Fences are subject to a number of stresses that can cause them to tumble to the ground. If your fence does not have a solid connection to the ground, it can quickly bend to wind and other forces. Various ways to set a post include placing the post deeply into the ground, using anchors that go into the ground or using a footing to hold the fence post steady.
Concrete is the standard footing material for fences. Traditionally, a hole is dug into the ground and filled with concrete, and the fence post is set into the concrete. There are now precast footings and containers that hold the concrete and fence post, which make the job easier. Wood fences do not require concrete footings and may even be harmed by them. Chain-link fences only require footings at the termination points and gate posts.
The type of fence, wind speed, weather exposure, post placement, soil composition and fence height all work together to determine the best diameter and depth for fence post footings. There is no one measurement that fits all situations. A slab-sided fence is much more vulnerable to wind forces than a chain-link fence that allows the wind to pass through, and fence footings in the cold of Minnesota are more likely to have frost heave problems than those in Alabama. Sandy soil provides a poor foundation for a fence post and requires a larger, deeper footing than clay soil does.
Manufacturer recommendations and municipal building codes also affect the size of fence post footings. For example, the Artisan Precast company requires a minimum 12-inch-diameter footing with a 30-inch depth for its fence products. The City of San Diego requires a minimum of a 12-inch-diameter footing that is 24 inches deep and set over a 3-inch bed of gravel with the fence post extending clear through the footing into the gravel.
Because most municipalities require permits to erect a fence, it is important to know and understand the legal requirements if you are a homeowner doing a do-it-yourself project. A fence that is not up to code won't pass an inspection and may prove very costly to do over again. If a professional company is doing the work for you, you should still know enough about the code to ensure that the fence is properly erected.
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