Stairs are a fundamental architectural element in buildings, providing safe and efficient vertical circulation. To ensure safety, accessibility, and usability, stair dimensions must comply with building codes. This article discusses the standard sizes of stairs according to building regulations and the nomenclature of their components.

Building Code Requirements for Stairs

Building codes establish minimum and maximum dimensions for stair components to enhance safety. While specific regulations may vary by jurisdiction, common guidelines are provided by the International Building Code (IBC) and the Americans with Disabilities Act (ADA). Here are key dimensions and requirements:

1. Tread Depth

• The tread depth (run) should be at least 11 inches (280 mm) according to IBC for commercial buildings.
• In residential applications, the minimum tread depth is typically 10 inches (254 mm).
• The tread should have a nosing of at least 0.75 inches (19 mm) if the depth is less than 11 inches.

2. Riser Height

• The riser height should not exceed 7 inches (178 mm) in commercial buildings (IBC).
• For residential buildings, risers are allowed up to 7.75 inches (197 mm).
• Open risers are permitted if the gap does not allow passage of a 4-inch (102 mm) sphere for safety.

3. Stair Width

• The minimum width of a stairway should be 44 inches (1120 mm) in commercial buildings when serving 50 or more occupants.
• For residential stairs, a minimum width of 36 inches (914 mm) is required.

4. Headroom Clearance

• The minimum headroom clearance should be 80 inches (2032 mm) from the nosing of the tread to the ceiling.

5. Handrails and Guardrails

• Handrails are required on both sides of stairs in commercial buildings if the width exceeds 44 inches.
• The handrail height should be between 34 and 38 inches (864–965 mm) from the tread nosing.
• Guardrails must be at least 42 inches (1067 mm) high in commercial applications.

6. Landings

• Landings should be at least as wide as the stairway and have a depth of at least 36 inches (914 mm).
• A landing is required at the top and bottom of every stairway.

Nomenclature of Stair Components

Understanding the terminology of stair components is essential for construction and compliance with codes. Here are the key components:

1. Tread

• The horizontal part of the stair where users step.

2. Riser

• The vertical component between treads that determines stair height.

3. Nosing

• The projecting edge of the tread that provides additional stepping space.

4. Stringer

• The inclined structural component that supports the treads and risers.

5. Handrail

• A railing along the stair to provide support and stability.

6. Baluster (Spindle)

• The vertical posts that support the handrail.

7. Newel Post

• A larger vertical post at the start or turns of a stair that provides structural support for handrails.

8. Landing

• A level platform between flights of stairs for safety and rest.

9. Flight

• A continuous series of steps without an intermediate landing.

By adhering to building codes and understanding stair component nomenclature, architects and builders can create safe, functional, and code-compliant stairways in residential and commercial structures.