Anatomy of a staircase

Every part named — and the US/UK differences that cause real errors.

The step itself

Two steps in section. The pitch line touches each nosing — headroom and pitch are both measured from it, not from the tread surface.

Tread: The horizontal surface you stand on.
Riser: The vertical face between one tread and the next. An open riser stair leaves it out.
Step: Tread and riser together.
Nosing: The part of the tread that overhangs the riser below it.
Going: The horizontal distance from the face of one riser to the face of the next.
Rise: The vertical distance from the top of one tread to the top of the next.
Pitch line: The imaginary line joining the nosings. Headroom and handrail height are both measured from it.

Going is not quite tread depth

UK going is riser face to riser face. US tread depth as the IRC measures it is nosing to nosing — the same number on a stair with consistent nosings, but the tread as a piece of timber is wider than either, because it includes the overhang. Three similar numbers, and mixing them up is how a stair ends up an inch short per step. StepCalc labels every input with which one it means.

The structure

String (UK) / Stringer (US): The raking member at each side carrying the steps.
Wall string: The string fixed flush against a wall.
Outer string: The one on the open side, carrying the balustrade.
Cut string: Cut to the profile of the steps, treads sitting on top.
Closed (housed) string: Parallel-sided, with the treads and risers housed into trenches and wedged.
String margin: The distance from the top of the string to the pitch line, measured at 90° to the pitch line.
Carriage: An intermediate bearer under a wide stair, with blockings supporting the treads.

The balustrade

Newel: The post at the foot, head and each turn, anchoring the handrail.
Baluster / spindle: The uprights between handrail and string.
Handrail: What the hand holds. Graspability is a code matter, not a style one.
Balustrade: The assembly of all three.
Guard: The barrier at an open edge. A handrail is part of it, but not all of it.

Changing direction

Winder: A tapered tread, narrower at one end, turning the stair without a landing.
Walk line: The assumed path of travel across a winder — 12″ from the narrow edge under the IRC. The going is checked here.
Landing: A level platform between flights.
Flight: An uninterrupted run of steps between floors or landings.