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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 omfortable
microclimate because of abundant shade and dry breezes. Nearby
bodies of water may increase your site's humidity or decrease
its air temperature.
Your homes 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
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.
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 wind- breaks 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,
prepurchase 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 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 Information
The following resources provide
more information on landscaping for energy efficiency.
* American Association of Nurserymen
(AAN)
1240 I Street, NW, Suite 500
Washington, DC 20005
(202) 789-2900
AAN serves as a network of organizations
representing garden centers, landscaping, and horticultural interests.
* American Society of Landscape
Architects (ASLA)
4401 Connecticut Avenue, NW
Washington, DC 20008
(202) 686-2752
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
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:
* The Energy Efficiency and
Renewable Energy Clearinghouse (EREC)
P.O. Box 3048
Merrifield, VA 22116
(800) DOE-EREC (363-3732)
Fax: (703) 893-0400
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.
This document was produced for
the U.S. Department of Energy (DOE) by the National Renewable
Energy Laboratory (NREL), a DOE national laboratory. The document
was produced by the Information Services Program, under the DOE
Office of Energy Efficiency and Renewable Energy. The Energy
Efficiency and Renewable Energy Clearinghouse (EREC) is operated
by NCI Information Systems, Inc., for NREL/DOE. The statements
contained herein are based on information known to EREC and NREL
at the time of printing. No recommendation or endorsement of
any product or service is implied if mentioned by EREC.
DOE/GO-10095-046
FS 220
April 1995 |
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