Geometrical staircases explained

People use curved, spiral, elliptical and helical as if they mean the same thing. They do not, and the difference decides what the stair costs and how long it takes.

The four geometries

Curved — a flight that turns on a constant radius. The classic sweeping stair in a hall.

Elliptical — the radius changes through the turn, so the stair opens out and tightens again. Harder to set out, and far more elegant when it is right.

Spiral — treads radiating around a central column, usually in a tight footprint.

Helical — the same rise as a spiral but with no column at all. The well stays open the whole height of the house, which is the entire point of it and the reason it is the hardest to build.

Why rolling our own steel matters

A stringer on a curve has to be rolled, not cut. Shops that subcontract rolling are limited to the radii their supplier will run, which is why so many curved stairs look subtly similar.

We roll in house, so the radius comes off your drawing rather than off a list. It also means we can change it late if a survey turns up something the architect could not have known about, without adding weeks.

Treads up to nine feet

A curved flight can carry width a straight one never could, because the load path runs along the curve rather than across a span. We build treads up to nine feet wide on a single flight — wide enough that two people pass without either of them moving, which is what a grand stair is actually for.

What it costs and how long it takes

A geometrical stair is not a straight stair with a bend in it. The setting out, the rolling, the tread cutting and the balustrade are all bespoke, and the programme runs eight to fourteen weeks depending on material.

For the most demanding of this work — open wells through three storeys, book-matched stone, plaster monoliths — we run a separate studio, Stairs Pro Atelier, with its own engineering and survey process.