When figuring out how to lessen the cooling or heating burdens in a building, there’s more to consider than just the actual structure. Strategic placement of plant life can be a major tool to improve the temperature inside a home; greenery can help reduce both cooling costs in the summer and heating costs in the winter—though to a lesser extent.
Landscaping for energy efficiency can involve trees, shrubs, and other vegetation. “All of these things can be manipulated to be advantageous for the home and for the grounds around the home in terms of energy consumption and comfort,” says Christian Kaltreider, a building science research engineer at Pacific Northwest National Laboratory. Whether you’re looking to shade a window to minimize summer heat, or block the winter winds from battering your house, some well-placed greenery can make all the difference.
How landscaping cools things down
Vegetation, but especially trees, can help cool to a home through two mechanisms. The first is intuitive: shade. Trees’ full summer foliage blocks sunlight, keeping buildings cool and reducing the need for a range of cooling mechanisms, but especially air conditioning. Shrubs and smaller plants, meanwhile, can prevent the sun’s heat from hitting the ground below, creating cooler microclimates around a home.
The second cooling mechanism is called transpiration, which is the process in which water within a plant evaporates out of its leaves. That evaporation releases moisture into the air, cooling that air down the same way sweat cools down our skin. Water can even transpire out of soils and mulches to contribute to this effect. Under the right conditions, a large tree could transpire up to 100 gallons of water per day.1 Transpiration is also why water-permeable surfaces, like soil or mulch, can also help create chill: The surfaces absorb water when it rains, and, when it’s hot, the moisture will evaporate into the air and also help cool the area.
The effect of shading and evapotranspiration from trees combined can reduce surrounding air temperatures by as much as 6 degrees Fahrenheit. The air directly under a tree will be even cooler, as much as 25 degrees Fahrenheit than the air directly above nearby blacktop. One study found that the strategic use of trees and other plants can have energy savings related to cooling needs that measure between 10% and 50%.2 A 1997 study conducted on two houses in Sacramento found that relocating large trees directly led to 30% energy savings on cooling.3
Planting placement for summer energy savings
“The largest source of heat gain in most homes is from the sun,” says Kaltreider, so shading surfaces that get a lot of direct sunlight is an impactful strategy.
To keep the indoors cooler, you should look to plant vegetation to shade the walls of your house, but not all walls are equal. To get the greatest benefits, you actually want to target the east and west sides of your home, where the summer sun hits hardest in North American summers, says Kaltreider. Trees and shrubbery focused on shading these areas will create much needed cooling on the two sides of the house that would otherwise concentrate the most solar heat. “Planting deciduous trees or shrubs on east and west facades is generally going to be a good plan in all but the coldest climates,” says Kaltreider.
There are also options beyond trees. Tall, fast growing, leafy plants like sunflowers can provide aesthetic summer shade to windows and walls lower to the ground. The benefit of something like a sunflower, says Kaltreider, is that you don’t have to commit to larger or heavier plants—plus, they’ll die back in winter, not obstructing any sunlight in the colder months.
If you’re in the northern hemisphere, the south-facing wall is the next biggest recipient of light and heat, so planting trees to shade that facade can also help with cooling needs. But too many trees on the southside might impede warming winter light, so be cautious.
There are also areas to consider beyond windows—namely the driveway or any other concrete surfaces. When sunlight hits a surface, whether that’s grass or concrete, some of that solar energy reflects back, and the rest gets absorbed as heat. Darker materials absorb more light and get much hotter than lighter ones—dark pavements or driveways can absorb up to 95% of sunlight’s energy. With that in mind, it’s good to try and plant trees or bushes at angles that provide shade to things like an asphalt driveway or slate patio. A tree shading a driveway will prevent that asphalt from absorbing too much heat and reradiating it back into the surroundings, says Kaltreider, minimizing the urban heat island effect.
