Facts and Codes
Most Municipalities in the US have adopted International Residential Code (IRC for Residential) and the International Building Code (IBC for Commercial) which specify rules for railing design and usage. A brief overview of these rules are outlined below. Note: Code interpretations vary across the country so it is imperative that you consult with your local code official before beginning any building project.
Guardrails are used to minimize the possibility of a fall and are generally required on balconies, stairs, ramps and landings that are above 30" high. Top rail heights need to be 36" high (in most states) for residential and 42" high for commercial.
Handrails are a horizontal or sloping rail intended for grasping by the hand for guidance or support. Handrails heights should be between 34-36" above the nose of the tread.
Gaurd Rail openings
Where Guard Rails are required on balconies, openings in the railings are restricted to an area no larger than what a 4" sphere will pass, on stairs the sphere size is slightly larger (see illustration below).
In the current IBC and IRC codes, the 4" ball rule is not a test under
load rule. It is a dimensional test, however interpretation of this
varies so you should consult with your local code official before
Post to post spacing, post rigidity and cable tension all work together in a system to prevent a 4 inch sphere from passing through the cables. We space our cables at 3" and recommend a maximum post to post spacing of 42 inches. See illustration Below.