2009 IBC: Fire rating requirements for wood fire stair enclosure

[Scott_R]

Building:

3-story, R2 apartment building with interior corridor and enclosed fire stairs.

Construction classification: VA (protected with NFPA 13R sprinklers)

Structure: Wood frame, wood floor trusses, masonry stair towers & elevator shaft

Code Used: 2009 IBC - New Jersey addition

Exit enclosures are constructed of CMU walls. Building is sprinkled. All ratings are 1-hour with the exception of exit enclosure which is 2-hour (masonry).

Questions

1. Can the masonry walls in exit enclosure be rated for 1-hour as stairs connect less than 4 stories (Section 1022.1 & Table 707.3.9)?

2. Do the platform and stairs "within" the exit enclosure need to be fire retardant wood and/or rated? Or can the lumber be untreated/unrated because it is within the enclosure (I can't find any code sections supporting this).

I understand the structural floors need to be 1-hour according to table 601, but what about the components of the stair inside the tower? In other words, is the stair platform considered a "structural floor" and need to be rated 1-hour as well as the "stairs" themselves?

Thanks.

 

[steveray]

SECTION 1022 EXIT ENCLOSURES

1022.1 Enclosures required. Interior exit stairways and interior exit ramps shall be enclosed with fire barriers constructed in accordance with Section 707 or horizontal assemblies constructed in accordance with Section 712, or both. Exit enclosures shall have a fire-resistance rating of not less than 2 hours where connecting four stories or more and not less than 1 hour where connecting less than four stories.

1. Seems so.

2. If you walk on it, it is a floor, rate it as such.

 

[Scott_R]

Thanks for the quick response and clarifications Steve!