by Jerry Peck - Codeman on Mon Jun 24, 2019 8:29 pm
The designer is correct ... sort of ... the answer is more complicated than just '10 feet or less' or 'more than 10 feet'.
We start with the separation distance based on type of construction (which was not stated). The exterior wall's minimum rating is then based on the occupancy and type of construction - referencing IBC Table 602, Fire-Resistance Rating Requirements for Exterior Walls Based On Fire Separation Distance.
The type of construction does not affect the exterior wall's rating in your F-2 question for any distance less than 10 feet as any distance less than 10 feet requires a 1 hour rated wall for F-2.
However, if the distance is 10 feet or greater, but less than 30 feet, then the type of construction matters.
Because the question is about F-2, the superscript note c (for open parking garages) does not apply.
We measure fire-separation distance this way: (bold and underlining are mine)
- 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.
- - 3. To an imaginary line between two buildings on the lot.
- - The distance shall be measured at right angles from the face of the wall.
If the building is at an angle to the other building (buildings are not parallel with each other), then we can presume that there will likely be a corner of the building which is closer to the imaginary line between the two buildings than the face of the walls are (there could be buildings where this may not be the case, but it is a safe presumption for square or rectangular buildings - and the shape of the building was not stated) - you would measure out perpendicular from the face of one wall at the corner to the imaginary line, and measure out perpendicular from the face of the other wall at the corner to that imaginary line.
Or, if the buildings are parallel with each other but are staggered so only part of the walls of the buildings are opposite each other (not enough information was given to know the separation layout), then measure from one building to that imaginary line, then the other building to its imaginary line, and where one parallel building ends and the other building keeps extending outward, only the parts of the walls which are withing the measurements below need to be rated.
As you can tell, I'm trying to envision the orientation of the buildings to each other without much information to go on, but I have hopefully addressed the two buildings sufficiently to answer the question beyond just a 'only the part of the buildings which do not have the required minimum separation distance need to be rated' simplistic answer
Where that measurement is less than 10 feet (from Table 602 for F-2 occupancy), a 1 hour rating of the exterior wall is required for those areas of the walls.
End result - where that measurement is 10 feet or greater, but less than 30 feet (also from Table 602 for F-2 occupancy):
- if the type of construction is IA, IB, a minimum 1 hour rating is required
- if the type of construction is IIB, VB, a 0 hour rating shown (no rating required)
- if other types of construction, a 1 hour rating is required
Where the measurement is 30 feet or greater - no fire rating is required.
Jerry Peck - CodeMan
AskCodeMan.com
Construction Litigation Consultant - Retired
Construction and Code Consultant - Semi Retired