Posts decide how long a fence lasts
Panels, pickets and rails can be replaced one at a time. A post that fails takes the surrounding section with it. Because posts are buried and covered, errors in setting them are invisible until the fence begins to lean. These are the five mistakes that most often cause it.
1. Setting posts too shallow
Depth gives a post its grip on the ground. A post that is too short in the ground acts like a lever, and wind or a leaning hand can rock it loose. A common rule of thumb is to bury roughly one third of the post’s total length, but the right figure depends on fence height, soil, climate and local rules. In cold regions, the depth of ground freezing is a major factor: soil that freezes and thaws can push posts upward over the seasons, which is the subject of our notes on frost heave. Tall privacy fences catch more wind than short picket fences, so they usually need deeper, firmer footings. The basics are in the post depth overview; confirm local requirements before digging.
2. Getting the spacing wrong
Posts spaced too far apart leave rails to span longer distances, which makes them sag and flex. Posts spaced much closer than necessary add cost and work. Spacing is often set by the panel or rail length, with common distances between six and eight feet, but check the manufacturer’s recommendations for your product rather than relying on a general figure. Heavy or solid designs and windy locations may call for tighter spacing. Open designs have less wind load, so the structure may tolerate more distance. Measure from the center of each post, not the edge, and mark every location before you dig so the last panel does not end up awkwardly short.
3. Doing the concrete poorly
Concrete is not a cure-all. Too little reduces the support, while a hole filled with mix to the very top can trap water against the post and speed rot in wood. A common approach is to slope the top of the concrete away from the post so water runs off. Mixing with too much water weakens the result, while too little leaves voids. Some builders use compacted gravel instead of concrete in certain conditions, and each approach has tradeoffs, which our comparison of concrete versus gravel post footings describes. Metal posts and wooden posts also behave differently, so follow guidance for your material. Fasteners and hardware near the base should suit damp conditions, and fence fasteners are worth choosing carefully.
4. Letting posts drift out of plumb or out of line
A post that is slightly out of plumb at the base looks much worse at the top of a long fence. Use a level on two adjacent faces of each post, and brace it so it cannot move as the concrete sets. Keep a string line pulled tight along the run to hold the posts in a straight row and at a consistent height. Corner and end posts take extra stress from tension and should be braced and set deeper where recommended. If you notice drifting, correct it while the concrete is wet; afterwards, straightening a leaning fence post is a repair job.
5. Rushing the backfill and curing
Attaching panels or hanging a gate before the concrete has cured loads posts that are not ready. Curing times depend on the product, temperature and moisture, so follow the instructions on the mix. If you use soil backfill, add it in layers and compact each one; dumping it all at once leaves pockets that settle later. Leave the posts undisturbed for the recommended time, even when the weather is pleasant and you are keen to finish. Heavy loads such as gates should wait longest.
A quick checklist
- Confirm local depth and frost requirements before digging.
- Mark every post location and check spacing against your materials.
- Mix concrete as directed and slope it away from the post.
- Check plumb and line before the mix sets.
- Wait for full curing before loading the posts.
Good post work does not eliminate every future repair, since soil, water and weather change, but it addresses the largest cause of leaning and failing fences.