Travel distance - unenclosed stairway


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    David Kaplan


    I've done this many, many times in my line of work.  You calculate the diagonal path running down the stairs.  It says so in the Code as well.  So as you have identified, it's the distance of the slope of the stairs, NOT the 2D length of the run.  When you get to a flat landing, though, you do in fact calculate the 2D length because that surface is not sloped.  It's only the actual diagonal stair flight where you calculate it differently.  Imagine a line connecting the nosings of the stairs - it's the length of that line.

    Any time you are using an unenclosed stairway as a part of the means of egress, and doing so to calculate the maximum exit travel distance from an upper level to the "exit," you have to calculate the path to wherever the exit is. 

    In a two story building, if you want to use this approach, you'd first start at some point on the 2nd floor.  You take the travel distance from that point to the top nosing on the unenclosed stair.  Then you take the travel distance down that stair (as I've described above) until you get to the bottom nosing at the 1st floor.  Then you take the travel distance from the bottom nosing to the exit door at the 1st floor.  Add all those numbers up.  If you can prove that this total is LESS than the maximum exit travel distance identified in the Code Table, then you are good to go.  Essentially, you are treating this stair no different than any corridor in the building.  It is treated as an egress path - it just happens to be a stair in this case.

    Hope this helps.

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