Structure and support · Frames & Load-Bearing Walls
Stair Flight and Landing System
This entry treats a stair as a structure rather than as a route, setting out what carries the flight, what a landing is doing besides being level, how an inclined member is held at its ends, and why the opening in the floor above belongs to the stair rather than to the floor.
Educational reference entry. How this system behaves depends on climate, jurisdiction, loading, substrate, the adjacent systems it meets, how the building is used, the manufacturer's instructions and qualified professional design.
Overview
What stair structure is
A stair is an inclined structure connecting two levels, and almost everything about it follows from being inclined. The flight is carried either on members running along its edges or on a single plate folded or cast into the shape of the steps; the steps themselves are carried by that structure rather than being it; and at each end the flight arrives at a level platform that is carried by something else again. Read as construction rather than as circulation, a stair is a short span at an angle, with a level platform at each end of it.
A landing belongs to the stair, not to the floor it happens to sit level with. It is carried by structure trimmed or built for it, and it is also the datum from which the flight arriving at it and the flight leaving it are set out. That is why moving a landing is never a local change: the platform moves, the structure carrying it moves, and the arrangement of both flights is reopened at the same moment.
The opening in the floor above is part of this assembly too, which is the point at which the stair stops being a stair and becomes a hole. Every floor system that meets a stair describes the opening rather than the stair — how the interrupted members are carried around it, what the trimmers are doing, how the plate works with a piece missing. This entry is the other half of that junction: the thing the opening exists for, and the reason the trimmers are where they are.
What stands at the open edge of a flight or a landing is a separate assembly and is not described here. Guarding — the infill, the posts or frame, the rail and the anchorage back into structure — is published once as its own system and referenced from every place a change of level occurs, including this one. This entry stops at the structure the guarding is anchored into, and everything about the edge assembly itself belongs to that entry.
Terminology
Common names and aliases
These names describe the same assembly. The encyclopedia keeps one entry per system so that a trade term or a regional name never becomes a second, thinner page.
- staircase structure
- stair carcass
- flight and landing assembly
- stair framing
- stair structure
- stairwell framing
Purpose
What this system is intended to do
The job the assembly exists to perform, conceptually. An intention is not a guarantee that any particular build achieves it.
- Carry people, and what they are carrying, between two levels on a structure that is inclined rather than level.
- Deliver that load into the building at a limited number of connections, at the head of the flight, at its foot, and at each landing.
- Hold the steps in position relative to one another so the flight behaves as one element rather than as a stack of separate pieces.
- Resist the outward action an inclined member produces at its ends as well as the bearing it applies there.
- Frame and carry the opening the flight passes through, so the interrupted floor still works around it.
- Present a datum at each landing from which the flights on either side of it are set out.
Composition
The roles this system is made of
What each part does in the assembly and what it depends on — never a product, a thickness, a fixing or a determination that anything is adequate for the role.
Order is not meaningful in this system. These roles interact as parts of one whole rather than stacking up in a sequence, so the list below is not a build-up and nothing should be read into the order it appears in.
- Primary supportFlight structure
The inclined members running along the edges of the flight, or the single folded or cast plate that replaces them. Whichever form is used, this is what spans between the two levels. The steps are carried by it rather than being it, which is the distinction that lets the same arrangement be built in timber, in steel or in concrete.
- Primary supportLandings at head, foot and turn
The level platforms within the stair. Each is carried by structure of its own, usually trimmed into the floor or built off the surrounding walls, and each is also the datum from which the flights meeting it are set out. A landing is part of the stair rather than a piece of the floor it sits level with, so it moves with the stair and takes its supporting structure with it.
- Primary supportIntermediate carriage beneath the flight
An additional inclined bearer under a flight, introduced where the steps are not carried by the edge members alone. It is present in some flights and absent in others, and whether it is there changes what the edge members and the steps are each being asked to carry rather than changing how the stair looks.
- AttachmentHead and foot connections
The connections where the flight hands its load into a trimmer, a wall or a slab. An inclined member pushes outward along its own line at each end as well as bearing down, so a connection arranged only to support weight leaves the outward part of that action to be resisted by whatever happens to be adjacent to it.
