Cable Railing Systems

Designing for building code compliance, maximum aesthetic effect, and sustainability
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Sponsored by Atlantis Rail Systems
By Peter J. Arsenault, FAIA, NCARB, LEED AP

Learning Objectives:

  1. Identify the required safety and performance characteristics of horizontal cable railing systems as defined by building codes and national standards.
  2. Investigate the design potential and innovative opportunities to create railing systems that are visually advanced and sustainable by nature.
  3. Assess the functional contributions of cable railing systems as they contribute to green and sustainable design.
  4. Specify cable railing systems in a variety of green and conventional buildings, and make appropriate selections related to specific design conditions.

Credits:

AIBD
1 AIBD P-CE
SAA
SAA 1 Hour of Core Learning
HSW
1 AIA LU/HSW
IACET
0.1 IACET CEU*
AAA
AAA 1 Structured Learning Hour
AANB
AANB 1 Hour of Core Learning
AAPEI
AAPEI 1 Structured Learning Hour
MAA
MAA 1 Structured Learning Hour
NLAA
NLAA 1 Hour of Core Learning
NSAA
NSAA 1 Hour of Core Learning
NWTAA
NWTAA 1 Structured Learning Hour
OAA
OAA 1 Learning Hour
 
This course can be self-reported to the AIBC, as per their CE Guidelines.
This course is approved as a core course
This course is approved as a Structured Course
Approved for structured learning
Approved for Core Learning
This course is approved as a Core Course
Course may qualify for Learning Hours with NWTAA
Course eligible for OAA Learning Hours
This course can be self-reported for Learning Units to the Architectural Institute of British Columbia

Whenever an interior or exterior guardrail is needed, say along a raised deck, floor, or stairway, that guardrail needs to meet some specific structural requirements dictated by building codes and standards to protect the safety of people standing or walking along that guardrail. Guardrails can also be a strong visual element of the space design where they are used. On one hand, they can be intended to look heavy, bold, and traditional, or conversely designed with a minimized appearance so as not to detract from the surroundings. Materials used can run the full gamut from wood, metals, glass, concrete, and others. Recently, a popular choice has been to use steel cables run horizontally instead of vertically which often achieves two design objectives. First, the horizontal lines often complement the surrounding design and introduce a feeling of movement along the guardrail. Second, the comparatively small diameter of cables compared to other materials means there is a reduced visual interruption when looking through the guardrails out to the area beyond. This preserves views or simply allows better visual access between separate areas. For these, and perhaps other reasons, architects have turned to cable rail systems for interior and exterior installations on all types of buildings, in all climate areas, and with all manner of design vocabularies.

All images courtesy of Atlantis Rail Systems

Guardrail systems that use horizontal stainless steel cables as part of a fully coordinated and engineered system provide safety, security, and a wide range of visual styles.

With the above in mind, this course provides information related to the best practices for horizontal stainless steel cable railing systems used in commercial and residential applications. It includes a brief overview of cable railing as well as the current general and specific code, safety, and engineering requirements and best practices to create functional, appealing indoor and outdoor railing systems. It also includes an in-depth explanation of stainless steel materials, their elemental makeup, and treatments for increased sustainability. Of significance, it points out the need to select manufacturers of a cable railing system that can demonstrate independently tested and engineered solutions that meet or exceed code and safety requirements. By demonstrating how to identify key design criteria in specifying stainless steel cable railings, it is intended to encourage the development of ideas for creatively integrating cable railing into design projects.

Cable Railing Systems Overview

The use of steel cables in construction is hardly new. They have been used to support bridges, pull trolley cars, and carry building loads since steel was first used in the late 1800s. It was recognized early on that even thin cables created from clusters of steel wire can carry very high tensile loads while adding relatively small dead loads from the weight of the cables. As a flexible material when not stressed, it is also fairly easy to work with. This combination of attributes has made steel cable an attractive choice for many nautical, industrial, and construction applications seeking lightweight, durable, and strong solutions for structures and personnel protection.

The process of connecting the cables to building structures, posts, top rails, etc. is also not new. Many standard and customized hardware solutions have been in use for decades based on proven engineering and performance in the field. Of course, with an industrial and nautical approach to their use, the hardware carried a similarly utilitarian appearance. Over time, as architectural applications were being sought out, connection hardware has become available that is more consistent with architectural design aesthetics. (Of course industrial-looking products remain available too.) The variety of finishes on the hardware have also become more available, allowing more choices at reasonable cost points.

Currently, manufacturers offer complete railing systems with standard cable types, parts, pieces, and options that can be selected and specified to suit a specific building design. The standard material of choice for the cables and the connection hardware is stainless steel, which requires no other finish, blends well with virtually all design aesthetics, and creates a minimal visual impact. Standard offerings are also available for vertical metal posts and horizontal metal top rails that are all specifically designed to work with cabling and connection hardware to create a fully coordinated, engineered guardrail system. When the use of wood is desired, there are systems that are designed to work with solid wood or composite products provided by others. Any of these systems can typically be used along a horizontal deck or floor as well as be configured for use along runs of stairs and landings. Some manufacturers also offer optional items such as solid bottom rails and integrated LED lighting that can be incorporated.

