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Landscaping
for Energy Efficiency
Are
you looking for cost-effective yet eye-pleasing ways to lower
your energy bills? Planting trees, shrubs, vines, grasses, and
hedges could be the answer. In fact, landscaping may be your best
long-term investment for reducing heating and cooling costs, while
also bringing other improvements to your community.
A well-designed landscape will:
· Cut your summer and winter energy costs dramatically.
· Protect your home from winter wind and summer sun.
· Reduce consumption of water, pesticides, and fuel for
landscaping and lawn maintenance.
· Help control noise and air pollution.
This publication covers landscaping tips to save money year-round;
ways that landscaping helps the environment; important climate,
site, and design considerations; landscape planning; and tree
and shrub selection. You can get additional information on regionally
appropriate species from your local nursery and landscaping experts.
Landscaping Saves Money Year-Round
Carefully positioned trees can save up to 25% of a household's
energy consumption for heating and cooling. Computer models devised
by the U.S. Department of Energy predict that the proper placement
of only three trees will save an average household between $100
and $250 in energy costs annually.
On average, a well-designed landscape provides enough energy savings
to return your initial investment in less than 8 years.
An 8-foot (2.4-meter) deciduous (leaf-shedding) tree, for example,
costs about as much as an awning for one large window and can
ultimately save your household hundreds of dollars in reduced
cooling costs, yet still admit some winter sunshine to reduce
heating and lighting costs. Landscaping can save you money in
summer or winter.
Summer
You may have noticed the coolness of parks and wooded areas compared
to the temperature of nearby city streets. Shading and evapotranspiration
(the process by which a plant actively moves and releases water
vapor) from trees can reduce surrounding air temperatures as much
as 9 degrees F (5 degrees C). Because cool air settles near the
ground, air temperatures directly under trees can be as much as
25 degrees F (14 degrees C) cooler than air temperatures above
nearby blacktop. Studies by the Lawrence Berkeley Laboratory found
summer daytime air temperatures to be 3 degrees F to 6 degrees
F (2 degrees C to 3 degrees C) cooler in tree- shaded neighborhoods
than in treeless areas.
A well-planned landscape can reduce an unshaded home's summer
air-conditioning costs by 15% to 50%. One Pennsylvania study reported
air-conditioning savings of as much as 75% for small mobile homes.
Winter
You may be familiar with wind chill. If the outside temperature
is 10 degrees F (-12 degrees C) and the wind speed is 20 miles
per hour (32 kilometers per hour), the wind chill is -24 degrees
F (-31 degrees C). Trees, fences, or geographical features can
be used as windbreaks to shield your house from the wind.
A study in South Dakota found that windbreaks to the north, west,
and east of houses cut fuel consumption by an average of 40%.
Houses with windbreaks placed only on the windward side (the side
from which the wind is coming) averaged 25% less fuel consumption
than similar but unprotected homes. If you live in a windy climate,
your well-planned landscape can reduce your winter heating bills
by approximately one-third.
Landscaping for a Cleaner Environment
Widespread tree planting and climate-appropriate landscaping offer
substantial environmental benefits. Trees and vegetation control
erosion, protect water supplies, provide food, create habitat
for wildlife, and clean the air by absorbing carbon dioxide and
releasing oxygen.
The National Academy of Sciences (NAS) estimates that urban America
has 100 million potential tree spaces (i.e., spaces where trees
could be planted). NAS further estimates that filling these spaces
with trees and lightening the color of dark, urban surfaces would
result in annual energy savings of 50 billion kilowatt-hours --
25% of the 200 billion kilowatt-hours consumed every year by air
conditioners in the United States.
This would reduce electric power plant emissions of carbon dioxide
by 35 million tons (32 million metric tons) annually and save
users of utility-supplied electricity $3.5 billion each year (assuming
an average of $0.07 per kilowatt-hour). Also, some species of
trees, bushes, and grasses require less water than others. Some
species are naturally more resistant to pests, so they require
less pesticides. Another alternative to pesticides is integrated
pest management, an emerging field that uses least-toxic pest
control strategies.
One example is to introduce certain insects such as praying mantises
or ladybugs to feed on-and limit populations of-landscape-consuming
pests. Certain grasses, such as buffalo grass and fescue, only
grow to a certain height -- roughly 6 inches (15 centimeters)
and are water thrifty. By using these species, you can eliminate
the fuel, water, and time consumption associated with lawn mowing,
watering, and trimming. Also, recent studies have found that gasoline-powered
mowers, edge trimmers, and leaf blowers contribute to air pollution.
Climate, Site, and Design Considerations
Climate
The United States can be divided into four approximate climatic
regions: temperate, hot-arid, hot-humid, and cool. The energy-conserving
landscape strategies you use should depend on which region you
live in. These landscaping strategies are listed by region and
in order of importance below.