- Finish surfaceTreads
The surfaces a foot lands on, understood as positions within the flight rather than as whatever covering is later applied over them. They are carried by the flight structure, they are the part of the assembly that takes the wear, and they can often be recovered or replaced without the flight itself being disturbed.
- Edge and terminationRisers and nosings
The vertical face closing one step to the next, and the profile terminating the front edge of a tread. Risers are present in some flights and deliberately absent in others; where they are present they restrain the treads as well as closing the step, so taking them out changes the structure and not only the appearance.
- Edge and terminationThe trimmed opening in the floor above
The opening the flight passes through, together with the doubled members or beams carrying the floor members that were interrupted to form it. The opening exists because of the stair and moves when the stair moves, which is why it is framed as structure rather than cut once the floor is down.
- Finish surfaceSoffit lining to the underside
The lining closing the inclined underside of a flight, which turns the sloping space beneath it into a finished surface or an enclosed cupboard. It conceals the flight structure, and in doing so it decides what can be seen or reached if that structure is ever in question.
Interaction
How the parts work together
The reason this is a system rather than a list of parts: what depends on what, and what stops working when one part is changed.
The flight, the landing and the opening are one chain rather than three items. Fix the landing and the flights above and below it are set out from it; move the landing and the opening in the floor above is in the wrong place, and the trimmer carrying the interrupted members moves with it. None of the three can be adjusted on site without the other two being adjusted at the same moment, which is why a stair is one of the few assemblies where a small change requested late is genuinely a redesign.
Replacing a landing with tapered treads at a turn changes the load path there rather than the appearance of it. A landing is a supported platform carried at its own bearings; tapered treads are steps that still have to be carried, and what carries them through the turn is a question the landing had already answered. The two arrangements look like alternatives on a plan and are different structures at the point where the stair changes direction.
Risers and treads hold one another where both are present. A riser closes the step and also braces the tread it meets, so a flight built without risers is not the same flight with the faces left open: the treads are then relying on their connection to the edge members alone, and the edge members are relying on something else to keep them in plane with each other.
Each end connection is resolving two actions at once. The flight bears down, which is the part that gets drawn, and it also pushes outward along its inclination, which is the part that finds the least stiff thing nearby. Where a flight arrives at a trimmer, that outward action is being handed to a member whose own job is to carry a floor around a hole, so the trimmer is answering the stair and the floor in the same piece of structure.
The soffit lining is the last component and it removes access to every other one. Once the underside is closed, the end connections, the carriage and the fixings between the steps and the edge members can be reached only by taking the lining down again. What sits behind it is therefore worth recording while it can still be seen, because nothing about the finished stair reveals which of the arrangements above was actually built.
Materials
Material families commonly met in each role
Commonly encountered, not recommended. Whether a material suits a given project depends on the whole assembly, the exposure, the manufacturer's documentation and qualified professional review.
Primary support
Flight and landing structures are commonly formed from these families, and the choice tends to follow the building around the stair rather than the stair itself. What any of them can carry, and how a flight in each is connected at its ends, is a structural determination made for the particular stair.
Substrate
Sheet and unit families are commonly encountered forming landing decks and the backgrounds beneath applied step surfaces. Whether a background is being asked to span, to spread a load or only to receive a covering is decided by the designer.
Finish surface
These families are commonly encountered as the walked surface of a flight or landing. How a surface behaves underfoot, in wear and when wet is a matter for the designer against the product documentation and the use the stair is being put to.
Edge and termination
Step edge profiles and the boards forming risers are commonly drawn from these groups. A profile terminates an edge that the flight structure has already formed; it does not create that edge and does not by itself determine anything about how the step performs.
Attachment
Connection components at the head, the foot and the landing bearings are commonly formed in these metal families. What a given connection is capable of belongs with the manufacturer's documentation and the structural designer.
Protection
Board and plaster families are commonly encountered closing the underside of a flight. Where the stair sits within a route whose fire duties have been determined by others, the lining is part of that determination rather than a separate finishing decision, and the determination itself sits outside this entry.
Boundary
Where this system ends and meets another
The edge of this system. Everything above is inside it; each junction below is a condition at its boundary, where an adjacent system or an adjacent building condition takes over. Junctions are where most assemblies actually fail, so they are set out explicitly rather than left inside the prose. What resolves one is a detail designed for the specific building — not a rule of thumb.
