Why fence posts fail, and what makes them last

The panel is rarely what gives up first. Almost every failed fence failed at ground level.

The failure point

Timber decays where it is alternately wet and dry with air present, and that describes the few centimetres of post either side of ground level almost perfectly. Below that the ground is consistently damp and low in oxygen; above it the post dries. The result is that a post snaps at the base while the rest of it, and the panels, are still sound.

What actually extends the life

Pressure treatment matters, and treatments are not equal. Timber treated to a standard intended for ground contact lasts considerably longer than timber treated for above-ground use. If a post is cut on site, the fresh cut face is untreated and should have preservative applied.

How it is set matters as much. A post set in concrete that is domed to shed water away from the timber does better than one set in a hole that collects it. Postcrete is quick and widely used; a properly compacted concrete collar is slower and more durable.

Concrete posts remove the problem entirely. They are heavier, need more effort to install, and are less attractive to some eyes, but a concrete post and gravel board arrangement outlasts an all-timber fence by a wide margin, and the panels can be replaced without touching the posts.

Gravel boards

A gravel board is a board at the base of the fence that takes the ground contact so the panel does not. It is a small addition that keeps the expensive part of the fence out of wet soil, and it can be replaced on its own when it eventually goes.

What to ask

What are the posts made of, what treatment standard is the timber, how are they being set, and is there a gravel board. Those four answers tell you more about how long a fence will last than the panel style does.