How to Replace a Rotted Fence Post

In this video, This Old House landscape contractor Roger Cook adds new life to an old fence.

Pro Tip: Post depth matters more than you might think. For a three-and-a-half-foot fence, the post should go at least 28 inches in the ground. For a six-foot-high fence, you need to bury it a full 36 inches “due to the fact we don’t want the fence to heave in the frost,” as one This Old House project demonstrated.

Steps:

1. Mark cut lines onto post with a layout square. Position the lines above and below each horizontal rail.

2. Set the depth of cut on a circular saw to cut through the posts, but not into the rails. Saw along each pencil line.

3. Knock out the wood between the cuts with a hammer.

4. Use a cordless drill to remove any screws securing the post to the rails.

5. Slide a 24-inch-long 2×4 under the fence on each side of the rotted post.

6. Pull the fence section away from the rotted post.

7. Remove the rotted fence post and dig out any wood left in the fence-post hole. Toss the soil and rotted wood onto a tarp for easy clean up.

8. Enlarge the existing fence-post hole with a post-hole digger.

9. Stretch a tight line from one finial to the next to establish the height of the fence panels.

10. Set the new fence post into the hole, making sure its finial aligns with the layout line.

11. Connect the fence panels to the new post by inserting the rounded ends of the fence rails into the holes in the fence post.

12. Use a 6-foot level to ensure the fence panels are perfectly plumb. Then pour ¾-inch gravel around base of post.

13. Tightly compact the gravel by tamping it with an 8-foot-long 2×3.

14. Backfill around post with graded base, which is a mixture of ¾-inch gravel and stone dust. Add an inch or two of graded base, then compact it with the 2×3. Repeat until you’ve completely filled the hole around the post with compacted graded base.

15. Use a cordless impact driver and 3-inch decking screws to secure the new post to the fence rails.

16. Remove the 2x4s from below the fence and take down the mason’s line.

Pro Tip: As noted in This Old House Magazine, if a post is completely rotted out—usually because it’s been set in concrete, which traps moisture against the wood—you’ll need to dig it out and replace it. For a post that’s wobbly but still solid, you may be able to fix it by packing crushed stone around its base with a sledgehammer instead of replacing it entirely.

Tools:

Pro Tip: Always lay a plastic tarp or canvas drop cloth next to your work area before you start digging. As fence contractor Mike Sludock advises: “It keeps the dirt from messing up the grass or the garden.” This simple step makes cleanup dramatically easier once the new post is set.