How deep a fence post goes — below the frost line, on a gravel base, set in crowned concrete
A fence post needs more than a couple feet of concrete: dig below the frost line so it can’t heave, set the post on a 6″ gravel drainage base, and crown the concrete above grade to shed water. About ⅓ of the post is buried.
What this diagram shows
Cross-section of one fence post and its footing. The post stands above finish grade for the fence height, and roughly one third of its length is buried. The dug hole reaches below the dashed frost line, because a post set above the frost line heaves and lifts every winter. The bottom of the hole has a 6-inch tamped gravel base that drains water and keeps the post end dry; above it the post is set in a concrete collar that is crowned above grade so water sheds away from the post instead of pooling against it.
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