landscaping for energy efficiency

8/9/2019 Landscaping for Energy Efficiency

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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-terminvestment for reducing heating andcooling costs, while also bringing otherimprovements to your community.

A well-designed landscape will:

• Cut your summer and winter energycosts dramatically.

• Protect your home from winter wind

and summer sun.• Reduce consumption of water, pesti-

cides, and fuel for landscaping andlawn maintenance.

• Help control noise and air pollution.

This publication covers landscaping tipsto save money year-round; ways that land-scaping helps the environment; importantclimate, site, and design considerations;landscape planning; and tree and shrub

selection. You can get

additional informationon regionally appropriatespecies from your localnursery and landscapingexperts.

Landscaping SavesMoney Year-Round

Carefully positionedtrees can save up to 25%of a household’s energyconsumption for heating

and cooling. Computermodels devised by theU.S. Department of Energy predict that theproper placement of onlythree trees will save anaverage household between $100 and $250in energy costs annually.

On average, a well-designed landscape pro-vides enough energy

savings to return yourinitial investment in lessthan 8 years. An 8-foot(2.4-meter) deciduous

Landscaping forEnergy Efficiency

C L E A R I N G H O U

S E

ENERGY

EFFICIENCY AND

RENEWABLE

ENERGY

T O F E N E R G Y

D E P A R T

M E N

U

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N I T E D

S T A T S O F

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Mature deciduous trees provide shade in the summer and sunlightfiltration in the winter.

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 Technical Information Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiencyand 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

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

DOE/GO-10095-046FS 220

April 1995

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(leaf-shedding) tree, for example, costsabout as much as an awning for one largewindow and can ultimately save yourhousehold hundreds of dollars in reducedcooling costs, yet still admit some wintersunshine to reduce heating and lightingcosts. Landscaping can save you money insummer or winter.

Summer

You may have noticed the coolness of parks and wooded areas compared to thetemperature of nearby city streets. Shad-ing and evapotranspiration (the process by which a plant actively moves andreleases water vapor) from trees canreduce surrounding air temperatures asmuch as 9˚F (5˚C). Because cool air settlesnear the ground, air temperatures directlyunder trees can be as much as 25˚F (14˚C)

cooler than air temperatures above nearby blacktop. Studies by the Lawrence Berke-ley Laboratory found summer daytime airtemperatures to be 3˚F to 6˚F (2˚C to 3˚C)cooler in tree-shaded neighborhoods thanin treeless areas.

A well-planned landscape can reduce anunshaded home’s summer air-conditioningcosts by 15% to 50%. One Pennsylvaniastudy reported air-conditioning savings of as much as 75% for small mobile homes.

Winter You may be familiar with wind chill. Ifthe outside temperature is 10̊ F (-12̊ C)and the wind speed is 20 miles per hour(32 kilometers per hour), the wind chill is-24̊ F (-31̊ C). Trees, fences, or geographicalfeatures can be used as windbreaks toshield 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 aver-age of 40%. Houses with windbreaksplaced only on the windward side (theside from which the wind is coming) aver-aged 25% less fuel consumption than simi-lar but unprotected homes. If you live in awindy climate, your well-planned land-scape can reduce your winter heating bills by approximately one-third.

Landscaping for aCleaner Environment

Widespread tree planting and climate-appropriate landscaping offer substantialenvironmental benefits. Trees and vegeta-tion control erosion, protect water sup-plies, provide food, create habitat for

wildlife, and clean the air by absorbingcarbon dioxide and releasing oxygen.

The National Academy of Sciences (NAS)estimates that urban America has 100 mil-lion potential “tree spaces” (i.e., spaceswhere trees could be planted). NAS fur-ther estimates that filling these spaceswith trees and lightening the color of darkurban surfaces would result in annualenergy savings of 50 billion kilowatt-hours—25% of the 200 billion kilowatt-hours consumed every year by air

conditioners in the United States. Thiswould reduce electric power plant emis-sions of carbon dioxide by 35 milliontons (32 million metric tons) annually andsave users of utility-supplied electricity$3.5 billion each year (assuming an aver-age of $0.07 per kilowatt-hour).

