Questions & answers about stairway dimensions, stair clearances, headroom, codes.

Here we answer frequently-asked questions about the required dimensions and clearances for exterior or interior stairs.

This article series 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.

A Summary of Stairway, Railing & Landing Construction Dimensions, Codes, Standards & Rules

Stairway dimensions & construction requirements & codes questions & answers posted originally at STAIR DIMENSIONS, WIDTH, HEIGHT - be sure to see the specifications and codes provided there.

On 2019-01-22 by (mod) - can the floor opening for circular stair intrude over the treads below?

Steve

The IRC section on stair specifications that you cite does not quite fit a circular stairway, for which there are separate provisions.

You'll see in the most-recent circular stair codes that some want the builder to actually add guards to block access that would permit someone to try to put their foot in the very small inner triangular space on the treads.

About your second question, the final legal authority is your local building code compliance inspector. In my OPINION, I'm not happy about seeing the intrusion of the stair opening cutout into the walking space on the more-important wider section of the triangular stair tread.

Please take a look at CIRCULAR & CURVED STAIRS

and you will also want to see this example code for

SPIRAL CURVED & WINDER STAIR BUILDING CODE [PDF] (Juneau AK)

On 2019-01-22 by Steve C.

We're putting in a winding stairway, and I have two questions about headroom and stairway width per IRC 2015 section 11.7:

(1) "Stairways shall be not less than 36 inches (914 mm) in clear width at all points above the permitted handrail height and below the required headroom height." Does this mean that, if my stair width is 39", then only 36" of it needs to be clear - in other words, on a lower step, the outer 3" of the stairs could be tucked under the floor/ceiling?

(2) "Where the nosings of treads at the side of a flight extend under the edge of a floor opening through which the stair passes, the floor opening shall be allowed to project horizontally into the required headroom not more than 4 3/4 inches (121 mm)."

Does this mean, that, IN ADDITION to the situation in the first question, the floor opening can impinge another 4.75" into the step - meaning that for a 39" stair going under the floor opening only (39 - 3 - 4.75) = 31 1/4" of the step needs to meet the headroom requirement of 6' 8"?

The picture [below] attached shows what we're doing:

Step 7 is exactly 6' 8" below the upper floor level, so the original cut provides the headroom needed over the entire step.

Can we instead cut less by allowing the floor opening to impinge 7 3/4 inches into that step?

On 2018-08-07 by Smash

No gastric upset intended. Thank you very much for the quick reply.

On 2018-08-06 by (mod) -

Not in my opinion but as we repeat ad nauseum, your local building code official is the final legal authority in your country and city.

On 2018-08-06 by Smash

So if the "minimum clear width of the stairway at and below the handrail height" (IRC 2009) with hand rails on both sides needs to be 27", does that mean I could really have treads that were 27" in (unobstructed) width?

On 2018-08-06 by (mod) - minimum recommended stairway width is between 34" and 36"

The minimum recommended stair width is between 34" and 36" depending on codes in the country and city where your stairs are located - measured across the width of the tread, not measured as you describe. Some codes such as CA/OSHA specify a minimum stairway width of 24"

Separately at RAILING CODES & SPECIFICATIONS inspectapedia.com/Stairs/Railing_Codes_Specifications.php
you will find specifications for handrailing dimensions including measurements of how far from the wall or guard the handrail might protrude inwards into the stair space.
See the example sketch below

There you can read that the intrusion of the handrail (and / or the top of a guard that incorporates a handrail along its top) might intrude into the stairway width space from 0" (0mm)
to about 3 1/2" (88.9 MM)

On 2018-08-05 by Patty

What is the minimum width of stairwell at rail height? Inner rail to wall width.

On 2018-04-24 by (mod) - fix stairs that has the first step lower than the rest

By first step "lower" than the rest I think you're saying that the riser height is either much less than or much greater than that of the remaining stairs.

Typically you can repair that trip hazard by making a landing platform that puts the first step at the same riser height.

On 2018-04-19 by Kimmy

How could I fix stairs that has the first step lower than the rest

On 2018-01-22 by Dennis

Installation of last step will be 1/2 inch higher will this be up to code

On 2017-07-15 by (mod) -

Dick

Please take a look at STAIR HEADROOM at https://inspectapedia.com/Stairs/Stair_Headroom.php for details about the overhead clearance distances required over stairs.

However this is for new construction; the UBC doesn't address existing buildings, but rather new construction.

