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This document provides the stair dimensions required by building code specifications and includes sketches, photographs, and examples of defects used in inspecting indoor or outdoor stairs, railings, landings, treads, and related conditions for safety and proper construction.
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For a complete list of articles on stairs, railings, and ramps, their inspection, trip hazards, and good design,
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.
Stair and Railing Specification Topics for stair (U.S. and International Residential Codes) include the items listed below.
Stair Dimensions for Straight Stairway Runs: Stair width, landing length
Stairwell width and stair landing platform requirements are summarized by these sketches courtesy Carson Dunlop Associates.
The minimum recommended stair width is between 34" and 36" Across the width of the tread. Some codes such as CA/OSHA specify a minimum stairway width of 24" ..
The minimum recommended stair landing length is 36" (or a length and width sufficiently greater than the swing of the door if a wider door is present.
Is a landing required at the top of stairs?
Ordinarily, yes, a top landing is required. For example most exterior stairs approaching a building entry door encounter a door or storm/screen door that swings out. We need somewhere to stand when opening the door. But a stair top landing is not required if the the stairs rise to a doorway at which the door opens away from the stairwell.
Of course standing one step "down" from the door opening might place the door knob a bit high for shorter users of the entry.
Exceptions to stair dimension requirements may be made for stairs giving access to non-living areas of a building such as storage lofts and mechanical rooms. Check with your local building officials.
Specifications for Recommended Minimum Stairway Widths & Stair Lengths
Definition of Stairway Width or Stair Width - don't confuse stair width with stair depth
Watch out: it's confusing but many people refer to stair tread depth
If you stick to using the word stair tread depth you can avoid this confusion. Oops, that is, unless you start confusing tread depth with stair tread riser height. Stair tread depth is defined above as the horizontal distance from nose to nose or from riser face to nose on open riser stairs.
Stairway width is the horizontal width of the stair opening (blue arrow in our photo). For stairs enclosed by a wall on both sides, usually the stairway width is the distance between those walls.
Stair tread width (green arrow in our photo) is the horizontal left to right width of the stair tread.
At left our photo illustrates three different stair width measurements
Recommended Stairway Width
Stairwell width and stair landing platform requirements are summarized by the sketch above. The measurement locations for determining a stairway width are illustrated in our photo at left, courtesy Galow Homes. In the stairway shown, the owners opted for a 36" wide stairwell.
The minimum recommended stair width is between 34" and 36" across.
Handrailings reduce the nominal stairwell width
In these sketches and in our photographs used here, the required handrails have been omitted for clarity.
Handrailings will protrude into and may reduce the nominal the stairwell width.
For a 36" wide stairwell such as that shown above, the stair railing intrusion is not a problem, but for more narrow stairs it may be, especially where accessible stairways are required.
Stair Riser Defects
Bad Deck Stair Example: Nothing is right about the exterior stairs shown in our photo from a 1991 home inspection:
Stair tread nose projection and radius: stair treads should have a projecting nose that is rounded and projecting a maximum of 1.5 " over the tread below.
The requirements for a projecting stair nose over the tread below may be amended for open riser stairs in some jurisdictions, but in no case should the front of a stair tread be more than 1.5" back from the inside edge of the tread below - see sketch annotations. [Click any of our images to see an enlarged, detailed version]
Stair tread thickness: The minimum tread thickness for stair treads supported by risers is 1".
Notice that the minimum stair tread thickness is increased to 1.5" when the stair tread is not supported by a solid riser.
Sketch at above left courtesy Carson Dunlop Associates.
See BALUSTERS, STAIR & RAILING for full details of this topic.
For more details about balusters (vertical spindles in railing construction) see details
Example Building Code Specifications For Stairway Dimensions
California and other U.S. states often take as a starting point for state building codes pertaining to stair, landing, railing, tread and other stairway design specifications the national model building codes. The California CA/OSHA Section 1003.3.3 Stairways and Landings provisions, as well as the California Building Code (CBC) illustrate:
CA/OSHA: California Stair & Railing Code details
The following stair dimension example citation is from CA/OSHA Subchapter 4. General Industry Safety Orders, Article 17. Ramps, Runways, Stairwells, and Stairs. Note: this code establishes minimum occupational safety & health standards that apply to all places of employment in California. This is not a residential building code requirement, but this text in our OPINION models stair construction safety & design specifications.
CA/OSHA Section 1626. Stairwells and Stairs.
CA/OSHA Title 8 Section 1626. Stairwells and Stairs  With added stair details quoting from the CBC 1003.3.3
(b) The following requirements apply to all stairways as indicated:
(c) Stair rails and handrails. The following requirements apply to all stairways as indicated:
Some codes (CA/OSHA Title 8 Section 1626) may cause a little confusion between the definition of handrail and guardrail, by adding a third term, "stair rail":
See HANDRAILS & HANDRAILINGS for handrail and stair rail code & construction details
At least in the 2006 IRC Section R202 these terms are defined clearly:
Definition of "stair rail" as guardrail: In general people speak of guardrails or guards as installed along balconies or elevated walkways and decks. When we enclose open side(s) of a stairway with a "guardrail" some codes such as the 2006 IRC Section R202 use the unfortunate term "stair rail". More unfortunate if readers don't continue along to discover that the horizontal members described in ((B) above must be further enclosed with balusters.
Definition of handrail or hand railing: Handrail [or hand railing] . A horizontal or sloping rail intended for grasping by the hand for guidance or support.
See HANDRAILS & HANDRAILINGS for details about stairway handrailing dimensions, graspability, railing heights, railing continuity, termination, projection distances and all other parameters.
(d) Temporary Service [stairs] - Temporary service stairs, treads, landings:
The following requirements apply to all stairways as indicated:
Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.
Continue reading at STAIR HEADROOM or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Frequently Asked Questions (FAQs)
Question: (Dec 28, 2011) Richard said:
I want to build a box on the floor of my hair salon to elevate a chair which will be put on top the box. The box will be about 42" x 64". I want to make it about 8" higher than the floor. It will be in a traffic area. I have tried to research the New York State building codes on line but can find no reference to start. Is it a step? or stair? or landing? or platform? or uneven floor? Its just a box on the floor but it must have a name in the codes. Will it need railing? or noseing or edging? or a distinctive something so people dont fall (trip) over it? Any advice and direction to code #'s will be appreciated. Thank you very much
Richard that's a new one for me, and I have not found a code citation for elevated salon chairs. Because the local building code inspector has the final authority, I'd give them a call and ask for advice. I've found that the folks in the building department are very helpful when they see that someone wants to do right rather than trying to get over on the inspector.
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