Temperate
· Maximize warming effects of the sun in the winter.
· Maximize shade during the summer.
· Deflect winter winds away from buildings.
· Funnel summer breezes toward the home.
Hot-Arid
· Provide shade to cool roofs, walls, and windows.
· Allow summer winds to access naturally cooled homes.
· Block or deflect winds away from air-conditioned homes.
Hot-Humid
· Channel summer breezes toward the home.
· Maximize summer shade with trees that still allow penetration
of low-angle winter sun.
· Avoid locating planting beds close to the home if they
require frequent watering.
Cool
· Use dense windbreaks to protect the home from cold winter
winds.
· Allow the winter sun to reach south-facing windows.
· Shade south and west windows and walls from the direct
summer sun, if summer overheating is a problem.
Microclimate
The climate immediately surrounding your home is called its microclimate.
If your home is located on a sunny southern slope, it may have
a warm microclimate, even if you live in a cool region. Or, even
though you live in a hot-humid region, your home may be situated
in a comfortable microclimate because of abundant shade and dry
breezes. Nearby bodies of water may increase your site's humidity
or decrease its air temperature.
Your home's microclimate may be more sunny, shady, windy, calm,
rainy, snowy, moist, or dry than average local conditions. These
factors all help determine what plants may or may not grow in
your microclimate.
Siting and Design
A well-oriented and well-designed home admits low-angle winter
sun, rejects overhead summer sun, and minimizes the cooling effect
of winter winds. If you are building a home, pay attention to
its orientation.
In the northern hemisphere, it is usually best to align the home's
long axis in an east-west direction. The home's longest wall with
the most window area should face south or southeast. The home's
north-facing and west-facing walls should have fewer windows because
these walls generally face winter's prevailing winds.
North-facing windows receive little direct sunlight. You may be
able to design and orient your new house to maximize your homesite's
natural advantages and mitigate its disadvantages. Notice your
homesite's exposure to sun, wind, and water. Also note the location
and proximity of nearby buildings, fences, water bodies, trees,
and pavement -- and their possible climatic effects. Buildings
provide shade and windbreak. Fences and walls block or channel
the wind. Water bodies moderate temperature but increase humidity
and produce glare. Trees provide shade, windbreaks, or wind channels.
Pavement reflects or absorbs heat, depending on whether its color
is light or dark.
If your home is already built, inventory its comfort and energy
problems, then use the following landscaping ideas to help minimize
these problems.
Shading
Solar heat passing through windows and being absorbed through
the roof is the major reason for air-conditioner use. Shading
is the most cost-effective way to reduce solar heat gain and cut
air-conditioning costs. Using shade effectively requires you to
know the size, shape, and location of the moving shadow that your
shading device casts. Remember that homes in cool regions may
never overheat and may not require shading.
Trees can be selected with appropriate sizes, densities, and shapes
for almost any shading application. To block solar heat in the
summer but let much of it in during the winter, use deciduous
trees. To provide continuous shade or to block heavy winds, use
evergreen trees or shrubs.
Deciduous trees with high, spreading crowns (i.e., leaves and
branches) can be planted to the south of your home to provide
maximum summertime roof shading. Trees with crowns lower to the
ground are more appropriate to the west, where shade is needed
from lower afternoon sun angles. Trees should not be planted on
the southern sides of solar- heated homes in cold climates because
the branches of these deciduous trees will block some winter sun.
A 6-foot to 8-foot (1.8-meter to 2.4-meter) deciduous tree planted
near your home will begin shading windows the first year. Depending
on the species and the home, the tree will shade the roof in 5
to 10 years. If you have an air conditioner, be aware that shading
the unit can increase its efficiency by as much as 10%.
Trees, shrubs, and groundcover plants can also shade the ground
and pavement around the home. This reduces heat radiation and
cools the air before it reaches your home's walls and windows.
Use a large bush or row of shrubs to shade a patio or driveway.
Plant a hedge to shade a sidewalk. Build a trellis for climbing
vines to shade a patio area.
Vines can shade walls during their first growing season. A lattice
or trellis with climbing vines, or a planter box with trailing
vines, shades the home's perimeter while admitting cooling breezes
to the shaded area.
Shrubs planted close to the house will fill in rapidly and begin
shading walls and windows within a few years. However, avoid allowing
dense foliage to grow immediately next to a home where wetness
or continual humidity are problems. Well-landscaped homes in wet
areas allow winds to flow around the home, keeping the home and
its surrounding soil reasonably dry.
Wind Protection
Properly selected and placed landscaping can provide excellent
wind protection, which will reduce heating costs considerably.
