Design Considerations

StraightStaircase

HelicalStaircase

CompoundHelical

Staircase

Staircase design involves a lot of variables including code requirements, ADA accessibility requirements, step tread to riser ratios and more. This eBook is intended as a guide for architects and builders to simplify the design considerations that need to be addressed when adding stonework to the design.

You will learn the key criteria you need to know about when designing straight, spiral (helical) and compound helical staircases that include stone elements. Following these guidelines will make your stone staircase designs easier to bid, fabricate and install. This will in turn reflect favorably upon your budget and timeline constraints.We hope you find this eBook helpful and we welcome your feedback to make it better.

INTRODUCTION

Mark Loomis is a Registered Landscape Architect in the state of Texas.

He has accumulated over 25 years of experience ranging from land-scape architecture to architectural stonework technical detailing.

With a passion for geometry and 3D modeling, Mark has acquired a skill set that allows him to tackle technically challenging projects.

He also enjoys mentoring when the opportunity arises.

His other interests include generative design, digital fabrication and 3D printing.

He can be reached at mloomis@mstoneandtile.com

MARK LOOMIS

STRAIGHT STAIRCASEDESIGN CONSIDERATIONS

Straight run staircases are fairly simple and can be field cut by others in place using standard balustrade profiles. The example above shows a standard BA-303 balustrade staircase.

STRAIGHT STAIRCASES CAN BE FIELD CUT USING STANDARD PROFILES

BALUSTER AND NEWEL POST CONSIDERATIONS

There are two things to keep in mind when designing straight run balustrade staircases.

First, the balusters will need to be taller for the sloped conditions so that they can be field cut by others in place.

The second consideration is the newel post at the bottom of the stairs. It will need to be slightly taller than the standard newel post in order to receive the sloping balustrade. Please consider this illustration.

Notice that the field cut baluster and the newel post at the bottom of the stairs are taller than their counterparts in the level balustrade.

HELICAL STAIRCASEDESIGN CONSIDERATIONS

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.

HELICAL STAIRCASES REQUIRE CUSTOM PIECES

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 slop-ing 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.

WHAT IS HELICAL GEOMETRY?

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.

HOW ARE HELICAL PIECES MADE?

COMPOUND HELICAL STAIRCASEDESIGN CONSIDERATIONS

Compound Helical (curving and sloping with more than one radius) staircases are the most complex staircases and demand custom cut pieces in order to negotiate the twisting geometry of the sloping curve. The issues discussed in the straight stair-case and helical staircase posts still apply, but there are additional requirements that must be met in order to have a successful project. One thing you might notice is that the joints are no longer perpendicular to the slope but rather they are vertical joints. There is a good reason for this!

COMPOUND HELICAL STAIRCASES ARE THE MOST COMPLEX CONDITION

Compound helical geometry occurs when a curved geometry is sloped and the radius of the curvature changes along the length of sloping curvature.Like helical geometry, the slope introduces a twist into the geometry that allows the architectural elements to remain level at all times. Unlike helical geometry, the radius change introduces a vertical tangent plane that must be considered when fabricating the helical pieces that cross this plane. Please consider the following illustration.

The green lines represent the flat plane geometry of the compound helical staircase above and the red lines are the helical lines that the decorative panel assembly follows up the staircase. The cyan planes are the vertical tangent planes that occur where the radius changes to a new radius.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 decorative panel assembly. The details of the decorative panels have been omitted for clarity.

WHAT IS COMPOUND HELICAL GEOMETRY?

Please consider the following illustration.

The piece on the left has vertical ends and the piece on the right has ends perpendicular to the slope.Notice how the left end of the vertical joint piece follows the vertical tangent plane where the radius changes. The piece with the joints perpendicular to the slope doesn’t follow the vertical tangent plane. This awkward relationship to the vertical tangent plane unnecessarily complicates the geometry of the piece.Not only that, but there’s more waste material taken away from the domain block of the perpen-dicular joint piece than there is from the vertical joint piece making the vertical condition more economical to fabricate.I hope these examples about staircase design considerations have been helpful to you. If you’re fascinated with geometry like I am, you might consider reading more about it in the excellent book, Architectural Geometry by Bentley Institute Press.

WHY ARE VERTICAL JOINTS IMPORTANT?

1. Straight Staircases a. Can be designed with standard profiles that are field cut into place by others b. Balusters and Newel Posts need to be taller at sloped conditions2. Helical Staircases a. Require custom helical pieces at base rails and hand rails b. Helical pieces require a specified radius and a specified slope3. Compound Helical Staircases a. Require custom helical pieces at base rails, decorative panels (if applicable) and hand rails b. Joints should be vertical to accommodate vertical tangent planes at changes in radius.

KEY TAKEAWAYS FROM THIS EBOOK:

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