Steel stairs and railings

A steel staircase comes down to four decisions: what carries the treads, how the flight is fixed to the structure, what the tread is covered with and what closes the gap in the railing. Each is decided separately, and each can be got wrong independently of the others.

The flight as a whole

The load-bearing part of a flight is the stringer, usually cut as a saw-tooth: triangular pads welded to a sloping beam, with the treads sitting on top. At the top the flight bears on a cast-in plate in the floor edge; at the bottom on a base plate bolted to the floor with anchors.

A stair flight from the side: the saw-tooth stringer, the treads, balustrade posts and handrail, a cast-in plate in the edge of the floor, a base plate on anchors below and an enlarged detail of a step with its rise and going — A flight in section with an enlarged step detail. A 17 cm rise and a 29 cm going are the pair the whole staircase is set out from.

The height of the flight is measured from finished floor to finished floor. It is the one dimension that cannot be refined later: once a screed goes down on top, all the steps are already welded, and the surplus has to be given to the bottom step — which then sits visibly lower than the rest.

What carries the treads

Six staircase options: on stringers, on strings, on a single central spine, spiral, a flight with a landing and an entrance porch — Six types. A single spine beam looks lighter but is harder at the joints: one beam holds each tread from both sides.

On stringers — treads on top; the most common and the simplest to fabricate.
Between strings — treads between the beams; stricter to look at, but the flight grows by two beam thicknesses.
Single spine beam — one beam down the middle; lighter to the eye, dearer in the joints.
Spiral — fits into 1.5 m, but carrying things up it is awkward; it is not taken as the only staircase in a house.
Flight with a landing — when a 90 or 180° turn is needed and the storey height will not fit one run.

What holds the staircase

The top and bottom joints work differently: the top one in tension, the bottom one in shear. The anchors differ accordingly, and a mistake at the top is the more dangerous of the two.

Six ways a staircase is fixed: a cast-in plate in concrete, a plate on anchors to the edge of the slab, a base plate in the floor, brackets to the wall, a support post under the landing and a fixing to a timber beam — Six fixing details. A cast-in plate beats anchors, but it has to be placed before the floor is poured.

The ideal is a plate cast into the floor in advance: the stringer is welded to it and the joint behaves as one piece. Without a cast-in plate, a plate is anchored to the slab edge — a workable solution, but it needs a slab of decent thickness and a clean hit between the reinforcement.

What the tread is covered with

Six tread options: chequer plate, timber on studs, expanded metal, open grating, glass and tiles on a backing — Six tread options. The difference between indoors and outdoors is fundamental here: inside, solid wins; outside, whatever water falls through.

Indoors, timber on studs is the usual answer on a steel frame: oak or ash, 40 mm thick. Tiles on a backing belong where the staircase meets the ground floor and must not read as different from it. Glass is an interior solution, expensive and needing toughening.

What closes the gap

Six railing infills: vertical balusters, horizontal rails, glass, cables, mesh and wrought iron — Six railing infills. No more than 12 cm is left between elements — otherwise a child climbs through the gap.

Vertical balusters are the safest option: nothing to climb, and the gap is easy to keep. Horizontal rails look more modern but turn into a ladder to the first floor in a house with small children. Glass keeps the view and costs twice as much; cables give a thin line but need tensioning and periodic adjustment.

Where to go next

An outdoor staircase is a different product: galvanising, treads sloped away from the door and open grating. The canopy over it is described in door canopies. If you also need technical stairs with platforms, see grilles, doors and hatches: the grating is the same. Price and lead time are in how ordering works.

Frequently asked questions

What counts as a comfortable step?

A 17 cm rise with a 29 cm going. The check is simple: twice the rise plus the going should land between 60 and 65 cm — the length of a pace. If the rise grows the going has to shrink, otherwise the staircase is unpleasant to walk down.

What height is a flight ordered to?

Finished floor to finished floor, not slab to slab. Screed and floor covering eat up to 8 cm — half a step — and a flight worked out from the structural level ends up with a first and last step that do not match the rest.

What gap is allowed in a railing?

No more than 12 cm between elements. That is the size a child cannot get through. It is also why horizontal rails are treated with care in a house with children: the gap is safe, but they are easy to climb.

What should an outdoor tread be covered with?

With something water and snow fall through: expanded metal or open grating. A solid chequer plate turns into an ice rink in winter, because the water freezes on it and stays.

Author: welder Updated: 20 August 2026