708.3 Exc 2 - 1/2 Hour Rating

[alora]

An owner is converting an existing, sprinklered, V-B, 6,000sf, 2-story structure being used as 2 business offices (upstairs/downstairs) into four separate 4-bedroom, 2-story dwelling units (R-2). It's a 4-sided building, and we're keeping the exterior walls, slab & roof as they are, modifying window/door locations for design & egress purposes.

Our plan is to re-use and re-design the existing sprinkler system under the applicable criteria (13R). This should allow us to utilize the exception mentioned in the title.

How have you (as building officials, or former building officials) addressed the allowance for a 1/2 hour fire-resistance rating?

Do you require a UL listing?

Do you allow the use of Table 721.6.2(1), though it does not include/define the finished rating?

(FYI: Our building official is requiring 1-hour, though it's verbal, and not through any adopted amendment. And, on top of that, the fire separation walls were already designed with U305.)

 

[High Desert]

708.3 is for shafts. Did you mean 709.3?

 

[mtlogcabin]

How have you (as building officials, or former building officials) addressed the allowance for a 1/2 hour fire-resistance rating?

Do you require a UL listing? No I do not believe one exist.

Do you allow the use of Table 721.6.2(1), though it does not include/define the finished rating? Yes

Another way is to use the Existing Building Code which should be what you would use for this project

RESOURCE A

GUIDELINES ON FIRE RATINGS OF

ARCHAIC MATERIALS AND ASSEMBLIES

 

[Big Mac]

I believe it was Section 708.3 in the 2006IBC and Section 709.3 in the 2009IBC, although I don't have my 2006IBC handy. At any rate, a NFPA13R sprinkler system is not adequate to permit the reduction to 1/2 hour. The section says "an automatic sprinkler systemin accordance with Section 903.3.1.1." Sprnikler systems in accordance with Section 903.3.1.1, are full blown NFPA13 sprinkler systems.

Section 903.3.1.2 addreses NFPA13R sprinkler systems.

Typically what we see is one-hour construction (5/8" type 'X' gwb on each side), but the opening protection is reduced to 20-minutes.

 

[High Desert]

Thanks Big Mac, you are absolutely right. A 13R system would still require 1-hour fire partitions.

 

[mtlogcabin]

Good catch Big Mac you are correct. A full NFPA 13 is required to get the reduction

 

[alora]

Interesting.

Talked with Fire Plans Examiner and they are allowing either 13 or 13R.

Discussed 903.3.1.1 & 903.3.1.1.1.

Either way, 1-hour has been designed.

 

[mtlogcabin]

Interesting.Talked with Fire Plans Examiner and they are allowing either 13 or 13R.

Discussed 903.3.1.1 & 903.3.1.1.1.

Either way, 1-hour has been designed.

If it is one-hour then it can be a 13R. In my state it is spelled out by the state that the building department has the final say on which sprinkler system may be used.

 

[TJacobs]

Its black and white...no interp or say necessary.

 

[coloradocode]

There are a couple of UL Designs that have a 1/2 hour rating. Check out designs U319 & U407. You can also use the calculated rating option in Sectioin 721 as noted by others.

The comments about the use of a NFPA 13 vs 13R system are partially correct. They are correct for the fire partitions between the units. However, the corridor can be 1/2 hour with either type of system. A little inconsistency in the code maybe?

 

[texasbo]

However, the corridor can be 1/2 hour with either type of system. A little inconsistency in the code maybe?

Correct. Footnote c. to Table 1017.1 allows reduction of corridor rating to 1/2 hr with sprinkler system in accordance with 903.3.1.1 or 903.3.1.2 where allowed. 903.3.1.2 is 13R.

 

[Francis Vineyard]

An owner is converting an existing, sprinklered, V-B, 6,000sf, 2-story structure being used as 2 business offices (upstairs/downstairs) . . .Do you allow the use of Table 721.6.2(1), though it does not include/define the finished rating?

(FYI: Our building official is requiring 1-hour, though it's verbal, and not through any adopted amendment. And, on top of that, the fire separation walls were already designed with U305.)

To reiterate what has been mentioned;

Table 721.6.2(1) is allowed with the Building Official approval to be used instead of a prescribed or UL design; please see 703.3

The “time assigned” or "finished rating" is determined as an assembly on the fire exposed side but including the least resistance side as applicable; please read 721.6.2

Regardless of whether the walls end up being a half hour or one hour fire-resistance rated remember the duct penetrations will be the same; please see 716.5.4 and 716.6

Sounds like there may have been a few changes to this building when it currently has a NFPA13 system in a office; typically B use group of this size.

Apparently the Building Official has you on the right path, because there seems to be more going on here than what meets the eye.

Hope we’ve answered you questions.

 

[alora]

Yes.

Thank you.