Furthermore, these benefits will increase as the trees and shrubs
mature. The best windbreaks block wind close to the ground by
using trees and shrubs that have low crowns.
Evergreen trees and shrubs planted to the north and northwest
of the home are the most common type of windbreak. Trees, bushes,
and shrubs are often planted together to block or impede wind
from ground level to the treetops. Or, evergreen trees combined
with a wall, fence, or earth berm (natural or man-made walls or
raised areas of soil) can deflect or lift the wind over the home.
Be careful not to plant evergreens too close to your home's south
side if you are counting on warmth from the winter sun.
A windbreak will reduce wind speed for a distance of as much as
30 times the windbreak's height. But for maximum protection, plant
your windbreak at a distance from your home of two to five times
the mature height of the trees.
If snow tends to drift in your area, plant low shrubs on the windward
side of your windbreak. The shrubs will trap snow before it blows
next to your home.
In addition to more distant windbreaks, planting shrubs, bushes,
and vines next to your house creates dead air spaces that insulate
your home in both winter and summer. Plant so there will be at
least 1 foot (30 centimeters) of space between full-grown plants
and your home's wall.
Summer winds especially at night can have a cooling effect if
used for home ventilation. However, if winds are hot and your
home is air conditioned all summer, you may want to keep summer
winds from circulating near your home.
Planning Your Landscape
Before you start landscaping, you must first develop a plan. The
components of your plan could include deciduous trees and plants,
coniferous trees and plants, earth berms, walls, fences, sheds,
and garages. This section will help you create a landscape plan
before you plant around your existing home or before you begin
construction on a new house.
Use paper and different-colored pencils to begin designing your
landscape. First, sketch a simple, scaled drawing of your yard.
Locate its buildings, walks, driveways, and utilities (e.g., sewer,
electric, and telephone lines). Note the location of all paved
surfaces -- streets, driveways, patios, or sidewalks -- near your
home. Then identify potential uses for different areas of your
yard: vegetable gardens, flower beds, patios, and play areas.
Draw arrows to show sun angles and prevailing winds for both summer
and winter. As you sketch, circle the areas of your yard needing
shade or wind protection. Indicate with arrows how you want views
to be preserved or screened. Mark routes of noise pollution you
wish to block. Also, highlight areas where landscaping height
or width may be restricted, such as under utility lines or along
sidewalks.
Notice yard areas that suffer from poor drainage and standing
water. Some trees and shrubs will not grow well in poorly drained
areas; others will. Note existing trees and shrubs. Plan for their
replacement if they are old or sick and if they provide valued
shade or windbreak.
Perhaps you want more defined property boundaries or less traffic
noise. Consider a "living fence" of dense trees, bushes,
or shrubs. Depending on its location and application, this hedge
can be customized to be tall, short, wide, narrow, open, or dense.
Privet is a species of shrub that grows in most parts of the United
States and can serve as a living fence.
Areas of lawn not used as picnic or play areas can be converted
to planting beds or xeriscaped areas. Xeriscaping is a landscaping
technique that uses vegetation that is drought resistant and is
able to survive on rainfall and groundwater once established.
Converting a traditional lawn to alternative, water-conserving
grasses or other forms of xeriscaping saves energy and reduces
water consumption.
Perhaps you live in an urban area where yards are small and neighbors
close. Your neighbor's yard may be the best place for trees to
shade your south-facing windows. Your yard may be the best location
for their windbreak. Bringing your neighbors into your plans could
benefit everyone involved.
The more you identify your goals and familiarize yourself with
your yard's features -- current and proposed -- the better your
chances for success with your landscaping projects.
Selecting and Planting Trees and Shrubs
Trees and shrubs come in all shapes and sizes. How you select
your trees and shrubs and how you plant them will directly affect
your home's comfort and energy efficiency.
Trees and shrubs have a life span of many years and can become
more attractive and functional with age. But poor planning of
landscape improvements often creates trouble. Ensure proper plant
placement and minimal maintenance before you plant!
Shape Characteristics
Tree shapes are very diverse think of the difference in shape
between an oak and a spruce. The "Shading" section under
"Climate, Site, and Design Considerations" above discusses
how to use varying tree and shrub characteristics to maximum advantage
when landscaping.
The density of a tree's leaves or needles is important to consider.
Dense evergreens, like spruces, make great windbreaks for winter
winds. If you are just looking to impede summer winds, choose
a tree or shrub with more open branches and leaves. Such trees
are also good for filtering morning sun from the east, while denser
trees are better for blocking harsh afternoon summer sun.
