Building components · Concrete & Reinforcement
Concrete Cover Zone
Explains cover as a zone of the element with a job to do, rather than as a number quoted on a drawing, and why its continuity around the reinforcement is the thing that matters.
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 cover zone is
Reinforcement works because it is embedded. The cover zone is the concrete outside the outermost bars — between the steel and every surface of the member — and it is the only thing standing between the reinforcement and the air, water, salts and heat on the other side of that surface.
It is a zone rather than a line, because it exists on every face and follows the reinforcement all the way round, including at ends, corners, links and projecting bars. Its job is continuous protection, so the question a reader should carry is not what the cover is at one point but whether it is present, sound and uninterrupted everywhere the reinforcement runs. A well-compacted, continuous cover zone is the durability of the member; a broken one is where deterioration starts.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a finish or a coating. A finish is applied to a concrete surface after casting and can be removed or replaced; the cover zone is part of the cast element and cannot be added afterwards.
- It is not a spacer. A spacer is a procured item placed to hold reinforcement away from the form face so the cover zone exists when the concrete arrives; the zone is the concrete itself, and spacers are the means rather than the thing.
- It is not the cover dimension. Cover in specification means a design value established for a member, exposure and design life; the cover zone is the physical body of concrete that value locates, and this entry describes the body and not the value.
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.
- covercrete
- cover concrete
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The reinforcement staying where it was placed while concrete is poured and compacted around it, since the zone is defined by the distance from steel to face.
- The concrete reaching and compacting fully in the space outside the bars, which is the most congested and least accessible part of many members.
- The exposure the surface actually faces, since a face exposed to weather, ground, salts or water is asking more of the zone than an internal face.
- The zone remaining intact over the life of the member, because chasing, drilling, spalling and surface damage all remove part of it.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Most deterioration of reinforced concrete begins with the cover zone being thin, porous, cracked or absent at a point, rather than with anything happening to the steel first.
The zone is what moisture and dissolved substances have to travel through to reach the steel, so how dense and continuous it is matters as much as its presence.
Cover is established before the pour, by where the reinforcement is held, and is fixed permanently the moment the concrete is placed. It is one of the least recoverable decisions on a concrete job.
Later drilling, chasing or fixing into a concrete face cuts into the zone, and whether that is acceptable at a given location is a question for the designer rather than for the trade doing the work.
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 cover is a single figure for a building. It varies by element, by face and by exposure, and the value applying at any one place is a design output for that place.
- That more cover is always better. The zone is unreinforced concrete on the outside of the member, and moving the steel further from the face changes how the member behaves as well as how it is protected.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What exposure has each face of this member been assessed against, and what does that imply for the cover zone there?
- How was reinforcement position held before and during the pour, and was it checked?
- Is there a record of cover achieved, and how was it established?
- If a face has been drilled, chased or damaged, what assessment has been made of the reinforcement behind it?
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 what the cover zone is and why it matters. It states no cover value, no tolerance and no dimension of any kind; cover is a design value and nothing here implies one.
- Required cover is determined for a specific member, exposure and design life by the engineer responsible, and verified against local requirements; a reference entry cannot supply it.
Concrete & Reinforcement Elements
The positions that govern how concrete is placed, joined and reinforced — the joints between pours, the zones around reinforcement, and the faces that form the finished surface.
Browse all concrete & reinforcement entries →