2009 IBC 705.8.1 Allowable area of openings - Multiple Wall Off-sets

[codewonk]

Where a building has wall off-sets creating multiple wall faces, is each wall face with a different "Fire Separation Distance" considered separately for the purposes of determining the maximum area of exterior wall openings per IBC Table 705.8?

Thanks for your help.

 

[peach]

yes... unless you interpret it different locally.

Some plan reviewers look at the closest separation and apply to the entire building (right or wrong).

 

[Builder Bob]

That depends, some look at each wall surface, some look at the average, some don't even look at all...... Ask the local AHJ (Peach had the right answer)

 

[Rio]

The code seems to be clear on this, with it saying (no code book in front of me at the moment) that 0-3' no openings, 3-5' 25%, etc. It doesn't say that if one part is less than 5' and the rest is more than 5' then the total has to be calculated as if it were less than 5'.

 

[mtlogcabin]

Agree with Rio remember the maximum area is calculated per story. This is sometimes overlooked by designers.

 

[codewonk]

Not requiring each wall plane to be considered separately opens the door to abuse. As noted previously, if a wall plane under consideration has a fire separation distance of 5 feet to less than 10 feet in a non-sprinklered building, I'm limited to 10% for unprotected openings. If I'm allowed to include all the wall planes in the calculation, I could render a design with unprotected openings well in excess of 10% and locate the same in the most restrictive wall plane.

Would be nice if the "I" Codes were more implicit sometimes. But then, we wouldn't have so much fun beating up the code!!

 

[mtlogcabin]

704.8 Allowable area of openings.

The maximum area of unprotected or protected openings permitted in an exterior wall in any story shall not exceed the values set forth in Table 704.8.

If the intent of the code is to limit the maximum allowable area of openings to be restricted to "any story" the same logic should be applied to wall planes. Each wall is a seperate wall just like each story is a seperate story.

 

[Examiner]

Yes it applies per story and yes the wall offset are treated separately. Your openings could get larger at each offset as they get farther away from the Property line.

 

[texasbo]

If I'm allowed to include all the wall planes in the calculation, I could render a design with unprotected openings well in excess of 10% and locate the same in the most restrictive wall plane.

I think you might be misinterpreting the code and the opinions you've been given. You could not exceed the allowable opening area for that portion of the wall that is under consideration.

In other words, using your 10% example, that would only be 10% of the area of the wall that is closest to the property line, not 10% of the entire length of the wall.

 

[High Desert]

texabo, I think codewonk was saying you do them separately or you could end up with more openings than allowed.

 

[codewonk]

Texsabo, I agree with you and High Desert.