A common model code for existing buildings is the IEBC at https://inspectapedia.com/Design/2009_IEBC_COMPLETE.pdf

Excerpt: [B] 307.3 Stairways. Existing stairways in an existing structure
shall not be required to comply with the requirements of a
new stairway as outlined in Section 1009 of the International
Building Code where the existing space and construction will
not allow a reduction in pitch or slope

However this code does permit a building inspector to define an unsafe condition and require its remedy.

On 2017-07-15 by Dick

I have an existing stair to the basement that has 5 foot overhead clearance how much clearance does the UBC require?

On 2017-05-30 by Brandon - stairway built too narrow

I have an existing stair to my basement that is 34" wide. I am planning a second floor addition and the only place to fit a stair is stacked over the existing. This would place a stair in between a load bearing wall and a kitchen wall with cabinets and appliances installed.

I could achieve the 36" width requirement if I used 3/8" Sheetrock and removed 1 1/4" from the studs on the kitchen wall. Is that option something a local building inspector would find acceptable or would I have to file for a variance?

On 2017-05-19 by (mod) -

Melissa

Please see ATTIC STAIRS at https://inspectapedia.com/Stairs/Attic_Stair_Specifications.php and then let me know if any questions remain and I'll be glad to researh further details.

On 2017-05-18 2 by Melissa

How wide are stairs required to be if they are in a garage and just access to storage area not living area?

On 2017-05-03 by (mod) -

Anon: I'm not clear on "roof height"

If you mean that the stairs have to ascend a total height or rise of 11ft 5in or 11 1/2 feet, if you figure a typical individual step height of around 7" (much taller is unsafe), then divide 7" into the total inches of rise - or 138". 138/7 = 19.7 - that says I need about 20 steps to get up there.

Now if my typical step tread depth is 10" (a very bare minimum) then I need 200 inches of horizontal run for the stairs.

200 / 12" per foot = 16.6 feet of horizontal run. So you can't squeeze 16.6 feet of horizontal travel (as you climb up the 11.5 feet of total rise) into 12 feet as a straight run.

You might be able to build a stair with a landing or turn, however.

On 2017-05-03 by Anonymous

I have to construct a concrete stair of length 12feet bredth 6.5 feet and roof height 11.5. Is,it possible to construct u shaped stair

On 2017-04-30 by Anonymous

What is the minimum stair width as per AISC and osha why?

On 2017-04-24 by (mod) -

Mike,

That is not a dimension with which I am familiar. Perhaps you could use the page top or bottom contact link to send me a sketch or photos so that I could understand the question better.

On 2017-04-23 by Mike

What is allowable distance from balusters to the end of return nosing on the open stringer stairs?

On 2017-04-15 by (mod) -

Thanks for the comment, Larry.

I'd worry that an added-on stair tread nose may create an unsafe walking edge - breaking away - unless it's rabbeted or otherwise very securely connected to the tread. Lots of work. I'd be tempted to just replace the treads.

On 2017-04-15 by larry lemire

tried to correct a set old of stairs adding another 1 ' to tread nosing on dont do this its thes same thing

On 2017-04-15 by (mod) re: adding a nose to existing stair treads?

Thanks for the comment, Larry.

I'd worry that an added-on stair tread nose may create an unsafe walking edge - breaking away - unless it's rabbeted or otherwise very securely connected to the tread. Lots of work. I'd be tempted to just replace the treads.

On 2017-04-15 by larry lemire

tried to correct a set old of stairs adding another 1 ' to tread nosing on dont do this its thes same thing

On 2017-04-10 by (mod) re: list all of the ways that stairs must comply with laws?

You might want to check the ARTICLE INDEX for stairs given at the end of this article. There you'll find a very extensive list of stair specifications as well as citations from multiple stair building codes.

You need to determine the type of stairs you are building and then to review the building code specifications.

On 2017-04-10 by atumanyire bylon

cant you list for me the conditions to be considered when constructing stairs so as to comply with the by law?

On 2017-04-10 by Anonymous

can't you list for me the conditions to be considered when constructing stairs so as to comply with the by law?

On 2017-02-25 by (mod) re: Can I build a new 29" wide stairway

The stair has to fit in the available space but also needs to have safe width and tread dimensions, headroom, etc. Often a turn in the stairway can solve some of the fit problems;

On 2017-02-23 by Jake

Hello, I have a question. I live in Michigan, my house was built in 1976, the basement stairway is in bad shape and I need to replace it. However, due to space constraints I need to build a 32" wide stairway (29" with tread, 10" deep) is this possible, acceptable, or allowable? Your input will be really appreciate it. Thanks

On 2017-02-16 by Gerry

Thank you that's what I was thinking

On 2017-02-14 by (mod) re: moving a basement door onto steps - angling steps for a turn

Sorry Gerry- so many readers that sometimes we get behind in replying to comments.
I'm not sure what specifics I can add as you already understand the math.

