Do I need 2 or 3 stringers?

Do I Need 2 or 3 Stringers for My Staircase?

Brief Summary

The number of stringers needed for a staircase depends on its width and the type of treads being used. For stairs up to 36 inches wide, three stringers are typically sufficient. However, for staircases wider than 36 inches, at least four stringers are necessary to ensure adequate support and comply with building codes.

Expanded Answer

Understanding Staircase Stringers

Stringers are the structural backbone of a staircase, providing support for the treads and risers. They run along the sides of the stairs, transferring the weight of the staircase and its users to the floor or supporting structure.

Building Code Requirements

• Minimum Width: The International Residential Code (IRC) mandates that residential staircases must have a minimum width of 36 inches.
• Stringer Spacing: The IRC also states that stringers should be placed no more than 16 to 18 inches apart. This ensures adequate support and prevents excessive deflection or “bounce” in the treads.

Number of Stringers Based on Stair Width

• Up to 36 inches wide: For staircases with a width of 36 inches or less, three stringers are typically sufficient. Two stringers are placed along the outer edges, and a third stringer is positioned in the center for added support.
• Wider than 36 inches: For wider staircases, additional stringers are needed to maintain structural integrity and comply with code requirements. A general rule of thumb is to add one stringer for every additional 16-18 inches of width.

Other Factors Affecting Stringer Quantity

• Tread Material: The type and thickness of the tread material can influence the required number of stringers. Thicker or heavier treads may require more stringers for adequate support.
• Load Requirements: If the staircase will be subjected to heavy loads, such as in commercial settings or for outdoor use, additional stringers may be needed to ensure structural safety.
• Design Preferences: In some modern designs, like floating staircases, a single central stringer (mono stringer) may be used for aesthetic purposes, even for wider stairs. However, this requires careful engineering and specialized construction techniques.

Conclusion

The number of stringers needed for a staircase depends on its width, tread material, load requirements, and design considerations. For most residential staircases up to 36 inches wide, three stringers are typically sufficient. However, wider staircases or those with specific design or load requirements may necessitate additional stringers. Always prioritize safety and compliance with building codes when determining the appropriate number of stringers for your staircase project.