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Many customers ask 'How deep should I set my fence post?' and the honest answer is that the depth and diameter of any post hole will depend greatly on the style of fence, the area in the country installed, and other variables such as wind load, and digging conditions. All fence posts should be cemented in the ground below frost level. Check your local frost level and dig deeper by at least 6". Here in Ohio a typical 6' high wood fence would have a minimum 9" diameter x 36" deep hole. This is assuming that the fence isn't installed in a swamp with a lot of wind. Southern locations without frost will find this overkill. North of Ohio, installers may go deeper in depth and larger in diameter. A general rule of thumb is to dig the diameter of the hole at least 3-4 times the diameter of the post. For example, if setting 4 x 4 wood posts, dig holes 9-12" in diameter. Posts should be centered in the hole and the posts should always have concrete under them. Always leave concrete down from grade or the ground surface 3-5" and back fill with dirt. When the ground freezes, the ground squeezes the concrete footer like a tube of toothpaste and will 'heave' the post if you fill the concrete clear to the top of the hole. Filling concrete clear to the top will create a 'lip' and water, ice, and snow will gather underneath it. Leaving your concrete level down and backfilling with dirt will help prevent this as well as 'belling' the hole. The shape of the hole is as important, if not more important than the depth. Holes should be 'bell-shaped', not 'carrot-shaped', meaning the bottom of the hole should be larger in diameter than the top.
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