Dear Jim: We are landscaping our new house. We like a wooded yard for shade and to enhance the energy efficiency of our home. Where should we plant trees, and which are best? What materials are good alternatives to grass for ground cover?
Dear Mark: Wise landscaping can do more than just create an attractive yard. It can also lower your utility bills, summer and winter, and improve your family’s comfort year-round. Trees, being a key component of any residential landscaping design, can have the greatest effect on your utility bills.
For one, the evaporation of moisture from leaves actually cools the air around your home, akin to how perspiration cools your skin. And by taking advantage of passive solar heating during winter, with the proper placement and selection of trees, you can use less electricity to heat your home.
The primary goal of efficient landscaping with trees is to shade your home during summer yet allow the sun to pass through during winter. Additional goals are, depending on your climate, to allow cool evening breezes to flow around your house or to provide moisture for evaporative cooling of the air near your home.
In an average temperate climate, a typical efficient tree landscaping plan has deciduous trees that lose their leaves in the fall to the south, southeast and southwest. The leaves block the sun during summer, but during winter, the sun shines through to heat your home.
Plant dense evergreens along the north, northeast and northwest sides, which block cold winter winds. With shorter days and the sun lower in the sky in winter, not much solar heat comes from these directions.
In hot, humid climates, shading during summer is most important. Taller trees should be planted closer to your home to block the sun, which is higher in the sky.
For ground cover, there are alternatives to grass, such as ground cover plants and gravel. Both have their advantages and disadvantages for landscaping a house. Low-growing ground cover near your house can help to keep it cool during summer. The leaves block the sun’s heat from absorbing into the ground, and they give off moisture for natural cooling. Ground cover has a lesser effect on efficiency during winter.
The cooling effect from ground cover is most effective in drier climates because there is more evaporation. In hot, humid climates, the additional moisture from plants near the house will further increase the relative humidity level. This is more of a problem if you rely on natural ventilation than when using air conditioning with the windows closed.
Landscaping with gravel eliminates the need to water grass, but it can increase the air temperature around your house, particularly in the evening. The thermal mass of the gravel stores the afternoon sun’s heat, which helps in the winter. If you use gravel, make sure it’s shaded by deciduous trees during the summer.
Jim Dulley is an energy and home improvement specialist and writer.