Steel Stringer Spacing for Open-Riser Steel Stairs Explained

What stringers do in an open-riser staircase

In an open-riser steel staircase, the stringers are the structural spines that carry the treads and transfer the weight of people and objects down to the floor or landing. Because there are no risers closing the gap between treads, the stringers and the tread connections are doing all the work that a solid stair would share with its risers.

Understanding this role helps explain why spacing matters so much. Each tread must be supported securely at its ends, and the stringers must be stiff enough that the stair does not flex or feel bouncy when someone walks on it.

Factors that affect stringer spacing

There is no single spacing that suits every staircase. The main factors include:

• Tread width and depth, which set how far each tread must span
• The steel profile and wall thickness of both the stringers and the treads
• The stair width and the number of stringers across it
• The intended use, such as a private home or a shared building
• Whether the treads are fixed to one stringer or to both sides

Stronger, deeper profiles allow wider spacing, while lighter sections need closer support to keep the treads rigid.

Two-stringer and three-stringer layouts

Most open-riser steel stairs use two outer stringers, one on each side. This is the usual arrangement for narrower stairs where the treads are fixed to the stringers at both ends. For wider stairs, an additional center stringer is often added so that the treads do not sag or vibrate under load.

When a center stringer is used, it should be positioned so the tread load is shared evenly. The exact location is part of the drawing and should match the tread profile and the way the connections are made.

Planning the layout step by step

A practical planning sequence helps avoid surprises. Start by measuring the total rise and run of the staircase and confirming the number of steps. Then decide on the tread width and the stair width, since these two dimensions drive how many stringers are needed.

• Measure the opening carefully on site before drawing anything
• Choose the tread profile and confirm the stringer section
• Mark the intended stringer positions on the floor or landing
• Check clearances at the top and bottom connections

Once the layout is drawn, the specification can be reviewed and approved before production begins.

Safety, standards and engineer checks

Railings and stair geometry in Israel are governed by the national standard SI 1142, which covers the requirements for guardrails and handrails. Spacing and load values are not something to guess at from general advice, so the exact figures for your staircase should be checked with the project engineer.

Where the stairs serve a building committee or a commercial space, the engineer's approval is especially important, and the drawings should show the stringer spacing clearly so the installer can follow them.

Finishing and installation considerations

Stringer spacing also affects how the staircase is finished and fixed. Hot-dip galvanizing and powder coating add protection against weather and wear, and the dimensions must allow for the coating thickness at the connections. Installation requires the stringers to be level, plumb and fixed firmly to the floor or wall, so the spacing should be checked again on site before the treads are installed.

Frequently asked questions

Is there one standard stringer spacing for all steel stairs?

No. The right spacing depends on the tread width, steel section, stair width and expected load. An engineer should confirm the layout for each staircase.

When do I need a center stringer?

A center stringer is usually considered for wider stairs or where the treads would otherwise flex. The decision depends on the tread profile and the load it must carry.

Can I use lighter steel to save material?

Lighter steel may require closer stringer spacing to keep the treads rigid. Reducing the section without an engineer's review can lead to a stair that feels unstable.

Do I need to measure on site before ordering?

Yes. On-site measurement is part of the standard process so the stringers, treads and connections are made to the real dimensions of the opening.

Common mistakes to avoid

Choosing stringer spacing by eye or copying a layout from another staircase can lead to weak or wobbly treads. Skipping the on-site measurement and engineer check is the most common and costly error.

Our recommendation

Measure the opening precisely, decide the tread profile first, and have the stringer layout confirmed in a written drawing before production starts. This avoids changes during fabrication and installation.

Summary

Stringer spacing for open-riser steel stairs is set by tread width, steel profile, stair width and load, and should be confirmed with an engineer and a precise on-site measurement.

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