Energy efficient landscaping – Mother Earth News

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Not only can it lower your utility bills, energy efficient landscaping can increase the value of your property.

ILLUSTRATION: MOTHER EARTH NEWS STAFF

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Despite what you may think, a strong windshield is not the most effective way to protect an area.

MOTHER EARTH NEWS STAFF

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Conifers provide the best protection against the winter wind, while deciduous trees can channel the summer breeze.

MOTHER EARTH NEWS STAFF

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A penetrable barrier will create a much larger wind shadow.

MOTHER EARTH NEWS STAFF

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The United States has 42 million acres of yards (an area about the size of New England). Most of these yards waste water, are sprayed with chemicals, do not use native plants, and cannot support wildlife. Only a small percentage take advantage of their natural ability to protect a home from the elements. According to the US Department of Energy, a recent report from the US Forest Service and numerous academic studies, energy efficient landscaping can significantly reduce a home’s utility bills. Of how many? Between $ 300 and $ 750 per year according to these same studies, and that doesn’t even include the added value that low utility bills and a well-designed landscape add to home resale prices (15% according to a survey by the National Gardening Association).

Temper the sun

The strategy for dealing with the sun is simple: block it when it’s hot, let it in when it’s cold. What is more complicated is where to place and not place the plantations to achieve these goals. In many cases, cutting down trees can be even more important than planting them.

As landscaper Robert Kourik noted, “the old-fashioned idea that an energy efficient landscape means a grove of deciduous trees along the south side of a house. [so the leaves will block the sun in the summer, but drop off and let the sun in during the winter] is not only ineffective, but often counterproductive. For most of the country, heating costs more than cooling, so a home’s southern exposure usually needs to be clear to let in the heat from the sun. Even deciduous trees without leaves can block 25-60% of solar energy.

Large shade trees should be placed on the east and west sides of the house. Because the summer sun rises high in the sky, it is the roof and the east and west walls that receive the direct heat and therefore need the most protection. If you don’t have plants established in the east and west, place fast-growing deciduous vines on a trellis along a wall. This will give almost immediate cooling benefits while you wait for the larger, slower growing trees to mature.

To determine where to plant shade trees in the east and west for the most effective solar control, you need to know the path of the sun to the location of your home. Maps from the local library will show the position of “your” sun in the sky for different seasons and times of the day. By knowing the position of the sun, you know exactly where to place your plants to maximize summer cooling without interfering with necessary winter heat.

In Columbus, Ohio, for example, the midday summer sun is 73 degrees high in the sky. From the southwest to the southeast corner of a Columbus house, trees should be planted along a line that deflects at an angle of 73 degrees due south. The south-facing fan-shaped area between these “lines” should be free from tall trees providing shade. This will ensure maximum heat during the winter while blocking out the hottest summer sun. If you need to plant trees or shrubs in the south and don’t want to block out the sun, knowing the position of the winter sun tells you how far away from the house you should plant.

In warmer parts of the country, like southern Florida, it’s ideal to have tall canopy palms near the south of your home. These will let in some winter sun while providing year round protection from the hot midday sun. Planting deciduous vines on “eyebrow” trellises attached to the underside of southern and western eaves can block out the sun during the hottest times of the year without removing winter heat. In hot, humid areas, plant placement and choice of species are essential when planting near your home, otherwise you could create excessive moisture.

A quick and refreshing energy saver that even the laziest gardener shouldn’t overlook is air conditioner shading. Shading can immediately increase its performance by 10%.

Sculpt the wind

The wind has a powerful cooling effect. The heat loss from the surface of a building increases in proportion to the square of the wind speed (that is, if the wind speed doubles, the heat loss quadruples), as anyone who has experienced the wind chill effect.

A strong barrier is not the most effective windbreak; a penetrable windbreak will actually create more shade in the wind. A windbreak – which should be planted perpendicular to the prevailing winds – can reduce wind speed for a distance up to 15 times the height of the barrier. Maximum protection downwind of a barrier is less than 5 times the height of the barrier. A 25 foot high windbreak, for example, should be placed within 125 feet of your home.

Dense evergreen conifers make good windbreaks for cold climates as they branch down to the ground and provide effective wind control year round. A spruce top windshield can reduce wind speed by 80%, slowing a wind from 12 mph to 3 mph. Factoring in the wind chill effect on a 20 ° F day, that means the difference between what looks like subzero temperatures and an almost imperceptible cooling breeze (similar to the breeze generated by walking).

Because windbreaks block air flow, wind speed increases through openings and around its outer edges (much like water in a dam gains speed at an opening). Windbreaks should extend 50 feet wider than the area you are protecting (if that is not possible, move the windbreak closer to the house and extend it as much as you can).

If you are planting a new shelterbelts, use a fence for immediate wind protection and plant fast growing trees and shrubs with your ideal shelterbel trees. Be prepared to lose a few fast growing trees to the wind and carry them away when they hamper the maturation of your ideal shelterbel trees. A windbreak fence should be louvered to increase the length of its shade to the wind.

Cool

The increased wind speed created by openings in windbreaks can be used to your advantage in warm climates and during the summer in temperate and cool climates. (This assumes that the prevailing winds in summer are coming from a different direction than those in winter. If they are coming from the same direction, choose your wind strategy based on the size of your utility bills: is it does it cost more to heat or cool your home?) A funnel of trees or tall hedges that guide the winds through your home can provide constant natural cooling. The plants act like a large wind shovel that can transform even light and imperceptible prevailing winds into cooling breezes. If the narrower end of the funnel is covered by a walkway or a tree with a high canopy, the cooling effect is even better.

There is more to making a property green than just making it energy efficient, but it’s not a bad start. If most American homeowners made a few key landscaping changes, the collective energy savings would amount to shutting down 23 large power plants or taking more than 26 million cars off the road.

Marshall’s book, Energy efficient and environmental landscaping , is available from Appropriate Solution Press.

Posted on October 1, 1994

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