The traditional farmhouse, with its copse of shade trees out front and its bank of north- or west-facing evergreens, is one of rural America’s most idyllic sights. But to Philadelphia landscape architect Larry Weaner, that time- honored arrangement of home and flora makes for more than just a pretty picture. It’s one very smart strategy for saving energy. “When the farmer builds his house, the first thing he does is plant trees to shield it from the summer sun and the winter winds,” he says. “Those trees go a long way toward moderating the temperature of his home.”
Indeed, when it comes to saving energy on the homefront, trees are a natural for any house, anywhere. Studies have shown that well-placed trees, bushes, and other plants can slash a home’s air-conditioning needs by a whopping 40 percent and trim its demand for heating by a third. Those big reductions translate into equally big savings on energy bills, and they’re a boon for the environment. Trees curb global warming by consuming the greenhouse gas carbon dioxide, purify the air as they exude oxygen, and provide a habitat for increasingly embattled wildlife.
They even cut the local utility a break. Customers using trees to cut down on energy needs may enable a utility running at full tilt to keep up with demand (and stave off the kind of blackouts that hit California last year); they may also eliminate the need for expensive utility expansions. For that reason, scores of utilities across the country offer their customers free shade trees or rebates to those who already have them in the ground.
Sun and wind
The principles underlying the farmer’s elegant—and inexpensive—approach to energy efficiency are as basic and unbending as the cycle of seasons itself. In the summer, the leafy canopies of strategically placed deciduous trees naturally shade a house from the sun’s hot beams and keep indoor temperatures down. Conversely, in winter when their leaves are down, those same trees allow the sun to pour into a home when its warming rays are needed most.
Trees and shrubs can control the winds that affect a home’s temperature, too. A row of evergreens blocks the intrusion of heat-sapping arctic blasts, while other plants can be positioned to direct summer’s welcome cool breezes right through your front windows. And where plants are in short supply, nonliving landforms such as hills, berms, walls, and fences can stand in for them.
These simple strategies are most effective when trees and structures are planted in just the right spots to intercept the sun or wind before it reaches the house. To reap the full energy-saving benefits of landscaping, you’ll need to identify those locations in your own yard and craft a plan to fill them before you dig any piece of landscape architecture, plant or otherwise, into your ground.
Block the beams
The sun strikes your house with the greatest intensity on its southern and western fronts. Plant deciduous trees along those exposures. In summer, their canopies will blunt the sun’s beams; in winter, they’ll allow their passage.
Tall-growing trees with dense foliage are best for summer shading because they’ll protect both your windows and the roof. Choose a variety that’s native to the area or viable for the plant hardiness zone you live in. Plants suited to their environment tend to thrive with little maintenance, tolerate droughts, and resist disease better than foreign species do.
Small, short trees will suffice for your home’s eastern exposure, where the sun comes in weak and low. Their low-branching canopies will intercept those early morning beams. If you like some sun with your breakfast, you may prefer a tree that merely filters light, such as a dogwood or a Japanese maple.
For a list of shade trees that are best suited to your area, contact your local agricultural extension agent (under Forestry and Wildlife Assistance in the Blue Pages of your telephone book) or consult the two guidebooks listed in “Further Reading” at left.
Landscaping isn’t the quickest route to a cooler home. A sapling won’t offer significant shade for at least five to eight years. You might be tempted to cut the waiting time by planting fast-growing varieties of trees, such as tulips or poplars, but landscape architect Weaner doesn’t recommend it. “Fast-growing trees aren’t ideal for around the house because they’re weak-wooded and their branches could come down on your house in a storm,” he says. A better strategy, according to Weaner, is to plant fast- and slow-growing varieties together and then remove the fast trees after the slow ones have caught up.
You can also buy your trees time to grow by shading with nonliving structural devices such as awnings, umbrellas, and overhangs in the interim. Or station a trellis in front of a sunny wall or window, and train shade-giving vines to grow up and around it. (Erect any trellis at least a foot away from your home’s exterior to allow air to circulate and prevent moisture from causing rot or mildew.)
Most of the heat that raises your home’s indoor temperature arrives from the sky, but some rises from the ground, too. Driveways, sidewalks, patios, and other open surfaces absorb solar radiation and reflect it onto walls and windows throughout the day and night. Intercept the radiation with low-growing shrubs, climbing vines, or potted plants.
Wind in the pines
You don’t need trees to shade the north end of your house because it’s beyond the reach of the warming sun. But landscape plants there can buffer your home against the heat-sapping winter winds bearing down on it from the north and northwest. Your house is also likely to be buffeted by prevailing winds sweeping in from the west.
Planted perpendicular to the wind, a row of evergreens will slow and deflect its flow from your house. Spruce and white pine can fill out a sturdy windbreak. Plant them in a single row, spaced five to six feet apart; if you have room, create multiple rows, with trees staggered to fill in the openings in the row in front of them. Some air, however, should be allowed to pass through any windbreak to prevent winds from climbing over and then slamming back down onto a house. But be sure not to leave big gaps, because the wind will funnel through them at a high speed.
Height counts. To deflect winds over a single-story house, a windbreak should be fifteen to twenty feet tall if planted next to it, higher if further away. Shorter windbreaks can’t send winds aloft, but they can calm them and lessen the heat they steal. And the windbreaks don’t have to be fashioned from plants. Fences, walls, and even hills can all be erected to slow and redirect chilling winds.
Windbreaks aren’t just for winter, either. Just as easily as they shunt cold wind from a house, they can be positioned to direct cool, summer breezes right up your front steps.
The challenge to landscaping for energy efficiency is to arrange these individual plantings, structures, and landforms so they function in harmony with each other. You’re not cashing in on your landscape’s potential if the tall evergreens that are neatly deflecting an arctic westerly from your house are also blocking the sun’s warming rays. Finding that optimal arrangement will take some planning, but when you do, you’ll reap smaller energy bills, naturally and cheaply. Just like a farmer does.
Careful where you plant
As shade trees grow up, they offer cooling shade, but their root systems grow down and out, too, and create a host of uncool problems such as heaving sidewalks, cracks in a home’s foundation, and broken gas lines and water mains. To avoid them, plan before you plant.
Phone first. Call your local utility company to check if the roots of your intended tree will interfere with underground cables and gas, water, and sewer pipes. Also, consider how your tree’s canopy may affect overhead electric, phone, and cable wires as it grows.
Keep your distance. Strong-wooded trees such as oaks should be planted no closer than twenty-five feet from a house; weak-wooded ones, whose branches could fly into a house, should be even further away. Smaller trees, such as dogwoods, can be as close as eight feet, but be aware that insurance companies and fire departments recommend at least thirty feet of “defensible space” (absence of flammable vegetation) around your home. Most insurance companies offer guidelines on defensible space, and may deny renewal of your policy or increase your premium if your planting scheme does not meet their requirements.
Space it out. Consider your sapling’s girth at maturity. To keep large shade trees from growing into each other, plant them fifty feet apart; plant medium-size ones thirty-five feet apart, and small ones, fifteen to twenty feet apart.