Exterior Wall Fire Ratings

[Mech]

2009 IBC

Type 3B Construction w/ separated occupancies

Non- sprinklered building

How do I determine the fire rating requirements, if any, for walls 1, 3, 4, & 5 in the sketches below? Do I apply a fire separation distance for exterior walls? Is the rating that which is required for separated construction or the rating required between dwelling units? Are the ratings non-existent because the walls face walls of the same building?

Wall 4 is the upper portion of wall 1 and wall 5 is the upper portion of wall 3. For separated occupancies, 2 hour fire separation is required between A-2 & R-2. One hour fire separation is required between R-2 dwelling units. The 12' x 13' area is a window well that extends from the roof on the first floor up to the fourth floor roof.

Wall 2 is load bearing and I know it needs a 2 hour rating. Load bearing vs non-load bearing conditions for walls 1, 3, 4, & 5 are not yet determined.

Thanks

 

[steveray]

Besides Tables 601 and 602?....601 gives you at least 2hr exterior bearing walls...and maybe 1 for nonbearing (602)

 

[Mech]

From Table 601, if the walls are non-load bearing, I go to Table 602 and look at fire separation distance.

Fire separation distance is measured from the building face to the closest interior lot line; the centerline of a street, alley or public way; or to an imaginary line between two buildings on the property.

Fire separation distance is not applicable in this scenario because I have an exterior wall facing an exterior wall from the same building. Or do I assume fire separation distance is greater than 30 resulting in a fire rating of 0?

 

[JBI]

You have 13' between the opposing walls. 6' 6" FSD for each wall (a bastardized application of the 'imaginary line' strategy).

 

[Builder Bob]

The imaginary line can be fluid in motion. For example, if two buildings are 15 feet apart, the exterior wall of the new construction could be one hour rated and the imaginary line set at five feet, thus leaving the other existing building in compliance with the codes.

 

[steveray]

Interesting concept.....Technically you do not need to separate the building from itself......If there is no lot line....

FIRE SEPARATION DISTANCE. The distance measured from the building face to one of the following:

1. The closest interior lot line;

2. To the centerline of a street, an alley or public way; or

3. To an imaginary line between two buildings on the property.

The distance shall be measured at right angles from the face of the wall.

 

[JBI]

steveray, I know, that's why I added "(a bastardized application of the 'imaginary line' strategy)" at the end o my post.

 

[Francis Vineyard]

In accordance with section 705.2 is the roof a projection of wall 2 to the lot line if its only attatched to walls 1 & 3 or does this matter?

 

[Mech]

The lower sketch shows the second floor. The low roof is approx. 13 ft wide from the inset portion of the building to the adjacent building on the opposite side of the same lot line. The low roof is approx. 12 inches above the R-2 dwelling unit floor and approx. 3 ft below the adjacent building roof.

The upper sketch shows the typical third / fourth floors.