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Guide to cable railings or wire rope guardrails: this article describes and includes illustrations of cable or wire rope railings or guardrails used along decks, balconies, walkways and stairways. We include definitions of guardrail, a handrailing or stairway handrail, nad other terms that assist in understanding the building code, construction, and safety requirements that wire cable type railings must meet.
We describe the key installation features necessary for cable railings and we explain both the 4-inch sphere rule problem faced by cable railings and the ladder-effect or climbability problem that these systems must also address. Installing a cable railing according to the manufacturer's specifications for spacing, tension, support, and other parameters (described here) improve the safety of cable railings. Where the presence of children argues against any sort of horizontally-run guard railing member, cable railing manufacturers can provide vertical cable railing designs.
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Building Code & Manufacturer Specifications for Cable (Wire Rope) Used in Stair & Guardrail Installations
What's a Railing? What's the difference between a guardrail and a handrail?
It is important to be clear in our terminology as building codes specify different requirements for handrailings than for guardrailings in terms of construction, height, and graspability. 
Definition of Guard railings
Properly, questions about cable railings or wire rope rails are asking about a guard rail, a type of safety "fencing" or "railing" used along the outer side of balconies and stairways, not a "hand railing". Below in this article we discuss the installation and safety of cable-type guardrailings.
Our photo at left illustrates a home-made (and unsafe) cable guardrailing around the top of a stairwell opening in a New York home inspected by the author. The cables were visibly slack, incomplete, and the entire assembly so wobbly that it would easily collapse if leaned-on or stumbled-against.
At Guardrails on Balconies & Landings we provide details about all types of guard railings.
Definition of Hand Railings
Our photo (left) illustrates use of a wire cable "hand railing" along steps ascending the Pyramid of the Sun outside Mexico City.
Watch out: A wire rope or wire cable in the typical dimensions used at railings (1/8-inch to 3/8-inch in diameter) is not a graspable handrailing by any of the building code standards because of its small diameter.
See HANDRAILS & HANDRAILINGS for details about hand railing building codes, construction, inspection, & safety concerns.
Specifications for Installing Cable-Type Guard Railings along Balconies or Stairways
Cable Railing Specifications: railing height, cable diameters, cable spacing, cable support & cable tensioning
If you take a look at cable "railing" specifications provided by a company that sells components for cable railing construction [such as Atlantis Rail, Keuka Studios, or Wagner Companies, three suppliers of cable railing systems, you'll see that the "railing" is really a guardrail comprised of stainless steel horizontal cables of diameters of 1/8", 5/32", 3/16", and 1/4" depending on the application. Horizontal cables are stretched tight, 3" o.c. to form a barrier and are supported by a combination of structural posts and intermediate posts spaced 42" o.c. to 48" o.c. depending on the manufacturer's recommendations.
Wire Rope or Cable Guardrail / Railing Height - Balconies & Walkways vs Stairs
The International Residential Code (IRC) requires a minimum 36-inch-high guardrail for all decks, balconies, or screened enclosures more than 30 inches off the ground. 
The guardrail top height is in most jurisdictions 36" high (or more) in residential applications and 42" high in commercial installations. Along a stairway the railing height is governed by different rules because of the need to grasp the railing during use of the stairs. Handrails are required on all stairs more than four risers in height. Handrails cannot be less than 30 inches nor more than 42 inches above the nosing of the treads
Maximum Sphere Passage Rule vs. Cable Type Guardrails & Stair Rails - Importance of Proper Cable Railing Spacing, Tension & Cable Railing Rigidity
For child safety, the balusters or other decorative infill must be spaced less than 4 inches apart (a 4-inch-diameter ball should not pass between the balusters). 
Companies selling cable guardrailings point out that building codes (IBC and IRC) specify that the opening between vertical balusters or between horizontal railings (if the local code official will permit them) must be close enough together that a 4-inch sphere won't pass between them. 
For horizontal cables we point out that if the cable can be stretched or is not properly tensioned, the guardrail system may fail this 4-inch sphere test.
Also the largest opening between the bottom-most horizontal cable or guardrail member and an individual stair tread should not pass a 6-inch sphere.
