When it comes to fences, there’s one hard and fast rule; if they’re not straight, they don’t look good. It doesn’t matter if it’s a dainty white picket, a chain-link or a cedar privacy fence -- if it’s leaning, it visually throws off everything else in the landscape. When fences tilt, there’s rarely a simple fix. Bracing is temporary, and forcefully pushing the fence upright can cause a post to snap. Often, you'll do a lot of digging before the fence is permanently plumb.
Common Fence-Tilt Culprits
- Rotting support posts
- Inadequate post depth
- Insufficient concrete
- Disturbed soil
- Gravel-packed posts in clay soil
Fence contractors frequently use pressure-treated wood for posts even if the rest of the fence is cedar or redwood. Treated posts resist water and insect damage better than untreated wood, but even treated posts can deteriorate over time.
The damage occurs at ground level, especially if soil covers the concrete base around the post. Homeowners, eager for a “finished” look, push a couple of inches of soil over the concrete, but contact with the soil hastens post deterioration. Rotted posts are not salvageable; the only remedy is to dig them out and replace them.
Concrete and Post Depth
Sufficient concrete must be present to secure the post. Even if you filled the post hole to the top with concrete, it might not be enough if the hole itself is too small in diameter. A typical post hole, 32 inches deep and 12 inches in diameter, takes about 2 cubic feet, or three 80-pound sacks, of concrete, to support a four-by-four post.
Concrete failure can also cause fences to lean. A quickie, do-it-yourself, post-setting method involves dumping dry, sack-type concrete in the hole and allowing the moisture from the ground to eventually cure it. While this actually works sometimes, if there is too much or too little moisture, the concrete can cure incorrectly and crumble, leaving the posts virtually unsupported. Dig and remove deteriorated concrete and pour new concrete around the posts.
Shallow posts result in unstable fences that are at the mercy of high winds and frost heave. Fixing shallow posts requires removing the existing posts and redigging the holes a minimum of 10 to12 inches in diameter and deep enough to sink at least one-third the length of the post. In northern climates, frost line is deeper and the required depth of the post increases.
Your local building authority can tell you how deep frost line is in your community.
In some areas, packing fence posts with gravel serves as adequate support, but only if the soil percolates, meaning once it gets wet, the water drains away quickly. If you’re not sure what type of soil you have, run a percolation test before gravel-packing fence posts.
If a leaning fence post is gravel-packed and the soil percolates well, redig the hole to a diameter of 10 to 12 inches and position the post in the hole. Add a few inches of gravel, align the post with the rest of the fence posts, tamp the gravel and add some more gravel, checking the post’s alignment frequently.
Clay-based soils that hold water create a sponge effect around the base of a gravel-packed post, keeping it constantly wet and intensifying the risk of rot. In clay soils, poured concrete is a better choice.
You could call it New Subdivision Syndrome. Homeowners move into brand new houses, and the first thing they do is build their fences. A couple of years later, the subdivision is full of tilting fences as the backfilled soil settles. The best option is to wait a couple of years to put in the fence. If you can’t wait, use posts long enough to reach undisturbed soil. Fence tilt from disturbed soil can be corrected by digging around the posts, straightening them and pouring additional concrete in the hole to support them. Just wait until the soil settles before fixing your fence or you could be fixing it again next year.