Stair step height: Guide to Stair Riser Dimensions in Stair Codes, Construction & Stair Inspections InspectAPedia® -
Stairstep riser height specifications & codes
Allowable variation in stair step riser height by code & to avoid tripping
Suggestions for adapting pre-fabricated stairways to the to the actual overall stairway height without violating building stair codes & standards
Basic stair riser height dimensions required for safe stairs
Different dimensions for open versus closed riser stairways
Stair safety hazards, photos of defects & Sketches of stair design requirements
Questions & answers about stair and step riser heights and dimensions and building codes
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.
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Definition of stair risers: a stair riser is the vertical space between stair treads (treads are what you step on). If the vertical space is enclosed (see our drawing at page top), the enclosing board is called the stair riser. If the vertical space between stair treads is open (see our photo at left) the space is still a stair riser, but it's an "open riser".
Open stair risers with a more than 4-inch opening are a child hazard, as we detail below.
Stair risers, or the vertical distance between the stair treads, that are too tall are difficult to climb and are a falling or trip hazard.
Stair risers that are too short can also be a trip hazard if the stair treads themselves (the walking surface of the stair or step) are not large enough. As we discuss below, generally as we reduce the stair riser height below about 6-inches, we need to increase the "depth" (front to back distance) of the stair tread.
Stair risers that are uneven or irregular in height are also a serious trip and fall hazard. That's because when people walk up and down stairs we are mostly on "auto pilot" - our brains assume that each step height will be the same as the one we took just before. So a "surprise" such as a step that is taller or shorter, can make us fall - a particular hazard for the elderly, children, or people who are physically disabled and have trouble climbing stairs. (Also see ELDERLY & VETERANS HOME SAFETY).
Step riser specifications riser height (<= 7.75") - this means your stair risers should be less than or equal to 7 3/4 inches. No taller. Some codes specify slightly taller stair risers, from 8" to 8 1/4" (Canada, for example).
Step riser height uniformity (<= 3/8" variation) - this means that more than 3/8 of an inch in variation of the height of steps from one step to another is a tripping hazard.
Step riser slope (out of vertical) (<= 30 deg measured from horizontal surface of the tread) - this stair specification means the rather obvious hazard that if stairs are pitched or sloped users are more likely to trip and fall. Outdoor stairs that are exposed to wet or icy conditions are an even more serious falling hazard if the stairs are sloped.
Step stair riser openings: open stair risers are permitted provided the opening will not pass a 4" sphere (child safety). This 4-inch opening dimension has the same basis as the rule that requires that the opening between stair balusters must be 4" or smaller.
Stair Riser Defects
As we explained just above, the most common stair riser defects likely to lead to a fall include:
Stair risers of uneven height - no variation greater than 0.375 inches is allowed
Stair risers of improper height, too tall
Stair risers of improper height, too short
Bad Deck Stair Example:
Nothing is right about the exterior stairs shown in our photo (above) from a 1991 home inspection:
This stair stringer is too-deeply notched and could split;
The stair risers are too high, as our client is showing with our tape.
The stair treads are too narrow.
There is no railing and the height above ground is more than 36".
The deck and platform railing is open with no balusters.
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. Sketch courtesy Carson Dunlop.
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.
Stair riser height: ideal: 7 3/4, or in some jurisdictions 8 to 8 1/4" tall. Some older homes include a very steep stairway to access the home's attic. The stairs were very tall or "steep" when there was simply not enough horizontal space for a longer and less steep stairway. It may be impractical to fix this condition by a new stairway for the same reason - there just isn't enough space. Be sure to reduce the falling hazard at steep stairs by providing good lighting and secure handrails. (See Attic stairs)
Stair tread nosing: required, 1" to 1 1/2" projection beyond the riser face
Stair tread run (or horizontal depth): 8 1/4 to 9"
Stair tread thickness: 1" or greater, tread is supported by the riser.
Summarizing proper stair dimensions for Open Riser Stairs
Open riser stairs do not include a solid board or other material that fully encloses the open space between stair treads (see the sketch above).
Open riser stair treads should be to 9 1/4" in depth and will typically be greater at shorter stair riser heights.
Open riser stair treads must be at least 1 1/2" thick because the tread, not supported by a riser, may otherwise split.
