Building components · Stairs & Level Change
Stair Carriage
Explains the carriage as the support in the middle of a flight rather than at its edge, and why its presence is the reason a wide stair does not deflect between its strings.
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 carriage is
A stair carriage is an inclined member running beneath a flight, between the edge members rather than at them. It is introduced when the flight is wide enough that the treads would otherwise be asked to span the full width unaided, and it is commonly hidden entirely once the underside of the flight is lined.
Its presence is what makes a wide flight feel solid underfoot. The edge members carry the ends of each tread; the carriage supports the same treads somewhere between those ends, so the span each tread actually makes is shorter than the width of the stair. A flight can have one carriage or several, and a narrow flight commonly has none at all.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a stringer. A stringer is the edge member of a flight, is present in every flight built that way, and receives the ends of the treads. A carriage sits between the strings, supports the treads somewhere along their length rather than at their ends, and is added only when the width makes it necessary. A wide flight commonly has both.
- It is not a beam. A beam spans horizontally and carries a floor plane or other members; a carriage is inclined, is loaded by the underside of steps, and exists to shorten the span of those steps rather than to carry a structure of its own.
- It is not a stair soffit lining. The lining is the surface closing the underside of the flight; the carriage is one of the members that lining is commonly fixed to, and it is concealed by it.
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.
- carriage piece
- rough carriage
- intermediate stair bearer
- stair bearer
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The width of the flight, which is what decides whether an intermediate member is introduced at all and how many are used.
- What it bears on at the head and at the foot, since it is inclined and both of its ends need something to receive it.
- How the treads are connected to it along its length, because a carriage that does not actually make contact with the steps supports nothing.
- Whether the underside of the flight is to be lined, since the carriage is commonly what the lining is fixed to as well as what supports the steps.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The carriage shortens the effective span of every tread crossing it, which changes what the tread is doing rather than only adding support beneath it.
A carriage is fitted from below and is commonly blocked or packed up to the treads, so contact along its length is made rather than assumed.
Once the flight is lined underneath, the carriage and its bearings are entirely concealed, and whether they were ever properly in contact with the steps is not visible.
Movement between a tread and the member meant to support it beneath is a common source of noise in a flight, and it originates at a concealed contact rather than at the walked surface.
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 carriage is a spare stringer. It occupies a different position, is loaded differently along its length, and is present only when the width of the flight calls for it.
- That fitting a carriage automatically stiffens a flight. It does so only where it is genuinely in contact with the steps along its length, which is a workmanship matter concealed by the lining.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Does this flight have an intermediate carriage, and how many?
- What does the carriage bear on at the head and at the foot?
- How is contact between the carriage and the treads made and maintained along its length?
- Where a flight is flexing or noisy, has the condition of any carriage beneath it been established rather than assumed?
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 structural position beneath a flight. It states no width threshold, span, section size, spacing, fixing schedule or load capacity, and none can be inferred from it.
- Whether a given flight needs an intermediate carriage, and how many, is a structural design matter for a qualified engineer rather than a question answered by a reference entry.
Stair & Level Change Elements
The positions that make up a stair and the elements that carry people safely between levels — treads, risers, the members beneath them, and the guarding at the edge.
Browse all stairs & level change entries →