Also, some species of trees, bushes, andgrasses require less water than others.Some species are naturally more resistantto pests, so they require less pesticides.Another alternative to pesticides is inte-

grated pest management, an emerging fieldthat uses least-toxic pest control strategies.One example is to introduce certaininsects such as praying mantises or lady- bugs to feed on—and limit populationsof—landscape-consuming pests.

Certain grasses, such as buffalo grass andfescue, only grow to a certain height—roughly 6 inches (15 centimeters) and arewater thrifty. By using these species, youcan eliminate the fuel, water, and time

consumption associated with lawn mow-ing, watering, and trimming. Also, recentstudies have found that gasoline-poweredmowers, edge trimmers, and leaf blowerscontribute to air pollution.

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Landscaping may be

your best long-term

investment for

reducing heating and

cooling costs.


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Climate, Site, andDesign Considerations

Cl imate

The United States can be divided intofour approximate climatic regions: tem-perate, hot-arid, hot-humid, and cool. Theenergy-conserving landscape strategies

you use should depend on which regionyou live in. These landscaping strategiesare listed by region and in order of impor-tance 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.• Cool the air around the home by plant

evapotranspiration.• Allow summer winds to access natu-

rally 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 win-

ter 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.

M icrocl i mate

The climate immediately surroundingyour home is called its microclimate. If your home is located on a sunny southernslope, it may have a warm microclimate,even if you live in a cool region. Or, eventhough you live in a hot-humid region,your home may be situated in a comfort-

able microclimate because of abundantshade and dry breezes. Nearby bod-

ies of water mayincrease your site’shumidity or decreaseits air temperature.

Your home’s micro-climate may be moresunny, shady, windy,calm, rainy, snowy,moist, or dry thanaverage local condi-tions. These factorsall help determine

what plants may ormay not grow inyour microclimate.

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Carefully positioned

trees can save up to

25% of a household’s

energy consumption

for heating and

cooling.

Hot-Humid

Hot-Humid

Hot-Arid

Temperate

Cool

Cool

Cool

The climatic region in which you live affects the landscaping strategies you use.

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Si t i ng and Design

A well-oriented and well-designed homeadmits low-angle winter sun, rejects over-head summer sun, and minimizes thecooling effect of winter winds. If youare building a home, pay attention toits orientation.

In the northern hemisphere, it is usually best to align the home’s long axis in aneast-west direction. The home’s longestwall—with the most window area—should face south or southeast. Thehome’s north-facing and west-facing wallsshould have fewer windows because thesewalls generally face winter’s prevailingwinds. North-facing windows receive lit-tle direct sunlight.

You may be able to design and orient your

new house to maximize your homesite’snatural advantages and mitigate its disad-vantages. Notice your homesite’s expo-sure to sun, wind, and water. Also notethe location and proximity of nearby buildings, fences, water bodies, trees, andpavement—and their possible climaticeffects. Buildings provide shade andwindbreak. Fences and walls block orchannel the wind. Water bodies moderatetemperature but increase humidity and

produce glare. Trees provide shade, windbreaks, or wind channels. Pavementreflects or absorbs heat, depending onwhether its color is light or dark.

If your home is already built, inventory itscomfort and energy problems, then usethe following landscaping ideas to helpminimize these problems.

ShadingSolar heat passing through windows and being absorbed through the roof is themajor reason for air-conditioner use.Shading is the most cost-effective way

to reduce solar heat gain and cut air-conditioning costs. Using shade effectivelyrequires you to know the size, shape, andlocation of the moving shadow that yourshading device casts. Remember thathomes in cool regions may never overheatand may not require shading.

Trees can be selected with appropriatesizes, densities, and shapes for almost anyshading application. To block solar heat inthe summer but let much of it in duringthe winter, use deciduous trees. To pro-

vide continuous shade or to block heavywinds, use evergreen trees or shrubs.

