Stairway Width and 1011.2, Exception 1

[jfbrha]

Hello all-- longtime lurker, first time poster. This place has been a valuable resource over the years and I've come across a topic on a project that I'm not finding too much discussion around here.

I'm currently working on an existing two-story building, B occupancy throughout. The second story has an occupant load of 51 and is served by two exit stairs in a 1hr enclosure. The building is in Seattle which has a unique addition to the existing building code stating "Accessible means of egress required by Chapter 10 of the International Building Code are note required to be provided in existing facilities"

Would exception 1 in section 1011.2 would apply in this instance? Each stair is serving an occupant load of 25 or 26. The exception uses the language "Stairways serving an occupant load of less than 50 shall have a width of not less than 36 inches" which I interpret to mean that the stairways on this project could be 36" but there isn't consensus on the project team about this since the occupant load for the story is more than 50.

So, is the minimum width 36" or 44"? Thanks in advance for any help interpreting the intent of the exception.

 

[Sifu]

Not unique. In the IEBC as well. I take it that where one doesn't exist it might not need to be added. I would not take it as being able to remove an AMOE if one were present. But I think the language of the code being that a stair "serves" the story, and the IBC commentary directs us that the entire occupant load of the story must be 49 or less to use the exception.

2018 IBC commentary:
Exception 1 recognizes that relatively small occupant
loads of less than 50 permit a staggered file of
users where traveling in the same direction. Where
traveling in opposite directions, one column of users
must stop their ascent (or descent) to permit the
opposite column to continue. Again, considering the
relatively small occupant loads, any disruption of
orderly flow will be infrequent and brief. The use of
this exception is limited to buildings where the entire
occupant load of each upper story and/or basement
is less than 50

 

[Yankee Chronicler]

I'm currently working on an existing two-story building, B occupancy throughout. The second story has an occupant load of 51 and is served by two exit stairs in a 1hr enclosure. The building is in Seattle which has a unique addition to the existing building code stating "Accessible means of egress required by Chapter 10 of the International Building Code are note required to be provided in existing facilities"

This is not unique to Seattle.

IEBC 2021:

306.7.2 Accessible means of egress. Accessible means of
egress required by Chapter 10 of the International Building
Code are not required to be added in existing facilities.

Commentary:

This section indicates that accessible means of egress
are not required to be added as a result of undertaking
alterations to existing buildings. Strict compliance with
Section 1009 of the IBC is often technically infeasible.
The requirement for a 48-inch (1219 mm) clear width
between handrails in nonsprinklered buildings would
require many stairways to be widened. This often
would entail movement of major structural elements.
Where the building has accessible means of egress,
those building features would be expected to be maintained
(see Section 306.3).

I do note one discrepancy: Your quotation of the Seattle code says accessible means of egress are not required to be "provided." The ICC language says accessible means of egress are not required to be "added." Without access to documentation supporting the Seattle language, I don't want to specualte on why this discrepancy exists. This provision wasn't in the 2018 IEBC, so most likely Seattle added it after having seen the proposal to add the section to the 2021 IEBC.

Would exception 1 in section 1011.2 would apply in this instance? Each stair is serving an occupant load of 25 or 26. The exception uses the language "Stairways serving an occupant load of less than 50 shall have a width of not less than 36 inches" which I interpret to mean that the stairways on this project could be 36" but there isn't consensus on the project team about this since the occupant load for the story is more than 50.

Both stairs serve an occupant load of 51. The required width is 44 inches -- if new. If the existing stairs are only 36 inches wide, then they can remain at 36 inches wide unless there's a specific provision in the IEBC calling for making them wider. But that's not an accessible means of egress issue, that's a general means of egress issue.

So, is the minimum width 36" or 44"? Thanks in advance for any help interpreting the intent of the exception.

44 inches.

 

[walker.t]

Would exception 1 in section 1011.2 would apply in this instance?…but there isn't consensus on the project team about this since the occupant load for the story is more than 50.

IBC Commentary on 1011.2 Width and Capacity (partial quote)
1. Stairways serving an occupant load of less than 50 shall have a width of not less than 36”.

Commentary: The use of this exception is limited to buildings where the entire occupant load of each upper story and/or basement is less than 50.

This is a case where I disagree with the commentary. The commentary for 1005.3.1 Stairways goes through two examples for determining the width of stairways in a building with two stairways, in both cases they take the total occupant load of the story and multiply it by the width/occupant, then divide the resultant total width by 2 to get the width per stairway. So I don’t understand why for 1011.2 Exception 1 the commentary says the 50-occupant limit uses the entire occupant load of the floor, not just the portion of the occupant load assigned to the stairway.

So, is the minimum width 36" or 44"?

I would have said 36” because I would have used 51 occupants/2 = 25.5 occupants (use 26 occupants) per stair, but that contradicts the commentary on 1011.2 Exception 1.

 

[steveray]

There is an exception for the 48", not sure exactly what you are asking:

1009.3.2​

Stairways shall have a clear width of 48 inches (1219 mm) minimum between handrails.

Exceptions:

1. 1.The clear width of 48 inches (1219 mm) between handrails is not required in buildings equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2.

So......44"

 

[jfbrha]

Thanks for the replies. I was incorrect about the SEBC being unique regarding AMOE. There is no existing AMOE, and the building is sprinklered.

This is a case where I disagree with the commentary. The commentary for 1005.3.1 Stairways goes through two examples for determining the width of stairways in a building with two stairways, in both cases they take the total occupant load of the story and multiply it by the width/occupant, then divide the resultant total width by 2 to get the width per stairway. So I don’t understand why for 1011.2 Exception 1 the commentary says the 50-occupant limit uses the entire occupant load of the floor, not just the portion of the occupant load assigned to the stairway.

This was my thinking as well and my confusion about the commentary on the exception. For my own sake, I need to figure out how to arrive at 44" without the commentary on 1011.2 exception 1...

 

[steveray]

If it helps, the wording should probably be more like "stairways serving a room or space with OL 50 or greater"....Or whatever we use for doors...I think that section is better written...?

1011.2​

The required capacity of stairways shall be determined as specified in Section 1005.1, but the minimum width shall be not less than 44 inches (1118 mm). See Section 1009.3 for accessible means of egress stairways.

Exceptions:

1. 1.Stairways serving an occupant load of less than 50 shall have a width of not less than 36 inches (914 mm).

 

[Paul Sweet]

The code doesn't say "Stairways serving a floor with an occupant load of less than 50 shall have a width of not less than 36 inches (914 mm)."

This issue has gone back and forth for a long time. I think it was the occupant load of the entire floor at one time. The ICC probably didn't get around to updating the Commentary, or maybe they expect it to go back to the entire floor in the future.

 

[Yankee Chronicler]

The code doesn't say "Stairways serving a floor with an occupant load of less than 50 shall have a width of not less than 36 inches (914 mm)."

This issue has gone back and forth for a long time. I think it was the occupant load of the entire floor at one time. The ICC probably didn't get around to updating the Commentary, or maybe they expect it to go back to the entire floor in the future.

From the 2021 IBC Commentary on 1011.2

Exception 1 recognizes that relatively small occupant
loads of less than 50 permit a staggered file of
users where traveling in the same direction. Where
traveling in opposite directions, one column of users
must stop their ascent (or descent) to permit the opposite
column to continue. Again, considering the relatively
small occupant loads, any disruption of orderly
flow will be infrequent and brief. The use of this exception
is limited to buildings where the entire occupant
load of each upper story and/or basement is less than
50.

 

[Paul Sweet]

I read the commentary. It doesn't say what the code says.