How to Plant Trees for Energy Conservation

From the June 2003 issue of The Forestry Source

Research shows that buildings require less energy to keep cool during the summer when they have shade trees on their southern or western exposures. Credit for photo Arthur Plotnik, courtesy of TreeLink

Although the concept of planting trees around a house to help conserve energy is not a new concept, questions remain about its two most important elements: planting the right tree in the right place.

The right tree in the right place can provide shade and cool air in the summer and wind protection in the winter--all while simultaneously adding beauty and privacy to a landscape. Yet, the right tree in the right place also means appropriate tree selection and placement to minimize damage from falling limbs, conflicts with power lines, and other obstructions.

The Right Place

To reap the maximum, energy-saving benefits from trees, experts say it's important to know how the sun moves through the sky both during the day and during different seasons and how this affects tree placement.

"It's important to know the position of the sun during different times of the day and in different times during the year," says Mike Kuhns, an extension forester with Utah State University. "Many people plant trees on the south side of their homes, but a tree planted on the southwestern or western side will have more of an effect."

To provide shade from morning sun in the summer (roughly between the hours of 7:00-11:00 am), Kuhns recommends that property owners plant trees on the eastern and northeastern sides of the structure. To provide shade from afternoon sun (between the hours of 3:00-7:00 pm)--often be the warmest part of the day--he says trees should be planted on the west and northwest sides. Trees with a mature height of 25 feet should be planted 10-20 feet from the house.

Trees planted to the southeast, south, or southwest will only shade a building from summer sun if their limbs extend over the roof. However, in the winter, when sun is desired, trees planted on south side of a house--even deciduous trees--can cast too much shade.

"Don't discount the shade produced by these trees in the winter," says Kuhns. "Large or dense-crowned deciduous trees cast more shade than people think."

To avoid winter shading, Kuhns says that trees should be located no nearer than two to two-and-a-half times their mature size to the south side of a building. Trees planted to the southeast or southwest should be about four times their mature height from the building.

In addition to directly shading a house, trees can also be used to shade air conditioning units. However, any nearby branches should be pruned to allow at least several feet of space around cooling devices to encourage airflow.


The Right Tree

Naturally, deciduous trees are best for shading houses from the sun in the summer and allowing it to warm them in the winter. However, there is more to consider about a shade tree than simply whether or not it will lose its leaves.

If you envision the braches of a shade tree hanging over your house, you will want to restrict your deciduous tree selection to what Kuhns refers to as "strong-wooded, medium- to slow-growing" trees, such as oaks that have strong limbs. Fast-growing trees, such as cottonwoods and willows, have weak wood, and their limbs tend to break easily, which may result in property damage.

Kuhns recommends that people work to avoid future problems when planting trees. A four-foot-tall tree might end up being a 60 feet tall and 30 feet across, says Kuhns. Thus, he advises that homeowners anticipate the mature size and crown characteristics of any trees they plant.

He also suggests that people consider the location of power lines when planting a tree. Trees that grow into power lines cause electrical outages and increased line maintenance costs. They also can end up in poor health because of the severe pruning that is sometimes necessary.

Adapted from the Utah State University Forestry Extension publication, Planting Trees for Energy Conservation: The Right Tree in the Right Place, by Mike Kuhns.

For information, contact Mike Kuhns, extension forester, Department of Forest, Range, & Wildlife Sciences, 5230 Old Main Hill, Utah State University, Logan, UT 84322-5230; (435) 797-4056; mike.kuhns@usu.edu.

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