January, 2008
Inspection News and Views from the American Society of Home Inspectors

2006 IRC Stairway Requirements


Code Corner with Wisdom & Associates, Inc.

This installment of Code Corner will go over stairway requirements of the 2006 International Residential Code. Stairways are considered a means of egress in the home, so proper stairway dimensions are essential to occupant safety.

Before looking at the requirements for stairway dimensions, it is important to understand the different types of stairways. For the purposes of this article, there are three basic stairway types: typical staircases, winder staircases and spiral staircases.

Typical staircases consist of straight treads. Winder staircases consist of tapered treads that are narrower on one side than another, causing the staircase to curve. A staircase may consist of both typical stair treads and winder stair treads. The spiral staircase is defined as having all treads attached to a center pole. The attachment of treads to a center pole is what separates spiral staircases from winder staircases. This article deals only with typical staircases. A future article will address winder treads and spiral stairs.

All staircase types are subject to minimum dimensions. Typical staircases are required to have a minimum width of 36 inches. A common question is, “Are handrails included in the minimum width?” Handrails are allowed to pro-ject into the required 36-inch space. Typical staircases with a singe handrail on one side of the stairway can project into the required 36-inch space up to 4.5 inches. If a handrail is present on each side of the stairway, the total encroachment into the stairway can be increased to 9 inches. This encroachment applies from the handrail vertically down to the stair treads. In effect, the minimum 36-inch width applies to the portion of the stairway from the handrail vertically to the minimum headroom requirement of 6 feet 8 inches.

So, the minimum width of a stairway with a hand rail on one side is 31.5 inches below the handrail height and 36 inches above the handrail height. The minimum width of a stairway with a handrail on both sides would be 27
inches below the handrail and 36 inches above the handrail.



A common misconception about the minimum height requirement for stairways is how the height is measured. The 6-foot 8-inch minimum height for a typical staircase is measured from the plane of the nose of the treads to the finished ceiling. The simplest way to measure this height is to take a long, flat object like a 2"x4" and lay it on the nose of the treads. This provides a visual aid in determining where the plane of the treads is for measuring the ceiling height. Projections into the 36-inch clear width above the handrails are only allowed above the 6-feet 8-inch required ceiling height. If a stairway had a finished width of greater than 36 inches above the handrails, lighting sconces or similar items could conceivably project into this space as long as a minimum 36-inch width was maintained.

Typical stairs are subject to limitations in tread depth and riser height. The minimum allowed tread depth is 10 inches, and the maximum allowed riser height is 7-3/4 inches. In the past, the Uniform Building Codes did allow exceptions to the minimum tread rise and run in a
residential setting, but there are no such allowances in the International Residential Codes. An area where violations commonly occur is in the measurement of the run. Many times a stairway is constructed with a 10-inch-tread run with an overhang or nosing of 1/2 inch to 1 inch. While a 10-inch tread does meet the minimum run requirements of the code, the area of the stair under the nosing cannot be counted as part of the required tread depth. The actual run of a stairway tread is measured from nosing to nosing. Within any flight of stairs, the greatest tread depth shall not exceed the smallest by more than 3/8 inch and the greatest riser height shall not exceed the smallest by more than 3/8 inch.

Robert Moss, Wisdom & Assoc., Kenai, Alaska, is an ASHI Certified Member who joined ASHI in 2002. Visit his company Web site at www.wisdomandassociates.com.