Commercial Stair Design – Guidelines, Criteria and Dimensions

After seeing the popularity of my post on Residential Stair Design, I thought it made sense to explain the guidelines from the 2006 International Building Code for commercial buildings and common stairs in buildings with more than two dwelling units. It is much more complex and there are some exceptions if you need them so please contact me if you need help. These are the general rules.

Stairways have to be at least 44″ if you have an occupant load over 50 (and may be more if your occupant load is large). If under 50 occupants you can go to 36″ width. There are other exceptions for spiral stairs, aisle stairs and incline stairs but these types will have to be covered in a later post.

You need at least 80″ of head height measured off the tread nosings and it needs to be maintained for one additional riser depth at the bottom of the stairs.

The riser height must be between 4″ and 7″ and the treads must be at least 11″ deep.

If you have winders they need to be at least 11″ deep when you’re 12″ in from the narrow edge and the minimum depth must be 10″. You can’t use winders in required stairways unless they are within a dwelling unit.

The landings must be at least as deep as the stairs are wide (up to 4′-0″) and you can’t go up more than 12′-0″ vertically without a landing. Where a door opens into the landing it can’t project more than 7″ into the required depth of the landing.

Handrails must be mounted between 34″ and 38″ above the tread nosings and landings. Where they are circular they need to be 1.25″ to 2″ in diameter. If the handrail isn’t circular it needs to have a perimeter between 4″ and 6.25″ with a maximum cross section of 2.25″. The handrail needs to be mounted a minimum of 1.5″ off the wall.

Handrails in IBC buildings need to return to a wall, a guard or the walking surface or continue to another handrail. The IBC requires that your handrail extend 12″ past the top riser and one tread depth past the bottom riser. It important to note that the ADA will require you to go one tread depth plus 12″ past the bottom riser so it generally overrides the IBC.

Your handrails need to be on both sides of the stair and can’t project more than 4.5″ into the stair width on each side. On a very wide stair you need to space intermediate handrails no more than 60″ apart.

Most commercial buildings will also require the ramp design guidelines.

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44 thoughts on “Commercial Stair Design – Guidelines, Criteria and Dimensions”

  1. Sean O'Hara

    John, my assumption is that you mean the stairwell is wide and you are wondering if it should have a center handrail? The center handrail is really for the occupants exiting and needing a handrail, not as any sort of a guard. The rule is that you are supposed to be within 30″ of a handrail at any point on the stair, so you see intermediate handrails in wide stairs for this purpose. But, this rule includes a phrase that states that its only for the required width. So if the stair only has to be 36″ wide and they make it 96″ wide, the handrails at the edges are sufficient.

    Its also worth noting that generally if a building was built to code at the time and hasn’t been substantially modified its unlikely that they would be required to make modifications.

  2. Avatar
    John Baranick

    I have a question about stairway width/safety precautions. In a clinic in town, the building is one of those 60’s flat open Frank Lloyd Wright styles with wide, open stairwells. They have bannisters and all, but they are probably 6 to 8 feet wide. There was almost an incident where someone in a motorized wheelchair was backing up to turn around and almost went over the stairs backwards. Are there some sort of safety pillars or something that would restrict the opening size of the stairs to the legal minimum (or small enough to keep the above from recurring)? If so, what are the rules, etc?

  3. Sean O'Hara

    That depends on the number of occupants and is a bit complex. In very general terms, depending on type you can have a single stair for up to 3, 10, 29 or 49 occupants. Beyond that you need two stairs and above 500 occupants you need 3 with another one for every 500. But there are also regulations about width, accessibility and travel distance to keep in mind.

    This is definitely the realm of a competent architect. Please let us know if you need further assistance.

  4. Avatar

    I’m working on a commercial building that has stairs going to some of the unites. We are also ADA compliant with ramps , access , and stairs for access to most unites. My question is do I need to put a contrasting stripe at the bottom and the top of these stairs ? They are existing.

  5. Avatar

    I’m working on a decorative stairs to connect three floors of an office building. There are already several set of fire stairs in the building which provide adequate egress. This stair will be purely an aesthetic feature and for convenience of the staff and visitors.

    We would like to do something striking and beautiful with a winding stairs but I am confused about the requirement in 1009.11 that says the smallest radius must be twice the minimum width. I believe my minimum width is 44″, making the smallest radius 88″. I could have 11″ of run at the walk line if my minimum radius is about 4’3″. Blowing up the scale of this to 88″ as the smallest radius makes the design totally unworkable.

    What am I missing?

    Thanks!

  6. Avatar

    I was looking for the dimensions of the support post largely used in apartment staircases, (minimum/maximum) code,and common. Im right at 4″ mid-guage steel round tube?

  7. Avatar

    Are there any requirements for how stairs are marked inside public arenas? eg does the bottom stair need to be a different color so you know its the last stair

  8. Avatar
    kirk halvorsen

    in comercial does the handrail have to project past the last tread or can it be returned straight down to the top of the stringer ?

  9. Avatar

    Are there tolerances for levelness of a tread in a commercial building ?
    If so , can you tell me where I can find this code requirement?

  10. Sean O'Hara

    Yes, you’re right on their Brooke, good to hear from you. As you can imagine, with these older articles and ever changing codes, its important for people to make sure they consult with an architect to verify that they have the latest information.

  11. Avatar
    Brooke Schubert, AIA

    Hi Sean,
    Just wanted to note that the 2010 ADA Guidelines (effective March 2012) do NOT require the handrail to extend 12″ + one tread depth past the bottom riser. It aligns with the IBC by requiring the handrail to extend only one tread depth at the bottom of the stair.

  12. Sean O'Hara

    Two pipe railings are only acceptable in certain occupancies with low numbers of occupants, generally you need the 4″ spacing where you are over 30″ high.

