Building components · Paving & Decks
Pier Cap
Explains the cap as the weathering termination of a freestanding pier, distinct from a pile cap, which is a structural element at the foot of a building.
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 pier cap is
A pier cap closes the top of a freestanding masonry pier: a gate pier, a pier within a boundary wall, or a pier at the end of a run of walling. It projects beyond the masonry below it, is shaped to fall, and commonly carries a drip on its underside so that water leaves the cap rather than running back into the pier.
A freestanding pier is exposed on every side and is wetted from above as well, which is the condition the cap exists to address. Water entering the top of a pier travels down through the masonry and the joints, and the visible consequences — staining, frost damage, loosened bedding, a leaning pier — commonly appear a long way below where the water got in.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a pile cap. A pile cap is a structural element at the bottom of a building, collecting load from a group of piles and delivering it to a column or wall above; a pier cap is a weathering unit at the top of a freestanding pier and carries no building load.
- It is not a coping. The published stone coping, cill and weathering-unit entry covers the procured units themselves; a pier cap is the position at the top of a single isolated pier, exposed on every side rather than along a line, and it is commonly filled by a unit from that same range worked for the purpose.
- It is not a parapet. A parapet is the upstand wall itself at a roof or balcony edge, and it commonly has a capping of its own; a cap is the element closing the top of a pier.
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 pier cap
- pier capping
- pillar cap
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Projecting beyond the masonry below and carrying an effective drip, since a cap that sheds water onto its own pier is doing very little.
- Being bedded and, where appropriate, restrained, because a cap on an isolated pier is exposed to wind on every side and commonly sits above masonry that a gate is working.
- Falling in the directions it is meant to, which on an isolated pier means away from every face rather than in one direction.
- The joints within and beneath it, since water entering the bed joint under a cap reaches the pier by the shortest route available.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
An isolated pier is exposed on every side as well as from above, so it is wetted from directions a length of walling is not, and the cap is the only element addressing the top.
Water entering the top of a pier saturates masonry that has no sheltered side to dry from, and the damage shows lower down than where the water entered.
Freeze-thaw action works on masonry that is repeatedly saturated, and the top of a pier is the wettest and most exposed part of it.
Where a gate is hung on the pier, the cap sits above masonry that is worked every time the gate is used, which loosens bedding over time.
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.
Materials
Commonly incorporates
Materials this element commonly contains as a distinct constituent part, rather than being made of.
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 cap is ornamental. Its projection, its fall and its drip are the working parts, and a flat cap finishing flush with the pier below is decoration without function.
- That a leaning or spalling pier must be a foundation problem. Water entering an unprotected top is at least as common a cause.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Does the cap project beyond the pier and carry a drip on its underside?
- How is the cap bedded and restrained, particularly where a gate is hung on the pier?
- Are the joints in and beneath the cap sound, and is there staining below them?
- What is inside the pier, and can water that has already entered the top get out again?
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 size, projection, fall, fixing or bedding arrangement, and none can be inferred from it.
- Whether a particular pier, cap or gate fixing is sound is a matter for inspection by a qualified professional, not something a reference entry can determine.
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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