windbreak design

Contrary to myth, solid fences do not provide the best wind protection. The force of the wind on the flat solid surface creates both pressure on the windward side and pressure differences on the leeward side, somewhat similar to the way an airfoil works.

To illustrate this, keep in mind that snow fences are designed with porosity, which allows some of the wind to make its way through, but slows down and diverts airflow. As a result of the design, snow will tend to accumulate a few feet in front of the fence as wind vortices redirect.

When designing a wood fence for windbreaks, stagger boards 2 inches apart for every six inches of width. The ideal porosity for windbreak fences is 25-33%, and that gap will give a 25% porosity. This provides protection that will extend eight to ten times the height of the fence. Another option is to slope the fence material, if you intend to use the fence as shelter for livestock.

For home and farm applications, consider building the fence in staggered sections, with each panel offset from the adjacent ones by about a foot. This gap increases airflow redirection, while reducing wind load on the panels. Varying the height of the panels will also help in this redirection. The intention, of course, is not to stop the wind, but to reduce and redirect it.

When installing a windbreak intended to act as a snow fence, do not install the fence right at the point where the snow will stop. Rather, set the fence back several yards, at least, so that the snow that is blocked will fall and accumulate before the path or clear area you need. Remember that since windbreaks (if properly installed) will create an area of ​​protection eight to ten times the height of the fence, a four-foot fence will provide up to a 40-foot dead zone in front of the fence. .

Some permanent windbreaks are nothing more than a good line of trees or bushes. However, solid rows of trees provide less protection than porous rows, so don’t plant to create an impenetrable barrier. Instead, use staggered plantings, offset from each other.

Although it may seem counterintuitive, mesh fences can also provide good windbreaks. Materials such as mesh seen along the perimeter of golf driving ranges, plastic and resin mesh, and even chain-link fencing provide a nominal measure of protection. To illustrate the effectiveness of a simple screen, open your home window on a relatively calm, cold winter’s day and feel the coolness of the air blowing against the screen. Then stick your hand out and feel the difference. That screen has partially blocked convective heat transfer. It works similarly for wind.

Windbreaks, then, are not so much windbreaks as wind speed bumps are. Holding back the wind, to paraphrase Jim Croce’s song about spitting into the wind or ripping off the old Lone Ranger’s mask, shouldn’t be a fool’s errand!