Exterior Wall Fire Rating

[DwightB]

2006 IBC:

Is it the intent of the code writers to mean that Table 602 (fire ratings for exterior walls as based upon separation distance) should override the fire ratings in Table 601/Bearing Walls/Exterior? If so, this is not clearly stated. Section 602.1 clearly says "building elements SHALL HAVE a fire resistance rating NOT LESS than that specified in Table 601 AND exterior walls SHALL HAVE a fire resistance rating NOT LESS than that specified in Table 602.

Suppose I have a Type I-A structure, Table 601 says Bearing Walls/Exterior for Type I-A: 3 hour rating. Footnote "f" adds that I must also be "NOT LESS THAN the fire-resistance rating based on fire separation distance (table 602). Footnote "g" adds "not less than the fire resistance rating as referenced in Section 704.10 When I check Table 602, I see that if I am greater than 30' distance, the rating drops to zero. However, it seems that Table 601 allows a "0 hour" rating only for types II-B, III-B, and V-B construction.

I can think of many instances in the past where a building was judged to be a certain building construction type and then the decision is made to go with a "0-hour" exterior wall because of separation from adjacent structures. I don't see in 602.1 where that determination is allowed. The code says "building elements" (including exterior walls which are listed there in the table) AND exterior walls must meet Table 602. I believe any exterior wall must meet the most stringent of both listings. Am I correct?

 

[Coug Dad]

The more restrictive applies

 

[vegas paul]

I can tell by the footnotes you cited that you are reading the 2009 code... congrats on that! Section 704.10 clears this up, basically use the most restrictive. for the example you gave (IA) it is sort of confusing because table 601 will always dominate for exterior walls. But try the logic with a group H, VB building for instance that has a fire separation distance of 3 feet, and you'll see the difference.

Good question, though.

 

[allis_ch]

in case you didn't see my post at the nearly non existant ICC site - ditto on the most restrictive

 

[Plans Approver]

In the 2006 IBC (same in 2009):

1. Table 601 footnote g pushes you to Table 602.

2. Table 602 footnote a pulls you back to Table 601.

Since both tables apply, the most restrictive applies in 2006 (as well as 2009). So you are correct.

2009 IBC 704.10, at least, has a reference from Table 601, unlike 2006 IBC 714.5 which has the same language and isn't referenced from anywhere. You just needed to know it was there.

The real change in 2009 is the requirement for columns to be indiviually encased (2009-704.2), even 1 story columns. Whereas under 2006, 1 story columns could be hidden in a fire resistant rated wall (2006-714.2.1), in many cases.