The single most catastrophic mistake in amateur fence installation is digging shallow post holes. When high wind storms hit a solid 6-foot privacy fence, hundreds of pounds of lateral force act like a crowbar against the post footing.
The Universal Engineering Rule: The 1/3 Rule
A standard engineering guideline requires that at least one-third (1/3) of the total post length be buried underground. For a standard 6-foot high fence above ground, you must purchase an 8-foot timber and bury at least 2 feet (24 inches) in the earth.
Hole Diameter Guidelines
The diameter of the post hole should be three times (3x) the width of the post. For a standard 4x4 timber (actual size 3.5" x 3.5"), dig a hole 10 to 12 inches in diameter to ensure adequate concrete encasement around all sides.
