1998 Iowa Turfgrass Research Report
Trees Can Reduce Energy Consumption
Jeff Iles
Trees planted in key positions around homes and businesses can reduce energy consumption and save money. For example, properly placed trees can slash air-conditioning demand in summer by as much as 50 percent. Thoughtfully placed trees also can reduce winter heating costs by 4 to 22 percent. But to achieve maximum energy savings and environmental improvement, appropriate tree species must be planted in strategic locations and in the correct relationship to the buildings or areas they are designed to benefit. Simply stated, the goal is to get maximum shade in summer but minimum shade in winter.
Highest priority should be given to planting shade trees due west of west-facing windows followed by planting trees east of eastern windows. Trees located on the east and west sides of buildings offer the most advantageous combination of solar control and energy savings by blocking early morning and late evening sun in the summer but offering no obstruction to winter sunlight. Select trees that can be planted within 20 feet of windows and will grow at least 10 feet taller than windows. If space permits, use tree combinations to create a continuous planting opposite all major west and east-facing windows. But don't waste time and financial resources planting trees on the south side of buildings! A large tree oriented to the south will cast little, if any shade on buildings to the north in summer. And in winter, the same tree will cast an undesirable shadow on structures to the north for most of the day. If shade trees are already present on southern exposures, removing their lower branches will permit more sunlight to reach the buildings to the north in winter.
Deciduous trees (those that drop their leaves in autumn) are the preferred natural heating and cooling regulators in temperate climates. To obtain maximum benefit, the "ideal" shade tree should have a broad crown and dense foliage in summer when shade is most desirable. Then when temperatures begin to cool in fall, the ideal tree would lose its leaves, permitting the suns energy to penetrate a sparsely-branched canopy. Trees meeting these criteria are classified as "solar friendly." Kentucky coffeetree, ash, and sugar and red maples are good examples of solar friendly trees because they provide dense summer shade and sparse winter branching.
In general, large-growing trees are best because they provide the maximum environmental benefit per tree. But because "solar friendly" trees are most effective when planted close to the east and west sides of buildings, only sturdy trees with good branching habits that resist damage from storms should be planted. Do not plant large, fast-growing, weak-wooded species like silver maple and cottonwood next to homes and businesses. Also avoid trees that drop their leaves late in the fall (Norway maple), trees that retain their leaves throughout the winter (oaks), have exceptionally sparse branching (ginkgo), or are densely-branched (littleleaf linden). To aid municipal tree managers in making tree selection decisions, a list of recommended deciduous shade trees for energy conservation is provided on the next page.
Common name
Scientific Name
Mature height
Mature spread
Red maple
Acer rubrum
40 - 60'
30 - 50'
Sugar maple
Acer saccharum
60 - 75'
40 - 60'
Black maple
Acer nigrum
60 - 75'
40 - 60'
Ohio buckeye
Aesculus glabra
40 - 60'
40 - 60'
Black alder
Alnus glutinosa
40 - 60'
20 - 40'
River birch
Betula nigra
40 - 70'
40 - 50'
Northern catalpa
Catalpa speciosa
40 - 60'
20 - 40'
Common hackberry
Celtis
occidentalis
40 - 60'
40 - 60'
White ash
Fraxinus americana
50 - 80'
40 - 60'
Green ash
Fraxinus
pennsylvanica
50 - 60'
30 - 40'
Blue ash
Fraxinus
quadrangulata
50 - 70'
40 - 50'
Kentucky coffeetree
Gymnocladus
dioicus
60 - 75'
40 - 50'
Tuliptree
Liriodendron
tulipifera
70 - 90'
40 - 50'
Ironwood
Ostrya virginiana
30 - 40'
20 - 30'
Amur corktree
Phellodendron
amurense
30 - 45'
40 - 50'
American linden
Tilia americana
60 - 80'
40 - 60'
If a site isn't large enough to accommodate large-growing tree species, you might consider using woody plants to establish a zone of insulating dead air space along the walls of buildings. Plants like arborvitae and juniper installed close to buildings will create a layer of still or slow-moving air that can slow heat loss in winter and heat gain in summer. This technique is most effective when plants are installed in a continuous line that extends along the walls to be protected and around the corners. Landscape interest can be created by using a variety of plants, but take care to group like kinds together.
In addition to shielding buildings from environmental extremes, plant materials can be used to minimize the so-called "urban heat island effect." Researchers have found that summer temperatures in urban areas can be two to eight degrees (Fahrenheit) higher than in rural surroundings. To moderate high temperatures during the summer months, large-growing trees can be carefully located to shade paved surfaces during the hottest time of day, and nonpaved surfaces should be covered with either turfgrass or another perennial groundcover, shrubs, and/or low-growing trees. The use of light-colored parking lot surfaces also is recommended.
Energy-conserving landscapes do not
happen by accident. Rather, careful planning and preparation
is required to realize environmental and financial benefits
from strategically placed woody plants. Before you plant
that next tree, make certain it is positioned for aesthetic
beauty and energy conservation.
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ISU Horticulture:Publications:1998 Turfgrass Report | College of Agriculture |