As a general rule, fence suppliers recommend a minimum footing depth of 24 inches for a 4ft chain link fence post, with an additional 3 inches for each foot of height (for example, 27 inches for a 5-foot post). The minimum hole diameter should be four times the maximum cross-section of the chain link fence posts.
These are general recommendations as a basic or minimum guideline. However, there are a variety of factors that can affect the recommended (or required) foundation depth. Environmental factors such as soil and weather conditions can have a significant impact on the stability of a fence and require installation adjustments. Local ordinances often specify minimum depths for foundations and other elements of fence construction.
This article will take you through the factors that determine the appropriate chain link fence post depth and then provide basic instructions on setting fence posts.
One element of the formula focuses on soil stability based on soil composition. There are three types of soil: sandy, loamy and clayey. Although soils are usually a combination of all three, each has its own characteristics that affect the stability of the fence.
ㆍSand - The coarsest soil and therefore the most porous sand, it does not change much with changes in moisture conditions. Contrary to popular belief, sand can prove to be strong and stable once compacted. It provides a suitable medium for fence construction and requires little special consideration.
ㆍLoam - Loamy soil, more porous than sand but still rather coarse, does not change much under moisture conditions. However, its soft and flexible nature means that it offers less stability. This should be taken into account when planning the depth of the foundation.
ㆍClay - In contrast to sand and loam, clay is dense and hard. It provides a strong base when dry, but is more prone to swelling and shrinking due to water and moisture. This means that when clay soil absorbs water or dries out, it changes in ways that can cause problems for fencing.
ㆍWind - Another major factor is wind. It is probably the most important factor in determining foundation depth, as it is the only reasonably predictable force. The higher the wind force (usually in areas with strong storms), the deeper the column.
ㆍFrost line - Freezing and thawing can also exert strong forces on a fence. A force called sinking occurs when ice under a fence post causes it to expand and 'lift' the post. To prevent this, posts for chain link fences must be set deeper than the frost line or the maximum depth at which the soil can freeze.
Regardless of the different factors associated with the depth of the foundation, the foundation itself must be properly excavated to ensure maximum strength. This means digging a bell-shaped hole, or a hole that is wider at the bottom than at the top. The opposite of a bell-shaped hole is a carrot-shaped hole (thinner at the bottom and wider at the top). Bell-shaped holes provide greater stability by providing more support at the very bottom of the column, keeping it upright and aligned.
Fence suppliers recommend that the terminal post footings be 10" wide at the top and 12" wide at the bottom. The chain link fencing posts should be 8" wide at the top and 10" wide at the bottom.
Once the footings have been dug to the right shape and size, the posts must be secured with concrete. To obtain the right mixture, use 1 part cement, 2 parts sand, and 4 parts gravel. Make sure the solution is heavy and not too watery as this can cause the concrete to crack and weaken. While the concrete is still wet, use a carpenter's level to ensure that the posts are perfectly vertical. Finally, at the base of the post where it meets the ground, ensure that the concrete slopes away from the post to allow for proper drainage.
With an investment like fencing, you need to be sure that you are getting a quality product at an affordable price. Contact us today to get started on your project and see how much you will save.
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