Stairways — What every builder should know
By Ken Harward
Vice President - Construction Science Division Burgess Construction Consultants, Inc.
We often rely on others to check critical distances during the construction process, however it behooves us to be armed with this knowledge ourselves. Nothing heightens the awareness of subcontractors quite like a code savvy builder who carries a tape measure and knows how to use it. We can wait and hope that the city inspector catches the framer’s mistake, better still to catch it ourselves.
I vividly recall the experience I had removing and replacing what by appearance was a beautiful stairway inside an occupied home. This incident brought to light the intent of building codes and their role in reducing injury to occupants. The appearance of this particular stairway was deceiving as slips and falls had occurred on more than one occasion, prompting examination and conclusion that the stairs were not properly framed nor code compliant. Beautiful as it was and although it had undergone construction and inspection by multiple competent parties, this particular stairway turned out not to be so lovely after all.
To lay the foundation for stairway construction, it is important to note that stairways are regulated in the “egress” section of the International Residential Code (IRC), meaning that they are addressed from the perspective of the means of “going out” safely in times of duress. For this reason, continuity, consistency and eliminating obstructions are major considerations and are addressed in section R311.7 of the 2009 IRC. It is important to review the code version enforced by the jurisdiction in which you build as well as any additions or changes that a jurisdiction may have made to the code. The dimensions provided below are general in nature and do not apply to all stairway types such as spiral stairways and bulkhead enclosure stairways.
STAIRWAY WIDTH The minimum required width of area between the top of the handrail and below the ceiling above is 36”. This area must be clear and free of obstruction. The minimum required net width between a single handrail and the opposite sidewall is 31.5". The minimum required net width between handrails of a stairway with handrails on both sides is 27”.
HEADROOM The minimum headroom height is 6'8" which is required in all areas of the stairway and is measured vertically from the sloped line connecting tread nosings or the floor of the landing.
WALKLINE
RISERS
The walkline of winder treads should be located 12” from the narrowest portion of each tread and measurements for minimum tread depth should be taken here.
The maximum riser height is 7 3/4”. Risers may not vary in height within any flight of stairs by more than 3/8".
8 GREATER DFW METROPLEX BUILDING SAVVY MAGAZINE Vol 3 2011
TREAD DEPTH The minimum tread depth is 10” and is measured at a right angle from nose of tread to nose of tread. The depth of treads may not vary more than 3/8” in any flight of stairs.
“Consistently shaped winders at the walkline shall be allowed within the same flight of stairs as rectangle treads and do not have to be within 3/8” of the rectangular tread depth”. This language is taken verbatim from the 2009 IRC and permits the two different tread shapes to exceed the 3/8” tread depth variance. Where this occurs, the rectangular treads may not vary in depth more than 3/8” from one tread to the next and the same is true for winder treads. It is only the transitions from winders to rectangular shaped steps that are exempt from the 3/8” variance rule. Winder treads must also have a minimum tread depth of 10” which is measured at the walk line which is 12” from the narrowest portion of the tread. The minimum tread depth of a winder tread is 6” and is measured at the narrowest point of winder treads.
PROFILE Nosing is required on stairways with solid risers unless the depth of treads is a minimum of 11”. The maximum radius of curvature of a stair nosing is 9/16”. Nosing beveling shall not exceed 1/2”. The minimum projection distance of required nosing is 3/4” and the maximum projection distance is 1 1/4” as measured from the riser immediately below the nosing. The maximum projection variation from one nosing to the next is 3/8”and also applies to the nosing at floors and landings.
LANDINGS Either a floor or a landing is required at the top and bottom of each stairway. The maximum vertical rise of a flight of stairs is 12', otherwise a floor or landing is required.
BEST PRACTICES
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