You cannot force both rise and run if they do not accomodate a step riser height and tread depth that is safe to walk upon. Typically that's a 10-11" deep tread and a rise around 7".

I would calculate the number of steps (42/7=6) and the run (6 x 10 = 60) to show that you cannot fit a run that's half that length.

Sometimes, if there is headroom over the landing, you can build stairs with a turn, as you suggest, but I'd prefer to see rectangular steps and a square landing - far less trip prone.

On 2017-02-08 by Gerry

I moved a basement door on steps that weren't done properly to begin with.

The rise is 42 inches run is 30 inches at the top step door is on the left so will need angled steps for the turn. how many steps do I need. I'm pretty sure I can figure the math out and angles that will work after that, but any additional help would be appreciated. Thank you in advance

On 2017-01-26 by (mod) re: will the stairway width be considered too small when I add handrailings?

Sorry but I don't quite understand the question. I don't know what slipping the distance means.

But at the end of the day the answer to this question lies with your local building department.

You might want to ask them to take a look at the hallway and the stairs and to tell you what they will accept.

Often a local building department is not going to require extreme modifications to a building and they may give you a grandfather clause that allows your Stairway to be more narrow than the modern standards.

On 2017-01-26 by Mike

I am replacing my narrow interior steps in my old house built in the 1920s if i i follow the minimum required code of 36" wide on the steps my hallway will become to narrow at 32"wide. am i allowed to slip the width right down the middle so my steps and hallway width are equal?

On 2016-08-07 by (mod) re: central handrail on wide stairs

Yes Donald in that wider stairways, depending on where you live and what building codes apply, may require handrails on both sides of the stairway. And of course all open stairs need guards on both sides.

There are not standards or codes that support the complete omission of handrailings on ordinary-use stairways.

On 2016-08-06 by Donald Groden

Is there a code requirement for the insulation of handrails to be determined by the with of the stairs ?

Question: elevated salon chair steps

(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

Reply:

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.

Question: how to build stairs using concrete blocks

(July 17, 2014) Alan James said:
i want to build stairs using 16 inch X 4 " X 8" concrete blocks. The run is 416 inches and the rise is 259 inches. By using the formula i get a 8.9 inch rise for each step. Is this legal and if not how do I make the stairs??

Reply:

Alan

8.9 inches is too much rise per step. You'd need to extend the horizontal run and add steps to lower the individual rise or add a platform or landing to achieve the same. I think in general if you are using 4" (thick" blocks you're in trouble if your step plan calls for using pairs of them per step as the steps will be too high.

Question: Do exterior contrete stairs leading to two terraces apartments have to be a certain width?

(Feb 11, 2015) Do exterior contrete stairs leading to two terraces apartments have to be a certain width? One owner wishes to put in chairlift up side of staircase railing. Stairs are 84cm wide. said:
Do exterior contrete stairs leading to two terraces apartments have to be a certain width? One owner wishes to put in chairlift up side of staircase railing. Stairs are 84cm wide.

(Nov 3, 2014) carmel fennessy said:
oueurn but not a spiral thank youstion can i fit a 32 inch wide staircase into a space 60x60x96 with a platforn and t

Reply: 36" starway width standard

Do:

Stairway width (in the U.S. - you don't say where you are located) should be equal to or greater than 36" of clear unobstructed distance measured at all points above the [permitted] hand-railing height.

84cm stair width, assuming that's the unobstructed width, is 33" or already less than the 36" recommended.

For an example building code pertaining to chair lifts and wheelchair lifts I look at ASME A18.1- 2003, Safety Standard for Platform and Stairway Chairlifts

Also see

California's Subchapter 6. Elevator Safety Orders
Group 2. Existing Elevator Installations, Article 15. (a) Inclined stairway chairlifts shall comply with ASME A17.1-1993, Section 2002, Inclined Stairway Chairlifts, which is hereby incorporated by reference, except Rule 2002.10a and Rule 2002.10c(2).
NOTE: The installation of all inclined stairway chairlifts are subject to local building codes, fire regulations, and contractors licensure.
(Title 24, Part 7, Section 7-3094.4)

NOTE: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code; and Section 18943(b), Health and Safety Code.