Deciduous trees with high, spreadingcrowns (i.e., leaves and branches) can beplanted to the south of your home to pro-vide maximum summertime roof shading.Trees with crowns lower to the groundare more appropriate to the west, whereshade is needed from lower afternoon sunangles. Trees should not be planted on the

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N o r t h

W e s t

During the summer, tall spreading trees planted close to the home shade the roof.Broad, shorter trees on the west side block afternoon solar heat. A windbreak onthe northwest side can shield the home from prevailing winter winds.

If you live in a windy

climate, your well-

planned landscape

can reduce your

winter heating bills

by approximately

one-third.

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To cool the south and west sides of thehome, reduce paved areas, plant shade trees,or add a trellis.

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southern sides of solar-heated homes incold climates because the branches of these deciduous trees will block somewinter sun.

A 6-foot to 8-foot (1.8-meter to 2.4-meter)deciduous tree planted near your homewill 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 awarethat shading the unit can increase its effi-ciency by as much as 10%.

Trees, shrubs, and groundcover plantscan also shade the ground and pavementaround the home. This reduces heat radia-tion and cools the air before it reachesyour home’s walls and windows. Use alarge bush or row of shrubs to shade apatio or driveway. Plant a hedge to shadea sidewalk. Build a trellis for climbingvines to shade a patio area.

Vines can shadewalls during theirfirst growing season.A lattice or trelliswith climbing vines,or a planter box withtrailing vines, shadesthe home’s perimeterwhile admitting

cooling breezes tothe shaded area.

Shrubs planted closeto the house will fillin rapidly and beginshading walls andwindows within afew years. However,avoid allowingdense foliage togrow immediatelynext to a home

where wetness orcontinual humidity are problems. Well-landscaped homes in wet areas allowwinds to flow around the home, keepingthe home and its surrounding soil reason-ably dry.

Wind ProtectionProperly selected and placed landscapingcan provide excellent wind protection,which will reduce heating costs consider-ably. Furthermore, these benefits willincrease as the trees and shrubs mature.The best windbreaks block wind close tothe ground by using trees and shrubs thathave low crowns.

Evergreen trees and shrubs planted to thenorth and northwest of the home are themost common type of windbreak. Trees, bushes, and shrubs are often plantedtogether to block or impede wind fromground level to the treetops. Or, evergreentrees combined with a wall, fence, or earth berm (natural or man-made walls or

raised areas of soil) can deflect or lift thewind over the home. Be careful not toplant evergreens too close to your home’ssouth side if you are counting on warmthfrom the winter sun.

A windbreak will reduce wind speed for adistance of as much as 30 times the windbreak’s height. But for maximum protec-tion, plant your windbreak at a distancefrom your home of two to five times themature height of the trees.

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Properly selected and placed evergreen treesand shrubs can shelter the home from winterwinds and reduce heating costs.

To block solar heat

in the summer but

let much of it in

during the winter,

use deciduous trees.

A trellis with a climbing vine can shade a home andallow air circulation.

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If south winds are a problem in the winter,plant evergreens far enough away to liftwinds without shading the home.

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NORTH

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If snow tends to drift in your area, plantlow shrubs on the windward side of yourwindbreak. The shrubs will trap snow before it blows next to your home.

In addition to more distant windbreaks,planting shrubs, bushes, and vines nextto your house creates dead air spaces that

insulate your home in both winter andsummer. Plant so there will be at least1 foot (30 centimeters) of space betweenfull-grown plants and your home’s wall.

Summer winds—especially at night—canhave a cooling effect if used for home ven-tilation. However, if winds are hot andyour home is air conditioned all summer,you may want to keep summer windsfrom circulating near your home.

Planning Your Landscape

Before you start landscaping, you mustfirst develop a plan. The components of your plan could include deciduous treesand plants, coniferous trees and plants,earth berms, walls, fences, sheds, andgarages. This section will help you create alandscape plan before you plant aroundyour existing home or before you beginconstruction on a new house.

Use paper and different-colored pencils to begin designing your landscape. First,sketch a simple, scaled drawing of youryard. Locate its buildings, walks, drive-ways, 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 differentareas of your yard: vegetable gardens,flower beds, patios, and play areas.

Draw arrows to show sun angles and pre-vailing winds for both summer and win-ter. As you sketch, circle the areas of youryard needing shade or wind protection.