Available cable railing systems fall into two basic categories as follows.

The two common types of cable railing systems include surface-mount systems (left) and through-post systems (center). Note that through-post systems will require some staggering of cable heights at corners (right).

Surface-Mount Systems

In this case, the hardware that holds the cable is, as the name implies, literally mounted to the surface of posts and other components of the system. This means that everything is visible making the installation of the cabling and connector hardware easy and predictable. These systems also offer greater flexibility in design both for guardrails and stairs where the required angles are self-adjusting based on using point-connected hardware. They also make it easier to adjust the tensioning on the cables to the proper levels. Regarding to the impact on the vertical posts, surface-mount systems do not require holes drilled all the way through them, so the inside of the posts are not exposed to the elements at the point of tension. Since the posts are stressed on the front face, there is typically less overall loading stress on the post. Surface-mount hardware is the recommended choice for installing cable on composite railing systems. While all of these advantages are good, there are a few disadvantages of which to be aware. The obvious one is that the hardware is all visible, which may or may not be consistent with the design intent of the railing. Since all of that visible hardware is likely high-polish finished and mechanical, surface-mount systems are usually higher in price compared to other options. Generally, cable railing hardware is only installed at the termination of run, end and corner post, and in some cases can transcend corners. All mid posts, regardless of material, are usually drilled to allow cable to pass through.

Through-Post Systems

In this type of cable railing system, the end and corner posts (regardless of material) are drilled through so the cable and mounting hardware can pass from the front to rear side, allowing for fastening and tensioning on the rear side of the post. This is a fundamentally simpler design with the hardware mostly hidden from sight. It also usually carries a lower price than surface-mount systems. However, there are some significant points to be aware of related to through-post systems.

First is the limited choices of hardware that are appropriate to this installation, which may or may not be an issue with the overall design. More significant is the impact on the posts, which will be exposed to the elements at the point of tensioning and need to be considered in the design. Like surface mount, the mid posts should all be drilled for cable to pass through, but tension will be applied to end and corner posts from behind, where the elements can have access to the inside of the post. Material choice is critical for this reason when using wood for posts. Corners will require either double posts (one for each direction of cabling) or the cable heights will need to be staggered in a single post. The tensioning of the cables is a bit more labor intensive due to the concealed nature of the system. Since the post will be loaded from behind rather than the front, it will impose different stresses on the post and is not advised for posts made of composite materials. If this type of system is used for stairs or other angled installations, some very precise drilling will be required.

The decision on which type of system to use will be based on project requirements, the overall building design, and other relevant design considerations. Both are common, and it is ultimately the architect’s choice to specify the preferred version and design accordingly.

Building Code and Engineering Considerations

Regardless of the type of system used or materials selected for the non-cable components, all cable railing systems must meet some stringent requirements as follows.

Guardrail Code Basics

The International Building Code (IBC) and the International Residential Code (IRC) have some long-held standards related to guardrails in general. That said, local and state code requirements may differ and must be complied with. Both codes require guardrail protection any time there is a walking surface that is 30 inches or more above the adjacent walking surface (grade or floor surface below) as a basic standard for fall protection (IBC 1015.2/ R312.1.1). It may be acceptable to omit such a guardrail only if the height difference between walking surfaces is less than 30 inches. If placing a guardrail where not required, the design and installation should be consistent with the manufacturer’s engineered design and not altered by reasoning that a guardrail is not required. The height of the guard itself is viewed as a significant aspect for safety, although there are some variations in the minimum acceptable height. The IRC states that 36 inches is the minimum height for residential guards (R312.1.2), while the IBC requires a minimum of 42 inches for commercial guards (1015.3). Some local variations such as the State of California require a minimum height of 42 inches everywhere. There are also some specific exceptions in the IBC for special conditions, such as assembly occupancies and certain multifamily buildings.

The codes recognize that most guardrails are not solid materials, but rather are made up of spindles, rails, cables, or some similar linear materials. Therefore it becomes the spacing between those components that is critical for safety. Here, all of the codes state that a 4-inch sphere cannot pass through any part of the railing (IBC 1015.4/ R312.1.3), which often prompts most railing systems to space components 4 inches apart. There are exceptions for the area directly above a stair tread, where a 6-inch sphere cannot pass through.

It is important to recognize that there are separate code requirements related to handrails on stairs, which are defined as the place where a person grips a railing (with its own set of requirements) and are separate from the requirements for a guardrail along the stairs. The height of guardrails along stairs must be between 34 and 36 inches in height above the front face of stair treads and have other detailed requirements (IBC 1014/ R311.7.8). In cases where the stairs are open (i.e., no wall to enclose them), then the requirements for both handrails and guardrails need to be coordinated.

Code requirements specific to cable railing systems include attention to height, cable spacing, and post spacing.

 

[ Page 1 of 5 ]       
Originally published in Architectural Record

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