Open riser stairs are allowed a"back slope of at most 1 1/2". Take a look at the sketch above. Because there is no solid vertical riser to enclose the space between stair treads, the concept of a stair tread "nose" does not apply. But if stair treads are constructed so that the front edge of a tread is more than 1 1/2" behind the back edge of the stair tread below, the treads can become a trip hazard.
See these detailed articles on the proper dimensions for safe stairs and steps:
Rules for Constructing Stairs that are Curved or Angled, & Winder Stairs
Angled or Curved stair treads are a particular trip hazard, especially because of the lack of uniformity and because the tread width at the inside of the curve can be too small for safe walking.
Our stair photo at above left shows tricky angled stairs that were squeezed onto a sidewalk in New York City. A passerby agreed to model the risk of falling. Sketch courtesy Carson Dunlop.
My daughter fell down curved stairs at a shopping mall where the triangular tread hazard was combined with a beautiful, architect-designed handrail that was about 8" in diameter - she was unable to grasp it as she was falling.
The photo shows her sister grasping n added handrail that was welded on to correct this unsafe condition.
The original "fat" hand railing that no one could grasp when falling is along the diagonal-right side of the photo.
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
Dan,
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)
"Stair risers of uneven height - no variation greater than 0.375 inches is allowed"
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.
Questions & Answers regarding this article
Questions & answers about stair and step riser heights and dimensions and building codes.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
"Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
Access Ramp building codes:
UBC 1003.3.4.3
BOCA 1016.3
ADA 4.8.2
IBC 1010.2
Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
Animal Allergens: Dog, Cat, and Other Animal Dander - Cleanup & Prevention Information for Asthmatics and regarding Indoor Air Quality.
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Asbestos Identification and Testing References
Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
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Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
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2005 ASHRAE Handbook : Fundamentals : Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
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1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
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Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
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Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
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"A Parametric Study of Wall Moisture Contents Using a Revised Variable Indoor Relative Humidity Version of the "Moist" Transient Heat and Moisture Transfer Model [copy on file as/interiors/MOIST_Model_NIST_b95074.pdf ] - ", George Tsongas, Doug Burch, Carolyn Roos, Malcom Cunningham; this paper describes software and the prediction of wall moisture contents. - PDF Document from NIS
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Piquet Wall Construction: See this photo of
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Plank House Construction: weblog from plankhouse.wordpress.com/2009/01/25/plank-house-construction/ and where plank houses were built by native Americans, see
Large 1:6 Scale Plank House Construction / P8094228,
Photographer: Mike Meuser
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Rubblestone Wall Filler: See this Lartigue House using exterior-exposed rubblestone filler between vertical timbers of a post and beam-framed Canadian building.
Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
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The Stairway Manufacturers' Association, (877) 500-5759, provides a pictorial guide to the stair and railing portion of the International Residential Code. [copy on file as http://www.stairways.org/pdf/2006%20Stair%20IRC%20SCREEN.pdf ] -
How to Clean Moldy Wood Framing & Sheathing How to clean/seal mold from/on exposed lumber or plywood subfloor or roof sheathing indoors - some suggestions based on our field and laboratory research
Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
Manufactured & Modular Homes: Modular Building Systems Association, MBSA, modularhousing.com, is a trade association promoting and providing links to contact modular builders in North America. Also see the Manufactured Home Owners Association, MHOAA, at www.mhoaa.us. The Manufactured Home Owners Association of America is a National Organization dedicated to the protection of the rights of all people living in Manufactured Housing in the United States.
Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.
Slips, Trips, Missteps and Their Consequences, Gary M. Bakken, H. Harvey Cohen, Jon R. Abele, Alvin S. Hyde, Cindy A. LaRue, Lawyers and Judges Publishing; ISBN-10: 1933264012 ISBN-13: 978-1933264011
Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or ISBN 10: 1-933264-01-2, available from the publisher, Lawyers & Judges Publishing Company,Inc., www.lawyersandjudges.com sales@lawyersandjudges.com and also from the InspectAPedia Bookstore (Amazon.com)
Steps and Stairways, Cleo Baldon & Ib Melchior, Rizzoli, 1989.
"The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
"The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
"Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
Weaver: Beaver Board and Upson Board:
Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver,
APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.
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