Indicate with arrows how you want viewsto be preserved or screened. Mark routesof noise pollution you wish to block. Also,highlight areas where landscaping heightor width may be restricted, such as underutility lines or along sidewalks.

Notice yard areas that suffer from poordrainage and standing water. Some treesand shrubs will not grow well in poorlydrained areas; others will. Note existingtrees and shrubs. Plan for their replace-ment if they are old or sick and if theyprovide valued shade or windbreak.

Perhaps you want more defined property

boundaries or less traffic noise. Consider a“living fence” of dense trees, bushes, orshrubs. Depending on its location andapplication, this hedge can be customizedto be tall, short, wide, narrow, open, ordense. Privet is a species of shrub thatgrows in most parts of the United Statesand can serve as a living fence.

Areas of lawn not used as picnic or playareas can be converted to planting bedsor xeriscaped areas. Xeriscaping is a land-scaping technique that uses vegetation

that is drought resistant and is able to sur-vive on rainfall and groundwater onceestablished. Converting a traditional lawnto alternative, water-conserving grasses orother forms of xeriscaping saves energyand reduces water consumption.

Perhaps you live in an urban area whereyards are small and neighbors close. Yourneighbor’s yard may be the best place for

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Originating in

Denver, Colorado,

xeriscaping is a

landscaping technique

that uses water-

thrifty species which

are often native to

the region. Once

established, they

are able to survive

on rainfall and groundwater.

This plan drawing is for a south-facing house in a hot, humid region. Dottedlines indicate potential problem areas. This home is exposed to hurricane winds.

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NORTH


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trees to shade your south-facing windows.Your yard may be the best location fortheir windbreak. Bringing your neighborsinto your plans could benefit everyoneinvolved.

The more you identify your goals andfamiliarize yourself with your yard’s fea-

tures—current and proposed—the betteryour chances for success with your land-scaping projects.

Selecting and PlantingTrees and Shrubs

Trees and shrubs come in all shapes andsizes. How you select your trees andshrubs and how you plant them willdirectly affect your home’s comfort and

energy efficiency.

Trees and shrubs have a life span of manyyears and can become more attractive andfunctional with age. But poor planning of landscape improvements often createstrouble. Ensure proper plant placementand minimal maintenance before you plant!

Shape Characteri sti cs

Tree shapes are very diverse—think ofthe difference in shape between an oakand a spruce. The “Shading” sectionunder “Climate, Site, and Design Consid-erations” above discusses how to usevarying tree and shrub characteristics tomaximum advantage when landscaping.

The density of a tree’s leaves or needlesis important to consider. Dense ever-greens, like spruces, make great windbreaks for winter winds. If you are justlooking to impede summer winds, choosea tree or shrub with more open branchesand leaves. Such trees are also good for fil-tering morning sun from the east, whiledenser trees are better for blocking harshafternoon summer sun.

Growth Should you plant slow-growing or fast-growing tree species? Although a slow-growing tree may require many yearsof growth before it shades your roof,it will generally live longer than a fast-growing tree. Also, because slow-growingtrees 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 resistantthan fast-growing trees.

Consider growth rate, strength, and brit-tleness when locating trees near walkwaysor structures. Ask whether the maturetree’s root system is likely to damage side-walks, foundations, or sewer lines. Thesmaller your yard, the more important it isto select a tree with manageable roots.

Sel ecti ng, Fi nal Pl anni ng,

and Purchasi ng

Landscape professionals can help youchoose and locate new trees, shrubs, or

ground cover. Share your drawings andtentative ideas with your local nursery orlandscape contractor. As long as you havedefined intended uses and spaces inwhich planting is actually possible, a com-petent nursery or landscape specialist will be able to help you make decisions.

When planting trees, shrubs, hedges, or bushes, find out how large the maturespecimen will grow. In all cases, determine

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Planting Tips

Many suburban and urban soils need loosening before you plant. If the soil iscompacted, till it to an area at least five times the diameter of the root ball.Plant your new trees and shrubs on a cool or overcast day to reduce the stressof relocating.

