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How To Fix a Leaning/Sagging Fence Section

Fixing a leaning fence is an important project for any fence owner. In this article, we will cover the most common reasons that a fence section is leaning or sagging, how to replace a fence post, how to set a fence post in concrete, and how to ensure the fence stays even and level throughout.

Two Common Reasons for Fence Leaning or Sagging

Rotting/Damaged Posts

Fences are designed with pickets going in between wooden posts that are driven into the ground and set in concrete. Even if you think you have a plastic fence, underneath the plastic will be wooden posts. These posts can rot or get damaged over time, causing the fence to lean due to the weight of the pickets exerting force on a weakened post. This is a common issue globally but may occur with more frequency in wetter environments such as the Northwestern US. This post will need to be removed, replaced, and set into concrete with the correct angle.

leaning fence
A Leaning Fence Section In Deforest, WI

Soil Heaving

As the ground freezes and thaws over an annual cycle, it will also expand and contract. Over multiple freeze/thaw cycles, this causes gradual movement in the soil which can cause a fence post to lean over. This is most common in areas with temperate climates and areas that experience multiple freeze/thaw cycles per year, such as the Midwest or Northeast of the US. This fence post is likely not damaged and will not require replacement, although it will need to be reset into concrete and have the angle corrected.

We have covered the two most common reasons for your fence to lean. Now, let’s take a look at how to fix these issues the right way.

Importance of the Frost Line

The frost line varies in different areas around the world. This is the depth below the ground that groundwater will freeze during the coldest part of winter. It is important when setting concrete to dig deep enough to get below the frost line to limit soil heaving. In Madison, WI, the frost line is as deep as 48”. In Barrow, AK, the frost line is 100’ In Phoenix, AZ, the frost line is nonexistent, which is why we do not commonly see basements in the region. Housing there does not need a deep foundation, and fences are the same.

How to Replace a Fence Post

Fence post replacement is generally the only possible thing that can be done with a rotting or damaged post. The first step is to remove the existing post from the two fence sections surrounding it. The post will be set in concrete underneath the ground so it cannot be simply pulled out; it must be dug out of the surrounding soil and completely removed. Discard this rotting post and concrete.

To put a new fence post in, get a 4x4 treated pine post that is at least the height of your fence plus the depth of the frost line. Do not cut this to size in advance as the hole you dig may not be exactly as deep as you want it to be. After this, set the post into concrete (covered later in this article).

There should already be a hole where the last post was but dig it slightly deeper if you have a long enough wood post to be able to. Deeper is generally better when it comes to righting a fence. 

How to Fix A Leaning, Undamaged Fence Post

For a section that is leaning due to soil heaving, the issue is likely due to the frost line being lower than where the bottom of the concrete currently supporting the post is. To fix this, dig out the existing concrete and remove it from the post. This is not very difficult as concrete generally does not adhere to the wood as there should be a vapor barrier separating the wood from the concrete. The concrete is usually already cracked due to the pressure caused by soil heaving. Dig the hole a bit deeper than it was originally and fill the bottom with some small rocks to keep the post supported by something.

After this is prepared, set the post into concrete.

leaning picket fence supports
Properly Secured Fence With 2x4's

How To Set A Post Into Concrete

After the hole is prepared, place the post in the hole, cover the underground portion in plastic to serve as a vapor barrier, and surround it with concrete. This can be wet or dry concrete, but we prefer dry concrete as it is easier to work with and generally has the same results over time. 

Set a 2x4 from the ground to the top of the post and use a level to ensure the post is 90 degrees from the ground (alternatively, check the other posts as they may be slightly askew and being uniform with the rest of the fence can look better than being perfectly 90 degrees). Wet the concrete thoroughly and let it cure for at least 48 hours before removing the 2x4 supports. At this point put the surrounding fence sections back onto the new post.

level fence
DeForest fence after repair

Final Thoughts

While the concrete is initially curing, take a look at the angle of the fence from multiple angles to ensure it is correct. Depending on the type of concrete used, you may only have minutes to fix this before it will cure and be set permanently in place. And remember, if you didn't put in the fence yourself you can always blame the last guys for why it doesn't look perfectly even.

Righting a leaning fence is important and necessary maintenance. If you are a homeowner in need of a high-quality fence maintenance contractor, look no further than EcoWash.


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