Hello:

[Michael Corbett]

Question is about a parapet wall. I find no definition of a parapet wall in the 2015 IBC. I have a 4S, 3B, R-2 multi family building. The parapet isnt a continuation of the exterior wall but is set in about 4' with only a soffit at the actual exterior elevation. Section 705.11.1 indicates the requirement to have the same fire resistance rating as that required for the supporting wall (2hr). Does the half truss require FT wood? It appears that Table 602 rules and thus its based on the fire separation distance? Any comments would be appreciated.

 

[RLGA]

Are you saying the parapet is set out from the wall by four feet? Is this condition continuous for the entire length of the wall? What is the reason that the exterior wall needs to be fire rated?

 

[Michael Corbett]

Hello: Meeting the construction type for an exterior non loading wall sends me to Table 602. Comes down to the fire separation distance I believe. Yes it is continous for the entire roof and acts as a screen.

 

[RLGA]

There are only two instances where a 2-hour exterior wall is required based on fire separation distance:

1. The occupancy group is F-1, M, or S-1 and the fire separation distance is less than 5 feet, or less than 10 feet if Type IA construction.
2. The occupancy group is H and the fire separation distance is 5 to less than 10 feet for all construction types except for IA, or is 10 feet to less than 30 feet for Type I construction.

If neither of those conditions apply, then a 2-hour exterior wall is not required per Table 602, even if the construction type per Table 601 requires a 2-hour exterior wall. If that is the case, Exception 1 to Section 705.11 applies.

I assume the construction type is a combustible one (Types III, IV, or V), so Exception 3 would not apply.

If the building is sprinklered, and the fire separation distance is at least 5 feet, then you are permitted 25% unprotected openings, so Exception 6 would apply and no parapet is required. However, if the building is not sprinklered, then the fire separation distance would need to be at least 15 feet to have no parapet.

If none of those exceptions apply, then a parapet is required.

In that case, you have three options:

1. Have the exterior wall extend to the required height of the parapet and the roof structure terminates at the exterior wall. Design the 4-foot extension as a projection per IBC Section 705.2. This would be the IBC textbook solution.
2. Design the soffit and vertical wall portion of the overhang to have a 2-hour rating. This method would work best for wood trusses. This is not textbook IBC, but can be used as an alternative design per IBC Section 104.11.
3. Extend the 2-hour construction up to the roof deck, design the joists with 2-hour construction back to the exterior wall (provide through a penetration firestop where joists extend through the exterior wall), and use 2-hour construction for the vertical portion of the overhang. This method would work best for metal trusses. Again, this is not textbook IBC, but can be used as an alternative design per IBC Section 104.11.

 

[Yikes]

Having a hard time visualizing it:

Is it simply a case where (A) the screen wall is in line with the exterior wall below, but there's an eyebrow / eave that protrudes beyond both , like this?




Or is it (B) where the screen wall is set back from the exterior building wall below, like this?

 

[Michael Corbett]

Your input was very helpful! Thank you for your explanation. I will follow the code paths you have offered and may follow up.

 

[RLGA]

@Yikes, this is how I interpreted the situation:

 

[Michael Corbett]

@Yikes, this is how I interpreted the situation:
View attachment 9343

@Yikes, this is how I interpreted the situation:
View attachment 9343