By Austin Regan
BC 403.5.2 Additional Exit Stairway “For buildings other than Group R-2 that are more than 420 feet in building height, one additional exit stairway… shall be provided in addition to the minimum number of exits required…”
In other words, if your tall building normally requires two stairways to meet Code, a third redundant stair will be required under the 2014 Code.
The Code revision committee was actually made up of many sub-committees, each with 20-30 professionals representing different construction and development related entities. Every section of the Code was reviewed. In order for the language of a section to be adopted unanimous consent of the committee was required. If unanimous consent could not be reached, the item would be sent to mediation. Only ten items went to mediation. This item was one of them.
Obviously the inclusion of another exit stairwell causes more of the building’s footprint to be devoted to space that cannot be rented, diminishing the potential return on the developer’s investment. So the fact that this would be a contentious issue was a surprise to no one.
The IBC adopted the redundant stair requirement based on studies it had commissioned regarding the destruction of the World Trade Center, and the science behind the logic for the extra stair was compelling. Timed egress studies showed that the amount of time it took a top floor occupant to exit a 50 story building via a stairwell was over 2 hours! As people were descending, fireman were ascending the same stairs; when an extra stair was added to the equation the travel time was cut in half.
Most of those on the egress committee did not dispute the logic that an extra stair made a building safer. The 420 foot cutoff seemed arbitrary given that most cities in the US only have a handful of buildings that reach that level. In New York City, a building of that height is not even considered tall in some neighborhoods. When excluding residential buildings (R-2) from the calculation it seemed the only cities that would be routinely affected were New York and Chicago… and Chicago does not follow the IBC.
Despite those concerns, the Code change was adopted. As always, there are exceptions which allow a designer to avoid the 3rd stair. Below are the exceptions:
- The building is a R-2 occupancy.
- All passenger elevators qualify as Occupant Evacuation Elevators Per BC 3008.
- The commissioner approves a timed egress analysis that shows that a combination of the required egress stairs and a certain number of Occupant Evacuation Elevators equals or is less than the results of the timed egress analysis for the egress stairs plus the redundant stairs. Every elevator bank must have at least one Occupant Evacuation Elevator and all exit stair widths must be 25% wider than what would otherwise be required based on Chapter 10 of the Code.
- The New building application is submitted within 18 months after the enactment of the code (October 2014).
I believe this may be the only section of the new Code that has a delayed enactment date. Part of the reason for the delay is there is an effort underway to petition the City Planning Commission to amend the zoning resolution to make the redundant stair exempt from floor area calculations. There is no guarantee this will happen.
The option to use Occupant Evacuation Elevators is also fraught with uncertainty. This type of elevator is a new concept. It is not certain that some of the specific requirements spelled out in BC 3008 are technologically or practically feasible.
There will be a certain urgency to getting proposed tall buildings off the boards and far enough along in their design to beat the 18 month enactment deadline.
As this has now been adopted nationally without the 18 month grace period, insurance companies may weigh in also and economically force some developer’s hands to provide the redundant stair well before the Code requires it.
In any case it would be wise for designers of tall buildings to require a timed egress analysis be done even on R-2 or lower buildings. The addition of an extra 6″ or one foot of width to the required stairs could have a significant impact on evacuation time and may be even a selling point for potential building tenants.