Money from trees? Only if you plant them in the right place
Study: Trees can cool your home, or cause your utility bills to rise.
Wed, May 04, 2011 at 08:49 AM
By Rodale News
You may have already read here that housework and gardening can lower your risk of heart disease and dying early. So if you’re ready to start digging, try planting a few shade bushes. But make sure you plan them in the right place. A study just published in the journal Energy and Buildings found that shade trees planted on the south and west sides of a building lowered homeowners’ utility bills, while those planted on the east side had no effect and those on the north actually cost them money in the long run.
The details: It’s a familiar idea that shade can lower your utility bills in the summer, but this is the first study of its kind to look at the actual impact on real homes and real utility bills, says study author Dr. Geoffrey Donovan, a research forester with the U.S. Forest Service. Donovan took aerial photographs of 460 homes in the Sacramento, Calif., area and analyzed tree placement, crown size, and how far each tree was from the house. Then he and a coauthor compared that with each homeowner’s electricity use and utility bills.
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.
What it means: A 5 percent decrease in utility bills may not leave you flush with cash, but that’s on top of the aesthetic value trees add to your property, the exercise you get planting and caring for them, and don’t forget: Trees absorb carbon dioxide and so help slow global warming. Because trees on the south and west sides of a home allow you to reduce your (greenhouse-gas emitting) fossil-fuel energy use, and absorb greenhouse gases at the same time, “they have double the carbon benefits than if they were out in the woods,” Donovan adds.
Want to try it out? Here are a few things to keep in mind:
• The bigger, the better. Donovan’s study looked only at trees, but “any shade canopy you put within 40 to 60 feet of your house will have the same effect,” he says. “The bigger it is, the greater the effect.” If planting a big tree isn’t in the cards for you right now, consider getting quick shade by investing in shrubbery. Visit a local garden center and look for bushes that provide the broadest canopy to start feeling the effects as soon as this summer. Pam Ruch, research editor at Organic Gardening, recommends the following species:
- Allegheny viburnum (V. rhytidophylloides)
- American cranberry bush viburnum (V. trilobum)
- Acoma crape myrtle (Lagerstroemia), best in Southern climates
- Diana hibiscus (Hibiscus syriacus)
• See if they’re free. The Sacramento electric company in Donovan’s study was giving away free trees to homeowners because the reduction in energy use during the late afternoon, when south- and west-shading trees are most effective, actually saves the utility company money (due to the complexity of how energy is priced for utilities). Check with your local provider and see if they have a similar program.
This article was reprinted with permission from Rodale.com.