• Dig a hole in the tilled soil. The hole diameter should be roughly twice thediameter of the root ball but the same height as the root ball.

• If your soil is very heavy or sandy, mix quality compost or potting soil withthe soil removed from the hole.

• Remove the plant from its container, gently freeing its roots.

• If the root ball is surrounded by burlap or wire, remove this before planting.

• Place the tree or shrub in the hole so that it sits at its original soil line.

• Firmly, but gently, fill the hole half full of the soil removed from the hole,and lightly tamp the area around the root ball to remove air pockets.

• Water well, then fill the hole to the top with soil. Water again.

• Build a watering basin 3 inches to 4 inches (8 centimeters to 10 centimeters)high around the new plant, about twice the diameter of the root ball.

• To retain root moisture and reduce weeds, cover the ground around thenew plant with 4 inches (10 centimeters) of mulch. Use well-aged organic

materials such as old leaves and grass clippings, bark, and aged sawdust orwood chips.

• Keep the plant well watered for the first year, but be careful not to drown it!Watering deeply twice a week is usually sufficient.


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Source List

The following resources provide more informationon landscaping for energy efficiency.

American Association of Nurserymen (AAN)1240 I Street, NW, Suite 500Washington, DC 20005(202) 789-2900

AAN serves as a network of organizations representing gardencenters, landscaping, and horticultural interests.

American Society of Landscape Architects (ASLA)4401 Connecticut Avenue, NWWashington, DC 20008(202) 686-2752

ASLA is dedicated to the advancement of knowledge, educa-tion, and skill in the art and science of landscape architecture.

National Arbor Day Foundation (NADF)100 Arbor AvenueNebraska City, NE 68410

NADF is a nonprofit educational organization dedicated totree planting and conservation. NADF sponsors NationalArbor Day each spring.

For general information about many kinds of energy efficiencytopics, contact:

The Energy Efficiency and Renewable EnergyClearinghouse (EREC)

P.O. Box 3048Merrifield, VA 22116(800) DOE-EREC (363-3732)Fax: (703) 893-0400

EREC provides free general and technical information to thepublic on the many topics and technologies pertaining toenergy efficiency and renewable energy.

Reading List

Common Sense Pest Control, edited by C. Timmons, avail-able from Taunton Press, Inc., 1991.

Cooling Our Communities: A Guidebook on Tree Plantingand Light-Colored Surfacing, H. Akbari, J. Huang, andS. Davis, available from Government Printing Office(Document #055-000-00371-8), Superintendent of Docu-ments, P.O. Box 371954, Pittsburgh, PA 15220-7954, 1992.

Landscaping Design that Saves Energy, A. S. Moffat andM. Schiler, William Morrow and Company, Inc., 1991.

Landscaping for Energy Conservation, W. R. Nelson, avail-able from the Building Research Council, College of Fineand Applied Arts, University of Illinois at Urbana-Champaign, One East Saint Mary’s Road, Champaign,IL 61820, 1991.

Xeriscape Gardening: Water Conservation for the AmericanLandscape, C. Ellefson, Macmillan Publishing Company,1992.

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spacing by the mature sizes. For thoseplants close to your house, plan for at least1 foot (30 centimeters) of extra clearance between the full-grown shrub and thewall of the home. This will prevent heavypruning or damage to home siding inthe future.

After considering the placement of yourtrees and consulting landscaping andnursery professionals, go back to yourdrawings or plans and add the new infor-mation on species, shape, and mature-sizespacing. This provides a final, prepurchasereview to make sure that all elementswill work well together—in the short andlong term.

When you are ready to purchase yourtrees and shrubs, avoid buying damaged

specimens. Thoroughly inspect the bark,limbs, and roots to make sure the plantwas handled carefully during growing,digging, and shipping. Reject plant stockwith 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 atall times. The plants will not survive if these root hairs are allowed to dry beforeplanting.

Contact your county extension agents,public libraries, local nurseries, landscapearchitects, landscape contractors, and stateand local energy offices for additionalinformation on regionally appropriateplants and their maintenance requirements

landscaping for energy efficiency

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