Building components · Stairs & Level Change
Stair Stringer
Explains the stringer as the edge-carrying member of a flight, and separates it from the intermediate support beneath a wide flight and from the beam that trims the opening it arrives at.
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 stringer is
A stair stringer is the inclined member running along the edge of a flight. The treads and, where present, the risers are carried by it, and everything applied to the flight ends up travelling through it to the structure at the head and the foot.
It is met in two broad forms that look very different but occupy the same position. A closed string has an unbroken top edge with the steps housed into its inner face; a cut string is notched to the profile of the steps so the steps sit on it and the step ends are visible. Both are the edge member; the difference is how the steps are received, not what the member does.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a stair carriage. A carriage is an intermediate member beneath a flight, added because the flight is wide; a stringer is at the edge and is present in every flight built this way, however narrow. A wide flight commonly has both, doing different jobs at different places across the flight.
- It is not a trimmer. A trimmer frames the opening in the floor that the flight arrives at and is part of the floor structure; a stringer is part of the flight and is supported by that structure rather than forming it.
- It is not a beam. A beam spans horizontally between supports; a stringer is inclined, is loaded by steps along its length rather than by a floor plane, and its two ends are at different levels — which is what makes its connections at each end the governing detail rather than an incidental one.
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.
- stair string
- cut string
- closed string
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- How it is connected at the head and at the foot, since an inclined member pushes as well as bears and both ends have to receive that.
- What it is bearing onto at each end — a trimmer, a wall, a landing or a slab — and whether that element was framed with the flight in mind.
- Whether the flight is wide enough that edge members alone are not how the steps are carried, in which case an intermediate member is introduced beneath.
- Whether it is cut or closed, which changes how much of its depth is continuous and where the steps transfer into it.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
An inclined member delivers both a downward and an along-the-slope component at each end, so the connections at head and foot carry more than the weight of the flight alone.
A flight is commonly made away from its opening and offered up to it, so the fit of the stringer at both ends depends on an opening built to the same set-out the flight was made to.
A stringer is a single long member set between two fixed levels, so an error at either level cannot be absorbed locally and appears as a difference at every step.
The stringer is commonly concealed behind a lining or plaster on one or both faces, so its condition and its end connections are established only when that is opened up.
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 the stringer is the decorative side of the stair. The visible face is commonly the stringer, but its function is carrying the steps and reaching the structure at each end.
- That a cut string and a closed string are different components. They are two ways of receiving the steps into the same edge position, and both are stringers.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What do the stringers bear onto at the head and at the foot of this flight, and were those elements designed to receive them?
- Are the stringers cut or closed, and does the flight rely on anything beneath as well as at the edges?
- How is the horizontal component of the load at each end resisted?
- Where an opening is being formed or widened for a new flight, what is trimming 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 a structural position. It states no span, depth, section size, fixing schedule, load capacity or fire rating, and no such value can be inferred from it.
- Whether a given stringer and its connections can carry a particular flight is a structural design matter for a qualified engineer, and nothing here substitutes for that assessment.
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 →