Fire Barrier Continuity

[Mech]

2015 IBC

707 Fire barriers

I am constructing a 3 hour rated fire barrier to create separate fire areas (S-1 being the most restrictive) at a high - low roof condition. The S-1 roof is high and the adjacent S-2 / B roof is low.

Does the fire barrier stop at the underside of the low roof sheathing / deck or the underside of the high roof sheathing / deck?


707.5 Continuity
Fire barriers shall extend from the top of the foundation or floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above and shall be securely attached thereto. Such fire barriers shall be continuous through concealed space, such as the space above a suspended ceiling. Joints and voids at intersections shall comply with Sections 707.8 and 707.9
Exceptions
1. (omitted)
2. (omitted)


Thank you.

 

[RLGA]

Fire barriers separate interior space. Above the lower roof, it becomes an exterior wall.

 

[steveray]

Like Ron said...low roof...Once the fire is through the roof we don't care.....

 

[IJHumberson]

Wouldn't Sect. 707.4 (2018 IBC) require the exterior wall to continue the rating up to the roof? It just seems like, otherwise, you'll have a non-rated wall immediately above and adjacent to a non-rated lower roof, thereby having no separation at all. To rate the wall only up to the lower roof level provides no separation at all.

 

[RLGA]

Wouldn't Sect. 707.4 (2018 IBC) require the exterior wall to continue the rating up to the roof? It just seems like, otherwise, you'll have a non-rated wall immediately above and adjacent to a non-rated lower roof, thereby having no separation at all. To rate the wall only up to the lower roof level provides no separation at all.

Actually, that section says the direct opposite and supports the position I posted. It says, "Where exterior walls serve as a part of a required fire-resistance-rated shaft or stairway or ramp enclosure, or separation, such walls shall comply with the requirements of Section 705 for exterior walls and the fire-resistance-rated enclosure or separation requirements shall not apply."

 

[Paul Sweet]

IBC 705.8.6 addresses windows above the roof of an adjacent structure. Exception 2 says: "Buildings on the same lot and considered as portions of one building in accordance with Section 705.3 are not required to comply with Section 705.8.6."

 

[ashipcase]

If I'm understanding correctly, you are doing a fire wall between two different roof levels. I would look at 706.6.1. Stepped Buildings. A fire wall separating buildings having different roof levels becomes an exterior fire wall with 0' separation between buildings. The wall shall terminate at a point not less than 30" above the lower roof provided the wall for 15' above lower roof is not less than 1 hour. As a general rule of thumb, if the fire has to travel less than 180 degrees to get to other areas, then the wall needs fire rating. You would only have 90 degrees between the lower and higher roof.

 

[Mech]

ashipcase - I am only creating a fire barrier, not a fire wall, although that would require a 3 hour fire rating as well for the occupancies under consideration.