education Center
This is an exciting, simple idea.
John Savageau, Long Beach