The trimmed opening the flight arrives through
This is the junction at which a stair stops being a stair. The floor entry describes what happens to its own members when they are interrupted; this entry describes what the interruption was made for. The two have to be read together, because the trimmer is simultaneously carrying the floor around the hole and receiving the flight's bearing and outward action.
Read about Timber Joisted Upper Floor →The structure the edge assembly is anchored into
Guarding at the open edge of a flight or a landing is a separate assembly, and everything about the infill, the posts, the rail and their anchorage belongs to it. What this system provides is the construction behind that anchorage, which is why where guarding will stand has to be known while the flight and landings are being designed rather than after they are built.
Read about Guarding System →A stair serving an inserted platform
A mezzanine names access openings as holes in its own deck, and a stair reaching it arrives through one of them. Because the platform is often carried on its own supports rather than on the building, the question of what the flight's head connection is actually fixed to is answered by the mezzanine's structure rather than by the building around it.
Read about Mezzanine Structure →A stairwell interrupting a floor plate
The floor plate collects horizontal action and delivers it to the elements that resist it, and a stairwell is a hole in that plate. Where the opening lies relative to those elements can matter more than its size, so the position of a stair is part of the stability arrangement rather than a layout decision taken alongside it.
Read about Lateral Stability →A flight cast with or bearing on the frame
A concrete flight may be cast into the structure around it or set on bearings that let it move relative to that structure, and the two produce different stairs. Which applies determines whether the flight is part of the frame's behaviour or a separate element resting within it, and it is decided in the frame design rather than at the stair.
Read about Concrete Frame →A flight or landing built into a wall
Where a flight or a landing bears into masonry, the wall is carrying a concentrated load at that point and the stair is relying on the wall staying where it is. That makes any later work on the wall, including forming an opening near the bearing, a question about the stair as well as about the wall.
Read about Load-Bearing Masonry →A stair bearing into a construction that divides spaces
A flight or landing built into a wall that separates spaces is a solid connection across that wall, and footfall arrives at it directly. Whether the stair can bear there at all, and what is done at the bearing if it does, belongs with the designer of the separating construction rather than with the stair builder.
Read about Flanking Control →The lined underside and the space beneath the flight
The soffit of a flight is an inclined ceiling to whatever is under it, and it is frequently also the top of a cupboard. Whether it is framed and boarded as a ceiling, what is stored behind it, and whether any access into it was designed are decisions taken about the space rather than about the stair, and they close off the stair's structure for as long as they stand.
Read about Framed Board Ceiling →A stair passing through a propping floor plate
A floor that props perimeter retaining walls is interrupted where the stair goes through it, and the propping action is locally absent at that opening. Whether a stair can be placed where it is wanted, and how the plate is trimmed around it, is a question about the box rather than about the stair.
Read about Basement Structure →
Considerations
Topics worth discussing
Which topics genuinely apply to this system and what to raise about them. Measured values, classes and ratings come from a qualified professional's design for the specific building, not from a reference page.
- Movement
- A stair connects two levels that may not move together, and it is a stiff element between them. Where the structure at the head is expected to deflect or a timber frame is expected to shrink, whether the flight is fixed at both ends or allowed to move at one is a structural decision taken from the building rather than from the stair.
- Acoustic
- A stair is a direct, solid route between levels and its bearings are connections into whatever it lands on. Footfall and airborne behaviour belong to the complete construction including those bearings and the flanking around them, are determined by a qualified professional, and no value is stated here.
- Fire
- A stair is frequently part of a route whose fire duties are determined by others, and the enclosure around it, the lining beneath the flight and the construction it is built into are all part of that determination. Nothing in this entry states or implies any such performance, and the determination itself belongs to the relevant authority and the designer.
- Buildability
- The stair is set out from levels that have to be known accurately before it is made, and a flight fabricated or cast to one set of levels does not fit another. Where a flight is made off site, the moment at which the levels are confirmed becomes one of the more consequential dates in the programme.
- Interfaces
- This system meets a floor, a wall, an edge assembly and a lined space, and each of those junctions is drawn by somebody different. The stair is one of the places where a detail that satisfies every trade separately can still leave the flight bearing into something nobody told the engineer about.
