Reduction in Egress Width

[LGreene]

I'm trying to find "proof" in the IBC of something that I thought I already knew, but I'm having trouble.

Imagine a vestibule, with a pair of doors on the interior (leading from the lobby to the vestibule) and a single door on the exterior. I didn't think that was allowed because it reduced the egress width from +/- 6' at the pair, to +/- 3' at the single.

In the IBC, I found this, which supports what I thought I knew:
1003.6 Means of egress continuity. The path of egress travel along a means of egress shall not be interrupted by a building element other than a means of egress component as specified in this chapter. Obstructions shall not be placed in the minimum width or required capacity of a means of egress component except projections permitted by this chapter. The minimum width or required capacity of a means of egress system shall not be diminished along the path of egress travel.

But in the Commentary, it says:
Note, however, that the egress path could be reduced in width in situations where it is wider than required by the code based on the occupant load. For example, if the required width of a corridor was 52 inches (1321 mm) based on the number of occupants using the corridor and the corridor provided was 96 inches (2438 mm) in width, the corridor would be allowed to be reduced to the minimum required width of 52 inches (1321 mm) since that width would still serve the number of occupants required by the code. In the context of this section, a “means of egress component” would most likely be a door or doorway.

If the occupant load of the building is 100, for example, isn't the Commentary saying that it's ok to have a pair of interior doors and a single exterior door, since the single door provides sufficient egress width? Is there another section of the IBC that affects this?

Thanks in advance!
- Lori

 

[steveray]

Think if you wanted to put a set of double doors on an office for aesthetics....every other door in the MOE would need to be double even with an OL of 100? It's the required OL that matters...

 

[Sleepy]

I think steveray is exactly correct. But one thing that has always confused me is that for a given capacity, stairs are required to be wider (with some exceptions) than doors, IBC 1005.3, and stairs have to be a minimum of 44 inches wide if the occupant load is 50 or more per 1011.2. Does that mean that the door at the bottom of the stairs needs to be 44" wide, even if otherwise a smaller door would be acceptable for the occupant load and capacity?

 

[Builder Bob]

Sleepy,

No..... The codes has multiple items that come into play for egress - The stairway width of 44 inches tends to be an accessibility issue as stairways may be as little as 36 inches in width --- In simple terms, the egress is only required to be as wide as the occupant load for designing the egress. Example story has 750 SF A-2 (Assembly) The required egress is only 49 * 0.2 = 9.8 inches of required width for egress for flat level surfaces or 14.7" width for stairs - only about a third of what is required by empirical methods of code.

However Code requires a minimum size door leaf (Side-swing) for accessibility (32" clear) , Stairs are required to be minimum of 36" or 44" (Accessibility) , etc., etc. etc.

Remember, the code has general rules which are superseded by specific rules - i.e. door leaf widths, stairway widths are specific to there application and supercede the general requirements for required width of egress as in this example.

Sometimes, Occupant loads will dictate a larger stairway or door than what code indicates as a minimum size...

 

[Sleepy]

Thanks Builder Bob, that is how I have always looked at it. But I think it is confusing because 1011.2 uses the term "minimum width" (meaning 36" or 44" for stairs) and 1003.6 also uses the term "minimum width" (meaning that it can not be diminished along the path of egress travel).

 

[Builder Bob]

IF I am not mistaken, the correct way to interpret section 1003.6 is below the minimum required egress width ---- which in my bad example above is only 9.8 inches. However, people tend to get hung up on the 32" 36" 44" benchmarks established by other sections of the code for specific applications.

 

[JPohling]

You just need to maintain the required egress width based upon the occupant load. 100 persons can easily exit thru a single 36" door exit width wise. You could then go thru a double door situation and back to a single door situation. all of these door conditions meet the exit width requirements. If the exit width required more than a single door width then that would need to be maintained........

 

[JBI]

Sizing the MOE is a function of occupant load, yes. BUT the minimum clear open width of doors (32" clear) or minimum width of stairs (generally 44", sometimes 36") are absolute minimums regardless of occupant load (see Builder Bob's example above).
Reductions cannot go below the greater of either the occupant load driven width or the absolute minimums.
In the OP and without additional details, it sounds like the double doors were well above the occupant load driven requirement, and could easily be met by the single exterior door.
As far as stairs at 44" and doors at 32", a couple reasons for those... on stairs occupants leaving have the width needed on the stairs for faster and slower occupants without knocking each other over AND (more importantly) allows for responders going up to pass by exiting occupants. At doors these two are not huge issues because you take one step going through the door. IMHO

 

[tmurray]

I would agree that creating a bottle-neck is poor design, but I don't know of anything in our code that prohibits it.

 

[ADAguy]

Except for the "Suits" who are waiting in the wings to point out the bottleneck as foreseeable and therefore "bad" practice. Consider if it were a wheelchair and a walker trying to exit that vestibule at the same time with many people pushing from behind?.

 

[Builder Bob]

Bad design is code compliant... AS far as a jury of peers go, I can state that I met my requirements for determination of the "minimums" of code and the design met those expectations. Remember, The builder or contractor that brags about building code complaint buildings is bragging about meeting the minimum requirements - almost like bragging about making a 70 on a test.