Baluster Spacing on a Staircase: What the Standard Is

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The standard rule for baluster spacing is that no gap between balusters should let a sphere pass through that could trap a child's head or body. Israeli railing requirements are set out in standard SI 1142, but the exact measurements depend on the railing type and building use, so confirm the final values with your engineer before installation.

Why Baluster Spacing Matters

Balusters, the vertical posts that fill the space between a handrail and the stair treads or landing, are there for safety. Their main job is to stop people from falling through or over the railing. The spacing between them is just as important as their height, because a gap that is too wide can let a small child slip through or get stuck.

When you plan a renovation, spacing is one of the first things an inspector or engineer will look at. Getting it right from the start saves time and avoids rework.

The General Principle Behind the Rule

The usual safety principle is simple: a sphere of a set diameter should not be able to pass between the balusters. This protects against head entrapment and against small bodies squeezing through. The idea applies whether the railing is made of iron, stainless steel, aluminum, or glass with posts.

Because the principle is about the size of an object that could pass through, the spacing is measured clear of the baluster faces, not from centre to centre. That detail changes the result.

Checking Your Design Against SI 1142

The Israeli standard SI 1142 covers railings and their safety requirements. It is the reference document for the design of guard rails and balusters. Rather than relying on memory or a rule of thumb from a friend, check the current version of the standard or ask your engineer to confirm the figures that apply to your project.

Confirm whether the stair is in a private home or a shared building.
Check any extra requirements for public or commercial stairs.
Keep a copy of the agreed specification with your order.

Measuring Spacing Correctly on Site

Measure the clear gap between the nearest faces of two adjacent balusters, not the distance between their centres. Measure at several points along the stair, because uneven installation can leave some gaps wider than others. Pay attention to the bottom of the railing, where the baluster meets the tread, since gaps there can be overlooked.

If you are renovating an existing stair, a simple gauge made from a piece of cardboard cut to the required diameter is a quick way to test each opening.

Balusters and the Overall Railing Design

Baluster spacing does not work alone. Height of the guard, the strength of the handrail, the fixing method to the stair, and the distance between the bottom of the rail and the tread all affect safety. A well-spaced baluster set on a weak or loose fixing still fails in use.

Discuss the whole railing with your fabricator, including the infill type. Solid panels, glass infill, and cable infill each follow different spacing logic.

Working With Your Fabricator and Engineer

A good fabricator will ask for site photos, take on-site measurements, and provide a written drawing and specification before production starts. Ask them to show the baluster spacing on the drawing, with the clear gap clearly marked. Approve the drawing before the work goes to the factory, so any change is made on paper rather than on finished steel.

If anything on the drawing is unclear, ask the engineer to confirm the figures against the current standard. This is a quick check that protects you later.

Frequently asked questions

Is the baluster gap measured centre to centre or face to face?

It is measured as the clear opening between the faces of neighbouring balusters. Centre-to-centre measurements can give a misleading result because they include the width of the posts.

Do the same spacing rules apply to balconies and stairs?

The safety principle is similar, but the figures and requirements can differ by location and use. Check the standard and confirm with your engineer for each situation.

Can I simply use a spacing I found online?

It is safer to base your design on the current standard SI 1142 and an engineer's confirmation. Online figures may be outdated or may not match your project.

What should I do if an existing stair has gaps that are too wide?

Measure the openings and have a professional assess the railing. Adding infill or replacing balusters is often more practical than trying to patch the existing design.

Common mistakes to avoid

The most common error is measuring between baluster centres instead of the clear gap, which makes wide openings look acceptable. Another is ignoring the gap at the bottom near the tread, where small children can get caught.

Our recommendation

Before ordering, have your fabricator mark the clear opening on the drawing and confirm the figures with your engineer against SI 1142. Approving the drawing first is the cheapest way to avoid a costly fix later.

Summary

Baluster spacing is about the clear gap, which should block passage of a sphere that could trap a child, and the exact figures should be confirmed against SI 1142 for your project.

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