In my OPINION the standards and model codes give some leeway to the LOCAL building code official (who's final word is law) to accept a narrowing of the stairway to provide for the inclined stairway lift installation, provided that means of egress for walking residents is not unduly hampered.

From the ASME standard I excerpt: "Lifts shall be installed so that means of egress is maintained as required by the authority having jurisdiction. "

Different rules may pertain for private residences than public buildings.

Question: inadequate headroom at apartment building stairs

(Apr 9, 2015) Concerned said:

My apartment building has decided to bump out a unit that is above a set of stairs. After they added the new wall and floor, my friend who is 6''1' tall now has to bend his neck or back to get down the stairs so he does not hit his head.

There is also no visible permit for this addition and I am not sure if anyone even came to my apartment building to tell the landlord that this is okay.

Surely my friend is not the only tall one, and what if there is an emergency and he forgets to bend over and he winds up smacking his head on this new "wall" and hurts himself? Though it is a smaller stairwell, it is the one that is used most.

What do I do about all of this and who do I talk to? I feel that this is unsafe construction just to add a little more room to an apartment that may not be necessary but simply wanted by the landlord.

In addition, if someone does hit their head going up or down the stairs and falls to the point of injury, are the building owners at fault?

Reply:

Concerned,

Certainly there are building codes and standards for safe passage on stairways, including headroom (See STAIR HEADROOM in More Reading just above).

It sounds as if modifications to the building or stairway were made without proper inspections & permits and that they are likely to be improper and unsafe. If your building management is not responding to your written concern your next recourse is to ask your local building department for help.

Question: can stair width change ? San Francisco Stair Code.

(Apr 15, 2015) Narrow Stair said:
Greetings -
I understand the minimum stair width in my area (San Francisco) is 36". Can I have the upper run of an L-shaped stair be wider, say 42", and have the lower run narrow down to the code minimum 36"? In other words, the stair gets narrower in the direction of egress, but not below code minimum.

Reply:

Narrow

What an interesting question. I don't know. This funneling-stair-design is not a design I've come across previously.

It is possible that your local building department would approve your stair funnel in a private residence, but in my OPINION it would be unsafe in a public building where during an emergency a crush might develop at the reduction in width.

Let me know what your local code official says.

Question: 8 1/2" tread depth stairs are too small

(Dec 3, 2015) Dan said:
I live in a apartment hous. It has 18 stairs to my upper room. They measure 8.5 inches per board. I wear a size 12 shoe and wondering if they are legal. I know there dangeros.

Reply:

Dan in the article STAIR DIMENSIONS, WIDTH, HEIGHT you'll see two live links you want to click on to read details

Watch out: it's confusing but many people refer to stair tread depth
see STAIR TREAD DIMENSIONS
and
also STAIR RISER SPECIFICATIONS ) as stair step or tread width, including our Canadiain stair dimension illustration just below.

Question: allowable variation in stair height

(Jan 22, 2016) Julio said:
are Stairs that are 1/4 or 1/2 shorter in height acceptable, if so what literature can I use

Reply:

Julio

Depending on where you live stair codes may vary but typically you are allowed up to 3/8" variation in riser height, or quoting:

Step riser height uniformity (<= 3/8" variation)

so 1/2" is a trip hazard. you can print this page or you better you can check with your local building department to obtain a copy of the code that applies where you live. >

Question: stair width vs building occupancy

(Feb 26, 2016) Anonymous said:
how wide does a stair needs to be if occupancy is greater than 50

Reply:

I don't know and don't have that specific reference; check with your local building department. let me know what you're told.

Question: steps to climb an 11" total rise

(Apr 12, 2016) Jerry said:
I have an 11 inch drop from a side exterior door of my house. Should I build a single concrete step: a) 7 inches height, b) 4 inches height, or c) something in-between?

Reply:

Jerry,

One 11 inch step, we both agree is too tall.

But two steps of different rise are also unsafe - a trip hazard.

All of your riser heights should be the same. To me that suggests two risers of 5 1/2" - with an increased tread depth, since short riser stairs are more comfortable and safe to walk up and down if the treads give more walking space.

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

...

Continue reading at STAIR DIMENSIONS, WIDTH, HEIGHT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• STAIR HEADROOM
• STAIR CODES & STANDARDS

Suggested citation for this web page

STAIR DIMENSIONS & SPECIFICATIONS FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to STAIRS RAILINGS LANDINGS RAMPS

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