Helical Staircases Require Custom Pieces
Helical (curving and sloping) staircases are more complex than straight staircases and demand custom cut pieces in order to negotiate the twisting geometry of the sloping curve. The issues discussed in the straight staircase post still apply, but there are additional requirements that must be met in order to have a successful project.
What is Helical Geometry?
Helical geometry occurs when a curved geometry is sloped. The slope introduces a twist into the geometry that allows the architectural elements to remain level at all times.
If you tried to use flat curving pieces on a slope they would start to lean to one side and the error is cumulative. In other words, the longer the run of sloping curvature, the more those flat curved pieces would start to lean.
Helical curved pieces will remain level throughout the run of sloping curvature regardless of its length. Please consider the following illustration.
The green lines represent the flat plane geometry of the spiral staircase above and the red lines are the helical lines that the wall caps follow up the walls.
Here’s the same construction geometry with the 3D model added so you can see the relationships in the final design. If you look closely you can see the geometry extending beyond the ends of the walls.
How are Helical Pieces Made?
Helical pieces require a specified radius and a specified slope. The radius is to the centerline of the element and the slope is determined by the tread length and riser height of the staircase. The following illustration shows one of the helical wall caps from the staircase above.
Notice the twist in the piece that is highly evident in the lower left view.
As you can see, helical staircases are more involved than straight staircases. They might use standard profiles like the BA-303 Balustrade in the straight staircase example, but the base rails and hand rails become custom helical pieces.