Installing a silt fence correctly is what makes it actually work. The core steps are: lay out the fence along the contour, trench in the bottom edge of the fabric, set the posts on the downhill side, attach and backfill the fabric, then inspect after every significant rain. Done right, the fence stays put and keeps sediment on your site instead of letting runoff undercut or blow it out.

Before you start

Walk the site and mark where runoff will travel. Silt fence belongs along the contour of the land (following a single elevation) rather than running straight up and down a slope, because contour placement spreads water out instead of concentrating it. Identify the downhill side of each run, since posts and backfill go on the side facing away from the flow. Measure your linear footage so you know how many rolls and posts to order. The Silt Fence Selector can help you match the right product and estimate posts before you dig.

How to install a silt fence, step by step

1. Lay out the line. Position the fence along the contour, parallel to slope elevation, with the ends turned slightly uphill so water cannot run around them.
2. Dig the trench. Excavate a trench about 6 inches deep and 6 inches wide along the layout line. This buried edge is what stops water from undercutting the fence.
3. Set the fabric in the trench. Place the bottom edge of the fabric into the trench so the lower flap sits along the uphill wall and bottom.
4. Drive the posts. Install posts on the downhill side of the fabric, spaced every 6 to 8 feet. Drive them at least 12 to 18 inches into firm ground. Standard fence uses wood stakes; wire backed fence uses steel T-posts.
5. Attach the fabric. Fasten the fabric to the posts on the uphill face so runoff presses the fabric against the posts rather than away from them.
6. Backfill and compact. Return soil over the buried flap and compact it. This anchors the fence and seals the bottom.
7. Join runs correctly. Where two sections meet, overlap and wrap the fabric around a shared post so sediment cannot escape through the seam.

Common installation mistakes

• Skipping the trench, which lets water undercut the fence almost immediately.
• Running the fence straight down a slope instead of along the contour.
• Putting posts on the uphill side, so water pushes fabric off the posts.
• Spacing posts too far apart, which causes sagging and blowouts in heavy flow.
• Leaving seams unwrapped, creating gaps sediment slips through.

Maintenance after installation

Inspect the fence after every significant rain. Remove accumulated sediment before it reaches roughly one-third of the fence height, repair any sags or tears, and re-anchor sections that have pulled loose. Wire backed fence holds up longer on high-flow runs, which is one reason many DOT specifications call for it.