Growth
Should you plant slow-growing or fast-growing tree species? Although
a slow-growing tree may require many years of growth before it
shades your roof, it will generally live longer than a fast-growing
tree. Also, because slow-growing trees often have deeper roots
and stronger branches, they are less prone to breakage by windstorms
or heavy snow loads. And they can be more drought resistant than
fast-growing trees.
Consider growth rate, strength, and brittleness when locating
trees near walkways or structures. Ask whether the mature tree's
root system is likely to damage sidewalks, foundations, or sewer
lines. The smaller your yard, the more important it is to select
a tree with manageable roots.
Selecting, Final Planning, and Purchasing
Landscape professionals can help you choose and locate new trees,
shrubs, or ground cover. Share your drawings and tentative ideas
with your local nursery or landscape contractor. As long as you
have defined intended uses and spaces in which planting is actually
possible, a competent nursery or landscape specialist will be
able to help you make decisions.
When planting trees, shrubs, hedges, or bushes, find out how large
the mature specimen will grow. In all cases, determine spacing
by the mature sizes. For those plants close to your house, plan
for at least 1 foot (30 centimeters) of extra clearance between
the full-grown shrub and the wall of the home. This will prevent
heavy pruning or damage to home siding in the future.
After considering the placement of your trees and consulting landscaping
and nursery professionals, go back to your drawings or plans and
add the new information on species, shape, and mature-size spacing.
This provides a final, pre-purchase review to make sure that all
elements will work well together -- in the short and long term.
When you are ready to purchase your trees and shrubs, avoid buying
damaged specimens. Thoroughly inspect the bark, limbs, and roots
to make sure the plant was handled carefully during growing, digging,
and shipping. Reject plant stock with signs of insects or disease
(cocoons, egg masses, cankers, or lesions).
After you purchase the plants, be sure to keep tiny root hairs
damp and shaded at all times. The plants will not survive if these
root hairs are allowed to dry before planting.
Contact your county extension agents, public libraries, local
nurseries, landscape architects, landscape contractors, and state
and local energy offices for additional information on regionally
appropriate plants and their maintenance requirements.
Source List
The following resources provide more information on landscaping
for energy efficiency.
American Nursery & Landscape Association
1250 I Street, NW, Suite 500
Washington, DC 20005
(202) 789-2900
Fax: (202) 789-1893
AAN serves as a network of organizations representing garden centers,
landscaping, and horticultural interests.
American Society of Landscape Architects (ASLA)
636 Eye Street, NW
Washington, DC 20001-3736
(202) 898-2444
Fax: 202-898-1185
ASLA is dedicated to the advancement of knowledge, education,
and skill in the art and science of landscape architecture.
National Arbor Day Foundation (NADF)
100 Arbor Avenue
Nebraska City, NE 68410
(402) 474-5655
Email: info@arborday.org
NADF is a nonprofit educational organization dedicated to tree
planting and conservation. NADF sponsors National Arbor Day each
spring.
For general information about many kinds of energy efficiency
topics, contact:
Ask an Energy Expert
Energy Efficiency and Renewable Energy Clearinghouse (EREC)
P.O. Box 3048
Merrifield, VA 22116
(800) DOE-EREC (363-3732)
Fax: (703) 893-0400
Email: doe.erec@nciinc.com
Consumer Energy Information Web site
EREC provides free general and technical information to the public
on the many topics and technologies pertaining to energy efficiency
and renewable energy.
Reading List
Common Sense Pest Control, edited by C. Timmons, available from
Taunton Press, Inc., 1991.
Cooling Our Communities: A Guidebook on Tree Planting and Light-Colored
Surfacing, H. Akbari, J. Huang, and S. Davis, available from Government
Printing Office (Document #055-000-00371-8), Superintendent of
Documents, P.O. Box 371954, Pittsburgh, PA 15220-7954, 1992.
Landscaping Design that Saves Energy, A. S. Moffat and M. Schiler,
William Morrow and Company, Inc., 1991.
Landscaping for Energy Conservation, W. R. Nelson, available from
the Building Research Council, College of Fine and Applied Arts,
University of Illinois at Urbana-Champaign, One East Saint Mary's
Road, Champaign, IL 61820, 1991.
Xeriscape Gardening: Water Conservation for the American Landscape,
C. Ellefson, Macmillan Publishing Company, 1992.
Related Links
Cooling Your Home Naturally
(PDF 160 KB) Download Acrobat Reader
Energy Savers: Landscaping
See the cooling and heating sections on DOE's Consumer Energy
Information Web site for links to information on other ways to
heat and cool your home energy efficiently.
This document was produced for the U.S. Department of Energy (DOE)
by the National Renewable Energy Laboratory (NREL), a DOE national
laboratory.
DOE/GO-10095-046
FS 220
April 1995
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