Fences are either open, to use as a trellis for roses or other plants, or they are closed to serve as a wind, sun or privacy screen.

The materials will depend largely upon the use to which the fence is to be put. The most popular, and probably the most attractive, fences are built of wood in various forms, but newer fences of asbestos-cement and corrugated sheet metal are colourful and stand up against rot better.

Because they are heavier, they are usually erected in a zigzag design, the better to stand up against prevailing winds.

The major problem in prolonging the life of a fence stems from rot at the ground line, for here it is susceptible to alternating wet and dry conditions.

Among the best woods for withstanding rot are California redwood and Southern cypress, white cedar and red cedar, chestnut, locust and arbor vitae. While painting the wood with preservatives often lengthens the life of your fence, this will do no good unless the preservatives penetrate.

That's why a post that has been machine-creosoted will resist rot, while a hand-creosoted post will not. However, if you use a good preservative on a clean, dry, unpainted wood, and give the wood two or three coats, you can do a good job.

Among the commercial wood preservatives you will find those of pentachlorophenol, copper napthenate (which has a green colour) and zinc napthenate, a clear solution.

In addition to the point where the post hits the ground, any place where two pieces are nailed together on a wooden fence is subject to rot. Therefore, it is wise to treat the wood where the members are joined before you put up the fence. This will preserve it much better than painting afterward.

Set your fence posts deep enough in the ground to resist the prevailing winds, at least 2 feet and even deeper. Set heavy posts in concrete. Tamp firmly in place so the fence will not wiggle. Hardware used should be galvanized.

Among the most popular types of fences are the traditional picket, the post-and-rail fence and the hurdle fence, but with increased stress on privacy screening, the louvered and lattice types are ever more popular.

The post-and-rail fence is made of posts spaced at 10 foot intervals with large slots cut in them. The 11-foot-long rails are tapered to flat ends, which are inserted in the posts. The hurdle fence has split rails built into a braced frame and nailed together, with the end pieces of each panel becoming the posts.

The picket fence, traditionally white, has posts spaced from 8 to 12 feet apart, rails 3x4 inches, and pickets 2 to 3 inches wide, pointed at the top.

The pickets should be 2 inches off the ground at the bottom and extend well above the top rail. The spindle fence is a kind of picket fence with round spindles that pass through holes in the rails.

There are many possible variations of board fences used for screening. A broad rail may be alternated with a narrow rail, or the boards may be applied vertically, like palings, with, perhaps, a staggering of the boards on either side of the rail. Boards may be slanted in a louver effect to give privacy while admitting air and sunlight.

A basket-weave fence can be constructed of thin, flexible boards and provides total screening and a handsome background for planting. It is somewhat difficult to build yourself, however.