IBC 2012 Egress Questions

[Engineer22]

Hey all,

Working on a project, and I have two basic IBC 2012 questions:

1) Minimum # of stairs needed for a 12' ceiling height?

2) Given project occupant load of 300, how many 36" wide doors are needed?
[2 doors? 300 x .2 = 60" --> therefore 2 doors needed to satisfy this requirement?]

Thanks for any guidance!

 

[RLGA]

1) Minimum # of stairs needed for a 12' ceiling height?

Not sure I understand the question. Two stairways are required unless a single means of egress is permitted from an upper story. If you're talking about the number of risers needed from floor to floor, then it depends. Risers are permitted to be 4 to 7 inches in height. If you want to minimize the number, start with 7 inches and divide the floor-to-floor height by 7 inches. This will give you the number of risers. If the division creates a fraction, then round up the number of risers and divide the floor-to-floor height by the revised number of risers to get the actual riser height.

2) Given project occupant load of 300, how many 36" wide doors are needed?
[2 doors? 300 x .2 = 60" --> therefore 2 doors needed to satisfy this requirement?]

Yes. A 36-inch door actually provides about 33 inches of egress width when measured between the stop and the face of the door in a 90-degree open position. Therefore, you will have 66 inches of egress width, which exceeds the 60 inches required.

 

[Engineer22]

Thank you!

Regarding the number of stairs needed for a 12' ceiling height:

I meant the minimum number of risers*

a) I assume 120" at 6" is the minimum, as it will give me 24 risers. Is this the answer?

Dividing 120" by 7" will give me an odd number.

 

[RLGA]

Actually, it is 144 inches (12 inches per foot at 12 feet = 144 inches), and, yes, it will be 24 risers using 6-inch risers.

 

[cda]

Welcome

 

[cda]

Have not heard someone calculate number of stairs.

So where do the landings calculate in??

 

[mark handler]

?
... number of stairs needed for a 12' ceiling height:

You do not design stairs to a ceiling height you design to the floor to floor height.

 

[fatboy]

And the result does not have to be a whole number....................

Assuming 144" finished floor to finished floor, you could go with 21 rises, at 6.875" (6 -7/8")=144.375, which you could lose the excess 3/8 total over the run of the stairs and easily still be compliant.

 

[steveray]

Just don't miss on the 144" as that is the max and if you miss you add a landing and would have to significantly redesign...

 

[rogerpa]

Just don't miss on the 144" as that is the max and if you miss you add a landing and would have to significantly redesign...

This has changed in 2015.
R311.7.3 Vertical rise.
A flight of stairs shall not have a vertical rise larger than 147 inches (3734 mm) between floor levels or landings.

 

[RLGA]

This has changed in 2015.
R311.7.3 Vertical rise.
A flight of stairs shall not have a vertical rise larger than 147 inches (3734 mm) between floor levels or landings.

That's true for the IRC, but for the IBC it is still 12 feet.

 

[PJC89]

Every occupant on every story must have access to minimum of two exits (i.e., exit stairway, horizontal exit, exterior exit door). When the occupant load exceeds 500 persons access to three exits must be provided. When the occupant load exceeds 1,000 persons access to four exits must be provided.

Each of the exit stairways must be sized to handle the occupant load it serves based on 0.3 inches/person but no less than 44 inches based on your situation. The exit door to the stairway must also be sized to handle the occupant load at 0.2 inches/person but not less than 34 inches clear width.

Refer to Chapter 10 (number of exits and egress width) https://up.codes/viewer/general/int_building_code_2012/chapter/10/means-of-egress#10