Building components · Paving & Decks
Fence Post
Explains the fence post as an element whose performance is set almost entirely by how it is restrained at its base.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a fence post is
A fence post is the vertical member that carries a fence: the panels, rails, boards or wires fixed to it along a boundary or a division within a site. It stands free on both sides, with nothing above it and nothing bracing it except the fence it carries and whatever holds it at its base.
Everything the fence collects arrives at the post as a turning force at ground level. Wind acting on a panel is carried by the post and resisted only by what the post is set into — a concrete surround, driven ground, or a shoe bolted to a base. That base restraint, rather than the post itself, is what usually decides whether the fence stays plumb.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a column. A column is a primary structural member carrying floors or a roof down to a foundation; a fence post carries no building load and exists to resist horizontal force from the fence it holds.
- It is not a balustrade post. A guarding post carries a guarding whose loading is defined by regulation and which is there to stop people falling; a fence post carries a boundary or a screen, and what follows from each of them failing is different in kind.
- It is not a masonry pier. A pier is a built mass carrying its own weight and terminated by a cap; a post is a single slender member whose restraint is concentrated at its base, and the two are commonly met alternating along the same boundary.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- gate post
- fencing post
- boundary post
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- How it is restrained at its base, since that restraint resists everything the fence collects.
- What that base acts against — the ground, a concrete surround, or a fixing into existing construction — because the restraint is only as good as what it bears on.
- The fence it carries, since a close-boarded panel and an open rail present very different areas to the wind.
- Its condition at the line where it meets the ground or the base, which is where it is wettest and where failures begin.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Horizontal force on the fence arrives at the post base as a turning force, which is why posts commonly fail by rotating or by breaking at ground level rather than by bending along their length.
The zone where a post meets the ground is alternately wet and dry and holds debris, and it is the point at which timber and coated steel posts alike deteriorate first.
A post in a concrete surround that traps water around it can be wetter than one set into free-draining ground, which is the opposite of what is commonly assumed.
Deterioration at and just below ground level is out of sight, so a fence commonly gives no warning before a post fails in a storm.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Clarifications
Commonly misunderstood
- That a stronger post makes a stronger fence. The base restraint is almost always what governs, and a heavier post in the same fixing fails in the same way.
- That a fence post and a guarding post are the same element in different settings. What each is required to resist, and what follows from it not doing so, are different.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- How is each post restrained at its base, and what does that restraint act against?
- What fence is being carried, and what area does it present to the wind?
- Where posts are set into the ground, what is the condition at and just below ground level?
- Where the fence line runs along a retaining structure or a boundary of uncertain ownership, what has been established about each?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- This entry describes a position. It states no post size, spacing, depth, height, fixing or wind load, and none can be inferred from it.
- Fence and boundary construction can involve ownership, party and planning matters as well as structural ones, and establishing what applies is professional work.
External Works & Paving Elements
The laying course, wearing course, edge restraint, deck framing, guarding posts and the enclosing and surfacing elements that make up the ground outside the building.
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