How to Install a Silt Fence


A silt fence, also called a filter fence, typically helps mitigate the short-term effects of erosion until a permanent solution is in place. The fence catches sediment that washes down slopes and keeps it from settling in waterways. Because the bottom part of a silt fence is buried in the ground, you can also use it as a barrier to keep most snake species out of your yard.

Constructing the Fence

  • Silt fence posts should be made of hardwood with a minimum length of 36 inches and a minimum thickness of 1-1/8 inches. Staple or nail woven geotextile fabric, which has a minimum 24-inch width, to posts spaced no more than 10 feet apart. Leave 6 inches of loose fabric, called a bury flap, at the bottom of the posts. A rule of thumb for the area that a silt fence can control is 1/2 acre for every 100 linear feet of fencing.

Preparing the Site

  • Dig a 6-inch trench at the bottom, or toe, of a downhill slope and reserve the removed dirt. Unroll the silt fence and place it on the ground along the trench line. If you’re using the silt fence to help manage erosion, place the posts on the downhill side of the fabric. If you’re using the silt fence as a snake barrier, orient the posts so they are on the inside, toward your yard, so snakes cannot climb the posts. Turn the end posts so the fabric wraps around each post.

Erecting the Posts

  • Drive one end post into the ground until the bury flap is inside the trench. Drive each successive post into the ground, stretching the fabric as taut as possible and making sure the top of each bury flap is level with the ground. Space posts 4 to 5 feet apart in areas where water tends to pool and 6 to 7 feet apart in areas of lighter water stress. Because the silt fence's purpose is to detain water and catch sediment, install the posts so the fence forms a "smile" pattern with the upslope ends slightly higher than the middle.

Filling the Trench

  • Fill the trench with the removed soil and over-backfill to fortify it. Tamp the ground in the trench to reinforce the fence so it forms a strong barrier that resists washouts. Compact the backfilled dirt around the posts to stabilize them. Make a compacted ridge with any leftover soil on the uphill side of the fabric. If the fence inadequately restrains the eroded sediment, you can reinforce its influence by building other rows of fencing parallel to the first one.

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