He found that trees placed on the south and west side of a house, and no more than 60 feet away from the actual building, could lower a homeowner’s utility bills by about 5 percent between May and September. However, trees on the north side actually raised their bills by 1 percent. Why? Because on that side of your house, trees act more like blankets than shade. “They slow radiant cooling of the house at night,” Donovan says, “and they don’t cast any house-shading shadows.” So they cost you some cooling after the sun goes down, without sparing you some heat during the day.
Check out the full article over at the Mother Nature Network.