Sizing exit door at existing unenclosed stairs

[dill bill]

I have a project in a 2 story building. My client and most of our work is on the 1st floor. The building owner occupies the second floor. The building is existing and has unenclosed 2 story stairs. The building owner would like to add a smoke barrier and door at the top of the stairs. Can we size the door based on the egress capacity of the stairs (width)?

Generating a life safety plan for the second floor would be a pain -it's a 25,000 SF church.

The best course of action would be to let the building owner do it on his own as a separate project as it is not needed by code, but this project needs to wrap up and our client is working with them as a function of good will.

 

[dill bill]

The existing stair is 48" wide. The building was built without sprinklers, so that would lead to an occupant load of 160 (48/.3). Now the building is has sprinklers and alarm, so 160*.15=24" required, so a single 36" door works.
I'm holding a 10 day old newborn and may not be thinking through this straight, but does that sound right?

 

[walker.t]

Can we size the door based on the egress capacity of the stairs (width)?

The size of any egress component is determined by calculating the occupant load served by that component per 2021 IBC 1005.3.2, so it’s not enough to just look at what the capacity of the stair is. Assuming the building was originally designed under the same requirements we have now, your stair width may serve as a clue as to what the occupant load it, but you need to confirm that. Which is where a life safety plan comes in handy…

Generating a life safety plan for the second floor would be a pain -it's a 25,000 SF church.

Building department where I do most of my work would want a life safety plan because adding a door changes the means of egress. Whether providing a life safety plan is convenient or not or whether that is an expense the owner would rather not pay is irrelevant. I don’t know if your second floor is 25,000 s.f. or what, but when I read “25,000 s.f.” I see the potential for a significant occupant load and I would want to know how you’re getting people from the second floor out of the building.

does that sound right?

Sounds like you’re good at multi-tasking! What you’re saying makes sense, but in my opinion you’re going about it backwards, you start on the second floor and work your way towards the exit.

 

[RLGA]

In my opinion, if the capacity of the door is equal to or greater than the capacity of the stairs, I would consider that acceptable reasoning.

Just FYI, a 36-inch wide door does not provide 36 inches of capacity--it will be closer to 33 inches of capacity. Door capacity is measured between the stop on the latch side and the face of the door when the door is in the 90-degree open position.

 

[Yankee Chronicler]

Just FYI, a 36-inch wide door does not provide 36 inches of capacity--it will be closer to 33 inches of capacity. Door capacity is measured between the stop on the latch side and the face of the door when the door is in the 90-degree open position.

Thank you for pointing this out. I am continually astonished at the number of architects who DON'T know this. 33 inches seems to be about right for a majority of 36" doors.

 

[dill bill]

Thanks for the replies.

Don't worry, they have more than one exit for the 25,000SF. I agree, best practice would be a full life safety plan, but best practice sometimes is tough to meet. If I'm required to stamp then maybe I'll reconsider that statement. In my best judgment I do not see it as a life safety issue and nothing I draw will change the use of the space; technically it's out my scope and maybe even the SFM since it is not required.

I try to be a fairly informed architect and am aware that a 36" door does not measure that clear. The SFM on this job was actually measuring existing doors in a few places to see if they were 32 or 33" clear.

I figure I can hold a sleeping baby and drink a cup of coffee and relax, or I can do the same and make some money...

 

[bill1952]

In my opinion, if the capacity of the door is equal to or greater than the capacity of the stairs, I would consider that acceptable reasoning.

Just FYI, a 36-inch wide door does not provide 36 inches of capacity--it will be closer to 33 inches of capacity. Door capacity is measured between the stop on the latch side and the face of the door when the door is in the 90-degree open position.

The capacity vs width question. 48" stair is 160. 33" door is 165. This gets trickier with 1005.4 Continuity and especially in aisles in assembly seating. Can a minimum 48" stepped aisle continue on a minimum 42" ramped aisle, when the capacity is over the number of occupants served?

 

[mtlogcabin]

The existing stair is 48" wide.

Is that the width between the handrails? If so that is the minimum width for an accessible means of egress stair in a non-sprinklered building

The building was built without sprinklers, so that would lead to an occupant load of 160 (48/.3). Now the building is has sprinklers and alarm, so 160*.15=24" required, so a single 36" door works.

Yes it should since the minimum width for a stair is 44 inches, which would = a 147 OL. A 36" door will handle that

Congratulations on the new baby