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This article provides building code specifications, sketches, photographs, and examples of the proper stair step height or stair riser dimensions and other stair riser requirements for indoor or outdoor stairways. We compare the code requirements for closed riser and open riser stairs and we include other basic stair tread and riser dimensions. We also discuss the allowable variation in stair or step riser height between individual steps in a stairway. Sketch at page top courtesy Carson Dunlop Associates.
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Stair risers are detailed here. For a complete list of articles on stairs, railings, and ramps, their inspection, trip hazards, and good design, see STAIRS, RAILINGS, LANDINGS, RAMPS - INSPECTIONS, CODES. Or see these detailed articles on specifications for proper dimensions for stairs, railings, platforms
Because more people are injured by trips and falls than other hazards, experts have looked closely at the specifications for stairs, steps, and rails to reduce the falling hazards. This work has been translated into stair and railing specifications that are similar among codes and countries (but not identical). -- IBC, IRC, BOCA, Kingston NY Stair Code, & other sources.
Definition of stair risers (stair riser height)
A stair riser (green arrow in our photo at above left) is the vertical distance (green arrow) between the walking surface of two stair treads (treads are what you step on) is the stair riser or riser height.
Stair treads: The stair tread is the horizontal walking surface (red arrow) of an individual step. The tread depth is measured from the forward edge of the step nose or edge of the step above out to the leading edge of the step being measured - the space beneath my foot in the photo at left. Stair tread depths shall be 11 inches (279 mm) minimum.The stair tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at right angle to the tread's leading edge. Details about stair treads are found at STAIR TREAD DIMENSIONS and at STAIR TREAD NOSE DIMENSIONS
Definition of & Detailed Specifications for Closed Riser Stairs
Closed riser stairs (demonstrated at left by the author's granddaughter Quinn Morgan Gilligan) include a vertical riser board (that my toe is kicking against). Stair risers are detailed at STAIR RISER SPECIFICATIONS. Photo by permission.
If the vertical space is enclosed (see our Carson Dunlop sketch above), the enclosing board is called the stair riser.
Summarizing proper stair dimensions for Closed Riser Stairs
Closed riser stairs include a board or other solid material that encloses the vertical space between stair treads.
Definition of & Detailed Specifications for Open Riser Stairs
Or simply put, open riser stairs have no enclosure (my toe, shown above would be facing into open space).
Open stair risers with a more than 4-inch opening are a child hazard, as we detail below.
Summarizing proper stair dimensions for Open Riser Stairs
Open riser stairs (shown at right in the sketch above) do not include a solid board or other material that fully encloses the open space between stair treads.
The lovely stairway shown at left rises to the main entry for the Maria Mitchell Observatory on the Vassar College Campus, Poughkeepsie, New York.
But are these open risers or closed riser stairs?
They are closed riser stairs (except for that broken missing riser at the first step) because the cast iron gridwork defines the limits of placement of the leading toe of a foot of someone ascending these steps.
Therefore the rules for stair nose design and projection apply to these steps.
Stair Riser Defects in Height, Slope, Consistency
Quick Summary of Stair Riser or Height Hazards
As we explained above, the most common stair riser defects likely to lead to a fall include:
Unsafe Deck, Deck Stairs & Deck & Stair Railing Example
See Deck & Porch Steps or Stairs for more details.
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Frequently Asked Questions (FAQs) about stair and step riser height codes and requirements
Question: Using pre-fab stairs - Is there an exception to the riser height variation for the very first step of the staircase?
Is there an exception to the riser height variation for the very first step of the staircase? Let me attempt to clarify the question. I have a deck (exterior porch) for which the distance from the top of the deck to the slab which forms the footing for the set of stairs is just shy of the 5 steps within a pre-fabricated 5 step stair stringer which can be purchased at a Home Depot or Lowes, for example.
