Separated Occupancies, table 508.4 versus table 706.4

[Ian]

Here is the basic info so far:

• 2018 IBC
• Mixed use building
• 2-story with A-2 (2275sf), B(790), F-1(5870sf) on lower level, and R-3 (2500sf) second level above A-2/B.
• No sprinklers (MT code is amended to remove sprinkler req. for some R occupancies),
• Type VB construction with frontage increases (no buildings within 30' all sides)
• Passes the calculation in 508.4.2 for allowable building area by using frontage increase factor of .75

I was thinking to use 508.4 separated occupancies and create 3 fire areas with 2-hr fire barrier between F-1 & B/R-3 and horizontal 2-hr between A-2/B & R-3 but now I'm uncertain if I am understanding this correctly. My local plans examiner said they want to see a 3-hr firewall between F-1 & B/R-3 based on the table 706.4. She doesn't seem to understand table 508.4 (she went as far as saying she thought it should be omitted from the code?). My question is, do I follow table 706.4 as it's the most restrictive separation, or can I follow the path of separated occupancies and follow table 508.4.

 

[RLGA]

Table 706.4 is only for fire walls. If you are using the separated occupancies and the allowable area works (which I think it should), then there is no need for a fire wall.

 

[cda]

Welcome

All two people from Montana are here.

 

[cda]

Welcome ….

 

[steveray]

Good first post Ian!...It sounds like you know what you are doing, the tougher part will be explaining it to the plans examiner....Maybe MT can help?

 

[Kearney.200]

you may want to reach out to the ICC they have a good power point on mixed occupancies based on the 2018

 

[mtlogcabin]

Here is the code path to use for what you are doing. It clearly shows you can use fire barriers from 707. As a designer it is your choice.

TABLE 508.4
REQUIRED SEPARATION OF OCCUPANCIES (HOURS)f
f. Occupancy separations that serve to define fire area limits established in Chapter 9 for requiring fire protection systems shall also comply with Section 707.3.10 and Table 707.3.10 in accordance with Section 901.7.

901.7 Fire areas.
Where buildings, or portions thereof, are divided into fire areas so as not to exceed the limits established for requiring a fire protection system in accordance with this chapter, such fire areas shall be separated by fire walls constructed in accordance with Section 706, fire barriers constructed in accordance with Section 707, or horizontal assemblies constructed in accordance with Section 711, or a combination therof having a fire-resistance rating of not less than that determined in accordance with Section 707.3.10.

Just curious about your R-3 classification and what specific use this is

 

[Ian]

Table 706.4 is only for fire walls. If you are using the separated occupancies and the allowable area works (which I think it should), then there is no need for a fire wall.

Thank you for confirming this! As long as I am understanding section 508.4 and how to use the frontage increase for the separation calculation then it works out. Here is my math:
2275sf/10500 + 790/15751 + 5870/14875 = .66 which passes since its less than 1

 

[Ian]

Here is the code path to use for what you are doing. It clearly shows you can use fire barriers from 707. As a designer it is your choice.

TABLE 508.4
REQUIRED SEPARATION OF OCCUPANCIES (HOURS)f
f. Occupancy separations that serve to define fire area limits established in Chapter 9 for requiring fire protection systems shall also comply with Section 707.3.10 and Table 707.3.10 in accordance with Section 901.7.

901.7 Fire areas.
Where buildings, or portions thereof, are divided into fire areas so as not to exceed the limits established for requiring a fire protection system in accordance with this chapter, such fire areas shall be separated by fire walls constructed in accordance with Section 706, fire barriers constructed in accordance with Section 707, or horizontal assemblies constructed in accordance with Section 711, or a combination therof having a fire-resistance rating of not less than that determined in accordance with Section 707.3.10.

Just curious about your R-3 classification and what specific use this is

Thank you for sending these sections. The issues I see is the last part, "or a combination therof having a fire-resistance rating of not less than that determined in accordance with Section 707.3.10."
Table 707.3.10 requires a 3HR barrier for F-1 occ.
Seems like there is contradictory info - table 508.4 calls for a 2-hr separation but both tables 706.4 and 707.3.10 call for 3hr. What do you guys think? Does table 508.4 need to be revised to say the same?

 

[mtlogcabin]

Yes it looks like the F-1 will require a 3 hour fire barrier in order to create a separate fire area for the F-1 use unless you can put the F-1 and B use in the same fire area where no occupancy separation is required between the 2 occupancy types and you are still under 1 in your area increase calculations.

 

[Ian]

We've established it needs to be 3-hr, but is it a barrier that can terminate at the roof or fire wall with vertical and horizontal extensions?

 

[mtlogcabin]

You are permitted to design it as a fire barrier or a firewall when creating separate fire areas. The plans examiner cannot dictate which one to use. It is the fire rating your are required to comply with and the code gives two choices when designing the vertical separation a fire barrier or a fire wall.