  13. Avatar

    Sean:

    Thanks for the info. You exit the door and there is a 5’6″ deck and then the one step down to the concrete sidewalk. The deck sits 12″ above the walk on one side and about 13″ above the walk on the other (48″ wide) point.

  14. Sean O'Hara

    Bill, with a strict reading of the code, the 44″ should be a clear width, so the carpet made it too narrow. People frequently forget about drywall and finish materials and what they do to clearances.

  15. Sean O'Hara

    Richard, generally speaking 1/4″ per foot is acceptable as a slope on a landing. Is the step within the clearances at the door or along the accessible path? If so, the step won’t work. Thanks, Sean

  16. Avatar

    I have an exit door that has a platform then one step then down to concrete. The concrete is 48″ wide and slopes 1″accross the face of the platform – so if you are at the bottom of the stairs the left site (0″) mark is 1″ higher than at the right side (48″) mark. is this permissable for a commercial application or does that pad have to be perfectly level.

  17. Avatar

    I have a building with a stairway width of 44 inches. Carpet was added to the stringers effectively reducing the width to 43.5 inches. Would this be an acceptable condition with an occupant load of over 50?

  18. Avatar

    gaurdrails on a combination stair and ramp system each opposing the other. does the 4 inch spacing upply at 42 inch high. or is a two pipe horizontal railing ok?

  19. Avatar

    Does the tread depth measurement include the nose or not? OSHA measures the tread as riser-to-riser, so it does not include the nose. Does IBC measure it the same way?

  20. Avatar

    Typical commercial exit stairs switch back within the confines of a shaft. Is a guardrail required per IBC 2006 in the center between the two flights at 42″ high, as well as handrails at 34″ high?

  21. Avatar

    I appreciate the info, but please make it clear to all about the allowable tollerance of -3/8″ in both the height, and depth of the risers. I was sued for an injury, and lost because the lower step of a 2 step stair was 3/4″ shorter than top step.

  22. Sean O'Hara

    Gary, I see you’re in the UK and honestly I’m not sure. With temporary structures in the states we often end up looking at OSHA rather than the building code. Basically a code dedicated to worker safety. I would have you talk to your local building department.

  23. Avatar

    I am looking for information on any design criteria for stairs to temporary accommodation units i.e. landing widths etc. I understand we are exempt from building regulations but there must be some standards which need to be complied with?

  24. Sean O'Hara

    No, the requirement is that you have a landing after 12′ of vertical climb. So 14 risers of 7″ height is only 98″. You can go to 20 risers @ 7″.

  25. Avatar

    In a commercial project, do I need to have a landing if I have more than 14 steps? Is this an IBC code? Have you ever heard of this? thank you for any information you have on the subject,
    Jill

  26. Sean O'Hara

    Tom, you can certainly light it from overhead or an adjacent wall. You also have step-light options placing the light only a foot or so above the treads.

    I haven’t heard concerns about exterior metal stairs and lightning but if it is a prominent feature it could happen. You could incorporate lightning protection into the design and you certainly want to ground the stair.

  27. Avatar

    Hi,

    For safety, what is the best way to light an outdoor metal staircase? Also, does one need to worry about the use of an exterior metal staircase during lightning?

    Thank you!!!

  28. Sean O'Hara

    James, assembly occupancies have their own section of the code. It allows steeper stairs, lower guardrails, narrower aisles, center handrails, etc.

    That being said the tread depth is a minimum, it can always be larger. Really that becomes a function of what the comfortable walking pace is. So 15″ or 12″ are both acceptable. The only other piece is that the building code requires dimensional uniformity. So you can’t switch tread to tread, only from one run to another.

  29. Sean O'Hara

    Savas, I’ll assume this is the International Building Code. If so, it doesn’t allow spiral staircases on areas with more than 5 occupants as a means of egress. I think you’ll need to look at turning some of the risers to make the distances work or working through the width with the building department.

  30. Avatar

    In our restaurant we are planning on adding a second floor dinning area which will hold 75+pp they are saying we needs 2 staircases each with a minimum of 4ft in the front that is no problem, but in the rear of building there’s not so much room our property in the back is only 16 ft long so we are thinking would it be possible to put a 4ft wide spiral staircase as our 2nd exit? At this moment we have a 3 ft stair case and we were told that it’s not wide enough that we must have atleaste 2 staircases 4ft wide.

  31. Avatar

    Why do some large sporting arenas have steps that have a 12″ tread depth climbing up concrete bleachers that are 30″ wide and some have steps that have a 15″ tread depth, and which is correct according to building codes or is this simple at the discretion of the architect?

  32. Sean O'Hara

    Where you measure the width is not called out in a really obvious way, but in the handrail section of the 2006 IBC it is under 1012.7. That allows projections of up to 4.5″ at or below the handrail height and also above the headroom requirement. So as long as your stringer is projecting less than the handrail and neither over 4.5″, then you can use the width measured above the handrail height.

  33. Avatar

    Where is the width of the stair measured? – From wall to wall or inside of stringer to inside stringer?

  34. Sean O'Hara

    If it is a required means of egress then you can’t have open risers in a commercial stair. If it isn’t, then you can have open risers but the opening can’t be more than 4″.

  35. Sean O'Hara

    There are quite a number of options for outdoor step materials. Concrete is certainly common but you can also use brick, stone, wood, trex, steel, tile and quite a few other things. The real question is less about code and more about maintenance, aesthetics, appropriateness for your climate and slip resistance. If you have more information about your application and location I’m happy to give you additional input.

  36. Avatar

    Hi,

    I googled and found this informative article: “Commercial Stair Design – Guidelines, Criteria and Dimensions”. Thank you! What kind of material besides concrete is acceptable by code for outdoor stairs?

    Thanks in advance!

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