5/8 fx on outside walls

[pottsth]

I have a 4 unit apartment building, 2 floors, 2 units teach floor. R2,5B w/ automatic sprinklers. I detailed the outside walls with 5/8 FX because the distances between buildings varies. Some are 25' apart, but in some cases the distance on a corner may go down to 12-13'. My builder wants to know if 1/2" regular is ok, and if not, what the minimum distance between buildings would be.

[Jerry Peck - Codeman]

Occupancy is R2
Construction Type is VB
Using the 2006 IBC (not knowing what code is applicable, but most areas are at least on the 2006 edition of the ICC codes)

Table 602, shows:
- First column is fire separation distance, you mentioned no separation less than 10 feet and all separation was <30 feet, go down to the third row.
- Second column in third row shows that this distance is divided into 3 sub-rows based on Type of Construction and VB is the center sub-row within that third row in the first column.
- Fifth column shows R occupancy is under that column, go down to the third row, the center sub-row, -0- is shown as the minimum fire-resistance rating of the exterior walls.

The exterior walls do not require a fire-resistance rating. However, if the walls did require a fire-resistance rating, keep in mind that the rating is from both sides, so installing Type X on just the interior surface does not help, the exterior surface would also need to be part of a fire-resistance rated design, and any windows and doors in those walls would also need to meet the requirements for openings in those fire-resistance rated walls (if a fire-resistance rating was required, none is).

FIRE-RESISTANCE RATING REQUIREMENTS FOR EXTERIOR WALLS BASED ON FIRE SEPARATION DISTANCE 'a' 'e'

Table 602 Fire Separation - fire resistance rating of exterior walls.jpg

Refer to notes 'a' and 'e' as they are at the end of the table title:
- a. Load-bearing exterior walls shall also comply with the fire-resistance rating requirements of Table 601.
- e. The fire-resistance rating of an exterior wall is determined based upon the fire separation distance of the exterior wall and the story in which the wall is located.

Note 'a' says to refer to Table 601 for load bearing exterior walls, and Table 601 shows, for Type VB, -0- fire-resistance rating for the walls. For other Types of Construction, Table 601 could change the from what is shown in Table 602, so be careful when using any table and make sure to read and check out the notes.