How to lay out stair guard posts

Locate sound connections before equalizing bays

Even bays can make a stair guard look orderly and simplify repeated rail pieces. They are useful only if each post can connect to suitable framing and the chosen rail assembly permits those spans. Start with the terminal posts and their actual attachments, then work inward.

An extra post may shorten rail pieces, but also adds a base or connection, more fittings and another interruption in the view. Fewer posts can open the appearance while requiring a different system or capacity. Compare these as complete assemblies rather than minimizing post count independently.

Establish the usable guarded slope

Choose the bottom and top terminal-post locations first. Measure their insets along the stair slope, not horizontally, and subtract them from the full slope length.

Guarded slope = stair slope − bottom inset − top inset

Equalize the clear bays

The planner finds the smallest whole post count that keeps every clear bay at or below the entered maximum, then divides the remaining clear length equally between the posts.

• Enter the horizontal width of a vertical post. The calculator projects it along the rail before subtracting the posts from the guarded length.
• Treat the maximum bay as a project or manufacturer limit—not a universal code value.
• Check that every proposed post has real framing or a designed connection.
• Do not add posts to a drawing without resolving fasteners, blocking, edge distances and waterproofing.

Check net rail lengths

For a 120-inch guarded zone at 30 degrees, 3.5-inch plumb posts each occupy about 4.041 inches along the rail. With three posts, two equal clear bays are about 53.938 inches. Two rails per bay need about 215.75 inches in total before joinery and waste.

Clear-bay limits in this planner are distances along the sloped rail. They must come from the actual system or project design. Insets locate the outside terminal faces within the first-to-highest-nosing baseline.