The answer -— as it often does in fencing construction — is complicated. Before thinking about the hole depth, you need to make sure you have the right plan for the fence’s posts. The line posts should be 2” below the height of the fabric and the terminal posts should be 2” above the height of the fabric. When it comes to hole depth, as a general rule, Fencing Direct recommends at least a 24-inch footing depth for a 4-foot fence, plus an extra 3 inches for every foot of height (for example, 27 inches for a 5-foot post). The minimum hole diameter should measure four times the largest cross-section of the post. If your math tells you that you need more than the height on products than we have available on the website please let us know before placing your order.
These are the general recommendations that serve as a kind of base or minimum guideline. However, multiple factors affect the recommended (or mandated) depth of the footing. Environmental factors like soil and weather conditions can have significant effects on the stability of a fence and call for installation adjustments. Local ordinances often regulate the minimum depth of the footing and other elements of fence construction.
This article will take you through the factors that dictate proper footing depth and then provide basic instruction on setting fence posts. At Fencing Direct, our sales and service staff have decades of experience in the industry and can support you in installing the highest quality products.
Soil conditions
The Chain Link Fence Manufacturers Institute publishes a guide with a formula for determining footing depth. One of the factors in this formula focuses on the stability of a soil based on its composition. There are three types of soils: sand, loam, and clay. While soils are frequently a combination of the three, each has its qualities that affect a fence’s stability.
Sand - The coarsest of soils, and thus most porous, sand does not change much with changes in moisture conditions. Contrary to popular belief, sand can prove strong and stable once compacted. It provides a suitable medium for fence construction and requires few special considerations.
Loam - Loam, slightly less porous than sand but still rather coarse, changes little across moisture conditions. However, its soft and flexible nature means it provides less stability. One should consider this in planning footing depth.
Clay - In contrast to sand and loam, clay soil is dense and hard. It provides a sturdy base when dry, but is much more susceptible to expansion and contraction with water and moisture. This means that as clay soaks up water or dries out, it shifts in ways that can prove problematic for fencing.
The U.S. Department of Agriculture maintains a Web Soil Survey page that provides soil information for every location in the United States. Reference this map and use your knowledge of soil conditions to adjust for depth in fence footing.
Weather conditions
Wind - Another major factor in the Chain Link Fence Manufacturers Institute’s guide for footing depth is wind force. It is perhaps the most important factor in deciding footing depth since it is the only force that can be reasonably predicted. The higher the wind force (often in areas with intense storms), the deeper the post.
Frost line - Freezing and thawing can also exert a powerful force on a fence. One such force, called heave, happens when ice forming under a fence post causes expansion that “heaves” the post up. To prevent this phenomenon, one must set the fence post deeper than the frost line, or the maximum depth at which soil freezes. The National Snow and Ice Data Center publishes a map of the average winter frost lines in the United States.
How to consult local laws
Often, local governments factor in these conditions and regulate minimum footing depth. Cities frequently publish these regulations online (for example, here are the fence regulations for Miami-Dade county, which require a minimum footing depth of 38 inches). These regulations can frequently be found with a quick internet search, but one can also contact the appropriate government agency to speak to a knowledgeable person.
Digging the hole
Regardless of the different factors relevant to footing depth, the footing itself must be dug properly to ensure maximum strength. This means digging a bell-shaped hole, or a hole wider at the bottom than the top. The opposite of a bell-shaped hole would be a carrot-shaped hole (thinner at the bottom, wider at the top). Bell-shaped holes provide for greater stability by providing more support at the very bottom of the post, keeping it upright and aligned.
At Fencing Direct, we recommend that the terminal post footings measure 10 inches wide at the top and 12 inches wide at the bottom. The line posts should measure 8 inches wide at the top and 10 inches wide at the bottom.
Setting the terminal post and line post
Once the footing is dug to the proper shape and specifications, the posts must be set with concrete. For a proper mixture, use 1 part cement, 2 parts sand, and 4 parts gravel. Make sure that the solution is heavy and not too watery since this can cause cracking and weakness in the concrete. While the concrete is still wet, use a carpenter’s level to ensure the post is perfectly vertical. Finally, at the base of the post where it meets the ground, make sure that the concrete slopes away from the post to allow for proper drainage.
Fencing Direct supports you every step of the way
We use one of the most well-established manufacturers in the country, delivering quality products to your door at a savings, while our staff of trained professionals can offer guidance throughout the entire process. As you plan, our Fence Builder allows you to draw out your entire project and receive a price in addition to a list of all the items required to complete your fence. Our customer service representatives provide prompt responses to all your questions, ensuring that you’ve always got an experienced and knowledgeable resource a phone call away.
With an investment like a fence, you’ll want to make sure you’re getting a top-quality product at an affordable price. Fencing Direct provides both, in addition to outstanding service. Contact us today to start your project and see how much you’ll save.
