The recent cold spell was all the more unpleasant because of strong, icy winds which also increased heating costs considerably. A windbreak could make a big differnece during that kind of weather.
It may be worthwhile for homeowners to go to considerable effort to shelter themselves and their property from such winter winds, according to a research report by Dave Pitt, University of Maryland assistant professor of landscape architecture, and John Kissida and Bill Gold, two of his associates. These winds can be controlled by careful placement of landscape materials, they say.
In Maryland, winter winds generally blow from the northwest. A 10 mile-per-hour northwesterly wind will make an actual air temperature of 44 degrees F. feel as though it were 32. As they are often of high velocity, winds can create serious soil erosion when they blow over extended areas of bare soil; they accelerate the rate of air exchange between a house's exterior and interior environments resulting in an increased demand for heating fuel; in areas of high snowfall they accelerate snowdrifting; and, unprotected broadleaf evergreen plants may be dessicated by direct exposure to winter winds.
For all these reasons, it is generally desirable to create windbreaks that will intercept and redirect winds before they reach houses, outdoor winter use areas where snowdrifts are undesirable, the report said.
A windbreak is an obstruction that is placed perpendicular to the path of wind flow and causes an alteration in the wind direction.
As wind strikes a windbreak, it mustmove over and around the obstruction. This wind direction alteration creates a small area on the windward side of the windbreak and a larger area on its leeward side that is protected from the full force of the wind. The extent of the leeward protection is related to the height and length of the windbreak.
Windbreaks that are impenetrable to wind create a strong vacuum on their protected leeward side which tends to suck the obstructed wind-stream into the protected zone. This reduces the level of leeward protection afforded by the windbreak.
Windbreaks that allow some wind peneration reduce the vacuum and consquently improve the windbreak's effectiveness.
Thus, the objectives of windbreak design are to achieve enough height to create protection for the desired distance on the leeward side, and to achieve enought peneration to reduce the effects of eddy currents and the leeward vacuum and still afford the desired amount of wind protection.
The windbreak should extend to the ground. Width has a negligible effect on protection except as it affects penetrability. If deciduous plants are used as a windbreak, four or five rows should be used. If deciduous palnts are used as a windbreak, four or five rows should be used. If evergreen plants are used, two to three rows should be enough. Rows should be staggered. Windbreak work most eficiently when the lengths is 17.5 times greater than the height of the mature plants.
While substantial opportunity exists to control the direction and velocity of wind, the report warned, before such a device is installed the visual consquences should be carefully evaluated. The height and foliage density that may make plants well suited for use may create visual screens that block distant views or reduce the feeling of spaciousness within a yard.
The design of a successful wind-control device requires an understanding of the physical principles of wind control and how different materials can be used, but it is equally important to understand how the materials will look in relation to the surrounding lanscape and how well they will hold up under continued exposure to wind.