Cable or Wire Rope Spacing & Tension Are Critical for Safe Guardrails
Our photo (left) shows an attractive railing with horizontal cables intended to permit a nice view of the Brooklyn NY skyline.
We also demonstrate how easily the cables can be separated as well as how attractive this guard railing is to children.
To have a chance of meeting the 4" sphere rule (maximum sphere passage <= 4 3/8") the cables must be installed with adequate tension and rigidity to prevent deflection by climbing or playing children or other forces that might be anticipated.
If the cable spacing is more than 3" o.c.) or the cable horizontal span is too great, if the intermediate posts spaced too far apart (more than 42" of horizontal distance o.c.), or if the cables are not adequately tensioned, the system may fail this safety test. Using a heavier gauge cable (3/16" diameter instead of the minimum 1/8" diameter) can also add rigidity.
The supporting structural posts and intermediate bracing also need to be strong enough to handle the forces created by properly tensioned horizontal cables. Wagner points out that
And where we have seen cable "guardrailings" installed, indeed a graspable and solid top rail was always provided. The top rail also provides a rigid horizontal support that prevents the whole system from collapsing as vertical posts would bend inwards as the horizontal cables are tightened.
Also, regular inspection of the tension and security of the cables is something I'd recommend, particularly in public areas where the system may be subjected to climbers and pushers.
At left we illustrate that these horizontal cables were very resistant to opening, and considerable force was required to cause enough deflection to pass a 4-inch sphere. Notice that a heavier gauge cable diameter was used (3/8"), adding to the cable rail's rigidity.
Atlantis points out that using a cable tensioner such as their RailEasy™ device permits on-site cable cutting to proper length and adjustment to proper tension without risking slack sagging cables due to mis-cuts or mis-measurement. The company also describes the proper order of tightening the tension on the horizontal cables, starting at the center cable and then alternating above and below that point as each cable is tensioned. 
The Ladder Effect of Horizontal Cable Railings - Safety Issues
Our concern with any horizontally-run guardrail structure is that it is climbable, and also that often we find the cables are loose enough that a child can easily slip between the cables - an installation or maintenance error, not a conceptual error.
The stretch and opening of horizontal guard cables can be minimized by placing intermittent posts at suitable intervals between the supporting posts. Atlantis suggests no horizontal space between posts should be 4 feet on center - a spacing that I usually see has been violated by the installer.
At least some of the cable railing suppliers offer vertical cable railings for installations where a horizontal railing is not approved or not suitable. In our OPINION, a vertical cable guardrail adequately addresses the climbability question (the ladder effect) and if properly tensioned, might pass the opening spacing requirements.
The Atlantis company's opinion is that because of their small diameter and lack of rigidity, horizontal cables are thin and not easy to climb.  Indeed in our photo where kids were tugging on the horizontal cables installed in a cable railing in New York City, the cables appeared rigid enough that there was not much visible deflection.
Our field experience is that children enjoy climbing horizontal cables and other horizontally run guardrailings. Perhaps due to playground practice, it's apparent that kids have little difficulty ascending the cables. OPINION: We do not recommend any type of horizontal guardrail intermediate members that can be climbed in locations where children may be present.
Stairway handrail & stair balusters & guard details are in this sketch.
Balusters (vertical posts comprising the barrier in guards and railings)
Hand-railing heights are given:
Sketch courtesy Carson Dunlop Associates.
Frequently Asked Questions (FAQs) about Cable or Wire Rope Guardrails & Railings
Question: what building codes regulate the use of cables on guardrailings?
The stainless steel cables are used in commercial, what's the IBC on cables in guards? - Scott Emerson 8/18/12
Thanks for the question, Scott. We do find both horizontal and vertical cable guardrailings installed in commercial locations such as the shopping center shown in photos earlier on this page, but ultimately the approval is up to local code enforcement officials. As for specific code requirements, the railings have to pass the same height, strength, spacing, and graspability rules as other types of railings. Please take a look at the article above and also see references  and let me know if questions remain.
Questions & answers or comments about Building Code Rules & Installation Specifications for Guardrail Cables: Wire Rope Railings, spacing, tensioning, support, cable diameters, inspection, safety hazards, applications, & code approvals
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