Reviewed and Revised on 10/17/2013
The correct selection and placement of trees and plants can help reduce summer heat and allow for heat gain in the winter. Shading the roof of a house can reduce the inside temperature by as much as 8-10 degrees Fahrenheit. Deciduous trees (trees which shed leaves in winter) provide summer shade. When the leaves fall, they allow the warmth of the sun to enter the home during the cold winter weather. Landscaping can also provide energy savings by diverting winter winds. Research conducted on the Great Plains has shown that up to 25 percent energy savings for heating is possible from windbreaks. An evergreen tree placed properly can divert cold winds away from the home.
Landscaping for Shade in the Summer
Summer shade is best provided by strategically locating plants along the sunny borders of the home. Shade the south-facing roof and wall surfaces that receive the most direct sunlight during midday when the sun is higher in the sky. Also place plants to shade walls that face generally east or west. These walls receive direct sunlight in the morning and afternoon.
To shade the roof or walls of a single-story house, plant medium or large trees 15-20 feet from the sides or corners of the house. Groups of trees have higher cooling effect than individual trees. Small trees can be planted closer to the house to shade the wall and window areas. The location of the trees is determined in part by the climate, latitude, and prevailing winds. Choose trees to shade the roof that are structurally strong, able to withstand high winds, and that do not continually shed twigs and small branches.
The recommended way to provide shade for your home is to plant deciduous trees in an arc encompassing the home on the east, southeast, south, southwest and west sides. Plant shade trees based on their mature height so they will be properly spaced and provide desired shade. Location also depends on the shape of the tree crown, the position of the sun, the height of the roof or walls, desirable views from windows, aesthetic appeal of the overall landscape, and presence of overhead buried wires and underground pipes. A small caliper tree will establish and grow faster into a large tree than a larger caliper tree. If the mature height and shape is not planned for in advance, the location of the tree may cause problems in the future.
Summer shade for a south-facing roof generally depends on having overhanging tree crowns. Trees that do not overhang the roof will not cast much shade at midday due to the high position of the sun in the sky. Thus, plant shade trees as close to the home as practical. Choose a species that is not susceptible to breakage. Leaves in gutters are an undesirable consequence of large deciduous trees near the home, but most people can cope with this nuisance. Promptly remove diseased, damaged trees or limbs to avoid damage to the home.
Tree arrangements that provide shade in summer may be detrimental in the winter if they block solar heating. Leafless deciduous trees may reduce the amount of sunlight reaching the home by more than one-third. However, the winter sun is typically less than 45 degrees above the horizon, so shading will be largely from tree trunks. For this reason, plant only those trees along the southern edge of the home that are needed for the summer shade. Prune the lower trunk to allow maximum solar heating of walls and roof in winter. As few as two or three large deciduous trees with well-developed crowns may suffice.
In hot climates, trees and shrubs can be used to provide shade for the outside portion of a split system air conditioner. A study by the American Refrigeration Institute shows that shading of this type can reduce the temperature inside the home as much as 3 degrees Fahrenheit. Be careful not to plant too close to the compressor. You do not want to obstruct the air flow or the access to the unit for maintenance. Screening the unit also adds to aesthetic value of the home.
Landscaping for Wind Protection
Another important climatic element to be controlled by landscaping is wind. Locate windbreaks upwind from the home. Distance from the home depends on the tree height. The optimum distance for reducing wind velocity is about one to three times tree height. However, a windbreak can provide reasonable protection at a distance of six times tree height.
Windbreaks can cause snow drift that can be a nuisance if a driveway is located between the trees and the home. Where possible, extend a row of trees 50 feet beyond the ends of the area being protected.
Design and composition of the windbreak depends on the space available and the species and size of trees. Where space is limited, a single row of evergreens is adequate. However, up to five rows of several evergreen species is more effective. Spacing in one-, two- and three-row windbreaks should be 6 feet between trees. Consider the mature shape of the tree when developing a landscape plan for a windbreak.
Most windbreaks also serve other purposes. They provide a visual screen for privacy once they reach 5 to 6 feet high. Well-planned and properly maintained, they are aesthetically pleasing. Choose tree and shrub species that provides protection and food to attract wildlife during the winter.
Evergreens planted close to the home can further reduce effects of wind. If allowed to develop into a thick hedge, spreading evergreens in front of the north and east wall provide additional insulation from the trapped dead airspace they create. If an entry is exposed to wind, an evergreen planting can shelter it.
A windbreak takes time to establish and be effective. For immediate relief from the effects of wind, construct a fence with an open weave pattern (e.g., basket weave). This creates a larger, protected downwind area than a solid fence. A solid fence provides a greater degree of shelter immediately behind the fence.
Landscaping to Reduce Heat Gain
Adding landscape plants, groundcovers or turfgrass between your house and paved areas can help reduce heat gain from asphalt or concrete surfaces, particularly in areas where the wind blows across the hard surface towards the house. The temperature a few inches above green materials is often 12 to 15 degrees Fahrenheit lower than above solid surfaces. Be careful not to plant right up to the home’s foundation. Leave at least a foot or so free of plants and mulch, since adding moisture to that area can encourage termite and other pest problems where they exist. Also be aware that watering, fertilizing and mowing some turfgrasses and other plants can use a lot of energy. Choose plants that are suited to your climate and yard’s conditions and will need only minimal or no supplemental water or fertilizer.
Adapted from: Landscaping for Energy Conservation by William C. Welch, Extension Landscape Horticulturist, Texas Agricultural Extension Service. Accessed October 14, 2009 at http://aggie-horticulture.tamu.edu/extension/homelandscape/energy/energy.html and Landscaping for Energy Conservation by Lloyd Walker, Steven E. Newman, Former Agricultural engineer and Greenhouse Crops Specialist, respectively, Colorado State University Extension. Accessed May 14, 2010 at http://www.ext.colostate.edu/pubs/garden/07225.html
Reviewed by Gail Hansen, Environmental Horticulture Department, University of Florida Revised by Steven E Newman, Horticulture and Landscape Architecture, Colorado State University