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Building components · Concrete & Reinforcement

Starter Bar

Explains the starter as the position where reinforcement is handed from one pour to the next, and separates it from the concrete upstand it is commonly confused with.

Form:Linear memberRoles:StructureAttachment

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 starter is

Reinforcement has to be continuous across the plane where one pour meets another, and it cannot be threaded into hardened concrete afterwards. Starter bars resolve that by being cast into the first pour with a length left projecting from it, ready for the reinforcement of the following element to be continued from them.

The position is defined by that hand-over. A starter belongs to the pour it was cast into and to the pour that has not happened yet, which is why it spends part of its life exposed on site. It also explains the practical problems attached to it: projecting steel is in the way, it is vulnerable to being bent, moved or cut, and what happens to it between the two pours is what determines whether continuity is achieved as designed.

Boundaries

How it differs from nearby elements

The distinctions that keep this entry from being a restatement of its neighbours.

  • It is not a kicker. The kicker is a short concrete upstand that locates the formwork for the element above; the starter is reinforcement that carries force into it. They are cast in the same operation and are routinely spoken of together, but one is concrete for position and the other is steel for continuity.
  • It is not a dowel across a slab joint. A dowel is arranged to transfer force across a joint while allowing movement along its axis, commonly by being debonded on one side; a starter is intended to be fully bonded into both pours so the reinforcement acts as continuous.
  • It is not a lap. The lap is the overlap through which force transfers between two bars; the starter is the projecting bar itself. Starters are commonly lapped with the following reinforcement, but the projecting bar and the overlap are different things and a lap can exist with no starter.

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.

  • projecting reinforcement
  • continuity bars

Dependencies

What it depends on

What has to be right elsewhere for this element to do its job.

  • Being cast into the first pour in the position the design requires, since that position cannot be adjusted once the concrete has set around it.
  • Surviving the interval between pours without being bent, displaced, damaged or cut, which is where most difficulties with starters arise.
  • How the following reinforcement is continued from it, since the hand-over is only complete when that connection has been made as designed.
  • Its condition when the next pour is placed, because it has been exposed to weather and site activity in a way that buried reinforcement has not.

Considerations

Topics that genuinely apply here

Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.

Structural transfer

The starter is how the reinforcement of two separately cast elements becomes one arrangement, so its position and its continuation are structural matters rather than sequencing details.

Buildability

Projecting steel obstructs working areas and is commonly in the way of access, edge protection and following trades, which is exactly why it gets moved.

Durability

Bars stand exposed between pours and the concrete around their base is a place where water can sit; what condition they are in when they are cast in is worth establishing rather than assuming.

Tolerance & fit

Bars cast into one pour have to line up with reinforcement detailed for a pour that does not exist yet, so setting-out error in the first pour arrives as a fixing problem in the second.

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 LibrarySteel reinforcing bar →Ordinary reinforcing bar is what is cast in and left projecting; the bar is procured, and the starter is the position it occupies between two pours.Materials LibraryStainless steel →Stainless reinforcement is met where exposure at a junction is a particular concern; whether it is used at all is a design decision for that structure.

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.

Primary supportConcrete Frame →Columns and walls rising off a floor are reinforced continuously with it through bars cast into the floor beneath.Primary supportPile Caps and Ground Beams →Reinforcement projecting from a cap is how the column or wall above is tied into the substructure that supports it.Primary supportRaft Foundation →Walls and columns off a raft are continued from bars cast into the raft pour.Primary supportBasement Structure →Base-to-wall continuity is made through projecting bars, in an element that also has to resist ground and water.Primary supportCantilever Retaining Wall →The stem's reinforcement is continued from bars cast into the base, which is where the bending in the stem is resolved.

Clarifications

Commonly misunderstood

  • That projecting bars can be bent out of the way and bent back as a matter of routine. Whether that is acceptable for a given bar is a question for the designer, not a site convenience.
  • That a missing starter can always be replaced by drilling and fixing a bar into the hardened concrete. That is a different arrangement with different behaviour, and it is a design decision rather than a like-for-like substitution.

Conversations

Questions for qualified professionals

Questions worth asking someone with the project in front of them. This page cannot answer them.

  • What continuity is this junction designed to have, and what role do the starters play in it?
  • Were the starters cast in the designed position, and how was that confirmed before the pour?
  • Have any starters been bent, cut or displaced since casting, and who has assessed the effect?
  • If a starter is missing or unusable, what arrangement does the designer accept in its place?

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 bar size, no projection length, no lap length, no bending limit and no dimension of any kind, and none can be inferred from anything written here.
  • What reinforcement is required at a junction, and whether any deviation on site is acceptable, is determined by the engineer responsible for the structure.

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 →