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Table 602 - Rating required for entire wall?

M

MNI55

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Oct 3, 2014
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Los Angeles
I have a IIB building in which a portion of the exterior wall has a fire separation distance of less than 10 feet. Am I correct thinking the portions of the exterior wall where the fire separation distance is less than 10' require a 1 hour rating where the portion of the wall with a FSD greater than 10 do not require a rating (say around the corner). The view above appears to be supported by a older version of the IBC handbook but not directly spelled out in the code that I have seen.

Thanks in advance for your thoughts.
 
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.

It is measured square off of the exterior building wall....unless it is a really odd shaped building, around the corner shouldn't matter...
 
steveray said:
The distance shall be measured at right angles from the
face of the wall.

It is measured square off of the exterior building wall....unless it is a really odd shaped building, around the corner shouldn't matter...
Click to expand...

Should be measured perpendicular to the property line/centerline/etc. If you consider a wall that is not parallel to the property line, then the setback would be somewhat less than called for if measuring 90-degrees from face of wall.
 
Here is the 2012 commentary. I believe what you are asking is the difference between the red and blue highlighted portions of the wall?

My understanding is that the imaginary line continuous passed the other building and the FSD does not change along the wall.
 

Attachments

Essentially my question is that if say the North wall requires a rating East, West, South walls of the building are evaluated based on their own fire separation distance. The North Wall Fire rating requirement does not impose the requirement on the other three walls. This may be an obvious answer but its not directly worded this way in the code that I can see.
 
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Draw the FSD line, and then measure perpendicular off of the buildings to it....It's that simple, the line can bend and curve to whatever makes it easier, but the line has to be there...
 
steveray said:
Draw the FSD line, and then measure perpendicular off of the buildings to it....It's that simple, the line can bend and curve to whatever makes it easier, but the line has to be there...
Click to expand...
Perpendicular to the FSD line, not from the building
 
Be careful, or a checker board approach to building houses/buildings on the lot will occur with corners touching and never having to rate any walls because the FSD was measured at 90 degrees to the face of the wall. Interpretation (as allowed by the code by the building official) need to include an arc at the corners so that the following design could not be presented.... if no walls are within 10 feet of the face of the wall at 10 feet, isn't this possible?

upload_2018-1-31_20-49-43.pngFor what it is worth, fire radiates in a circular or cone shape when blowing out of a window, thus a window at the corner could allow direct flame contact with the side wall of the adjacent corner.... fire or flames don't just travel in a straight line ---- if it did , why doesn't a candle flame appear more blocky in shape instead of a tapered cone as it is burning.
 
BB....The FSD line would have to run between the buildings somewhere and in that situation would have to touch them if it were a true checkerboard, so it would not fly....
 
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Correct, but the only way you would get out of it for one building would to be to put the FSD line on the exterior wall of the other building which would raise the requirements on that one.....
 
You measure at right angles from both buildings to the FSD line, not to the other building, unless the FSD line is on the other building, which would be a 0 FSD for that building with all of those restrictions. Which protects the other building by default...Draw a line at 45 degrees through the corner(s) and in theory, yes, at the corners, there is a flaw, but 1 inch away from the corner there is not....The problem self regulates IMO...
 
MNI55 said:
I have a IIB building in which a portion of the exterior wall has a fire separation distance of less than 10 feet. Am I correct thinking the portions of the exterior wall where the fire separation distance is less than 10' require a 1 hour rating where the portion of the wall with a FSD greater than 10 do not require a rating (say around the corner). The view above appears to be supported by a older version of the IBC handbook but not directly spelled out in the code that I have seen.

Thanks in advance for your thoughts.
Click to expand...
Please refer to attached. Is this what you are referring to? I hope so because I have the same question.

1704836194008.jpeg
 
Only that portion where the FSD is less than the minimum distance required by Table 705.5 (2021 IBC). Key element comes from the definition of FSD, specifically, being measured at right angles from the face of the wall.

Bigger issue I have seen is the transition on the interior, given that where FSD<10-ft, the wall must be rated for exposure from both sides.

2021 IBC - 705.5 Fire-Resistance Ratings​

Exterior walls shall be fire-resistance rated in accordance with Table 601, based on the type of construction, and Table 705.5, based on the fire separation distance. The required fire-resistance rating of exterior walls with a fire separation distance of greater than 10 feet (3048 mm) shall be rated for exposure to fire from the inside. The required fire-resistance rating of exterior walls with a fire separation distance of less than or equal to 10 feet (3048 mm) shall be rated for exposure to fire from both sides.

[BF] 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.
 
classicT said:
Should be measured perpendicular to the property line/centerline/etc. If you consider a wall that is not parallel to the property line, then the setback would be somewhat less than called for if measuring 90-degrees from face of wall.
Click to expand...

Nope. The IBC definition says otherwise:

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.
Click to expand...
 
classicT said:
Only that portion where the FSD is less than the minimum distance required by Table 705.5 (2021 IBC). Key element comes from the definition of FSD, specifically, being measured at right angles from the face of the wall.

Bigger issue I have seen is the transition on the interior, given that where FSD<10-ft, the wall must be rated for exposure from both sides.
Click to expand...

The 2018 IBC Illustrated Handbook has a figure showing how only a portion of the length of a wall may need to be rated due to the fire separation distance, they show a wall at an angle to an interior lot line. They do not comment on the practical issue classicT mentions of the transition between the rated and non-rated portions of a wall.

To only fire rate part of a wall seems odd to me, like a fire wall without opening protectives. I would have thought that the entire wall had to be rated in order for any part to be considered rated.
 
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