Fire Separation Distance - Contiguous Exterior Wall?

[Brainhurts]

Hi All - first off, I appreciate any insight you may be able to provide.

My question is regarding the interpretation of this bold portion below:

705.8.1 The maximum area of unprotected and protected openings permitted in an exterior wall in any story of a building shall not exceed the percentages specified in Table 705.8 based on the fire separation distance of each individual story.

"an" exterior wall - I interpret to mean a contiguous portion of an exterior wall (ie. openings and walls in the same plane). However, what if I inset for a balcony into the contiguous exterior wall? Do these insets have their own individual allowable opening % or are they part of the contiguous wall? The facade/balcony insets would have a sliding glass door opening further from the property line than the contiguous facade, but if they are calculated as being within their own "exterior wall" - the glass door would be 75%-90% opening area (not allowed). Regarding hazard - I would say the inset openings located further from the property line are less hazardous than an opening at the contiguous facade. In my example, both the contiguous exterior wall and the inset would land within the 25% allowable unprotected opening zone / FSD.

Thoughts?

 

[RLGA]

Here's my simple response: it depends.

If the "contiguous wall" was located at 10 ft. from the lot line and the "inset" was at 14 ft., then I would consider the contiguous wall and the inset as part of the same wall since the distance is within the same fire separation distance grouping per Table 705.8 (i.e., "10 to less than 15").

If the contiguous wall was located at 12 ft. from the lot line and the inset was at 16 ft., then you have two options: One is strictly per the code, and the other is a common-sense alternative that would probably need approval, but I have had no problem doing it in the past.

• Strictly per the Code: The percentage for "10 to less than 15" is applied to the contiguous wall, and the percentage for "15 to less than 20" is applied to the inset.
• Common Sense Alternative: Consider them at the same "plane" and apply the percentage for "10 to less than 15" to the entire wall. Even though the opening exceeds the area for a wall of that area at the other distance, the overall openness of the exterior wall still complies with the allowable area for a wall that is closer to the lot line.

 

[Brainhurts]

Excellent approach Ron - thanks for the feedback! I think going with the "zonal" approach makes sense in my case. Unfortunate that the IBC doesn't address this directly - or have a formula-based approached to FSD and opening protectives, that would allow for greater design freedom.

 

[Life_learner]

Brainhurts,
In the Commentary version of the IBC there is a great SECTION, showing that you measure from prop line to each exterior wall.
If your balcony wall is Recessed further back from property line you could be in a different category (just like Ron with RLGA noted).
Only issue is the “% open vs wall” may increase with a smaller amount of wall in plan.

 

[Yikes]

If the contiguous wall was located at 12 ft. from the lot line and the inset was at 16 ft., then you have two options: One is strictly per the code, and the other is a common-sense alternative that would probably need approval, but I have had no problem doing it in the past.

• Strictly per the Code: The percentage for "10 to less than 15" is applied to the contiguous wall, and the percentage for "15 to less than 20" is applied to the inset.

Brainhurts,
In the Commentary version of the IBC there is a great SECTION, showing that you measure from prop line to each exterior wall.
If your balcony wall is Recessed further back from property line you could be in a different category (just like Ron with RLGA noted).
Only issue is the “% open vs wall” may increase with a smaller amount of wall in plan.

Question: does the outer edge of the balcony itself count as its own "opening", under the definition of "floor area"?


In the image below, is the plane of the "opening" where the red line is, or back where the glass door is located?