How many steps make a flight?

[blugosi]

In a fully sprinklered building with MNS, I have a corridor a 125 cm wide corridor, with three steps in the middle, connecting two levels with a small elevation difference.

I am calculating the capacity at 0.15 inch (3.8 mm) per person.

Do the three steps require adjusting the capacity factor to 0.2 inch (5.1 mm) use for stairways?

If yes, I should replace the steps with a ramp.

Where do we stop counting steps as "means of egress components other than stairways" from IBC ed 2021, 1005.3.2 ?

 

[steveray]

Never…but i never thought about ramps having it easier but i guess i makes a little sense..Dies it need to be accessible? How are you getting out of a ramp in the first place…

 

[walker.t]

with three steps in the middle, connecting two levels with a small elevation difference.

Yes, your three risers are considered a stairway, therefore you must use the capacity factor in 1005.3.1 Stairways.

Definitions from 2021 IBC Chapter 2 (emphasis added):
Flight
A continuous run of rectangular treads, winders or combination thereof from one landing to another.

Stair
A change in elevation, consisting of one or more risers.

Stairway
One or more flights of stair, either exterior or interior, with the necessary landings and platforms connecting them, to form a continuous and uninterrupted passage from one level to another.

ICC commentary on 2021 IBC Chapter 2 definition of “Stair”
All steps, even a single step, are defined as a stair. This makes the stair requirements applicable to all steps unless specifically exempt in the code.

If yes, I should replace the steps with a ramp.

Remember to confirm you have the floor space for the 60” landings at the top and bottom of the ramp.

 

[Yankee Chronicler]

I'm not sure if "three steps" means four treads and three risers, or three treads and two risers. Either way, in my opinion that's a flight of stairs.

IBC 2021 definitions:

[BE] FLIGHT. A continuous run of rectangular treads, winders
or combination thereof from one landing to another.

[BE] STAIR. A change in elevation, consisting of one or more
risers.

IBC Commentary on the definition of "Stair":

All steps, even a single step, are defined as a stair.
This makes the stair requirements applicable to all
steps unless specifically exempt in the code.

 

[bill1952]

I'm not sure if "three steps" means four treads and three risers, or three treads and two risers. Either way, in my opinion that's a flight of stairs.

I'm just curious how you get one more tread than risers. I have always gotten one less, with landings at top and bottom.

I agree a single riser is a stair and two or more are flight.

 

[Yikes]

I agree a single riser is a stair and two or more are flight.

I'm going to push back on that.

1005.3.1 Stairways​

The capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.3 inch (7.6 mm) per occupant. [0.2 inch per occupant for sprinklered per exception#1.]
Notice that for 1005.3.1, it is not about "stairs", it is about "stairways".

What is a "stairway"? From IBC 202:
STAIRWAY. One or more flights of stairs, either exterior or interior, with the necessary landings and platforms connecting them, to form a continuous and uninterrupted passage from one level to another.

What is a "flight"? From IBC 202:
FLIGHT. A continuous run of rectangular treads, winders or combination thereof from one landing to another.
Notice the plural: treads or winders - - it must be more than one. the word "run" also implies a plural.

So if I had a 125 cm bottom landing, a riser, a 27.9 cm tread, another riser, and a 125 cm top landing, that would be a total of two risers and one tread. That would qualify as a "stair", but not as a "flight of stairs" and not as a "stairway". Per 1005.3.1, capacity for only two risers would be calculated at 0.15 inch per person in a sprinklered building (IBC 1005.3.2 exc. #1).

Another scenario for three risers would be to have a 125 cm bottom landing, a riser, a tread, a 125 cm intermediate landing, then one more riser, and a final 125 cm top landing.

 

[bill1952]

I was just using the IBC definitions.

FLIGHT. A continuous run of rectangular treads, winders or combination thereof from one landing to another.

STAIR. A change in elevation, consisting of one or more risers.

STAIRWAY. One or more flights of stairs, either exterior or interior, with the necessary landings and platforms connecting them, to form a continuous and uninterrupted passage from one level to another.

I didn't say a single rise is a "stairway". If your point is a single rise does not require using the 0.3" in calculating the capacity, the code seems to support that. (As a designer I would still use the 0.3, because I know low and single rise stairs are a bigger hazard than a longer run.)

There may be a gap in the code as a result of at least the Life Safety Code and I believe the legacy codes - or at least BOCA - did not permit single rise stairs once upon a time. I need to find the 1985 BCMC report on MOE, which was mostly adopted by all of the codes, and see what it says on single riser stairs.

1011.11 is a requirement for handrails on "stairways" but at least 2 of 5 exceptions regard single risers, which as you point out are not "stairways". Don't have to look very hard to find reasons for this kind of debate.

 

[steveray]

There may be a gap in the code as a result of at least the Life Safety Code and I believe the legacy codes - or at least BOCA - did not permit single rise stairs once upon a time. I need to find the 1985 BCMC report on MOE, which was mostly adopted by all of the codes, and see what it says on single riser stairs.

Probably thinking about this:

1003.5​

Where changes in elevation of less than 12 inches (305 mm) exist in the means of egress, sloped surfaces shall be used. Where the slope is greater than one unit vertical in 20 units horizontal (5-percent slope), ramps complying with Section 1012 shall be used. Where the difference in elevation is 6 inches (152 mm) or less, the ramp shall be equipped with either handrails or floor finish materials that contrast with adjacent floor finish materials.

Exceptions:

1. 1.Steps at exterior doors complying with Section 1010.1.4.
2. 2.A stair with a single riser or with two risers and a tread is permitted at locations not required to be accessible by Chapter 11 where the risers and treads comply with Section 1011.5, the minimum depth of the tread is 13 inches (330 mm) and not less than one handrail complying with Section 1014 is provided within 30 inches (762 mm) of the centerline of the normal path of egress travel on the stair.
3. 3.A step is permitted in aisles serving seating that has a difference in elevation less than 12 inches (305 mm) at locations not required to be accessible by Chapter 11, provided that the risers and treads comply with Section 1030.14 and the aisle is provided with a handrail complying with Section 1030.16.

Throughout a story in a Group I-2 occupancy, any change in elevation in portions of the means of egress that serve nonambulatory persons shall be by means of a ramp or sloped walkway.

 

[bill1952]

Certainly a remnant of what I believe was a code prohibition of single riser stairs at one time.