How landscaping can keep things warm in winter
Trees and shrubbery can also help winter energy efficiency by helping reduce the airspeeds around the home. When winter winds batter a building, that force of cold air can suck the heat away, contributing to cold temperatures inside. A heated house will be warmest inside, but will also be enveloped by a small layer of milder temperature right outside its walls as small bits of heat escape. Cold winds blow away that small insulating layer, quickening how much heat is lost from inside the house. Trees and shrubs can block those winds, helping a building preserve its heating, and preventing an excessive heating bill.
Planting placement for winter energy savings
Maximizing shade in the summer is essential, but in the winter it’s the opposite. Thankfully, while buildings in the summer tend to get the most sun exposure from the east and west, buildings in the winter tend to get the most from the south. So in the winter, you would want to make sure that light coming into any south-facing windows is not obstructed.
A good rule of thumb is to “not plant any trees, especially evergreen trees, within about 45 degrees of due south of your home,” says Kaltreider. Deciduous trees like oaks and maples will lose their leaves in the winter, but they can still block valuable sunlight coming in from the south. Keeping that window clear will bring as much light and heat as possible from the south.
Evergreen trees and shrubbery are also highly valuable shields from winter winds. Most American homes will tend to get those winds from the north thanks to the gravity and curvature of the Earth, so arranging leafy evergreen bushes to cover that facade of your home is a good strategy, says Kaltreider.
How to determine the right trees and plants for your home
Different regions vary greatly, so there really is no one-size-fits-all for tree species recommendations, says Kaltreider. “People should go to their local tree expert or nursery to learn about the native trees in their area,” he advises. The Arbor Day Foundation also has an online tool that can advise on the most suitable tree types to plant based on your location, shade needs, and soil type.
The most important takeaway for tree selection is to think about the need to balance shading in the summer versus sunlight access or wind blocking in the winter, and pick your mix of evergreen and deciduous trees accordingly. Working with a landscaper can help determine what to look for—and where to place them.
But one of the key factors to consider for deciduous trees is the pattern of when they drop and grow leaves, says Kaltreider. Ideally you’d want a tree that grows leaves just as things are starting to warm up, but drops those leaves around the time things get cold. Finding trees that line up best with the seasonal changes of your region would optimize those benefits.
More upgrades to keep the sun from heating up your home
Want more tips to keep your home cool without cranking up the AC? Luckily, there’s a lot you can do to improve your home’s temperature without sending your electricity bill–and carbon emissions–through the roof. Here’s the essential info on three other energy-saving options.
Cool roofs
A home’s roof can hit around 150 degrees Fahrenheit on a hot summer day. A roof covered in materials that reflect those rays, however, can be as much as 50 degrees lower. While there’s no official standard for what’s considered a “cool roof,” there are a host of options for minimizing how much the sun heats up your home from the top-down. We have the scoop on cool roofs in this guide.
Smart glass windows
The Department of Energy estimates that in the winter 30% of a home’s heat is lost through windows, while in the summer 76% of sunlight that directly hits a double-pane will enter to become heat. Luckily, new technologies that can change how much solar energy is allowed to pass through—or how much gets reflected away–are becoming increasingly available. Here’s what you need to know about smart glass windows.
Energy-efficient insulation and air sealing
The best cooling systems available still don’t work well for a home with a poorly insulated exterior—what contractors call the “building envelope”—or one that leaks a lot of air. The Department of Energy (DOE) estimates that the average home can save up to 20% on heating and cooling costs by beefing up the insulation in attics, floors, crawl spaces, and basement rim joists, and by addressing air leaks–so investing in insulation and air sealing is crucial for keeping it a comfortable temperature without wasting electricity.
- A Methodology for Calculating Cooling from Vegetation Evapotranspiration for Use in Urban Space Microclimate Simulations, Procedia Environmental Sciences, 2017 ↩︎
- Energy Savings from Tree Shade, Ecological Economics, 2010 ↩︎
- Peak Power and Cooling Energy Savings of Shade Trees, Energy and Buildings, Mar. 1997 ↩︎