Stairs: The Devil’s in the Details

Author

Expertise Includes:

    • Building Damage Assessment
    • Construction Defect Evaluation
    • Building Foundation Issues
    • Building Envelope/Water Intrusion
    • Building Codes and Standards
    • Exterior Wall & Roofing Systems
    • Structural Design - Collapse/Failure Analysis

Issues with stairs are interesting with respect to either personal injury, i.e., someone falling on a staircase; or construction defects, i.e., the stairs not meeting Code.  If you’ve ever had to design, build or just “make stairs work”, you can relate to the following sentiment:

“Stairs, Stairs, STAIRS!  I don’t want to discuss them right now!  Let’s talk about something more fun…”.  Whether they be straight-run, scissor, winder, or spiral, interior or exterior means of egress, stairs of all types are simply difficult to deal with, i.e., a PAIN!  However, as you know, if your structure has levels above the ground, stairs are necessary and unavoidable.  By the way, for the purposes of this article, the term “stairs” will be used interchangeably with the terms “flight”, “stairway”, or “staircase”.

I am a Structural Engineer by trade, however, during the site planning, design and construction phases of a personal home I designed from the ground up and had built in Charleston back in 2005, I also wore the hat of Architect, Site Supervisor, Project Manager, and Landscaper, just to name a few.  It was during that invaluable and (mostly) rewarding experience that I really got an appreciation for the complexity and nuances of stairway design and construction.  Therefore, in this article I will primarily discuss the true artform that is the design and construction of stairs.  This will include discussions of the Building Code dimensional requirements, design criteria, and just good ole practical in-the-field know-how.  Note that the purpose of this article will not be to provide an exhaustive recitation of the voluminous Code requirements related to stair design and construction, particularly where the Americans with Disabilities Act (ADA) accessibility is concerned.  Instead, I will reconcile the general dimensional requirements of both the International Building Code (IBC) and the International Residential Code (IRC), compare key differences between the two, and discuss the myriad of challenges and pitfalls with the design and construction of stairs.  To assist the readers, I have several helpful CAD detail illustrations included herein as well.

First, let’s compare some of the most basic dimensional requirements of the two governing Codes for rectangular, non-spiral, non-winder staircases, as follows:

Dimension IBC IRC
Egress stairway width 44” minimum 36” minimum
Headroom clearance 80” minimum 80” minimum
Tread width 11” minimum 10” minimum
Riser height 7” maximum; 4” minimum 7-¾” maximum
Nosing profile Curvature of 1/16” min, 9/16” max Curvature of 9/16” max

As you can see, with the exception of headroom clearance, the dimensional requirements differ somewhat.  An additional distinction the IRC requires is that “the greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch”.  See Figure 1 for a representative illustration of a typical residential stair tread in cross-section.  There are also many exceptions for different staircase types and certain special situations.  This comparison illustrates how the configuration of stairs depending on building type can quickly get complex.  For more in-depth (and considerably more detailed) dimensional information, the readers are referred to the applicable sections of the governing Codes, while ensuring that the edition referenced is the one adopted by the particular jurisdiction in question.  Subsequently, variations and exceptions within each jurisdiction come into play also.  So, let’s move on to an examination of stairs and how they are properly designed and built.

The design of stairs involves the layout of the risers and treads in both plan and cross-sectional views.  To accomplish this, the change in elevation (rise) and available space in plan (run) must be known.  Referring to the house I designed, let us consider as an example the plan layout and cross-sectional views of the interior winder staircase ascending from the 1st to 2nd floor living spaces of the house.  See Figure 2.  In plan, the “block” of floor space, which is the size of the actual opening, or “hole”, in the 2nd floor framing to accommodate the staircase, is depicted.  See Figure 3.  In the elevation section, a total rise of 11’-0¾” is accommodated, (a 3’-2¾” 1st flight rise, a 3’-11½” landing rise, and a 3’-10½” 2nd flight rise).  Also in section, the nominal tread width of 10½” (with the exception of the 1’-4” wide 1st tread), and the nominal riser height of 7¾” are designated. See Figure 4.  This is a depiction in plan of the “understory” staircase leading from the ground floor (garage) level to the 1st floor.  The house is an elevated “drive-under”, i.e. “beach house” style, with the living space over parking and storage.  See Figure 5.  This is the 1st Floor Plan showing the various staircases, but with no dimensions provided.  From a designer’s perspective, a great deal of trial-and-error is usually required to select just the right tread and riser sizes to allow the stairs to fit and ensure that the required residential step-to-step uniformity is obtained.  This can be a very time-consuming, frustrating exercise, and many an Architect has literally torn their hair out trying to get the stairs to work.

See Figures 6 & 7.  Note that the elevation views for the entry/egress stairs at the front left side and the rear deck are designated on these drawings, but the rises are not shown in any sections.  This is typical of Architectural drawing sets, not all of which contain building sections.  In these cases, it is up to the carpenters to layout and determine the required tread widths and riser heights.  Refer to Figure 8, the “Typical Interior Stair Framing Detail”, which depicts how the “stringers”, or saw-tooth cut main support members are laid out with a straight edge and cut.  It is during the cutting of the stringers that a major opportunity for mis-cuts and the resulting lost time and scrapping of material often takes place.  The cut lines, i.e., “chalk lines”, for these pieces have to be laid out exactly, and the depth of the member (i.e. 2×12 or deeper) must be selected properly.  Otherwise, major errors can occur.  Obviously, this can result in much head shaking, gnashing of teeth, and frustration on the part of the carpenters just to get the stairs to work out right.

Up to this point, field-built wooden staircases have been discussed, but there is also another important type of stairs which is widely utilized, especially for egress, in high-end single-family residential, multi-family residential, and commercial structures.  These are pre-engineered staircases, manufactured in a Fabrication Shop, and then shipped to the field.  For single-family residential dwellings, these would typically be wooden staircases, although metal and even glass can be used.  For multi-family and commercial structures, these would typically be fabricated of sheet metal, with the treads being made using a concrete topping over the steel tread “pans”.  The 1st to 2nd floor winder staircase in my personal house (Figure 2) is an example of a pre-engineered unit.  With pre-engineered stairs, many of the problems commonly encountered in the field can be avoided, although obviously errors can occur in the Shop also.

Being the Architect, Structural Engineer, and Field Supervisor for the field-built stair design and construction operations from my personal house project example afforded me the opportunity to experience all the various types of frustration which stairs are famous for.  However, all’s well that ends well, and in the end, we had four very nicely built staircases, perfectly sized and trimmed out beautifully.  But wait…I forgot about the 5th set…the attic pull-downs!  Enough already!

As a final point, another important requirement for stairs worth mentioning is that handrails should be provided on at least one side.  These handrails must be “graspable”, i.e., capable of being firmly gripped by hand.  The requirements for the grip size are provided in the Codes for various handrail cross-section shapes, such as circular, square, or other profiles.  The requirements for various types of handrails for stairs and other areas where they are required will be discussed in depth in a subsequent article.

George Sanford, PE, holds a Bachelor of Science in Mechanical Engineering from North Carolina State University in Raleigh, North Carolina. George has more than 20 years of applied structural engineering experience specializing in residential, commercial, and industrial structures and foundations. Throughout his career, George has designed and analyzed structures, supervised engineers, prepared construction documents (drawings and specifications).  He has an in-depth knowledge of many building codes, standards, rules, and regulations including the agencies that govern and provide guidance to building designers such as the International Code Council (ICC) American Society of Civil Engineers (ASCE), Steel Joist Institute (SJI) and the American Iron and Steel Institute (AISI).

Find Similar Posts: