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Ideal Stair Rise & Run Specifications Stair Building Rules of Thumb & Standard Measurements
POST a QUESTION or COMMENT about measuring and calculating to build stairways & low slope or low angle stairways, treads, risers, stairway run, stairway landings & platforms
Best practices for stair layout & design:
Here we describe the recommended measurements for stair building that give a good starting point from which you can adapt the stairs to your specific need in total stair rise or height and run or length.
We describe how to translate the stair rise and run into a specific number of stair treads and risers that will be uniform and of proper (safe) dimension.
We include a table giving standard access ramp, ladder, and stair specifications for slope, angle, and rise/run measurements for stair treads for various types of stairs, ramps, and ladders.
We also provide Conversion Formulas for Stair Rise/Run, Percent Slope & Angle Degrees Calculations.
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These notes describe an ideal stairway slope or angle and in a table we give the stairway as well as access ramp "steepness" expressed as stair or ramp angle, slope, and as typical step riser height and tread depth dimensions.
By "ideal stairway" we mean a stair that complies with building codes and recommended stair construction standards and that produce a stair that is comfortable to climb or descend.
We also refer readers to a companion article on designing comfortable stairways for people of limited mobility or seniors.
At STAIRWAY SLOPE or ANGLE & STAIR TREAD SLOPE we describe the maximum as well as recommended stairway angles or slopes and we explain how individual step dimensions (step rise and step tread depth or "horizontal run") translate into stairway angle.
Illustration: adapted from California Title 8, Ch. 7, §3231. Stairways [PDF] Fig. E, Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code; and Section 18943(c), Health and Safety Code. Retrieved 2018/07/04, original source: https://www.dir.ca.gov/title8/3231.html
[Click to enlarge any image]
Stair Building Rules of Thumb
Our photo below illustrates stair step tread run or depth and stair step rise or riser height; this particular stair is not a good one, sporting uneven riser heights and too-small tread run depth.
Ideal Stair Rule of Thumb
Perfect stair (for most users): Rise = 7", Run = 11"
The sum of one stair or step tread or "run" and one step height or "riser" should always be about 17" or 18" in total
As the step rise gets shorter
the step run must get longer
Stair Tread Rules of Thumb
The sum of two treads plus one riser
should add up to around 28" or 29"
Stair step or tread "depth" or run -
the horizontal walking surface of an individual step. It should be no less than 10". (IRC)
or
>= 8 1/4" to 9" in some codes or circumstances.
Stair tread nosing:
required, 1" to 1 1/2" projection beyond the riser face
Stair tread thickness: 1" or greater;
tread is supported by the riser.
Stair Riser Rules of Thumb
Maximum stair step riser height -
not more than 7.75" or in some codes <= 7.0" or in Canada <=8.25"
Minimum stair step riser height: -
not less than 4"
Step riser height uniformity -
no more than 3/8" variation between successive step surfaces, or in some codes <= 3/16" / 4.8 mm.
And because the combination of stair riser height and stair tread depth or run determines the overall slope of the stairway, here we include:
Stairway slope: 7" of rise over 11" of horizontal travel, or a slope of 7/11 (personal preference)
Stairway slope or angle of about 37° which equals approximately a 75% slope
The stairway angle or slope should be between 30° and 50°, ideally around 37°
I prefer a 33° stair that is approximately a 66% slope as is given by a 7/11 step rise/run ratio.
Step riser slope out of vertical: <= 30 deg measured from horizontal surface of the tread
Stair Handrails & Guardrails Rules of Thumb
Stair handrail required:
3 risers or more; 36" or more in some jurisdictions.
Stairway handrailings should be continuous,
graspable, and enclosed at ends
Stair center handrail required:
no more than 36" horizontal distance to a handrail on any stairway
Stair guardrail required:
3 risers or more; 36" or more in some jurisdictions.
Stair guard baluster spacing:
4" for solid balusters. 3 1/4" spacing between horizontal cables used in stair guards (3" in some sources)
Stair Landing Platform Rules of Thumb
Minimum recommended stair landing length:
36" in the direction of travel
Minimum stair landing width:
of the entry or width sufficiently greater than the swing of the door if a wider or slider door is present
Door shall not swing out over a stairway;
a platform or landing is required at same level as the adjacent walking surface
Stair lighting
Lighting is required over stairs
and shall have controls operable from top and bottom of stairway
Articles Detailing Each of these Stair Construction Rules of Thumb
Find the Total Rise, Run, & Slope of an Ideal Stairway
Using the numbers suggested above in the green range of the chart of dimensions for stairs, and looking at the slope or angle of a stairway represented by a single step (rise & run) we have the following:
Step Rise in inches = 7"
Step Run in inches = 11"
7" / 11" = 0.64 or about a 64% grade or percent slope
Let's convert % grade to angle:
To convert a % grade to slope we convert the percent slope to a decimal by dividing by 100, then find the inverse tangent of that value to convert to degrees. The inverse tangent is also called arctan or Arc Tan.
We had 7" / 11" = 0.64 or about a 64% grade or slope
64% grade / 100 = 0.64
Using any online or textbook trigonometry tables we look up the arctan value of 0.64 (as that's easier than re-learning the trigonometry to calculate it).
Arctan (0.64) = 32.6 deg stair angle, or about 33 degree angle or slope for our ideal stair
Watch out: for seniors or others of limited mobility, other stair dimensions are ideal.
Again using Mrs. Revere's elementary school algebra instructions, we can re-write the formula as
7" Riser Height = 0.7535 x Tread-Depth-Y
Tread-Depth-Y = 7" Riser Height / 0.7535
Common Ramp, Stair & Ladder Angle, Slope, Rise / Run Dimensions
Angle in Degrees°
Slope %
Example Rise / Run
Ramp Slope
0 - flat
0
0 / 12
7°
12%
1.44 / 12
18°
32%
3.84 / 12
Stairway Slope
30°
58%
6.4 / 11
32.6°
64%
6.4 / 10 or 7 / 11
37°
75%
6.75 / 9 or 7.5 / 10
45°
100%
7 / 7 or 7.5 / 7.5
50°
102%
7.14 / 7
Fixed Ladder
50°
102%
75°
373%
Runged Ladder
75°
373%
90°
N/A
Notes to the table above
OPINION: among common stair dimensions, angles, or slopes, we prefer the 32.6° angle or 64% rise stairway built using stair treads that are 11" deep and stair risers of 7" in height.
Going to a lower rise can also work as you'll see in the table above, but at stair steps with higher rise, to keep the stairway within acceptable overall angle the tread depths become more shallow, making the stairs more-difficult to use.
ROOF SLOPE CALCULATIONS explanation of the mathematics of calculating stair or roof slope, angle, pitch, rise, run, etc. as well as examples of using trigonometric functions such as tangent
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In addition to any citations in the article above, a full list is available on request.
Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
[7] The Circular Staircase, Mary Roberts Rinehart
[8] Construction Drawings and Details, Rosemary Kilmer
[9] Falls and Related Injuries: Slips, Trips, Missteps, and Their Consequences, Lawyers & Judges Publishing, (June 2002), ISBN-10: 0913875430 ISBN-13: 978-0913875438 "Falls in the home and public places are the second leading cause of unintentional injury deaths in the United States, but are overlooked in most literature. This book is unique in that it is entirely devoted to falls. Of use to primary care physicians, nurses, insurance adjusters, architects, writers of building codes, attorneys, or anyone who cares for the elderly, this book will tell you how, why, and when people will likely fall, what most likely will be injured, and how such injuries come about. "
[27] "The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
[28] Stair & Walkway Standards for Slipperiness or Coefficient of Friction (COF) or Static Coefficient of Friction (SCOF)
ANSI A1264.2
ANSI B101
ASTM D-21, and ASTM D2047
UL-410 (similar to ASTM D-21)
NSFI 101-B (National Floor Safety Institute)
NSFI Walkway Auditing Guideline (WAG) Ref. 101-A& 101-B (may appear as ANSI B101.0) sets rules for measuring walkway slip resist
OSHA - (Dept of Labor CFR 1910.22 does not specify COF and pertains to workplaces) but recognizes the need for a "qualified person" to evaluate walkway slipperiness
ADA (relies on the ANSI and ASTM standards)
[42] Stairways and Ladders, A Guide to OSHA Rules, OSHA, U.S. Department of Labor, 3124-12R 2003 - Web Search 05/28/2010 original source: http://www.osha.gov/Publications/osha3124.pdf. OSHA regulations govern standards in the construction industry and in the workforce Quoting from OSHA whose focus is on workplace safety and so excludes discussion of falls and stair-falls in private homes:
OSHA estimates that there are 24,882 injuries and as many as 36 fatalities per year due to falls from stairways and ladders used in construction. Nearly half of these injuries are serious enough to require time off the job--11,570 lost workday injuries and 13,312 non-lost workday injuries occur annually due to falls from stairways and ladders used in construction. These data demonstrate that work on and around ladders and stairways is hazardous. More importantly, they show that compliance with OSHA's requirements for the safe use of ladders and stairways could have prevented many of these injuries. -osha.gov/doc/outreachtraining/htmlfiles/stairlad.html
[43] International Building Code, Stairway Provisions, Section 1009: Stairways and Handrails, retrieved 8/29/12, original source: http://www.amezz.com/ibc-stairs-code.htm [copy on file as IBC Stairs Code.pdf]
[44] Model Building Code, Chapter 10, Means of Egress, retrieved 8/29/12, original source: http://www2.iccsafe.org/states/newjersey/NJ_Building/PDFs/NJ_Bldg_Chapter10.pdf, [copy on file as NJ_Bldg_Chapter10.pdf] adopted, for example by New Jersey. International Code Council, 500 New Jersey Avenue, NW, 6th Floor, Washington, DC 20001, Tel: 800-786-4452
[45] "Right Triangle Angle And Side Calculator", csgnetwork, retrieved 9/29/12, original source: http://www.csgnetwork.com/righttricalc.html -
Online sine / cosine functions permit calculation of lengths of sides of a triangle.
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.