Improve your home's energy efficiency through landscaping.
After decades of designing homes, one day it suddenly hit me: Most of our best efforts to create sustainable homes only cut back on our consumption of natural resources. On net, we’re still taking more than we give. Meanwhile, it’s easy to create a garden that actually produces valuable resources. Well-managed gardens create food, beauty and wildlife habitat while cleaning the air, enriching the soil and recharging groundwater reserves.
A good garden actually can improve your home’s comfort and energy efficiency. With a little basic knowledge and some observation, you can plan one that will work with your home as a whole system to reduce your fossil fuel use, while benefiting the rest of the world at the same time.
Gardening for a cooler summer
In climates with hot summers, air conditioning is often the biggest household energy cost. While that cool air may be a big relief, the temperature difference and life in a closed indoor environment may make us more susceptible to summer colds. What’s more, air conditioning separates us from fresh air, birds, butterflies and other warm-weather delights.
Shade and breezes are the two basic features of natural cooling that our ancestors knew well. Your garden can provide enough shade to reduce—or even eliminate—your need for air conditioning. According to the U.S. Department of Agriculture, carefully positioned trees can cut a household’s total annual energy consumption by 20 to 25 percent and may reduce air-conditioning costs up to 50 percent. Which would you rather look at, a tree or an air-conditioning unit? Which would you rather hear, a breeze rustling the leaves and birds singing…or that air conditioner?
Trees, shrubs and vines shade your house and yard and they cool the breezes flowing toward your windows and outdoor rooms. A well-planned landscaping program can reduce an unshaded home’s summer air-conditioning costs by 15 to 50 percent, according to energy expert John Krigger in his book Residential Energy (Saturn Resource Management, 2004).
As plants absorb carbon dioxide and release oxygen, evaporation from the leaf surfaces actually has a cooling effect on the surrounding air. In Design for Human Ecosystems (Island Press, 1999), landscape architect Michael Reilly observes that, through evaporation alone, one tree can produce cooling effects approximately equal to 10 room-size air conditioners working 20 hours a day.
When planning for shade, look first at your home’s orientation. The worst heat will come from the midday and afternoon sun (south and west), though in some areas you’ll want to block eastern morning sunlight too. Tall trees can block the midday sun at its higher angle, and shorter vegetation on the east and west will intercept lower-angle sunrays. Take special care to shade your roof and windows, which transmit the greatest amount of solar heat indoors. And shade your air-conditioning unit while you’re at it, to help it function more efficiently.
Notice whether nearby pavement or bodies of water reflect sunlight into your home and yard. Vegetation can help block that unwanted light. Or you might want to replace paving with groundcover or another less-reflective surface.
As you’ve probably observed, different plants give you different degrees of shading, depending on the density of their foliage. As a plant matures, its leaf density increases, and vine-like varieties offer shade sooner than slower-growing trees. You can create a shading plan that accounts for both your immediate and long-term needs by planting both fast-growing and slow-growing species. And, of course, remember that evergreen trees will shade your home in winter when you may miss the extra sun that would have shone through the bare limbs of a deciduous tree. Just be sure to select plants with an open branching structure. Otherwise, even the bare branches will block a significant amount of solar radiation.
If breezes pass over a body of water or through greenery on their way to your living space, all the better; it probably will arrive cooler than the surrounding air. If you’ve got too much of a good thing, you also can use plantings to slow a strong wind to a gentle breeze.
A cozier winter
Stay warmer in winter by selecting and placing plants to create a windbreak, let sunlight fall on your house and come in through your windows, and maintain a still-air pocket next to your house.
On the north and northwest sides of your house, evergreens are a good choice because they block the chill winds of winter.
Closer to the house, you can plant shrubs to hold a layer of still air against your outside walls. Be careful not to plant too close, or you might create new problems of moisture buildup or even branches and tendrils pushing their way under your siding.
A study done in South Dakota found that windbreaks to the north, west and east of houses cut winter fuel consumption by an average of 40 percent. With a windbreak on only one side, the homes still consumed 25 percent less fuel than similar unprotected homes, Krigger says.
If your climate has both hot summers and cold winters, plan your landscaping to help you in both seasons by planting deciduous trees on the south side and evergreens between your home and the cold north wind.
A little planning goes a long way when you use your garden to increase your home’s comfort and energy efficiency. By the same token, arbitrary landscaping that ignores how the sun, breezes, plants, pavement and water interact with your house actually will increase your energy bills. Take some time to observe the sun and wind around your home at different times of the day and year. Notice how your existing garden design may be helping—or hurting—your energy picture. And look for enjoyable ways to let the plant kingdom help you out.
Carol Venolia is an eco-architect who is passionate about reuniting humans with the rest of nature. She is the coauthor, with Kelly Lerner, of Natural Remodeling for the Not-So-Green House (Lark Books, 2006).
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