- Durability
- Wear on a stair concentrates at the front edge of each step and at the landings, and the connections that take the most repeated action are the ones that are hardest to reach. What is expected to be replaceable over the life of the stair, and what is not, is worth settling while the flight is still a drawing.
- Maintenance and access
- Once the soffit is lined, the flight's structure is behind a finish that has to be removed to reach it. If a stair ever moves, creaks or is suspected, the first question is what is behind the lining, and the answer is far easier to have on record than to establish by opening it up.
- Documentation
- The form of the flight, what it bears on at each end, and whether the opening was trimmed as designed are all invisible in a finished stair. That record is what makes the stair alterable later and what a structural engineer will ask for first.
Design
Questions the design has to answer
The decisions this assembly turns on. They are questions rather than answers, because the answer depends on the building.
- What does this flight bear on at its head and at its foot, and was each of those elements designed knowing it would be there?
- Is the landing carried by the floor structure, by the walls around it, or by something introduced for it, and who is responsible for that?
- Does the opening in the floor above appear on a structural drawing, with the trimming around it designed rather than assumed?
- Are the connections resolving the outward action of an inclined member, or only its bearing?
- Does this flight have risers, and does anything in the arrangement depend on whether it does?
- Where will guarding stand, and is there structure behind every position its anchorage will need?
- Is the underside of the flight to be lined, and if so is any access into the space behind it being designed in?
- If this stair is being made off site, at what point are the levels it is made to being confirmed, and by whom?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- A stair is read as a set of steps rather than as a structure, so the flight, the landings and the opening are treated as three separate items instead of one chain that moves together.
- A landing is assumed to be a piece of the floor it sits level with, when it belongs to the stair, is carried by structure trimmed for it, and is the datum the flights are set out from.
- The guarding at the edge is assumed to be part of the stair, when it is a separate assembly with its own entry, and this system only provides the construction its anchorage reaches.
- Risers are treated as a purely visual choice, when where they are present they are restraining the treads as well as closing the steps.
- The opening in the floor above is thought of as a hole cut in the floor, when it is framed structure that exists because of the stair and moves whenever the stair does.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- What is this flight bearing on at each end, and has the outward action of an inclined member been accounted for there?
- Who designed the trimming around the opening, and does the structural drawing show it in the position the stair actually needs?
- Is the landing's support independent of the flight, and what happens to it if the flight arrangement changes?
- Where can guarding be anchored into this stair, and does that need anything built in before the flight is finished?
- If the structure at the head is expected to move, is the flight fixed at both ends or free at one?
- What would need to be removed to inspect the flight's connections if this stair were ever in question?
- Is any fire or acoustic duty attached to this stair or the space around it, and who has determined what the enclosure and the bearings have to do?
What this page does not do
- This entry describes how the assembly is organised. It states no step, flight or opening geometry of any kind, numerically or otherwise, because stair geometry is regulated, is project-specific, and is settled by a qualified designer against local requirements.
- Nothing here describes the guarding at the edge of a flight or landing. That is a separate published assembly, and any question about it belongs there and with the professionals responsible for it.
- Whether a stair may be placed where it is wanted, and what the structure around it has to do, are design determinations made by qualified professionals for the particular building.
- Altering an existing stair, including removing risers, changing a landing or enlarging the opening above it, affects structure that is usually concealed and should be taken to a structural engineer before anything is opened up.
- No fire or acoustic performance is stated here; those are properties of complete, correctly detailed and correctly installed constructions in a specific context, determined by others.
Related systems
How this system relates to others
Every link states what the relationship actually is, rather than leaving a bare list of related pages to be read as a suggestion.
Commonly built alongside
Systems routinely present in the same building without a junction recorded between them and this one. Where two systems do meet, the junction is set out above instead.
Applications
Building contexts this system is used in
The functional parts of a building this assembly is commonly met in. This is membership, not a ranking and not a recommendation: several systems answer any one context, and which of them suits a project is a design decision. A context appearing here does not mean the system is suitable, permitted or adequate for it.
- Superstructure · Structure
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this assembly involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this system comes up.
Primary Structural Frames and Load-Bearing Wall Systems
Complete primary load paths from roof to foundation in masonry, timber, steel and concrete, together with the stability system without which none of them stands up.
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