Are green roofs easy or hard to maintain? Do they cost a lot? How much energy do they save, anyway? Test your knowledge in this "cool" quiz.
It's true! With their dark, non-reflective surfaces, standard rooftops are practically designed to trap light and heat.
While a flat or low-sloped roof makes for easier installation and more roof-scaping options, a basic green roof can be added to almost any building, even one with a steep, shingled rooftop.
In many cases, the difference between cool and hot is all in the color. Fortunately, a reflective white or light-colored coating typically costs the same as the old heat-absorbing dark stuff.
One of the many benefits of rooftop gardens is that they reduce stormwater runoff, absorbing an estimated 50 to 75 percent of rainwater.
The plants on a green roof take in water through their roots and release it through their leaves, cooling the air around them.
As its name implies, a roof mist cooling system uses just a fine mist -- less than 1 pint of water per square foot per day -- to cool rooftops through evaporation.
While the exact maintenance needs vary depending on the roof, rooftop gardens may need to be weeded, irrigated, fertilized, and replanted from time to time.
In addition to holding a watertight membrane down with their weight, the natural stones or pavers in a ballasted roofing system provide an insulating barrier against solar heat.
Tubular skylights are inexpensive and easy to install. A 10-inch diameter tube can illuminate up to 100 square feet, and a 22-inch diameter tube can illuminate up to 600 square feet.
A cool roof is a roof designed to maintain a lower surface temperature in bright sunshine by reflecting more light and releasing more heat than a traditional roof.
Green rooftops and rooftop gardens have been around for thousands of years and can last twice as long as conventional roofs.
Many different kinds of roofing materials meet Energy Star requirements, which are based on a product's ability to reflect sunlight.
The reflective properties of painted and unpainted metal make it a good choice for steep-sloped roofs, but its tendency to retain heat limits its effectiveness for flat or low-sloped roofs.
Thanks to new pigments and special reflective coatings, "cool" tiles and shingles are available in a wide range of colors.
Just like plants and trees on the ground, the vegetation in a rooftop garden reduces greenhouse gases by trapping and storing carbon.
A green roof costs anywhere from $10 - $25 per square foot, while a cool roof can be as inexpensive as 75 cents per square foot.
The urban heat island effect is the term used to describe the warmer temperatures in and around cities, due in part to the heat absorbed by rooftops and paved surfaces.
In addition to absorbing heat from the sun, a green roof acts as an insulator, preventing indoor heat from escaping through the roof in the winter.
This sprawling green roof saves the city $5,000 a year in utility bills and keeps summer rooftop temperatures 30 degrees cooler than surrounding buildings.
A 2006 University of Michigan study found that a 21,000 square-foot green roof would cost $129,000 more to install than a conventional roof, but would save $200,000 over its lifetime, primarily in energy costs.