Typical steel staircase construction details cover six joints: how each tread connects to the stringer, how the stringers connect at the top, how they bear at the bottom, how landings are framed and supported, how stringers are spliced, and how guard posts attach. Each joint has a few standard solutions, and the right one depends on what the stair fastens to, how it gets into the building, and what finish it receives. The details are designed by the stair's engineer or the engineer of record and shown on the shop drawings; this post explains what each one does so you can read them and ask the right questions.
For the installation sequence on site, see how to install metal stairs. This post stays with the details themselves.
Reading a typical steel stair section
Most stair detail sheets start with a section through a flight, cut along the stair. It shows:
- the floor-to-floor height and the finished floor at each end
- each riser and tread, numbered, with the rise and run
- the stringer profile, with its top and bottom cuts
- callouts (detail bubbles) pointing to each connection: top, bottom, landing, tread, rail post
- the headroom line above the nosings
- the guard and handrail line
The section is where the geometry is checked. The connection details are where the load path is checked: every tread load has to travel through the tread connection, into the stringer, and out through the top and bottom connections into the building.
Tread to stringer connection details
| Tread type | Typical connection | Notes |
|---|---|---|
| Plate or checker plate | Clip angles welded to the stringer; tread welded or bolted to the angles | Bolted treads can be replaced; welded treads are stiffer and cleaner |
| Bar grating | End plates on the tread bolted through the stringer web | Treads come as complete units with nosing; bolts allow removal |
| Concrete-filled pan | Pans welded to the stringers or set on angle supports, then filled on site | Common in commercial exit stairs; see steel pan stairs |
| Wood, stone or precast | Plate or angle brackets welded to the stringer, tread fastened from below | Bracket spacing and screw positions are set for the tread material |
| Mono-stringer | Tread plates or arms welded to the top of a central spine | Spine resists twisting from off-centre loads; a designed detail |
| Zig-zag stringer | Tread sits directly on the horizontal steps of the stringer | Tread fastened through the plate from below |
On channel stringers, the tread angles usually sit on the inside face, leaving the outside clean. On plate stringers, the tread supports may be welded inside, or the stringer may be cut to a sawtooth profile so treads sit on top. Weld size and spacing come from the design; oversized welds add heat and distortion without adding useful strength.
Top connection and fixing details
The top of the stair carries a large share of its load into the floor structure. The common details are:
- Shear plate or end plate to a steel beam. A plate welded to the end of each stringer bolts to the beam web or to a plate on the beam. Bolted connections make site fit-up easier.
- Seated connection. The stringer sits on a seat angle on the supporting beam or wall and is bolted to it, which helps carry the stair while it is fitted.
- Embed plate in concrete. A plate is cast into the slab edge or wall and the stringer is welded or bolted to it. Embeds have to be located before the pour; see embed plates.
- Post-installed anchors in concrete. A plate or angle on the stringer is anchored into the slab edge, with edge distance and embedment set by the designer and the anchor manufacturer.
- Wood header or rim. An angle or plate fastened with through-bolts or structural screws. The wood member has to be designed to take the stair; framing often needs doubling.
- Masonry. Anchors into solid or grouted block, never into hollow cores.
Whatever the detail, the supporting member is part of the check. A stair hung from an existing joist or a header sized only for the floor is a common problem on renovations.
Bottom connections and base plate details
At the bottom, each stringer usually ends in a base plate or a bent angle bearing on the slab.
- Slotted holes allow the stair to be adjusted to the actual slab position.
- Shims and non-shrink grout under the plate set the bottom riser height and level the stair side to side.
- Anchors are sized for the shear and any uplift the designer finds; the slab thickness and edge distance govern.
- Exterior stairs bear on a concrete pad or pier with a base plate held above grade so water drains away and the steel isn't buried.
- Stairs on a topping or finished floor may have the plate set into the topping so the first riser comes out right once flooring goes down.
Base plate design follows the same principles as a column or post base. Our guide to steel post base plates and concrete connections covers plates, anchors and grout in more depth.
Landing framing details
Landings turn a stair and break up tall flights. A steel landing is typically framed with channels or angles around the edge, with intermediate members under the deck, and decked to match the treads: pan and concrete, plate or grating. The supports vary:
- Wall bearing: the landing frame sits on ledger angles or embed plates in the shaft or adjacent walls.
- Posts: HSS posts carry the landing down to the slab or footing below, with base plates.
- Hangers: rods or flat bars hang the landing from the floor above, keeping the space below clear.
- Cantilever: the landing projects from a supporting beam or wall, which needs a stiffer, designed connection.
Where flights meet a landing, the stringers either bolt to the landing frame or are welded to it into one unit. One-piece assemblies need fewer site connections but are heavier and harder to get into the building. For when a landing is required and how big it must be, see steel stair landings.
Splices, slotted ends and movement
Field splices are needed when a stringer is too long to ship or carry in, or when a stair has to be galvanized in pieces that fit the kettle. Bolted splice plates are the usual detail; field welded splices need a certified welder on site and a touch-up of the finish.
Slotted ends do two jobs. They absorb construction tolerances, and in some buildings the designer slots one end deliberately so the stair can slide rather than act as a brace between floors that move relative to each other under wind or earthquake. Where that is the intent, the drawings say so and the installer must not weld or overtighten that end.
Stiffness is part of the design too. A long, light stringer can be strong enough and still feel bouncy. Stair engineers check deflection and vibration, not just strength.
Guard post and handrail connection details
Railings are often detailed with the stair:
- Posts welded to the face of the stringer or to plates on it, which keeps the tread width clear.
- Posts on top of the stringer with small base plates, common on plate stringers.
- Holes or nuts in the stringer for bolted posts, located on the shop drawing so they don't clash with tread connections.
- Wall rail brackets fixed to the wall structure, not just to drywall.
Guard posts have to carry the code guard loads into the stair, so the post connection and the stringer around it are designed together.
Getting stair details right on your project
We fabricate custom steel stairs, landings and railings with CWB certified welding and detail them in-house on our shop drawings, and engineering services are available where the stair or its connections need to be designed. We can prime or galvanize to suit. Installation is by your installer or contractor.
Send your drawings, floor-to-floor heights and photos of the opening for a free quote, or see our services for how detailing and fabrication fit together.
Frequently asked questions
How is a steel staircase connected at the top?
The stringers usually connect to a steel header, landing beam or slab edge with a plate or clip angles that are bolted or welded. On concrete, plates are anchored or welded to cast-in embed plates; on wood framing, through-bolts or structural screws into a designed header are common. The supporting member has to be checked for the stair load.
What is a steel staircase base plate?
A steel plate welded to the bottom of each stringer and anchored to the slab or footing. It usually has slotted holes so the stair can be adjusted, and it is shimmed or grouted to set the bottom riser height.
How are steel stair treads attached to stringers?
Common details are welded or bolted clip angles under each tread, end plates on grating treads bolted through the stringer, angle supports for concrete-filled pans, and plate brackets welded to the stringer with wood or stone treads fixed on top.
Why do steel stairs have slotted holes?
Slotted holes give the installer room to adjust for construction tolerances in the floors and walls. In some buildings the designer also slots one end so the stair does not act as a brace between floors that move relative to each other.
