If lower branches are not pruned, they can block breezes, insulating homes that are cooled only by air conditioning. To encourage air movement, remove lower branches or select trees with more open branches. Selecting the best location Since any outside air entering the home increases the load on the cooling unit, a row of trees to block winds can be useful if your home is totally air-conditioned. For breeze-cooled homes, locations that do not interfere with air movement will be better. Prevailing winds during the summer months originate in the south, southeast and east, with south winds predominating.
Windows are the best targets for shading since glass transmits sunshine directly.
You can determine the best location to plant shade trees by observing which windows admit the most direct sunshine during a single day in June, July or August. A tree planted between the incoming sunshine and your window will block the sun s rays and help reduce your cooling needs. Trees intended to shade side walls should be planted between 7 and 20 feet from the edge of the house in order for the benefits of shade to be realized within five years. The tree s shadow will also move more slowly across the walls on your home. The shadow of a tree planted ten feet from the house will move across the surface four times more slowly than it would if it were 20 feet away.