Open Riser Code Requirements

Learn open riser stair code requirements, including the 30-inch threshold, 4-inch sphere rule, and IRC riser height limits for floating stairs.

Open riser stair code requirements

Open riser stairs are allowed under the IRC. The key rule is the opening between treads. Under IRC R311.7.5.1, an open riser staircase can remain open when that part of the stair is 30 inches or less above the floor or grade below. Above that height, the opening must not let a 4-inch sphere pass through.

This is the rule most people mean when they search for open riser stair code, floating stairs code, or open staircase code.

Open riser code at a glance

Requirement	IRC rule
Are open risers allowed?	Yes. Open risers are permitted on residential stairs.
When does the 4-inch rule apply?	When the walking surface is more than 30 in. above the floor or grade below.
Maximum opening	Must not allow a 4-inch sphere to pass.
Maximum riser height	7 3/4 in.
Riser variation in one flight	No more than 3/8 in. between the tallest and shortest riser.
Handrail requirement	A handrail is required on stairs with 4 or more risers.
Guard requirement	A guard is required where the open side is more than 30 in. above grade or floor below.

What is an open riser stair?

An open riser stair leaves the space between treads open. It does not use a full vertical riser board. Many people also call this a floating stair or open staircase.

This stair style is common in modern residential design. It appears in wood, steel, glass, and cable stair systems.

When are open risers permitted?

Under IRC R311.7.5.1, open risers are permitted by default. The code does not require every stair tread to have a closed riser panel.

The main limit is the stair height above the surface below:

• If that part of the stair is 30 inches or less above the floor or grade, the opening between treads is not restricted by the 4-inch sphere rule in the same way.
• If that part of the stair is more than 30 inches above the floor or grade, the opening must be small enough that a 4-inch diameter sphere cannot pass through.

The 30-inch measurement is taken from the tread walking surface to the floor or grade directly below.

What is the 4-inch rule for open riser stairs?

The 4-inch sphere rule for open riser stairs applies when the stair height exceeds 30 inches above the surface below. At that point, the vertical opening between adjacent treads must be limited so a 4-inch sphere cannot pass through.

This rule is meant to reduce child entrapment risk. It is similar to the opening limit used in other railing code conditions.

How to make open riser stairs code compliant

If your floating stairs are above the 30-inch threshold, use one of these approaches:

• reduce the clear opening between treads
• add a horizontal element that blocks the 4-inch sphere
• overlap nosings enough to reduce the passable opening

The stair can still look open. It does not need a full closed riser to meet code.

Open riser stairs still need standard riser dimensions

An open riser staircase still has to meet normal stair geometry rules. The open design does not change the basic stair riser code.

Key IRC limits include:

• maximum riser height: 7 3/4 in.
• maximum variation within one flight: 3/8 in.
• risers can be vertical or sloped from the underside of the nosing above at no more than 30 degrees from vertical

If risers vary too much, the stair can fail code even if the openings are compliant.

Do open riser stairs need a handrail or guard?

Yes, often.

• A handrail is required on stairs with 4 or more risers.
• A guard is required where the open side is more than 30 inches above the floor or grade below.

These are separate rules from the open riser code requirement. A stair can meet the 4-inch opening rule and still need a compliant handrail or guard.

Frequently asked questions

Are open riser stairs up to code?

Yes. Open riser stairs are code compliant under the IRC when they meet the 30-inch threshold rule, the 4-inch sphere limit where required, and the normal riser height and uniformity limits.

Can floating stairs be code compliant?

Yes. Floating stairs can be code compliant if they meet the same rules that apply to other residential stairs. That includes riser height, riser consistency, handrail requirements, and the 4-inch sphere rule for open risers above 30 inches.

What code section covers open riser stairs?

The primary residential rule is IRC 2021 Section R311.7.5.1. Always confirm the adopted code edition and any local amendments before finalizing a design.

Do open riser stairs need closed risers?

Not always. A full closed riser is not required by default. Once the stair height exceeds 30 inches above the floor or grade below, the opening between treads must be restricted so a 4-inch sphere cannot pass through.

Related pages

• 4" Sphere Rule
• When is Handrail Required?
• Tread Depth and Risers