If I attach the pre-made stringer from the deck to the slab, ensuring that the top of the deck to the next stair down is the same height as the rest, then the riser height from the slab to the first stair is greater than a 3/8' variation from the rest of the riser heights by 1/8th of an inch (ie. it's 1/2 inch shorter than the rest of the stairs - I actually need to remove a half inch from the bottom most stair of the stringer to fit). If this is a violation of code, than it means I need to cut my own customer stringer. Just verifying. Any feedback is appreciated. - Dan
Reply: no stair step riser height variation greater than 0.375 inches is allowed
There is no exception for individual stair steps, first, bottom, top, or other. A difference in riser height can be a serious trip hazard at any location on a stairway.
Quoting from the article text above on stair and step height regularity and the amount of variation in stair step riser height that is allowed (presumably to avoid a trip hazard)
Minor Adjustments can fit a factory-built stair to the specific overall stair rise
As I read your note, you have just a 1/2" error to make up between the total elevation difference between the deck surface and the ground surface if you use a pre-fabricated stair way.
If you can split the adjustment between the top and bottom stair risers by trimming the stringer top and bottom, you'll have just 1/4" or 0.25" of riser height variation (one at stair top and one at stair bottom) - thus minimizing the trip hazard risk of the uneven risers and the variation will be within standards.
Watch out: be sure to measure the height difference (deck surface to ground surface) at a projected point along a horizontal line from the edge of the deck out to the location, in horizontal distance, of the front edge of the nose of the very first or lowest step of the stairway. That will avoid any error in calculating total stairway height due to any slope in the actual ground surface.
If you need a greater adjustment in the stair height between the ground surface and the deck surface in order to avoid having to re-cut a whole new pair of stair stringers, sometimes that can be accommodated by changing the height of the surface of the concrete or other masonry platform that many building departments and local codes require be placed as a landing at the bottom of the stairs.
Question: how do we set the step riser height for a very low angle staircase?
Perhaps one of the experts here could give advise on this. What are the rules for a low angle staircase? I am planning an exterior (built on grade) staircase on a slope too steep for a ramp.
My rise is 78 in. over 28 ft. and there is additional room for a landing at top and bottom. I am considering 3 ½” risers and 16” treads (using commonly available cement block). What rules-of-thumb should I follow to build a comfortable walk-able low angle staircase? If there is some formula to the ideal cadence; I would form this in concrete in order to achieve it. I do not want to feel like I am taking “baby steps” or alternately taking a “step-and-a-half” all the way up and down. - Tom 6/23/12
Reply: Here is a simple approach to calculating the stair rise & run for a low slope stairway
Great question. Bernie Campbalik who taught us carpentry, including stair building, used a rule of thumb that basically makes the run longer when the rise is shorter. I've seen several rules such as the sum of one tread and one riser should always be equal or greater than 17; I think we need to dig out some texts on stair design such as those in the references. The concept is that a low rise stair usually has, just as you suggest, a tread that provides a "longer" walking surface. Up to a point. If we make the rise too short, say an inch, it's not a step at all, it's a trip hazard.
Dan, Thanks for your response. I now think any rule can at best only make general recommendations for all the low-slope possibilities.
So I marked off the landing locations and simply walked up and down the slope while counting the number of steps I took as I did so. I repeated this a few times adjusting my gait somewhat and arrived at an average number.
In this case I took 14 steps to travel the slope which equates to 14 treads - 24” long. Then since the landing counts as one of the treads; I divided the rise by 14 which give me a riser height of 5.57”.
I also counted steps made on level ground over the same distance as the length of the stair and came up with 12 so I think 14 is conservative considering the slope but about right for my needs. I am not in a hurry to build but before I do I would still like to hear a professional opinion or two on this. Another possibility might include a landing midway up thus making all the treads shorter? Your input is appreciated.
Reply: stair design basics: calculating step riser height, step tread depth, total rise, total run, intermediate platform lengths
Please see the details about how to calculate step or stair rise & run over at Stair Rise & Run Calculations where we discuss this topic nearly to death.
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