Mathematical Equations for Railing Posts

Uniform Building Code and Local Requirements

• The Uniform Building Code (UBC) is a nationwide set of building specifications created to ensure the construction of structurally sound buildings. To a certain extent, states and local jurisdictions within states can alter UBC regulations, especially if more stringent. However, variations can also be adopted in specific code areas, and stair rails are an area where building requirements may vary slightly from state to state. Prior to constructing a stair rail, check with the local municipal building department for specifics.

Newel Post Railings

• Newel posts are usually placed at the beginning and end of the stair rail run. Newel posts are also placed at any pivot points along the stairs, should more than one landing be part of the stair design. Technically, they are beefed up spindles, serving both as a visual grounding design element of the stair railing, and as a structural stabilizing feature for the guardrail. While railing posts, or spindles, are generally slender, newel posts can be as large as 10 by 10 inches. Whatever the dimensions of a newel railing post, they must be no more than 4 inches from any spindle.

Railing Post Heights

• The UBC requires that guardrails be between 34 inches and 38 inches in height. To determine the maximum railing post height, decide on the height of the stair rail, measure the depth of the guardrail material and subtract the guardrail depth from the stair rail height. Let H stand for guardrail height, D stand for guardrail depth and R stand for railing post height. Then H - D = R. For instance, if the desired finished stair rail height is 36 inches and the guardrail material depth is 3 inches, substituting the numerical values into the equation gives 36 - 3 = 33. So the finished height of the railing posts is 33 inches.

Railing Post Spacing

• Known as the sphere rule (for the diameter of an infant's head), the UBC requires that railing posts be spaced no more than 4 inches apart. To determine the number of railing posts required in a given run of the stair rail, measure the inside distance between newell posts and divide this measurement by 4. Should the quotient not be an even number, the difference can be worked in by placement of posts slightly closer than 4 inches. Let D be the inside measurement between newell posts and N be the number of spindles needed. The equation is then D/4 = N. For example, if the distance between newell posts is 12 feet, or 144 inches, then the equation is N = 144/4 = 36. So you would need 36 railing posts.