Geometric staircases: swept, splayed and continuous

Ask three staircase companies what a geometric staircase is and you will get swept, splayed, curved and continuous used as if they all mean the same thing. They do not. They describe different moves, and knowing which is which is the difference between asking for the stair you actually want and paying for one you did not. Here is how the words are used on the tools, and where they overlap.

What makes a staircase geometric

The defining feature of a geometric, or geometrical, staircase is not simply that it curves. It is that it turns in one unbroken line with no newel posts breaking it. On an ordinary turned stair the newel post is the structural corner: the strings die into it and the handrail stops and restarts around it. On a geometric stair there is no such post. The strings themselves curve around the turn, and the handrail flows over the top of them in a continuous wreath. That is why a geometric staircase and a continuous wreathed handrail are really the same craft seen from two ends: you cannot have the flowing rail without the curved, newel-less structure underneath it. It is the form you see on grand Georgian and Victorian stairs that rise round an open well in one sweep, and it remains one of the most demanding things a stair joiner makes.

Swept, splayed, and swept and splayed

These two get muddled the most. Swept describes a curve introduced into a run that is otherwise straight. A string can be swept up into a landing instead of meeting it square, or the bottom of a flight can be swept out into the hall so the last few steps ease round rather than stopping dead. Splayed describes a string that opens outward in plan, so the stair widens as it comes down, most often at the bottom where the steps fan out to make a broad, welcoming base. Put them together and a swept and splayed flight is one whose lower steps both curve and flare, the classic grand entrance that sweeps and widens as it reaches the floor. It is a bigger move than a single feature bottom step such as a bullnose or curtail: those dress up the first tread, while a swept and splayed flight reshapes the whole bottom of the staircase.

Geometric, spiral, helical or winder

It helps to place geometric against the shapes it gets confused with. A spiral stair winds tightly around a single central column. A helical stair is a freestanding curve or ellipse with no central column and no straight sections, closer to a geometric stair but standing on its own rather than following a wall and well. A winder turns using tapered treads worked around newel posts or a solid corner, so unlike a geometric stair it keeps its newels and its straight flights. Geometric sits at the top of that family: a continuous curve, no newels, with straight and curved sections flowing into one another. It is a different discipline again from the contemporary floating looks, the mono-stringer and the cantilever, which get their drama from steel rather than from a worked timber curve.

The rules still apply

Because geometric is a design and joinery term, there is no separate building-regulations category for it, and no special British Standard governs it the way BS 5395-2 covers spiral and helical stairs. In practice that means a geometric stair has to meet the same rules as any other. The rise, the going measured along the walking line of the curved treads, and the pitch all have to stay within the normal limits, as on the rise, going and pitch page. The handrail has to sit at the regulated height and be easy to grip the whole way round the curve, as on the handrail requirements page. And the guarding has to stop a 100mm sphere passing through, with no gap a small child could get through, as on the guarding page. The curve makes all of that harder to achieve, not exempt from it.

What we look at on a survey

On a survey the first question is not which of these you would like, it is which one the space can actually take. A true geometric stair needs an open well and room for the curve to breathe. Force it into a tight opening and you end up with a winder wearing a curved handrail, which is a different and lesser thing. We look at the well, the floor-to-floor height, the headroom round the turn, and where the bottom step can land before we say a geometric or swept and splayed flight is on. Where it is, it is worth doing properly, because a continuous curved stair with a wreathed rail is close to the most valuable thing a timber staircase can be, and the hardest to copy.