Exterior Exit Stair Door Capacity Sizing

[KRS5]

I have a 4 story exterior egress stair. Do I need to size the exterior egress door(s) at the lowest level to accommodate the cumulative occupant loads from each floor? There are over 400 cumulative occupants coming down the stairs. I want to know if i need a single or pair of 36" doors at the exterior.

 

[classicT]

1005.6 Egress Convergence
Where the means of egress from stories above and below converge at an intermediate level, the capacity of the means of egress from the point of convergence shall be not less than the largest minimum width or the sum of the required capacities for the stairways or ramps serving the two adjacent stories, whichever is larger.

 

[Paul Sweet]

IBC 1005.3.1 says "Where stairways serve more than one story, only the occupant load of each story considered individually shall be used in calculating the required capacity of the stairways serving that story."

The only time you add them is when one stairway is coming from above and the the other from below.

 

[KRS5]

IBC 1005.3.1 says "Where stairways serve more than one story, only the occupant load of each story considered individually shall be used in calculating the required capacity of the stairways serving that story."

The only time you add them is when one stairway is coming from above and the the other from below.

So this would also apply to the capacity of the doors? I saw the section you cite but it doesn't specifically mention the capacity of doors serving the stairs.

 

[classicT]

What type of stairs are you dealing with? Exit access or interior/exterior exit stairway?

If an exit access, then you need to combine the OL to size the door.

 

[KRS5]

What type of stairs are you dealing with? Exit access or interior/exterior exit stairway?

If an exit access, then you need to combine the OL to size the door.

It is 2 hour exterior exit stair. Is there a code section that specifically says the occupant load shall be cumulative for sizing the egress door at the exterior exit level? Seems like there should be but I could not find one.

 

[classicT]

It is 2 hour exterior exit stair. Is there a code section that specifically says the occupant load shall be cumulative for sizing the egress door at the exterior exit level? Seems like there should be but I could not find one.

1028.2 Exit Discharge Width or Capacity
The minimum width or required capacity of the exit discharge shall be not less than the minimum width or required capacity of the exits being served.

So the width of the door at the point of exit discharge (door from shaft to exterior path to public way) is not required to be larger than the minimum width of any of the exit doors (doors into the shaft).

Where 1005.6 comes into play is most commonly exit access stairways, or where the exit discharge is at an intermediate floor. The other case that may apply is where you have occupants from the main floor entering the interior/exterior exit stairway from the level of exit discharge and combining with the egressing occupants of the second floor. If this is the case, then the combined occupant load should be used.

 

[KRS5]

1028.2 Exit Discharge Width or Capacity
The minimum width or required capacity of the exit discharge shall be not less than the minimum width or required capacity of the exits being served.

So the width of the door at the point of exit discharge (door from shaft to exterior path to public way) is not required to be larger than the minimum width of any of the exit doors (doors into the shaft).

Where 1005.6 comes into play is most commonly exit access stairways, or where the exit discharge is at an intermediate floor. The other case that may apply is where you have occupants from the main floor entering the interior/exterior exit stairway from the level of exit discharge and combining with the egressing occupants of the second floor. If this is the case, then the combined occupant load should be used.

Ah ha! This makes sense. Thank you.

 

[Paul Sweet]

Stairs are sized for the number of occupants on each floor because the required width is adequate to let everyone from one floor start down the stairs before people from above get to that floor.

The only time you have to add capacities is when stairs from 2 directions (generally above & below) converge. Each converging stair would be sized for the greatest number of occupants on a floor that use that stair (usually the largest floor or the one with the densest occupant load).