My last post referenced the term “exit enclosure”, and I received a few questions about its meaning. An exit enclosure is the enclosure around an exit. For our purposes it usually refers to a stairwell. According to the IBC, exit enclosures connecting 4 or more stories require a 2-hour fire resistance rating, and those connecting less than 4 stories require a 1-hour fire resistance rating (IBC-2009-1022.1). Exit enclosures must lead directly to the exterior or to an exit passageway, which will typically have the same fire resistance rating as the exit enclosure. The IBC includes some exceptions for exits which do not need to be enclosed, such as stairs in parking garages.
The exterior door for an exit enclosure is not usually fire rated, but occasionally I run across one that is. This happens when there is another wall of the building within 10 feet of a nonrated wall or unprotected opening. Openings in this wall must be C labeled – 45 minutes.
Here’s the text from IBC 2009 regarding exit enclosure exterior walls:
1022.6 Exit enclosure exterior walls. Exterior walls of an exit enclosure shall complywith the requirements of Section 705 for exterior walls. Where nonrated walls or unprotected openings enclose the exterior of the stairway and the walls or openings are exposed by other parts of the building at an angle of less than 180 degrees (3.14 rad), the building exterior walls within 10 feet (3048 mm) horizontally of a nonrated wall or unprotected opening shall have a fire-resistance rating of not less than 1 hour. Openings within such exterior walls shall be protected by opening protectives having a fire protection rating of not less than 3/4 hour.