The urban heat island effect might sound like some sort of comic book superpower or the premise for a dystopian science fiction movie, but it's actually a real world phenomenon. Because of high concentrations of concrete, metal, stone and other materials that absorb a lot of sunlight, urban areas are usually hotter than rural or suburban areas that have more green space [source: U.S. Environmental Protection Agency]. LEED standards try to limit this effect by awarding points for using a variety of methods to reduce that ambient heat. Driveways, sidewalks and patios can be built using special "high-albedo" building materials, which.reflect -- instead of absorb -- a majority of the sunlight that hits them [source: U.S. Green Building Council]. An albedo is a unit of measure used to gauge a material's reflectivity. High-albedo materials are any that reflect most of the sunlight that hits them [source: Taha].
Your home can qualify for points without using those special high-albedo materials. Instead, you can use plants and trees to shade reflective areas. Like most sections of LEED standards, the guidelines for how to provide this shade are extremely detailed and mathematically complex. To win the points, 50 percent of reflective areas have to be shaded. You will need to calculate that percentage based on the day of the year when shadows are the smallest; to be exact, shading should be calculated for June 21 at noon when the sun is directly overhead [source: U.S. Green Building Council].