Spiral Staircases are Helixes, Not Spirals


I think it’s about time we stopped embarrassing ourselves by calling helix shaped staircases spiral stair staircases, but that’s just my opinion. Calling a helix a spiral sounds wrong to me.

Should helix shaped staircases be called helical staircases?

For example, this could be called a helical staircase and…

…this could be called a bi-helical staircase.

Thank you. :slight_smile:


The current term is wrong but so widespread it is hard to change. The same term is used in Swedish and probably most other languages that even has a term for this kind of staircase. However this bugs me too.


I thought a helix was a spiral. A spiral can reduce or increase radius as it rotates. A helix is a subset of spirals that has a constant radius.


If a helix is a subset of a spiral, then a circle is too.


That would explain why Fredo’s Curvishear works.


it is, a circle is a two-dimensional spiral with a constant radius


and constant thread


…meaning a circle is both a spiral and helix, even though you typically wouldn’t refer to it as one.


We ran a specialty stair case shop for 10 years.

We reserved the use of the term spiral staircase for a stair revolving around a center post. This type of stair would only pass code as a secondary means of egress.

A stair with 2 curved stringers with constant radius we called a circular stair.

A stair with 1 curved stringer and 1 straight stringer we called a curved stair.

A stair following an ellipse we called an elliptical stair.

A stair that has 2 straight stringers we called a straight stair.

Stairs that didn’t fit 1 of the above situations we called a geometrical stair.


So, York Spiral Stairs needs to change their business name to York Double Helical Stairs? Somehow I don’t think they’ll be too psyched to do that.

Wikipedia and others seem to share in the debate.


From what I have learned from your responses, helixes are a type of spiral, so it’s not technically incorrect to call a helical staircase a spiral staircase. Although, according to Wikipedia, “in general, “spiral” is seldom applied if successive “loops” of a curve have the same diameter”, so that explains why it sounds wrong. Also, Wiki said, “helix” is a more useful description than “spiral”, so I think it might prevent some confusion. What if someone built a spiral shaped staircase when someone asked for a spiral staircase? Many people in the drafting community even call Z Zed to prevent confusion, so I think calling spiral staircases helical or bi-helical staircases might be beneficial. Although, people are used to the term spiral staircase (meaning a helical staircase) already, so changing terms might also cause confusion.


Perhaps this is why a 3D model is a better way to communicate what you’re talking about then those words :tomato::tomato:


In the UK we distinguish two types of circular staircase.

A spiral staircase has a central core to which the inner parts of treads are attached.

A helical staircase is one with no central core but two curved strings. On plan, both strings would describe a circle (or part of one) and there would be a void at the centre.

This may not be geometrically correct but it is commonly accepted.


Just like a circle is a special case of an ellipse … I think that a helix could be considered a special case of a spiral.

From Wikipedia (Spiral):

Two major definitions of “spiral” in the American Heritage Dictionary are:

  1. A curve on a plane that winds around a fixed center point at a continuously increasing or decreasing distance from the point.

  2. A three-dimensional curve that turns around an axis at a constant or continuously varying distance while moving parallel to the axis; a helix.

The first definition describes a planar curve, that extends in both of the perpendicular directions within its plane; the groove on one side of a record closely approximates a plane spiral (and it is by the finite width and depth of the groove, but not by the wider spacing between than within tracks, that it falls short of being a perfect example); note that successive loops differ in diameter. In another example, the “center lines” of the arms of a spiral galaxy trace logarithmic spirals.

The second definition includes two kinds of 3-dimensional relatives of spirals:

  1. A conical or volute spring (including the spring used to hold and make contact with the negative terminals of AA or AAA batteries in a battery box), and the vortex that is created when water is draining in a sink is often described as a spiral, or as a conical helix.

  2. Quite explicitly, definition 2 also includes a cylindrical coil spring and a strand of DNA, both of which are quite helical, so that “helix” is a more useful description than “spiral” for each of them; in general, “spiral” is seldom applied if successive “loops” of a curve have the same diameter.


In the side picture, the black curve at the bottom is an Archimedean spiral, while the green curve is a helix. The curve shown in red is a conic helix.


I think the grooves in a record do, come closer to meeting the first American Heritage definition of a spiral than you think! While the grooves separating tracks may have wider spacing than the grooves within a track, they are nonetheless still continuing to decrease in radius. Nothing in the definition says that the rate of increase/decrease can’t vary.

Where record grooves fail is at the inside terminus, where the radius becomes constant and non-zero.


It doesn’t matter what a technical person would call it, mere what the client would understand. They will just be concerned how dizzy they will be when they get to the bottom, or whether there is enough stair tread to walk upon, not whether it is described by a mathematical equation. Spiral has been used for these types of staircases since they were invented and is the most common term used to this day. So the question should be “what term does your clientele use?”


I think you are right!

A snow flake is not a snow flake it is an ice crystal, typically displaying delicate sixfold symmetry
It is a pavement not a sidewalk, or is it the other way around?

Ask yourself this question ’ In the grand scheme of things will this save lives, will this cause a building to collapse, or will the future of humanity be based on a design being called a helix or spiral"?

Seriously ?


What truly matters here? As others have pointed out, what we call that curving staircase doesn’t matter in end of the world terms. But it DOES matter in the real world, in that whatever term is used is used to communicate an idea to the person paying for the end product.

So let’s just assume for the moment that we come to consensus here and say “It’s a spiral staircase if the inner post supporting the stairs is vertical and straight, otherwise it’s a helical staircase.” What have we accomplished?

Confusion - that’s what we’ve accomplished. The paying customer takes one look, says it’s a “circular” staircase, why are you calling it something else? And if we don’t answer that question perfectly, the customer gets the impression that we think we’re better than them. If we answer poorly, going into background information (like recounting this topic) - especially in a pompous manner - we’ve now alienated the customer. And if we’ve done this sort of thing regarding other details, the customer may become so sick of us that we get fired!

In the last week, since this topic was first broached, I’ve actually talked about it with a few friends with varying backgrounds. With the exception of a professional mathematician (who was fascinated with the nuances), the universal reaction was: “They’re all circular staircases - some more fancy than others.”

So in the real world, I’m going to limit my terminology to “Circular” and, if the inner radius is sufficiently large, I might start saying “Curving” instead of “Circular”.


Just wait for the spiral elevator I’m working on as a part of bachelor thesis :stuck_out_tongue: .


Is your thesis on the benefits of large scale centrifuges in daily life? :stuck_out_tongue_winking_eye: