Stair width for five story stair enclosure

[BayPointArchitect]

Considering that each 6,800 S.F. floor has an occupant load of 68 with two stair exits available to each level, I am thinking that the occupant load for the stairway is only 34 and requires a stair width of only 36 inches per 2006 IBC 1009.1, Exception 1.

Something just doesn't seem right about a five story stair that is not a minimum 44 inches. What am I missing?

 

[FM William Burns]

Convergence.

 

[mtlogcabin]

Unless your elevator qualifies as an accessible means of egress the stairs need to be 48 inches between handrails

2006 IBC

1007.3 Exit stairways.

In order to be considered part of an accessible means of egress, an exit stairway shall have a clear width of 48 inches (1219 mm) minimum between handrails and shall either incorporate an area of refuge within an enlarged floor-level landing or shall be accessed from either an area of refuge complying with Section 1007.6 or a horizontal exit.

 

[BayPointArchitect]

IBC 1007.3 Exception #3: Clear width of 48 inches... not required at exit stairways... sprinkler.

Building is Type IIIB construction fully sprinkled.

Per my interpretation of 2006 IBC 1004.5, and recolection of the A.R.E. exam, convergence occurs only at the level of exit discharge where second floor occupant load meets basement load. Therefore, the first stair flight above and below first floor would need to be 44" with a combined occupant load where second floor (34 occupants) meets basement (another 34 occupants) for a total of 68. Cascading convergence as you make your way down the stairs went out with UBC.

 

[brudgers]

IBC 1007.3 Exception #3: Clear width of 48 inches... not required at exit stairways... sprinkler.Building is Type IIIB construction fully sprinkled.

Per my interpretation of 2006 IBC 1004.5, and recolection of the A.R.E. exam, convergence occurs only at the level of exit discharge where second floor occupant load meets basement load. Therefore, the first stair flight above and below first floor would need to be 44" with a combined occupant load where second floor (34 occupants) meets basement (another 34 occupants) for a total of 68. Cascading convergence as you make your way down the stairs went out with UBC.

Please don't rely on your recollection of the ARE for code interpretations because you are embarrassing the other architects on the board.

Or at least don't say your are.

 

[BayPointArchitect]

Ha ha, Brudgers.

I couldn't help but notice that your dog is missing his pink birthday hat.

... but I think you would concur that convergence is not an issue between floors 2 through 5?

 

[mtlogcabin]

If you base your occupant load on 100 sg ft per person you will seriously restricting any change of use on those floors. The actual OL of a telemarketing office or a debt collection agency or any cubicle office setting can easily be be twice what you have allowed for.

36 inch stairs for 6,800 sq ft floor would be poor planning.

 

[brudgers]

Ha ha, Brudgers.I couldn't help but notice that your dog is missing his pink birthday hat.

... but I think you would concur that convergence is not an issue between floors 2 through 5?

The combined occupant load of all the floors does not normally need to be considered, only the largest occupant load on any one floor [for typical buildings, if you're modeling the egress it could be another matter].

The reason that the occupant loads of multiple floors are not combined in determining stair width is because of the time it takes to descend. The people on floor 5 enter into the stair tower at the same time as those on floor 4. The occupants of floor 5 reach the 4th floor landing at the same time the occupants of floor 4 reach the 3rd floor landing.

Or rather that's the assumption in the codes, backed up by modeling and experience.

 

[BayPointArchitect]

If you base your occupant load on 100 sg ft per person you will seriously restricting any change of use on those floors. The actual OL of a telemarketing office or a debt collection agency or any cubicle office setting can easily be be twice what you have allowed for. 36 inch stairs for 6,800 sq ft floor would be poor planning.

The initial use will be a warehouse with the anticipated occupant load of 1 per 500. So the more restrictive office use of 1 per 100 is being considered for a future use.

I just found this in the Life Safety Table 7.2.2.2.1(a):

Minimum clear width...

44 in.

36 in. where total occupant load of ALL stories served by stairways is fewer than 50.

Considering that I have five stories with a combined occupant load greater than 50, the stairway must be a minimum 44 inches (except for handrails).

Thanks everyone!

 

[FM William Burns]

I would have sent you to 101 but would have been stoned...glad you found your clear width.

 

[brudgers]

I would have sent you to 101 but would have been stoned...glad you found your clear width.

Eh... All right. Two points, ah, two flats, and a packet of gravel.