# Construction Type IIIB/ exterior load bearing assembly (UL 349)



## LDC28 (Sep 1, 2020)

Hi there,
I am using UL 349 2 hour rated load bearing assembly in Type IIIB construction. UL349 gives several options for the for which face should be fire rated/ exposed to fire. Curious if UL349 needs to be configured to be exposed to fire on both sides or interior only? 

Thanks in advance!


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## classicT (Sep 1, 2020)

Given Type III-B, exterior walls must be 2-hr fire resistant construction per _IBC Table 601_.
_IBC Table 602_ would only increase it to 3-hr fire resistant construction if FSD<5 and occupancy is a group H.

Presume that you are referring to UL Assembly U349, which has (3) configurations. See complete listing at UL Product iQ

2-hr (fire from interior only)
2-hr exterior / 1-hr interior
2-hr (fire from either face)
To determine if the exterior wall must be rated from both exterior and interior, see _IBC Section 705.5 _(as follows).

*705.5 Fire-Resistance Ratings*
Exterior walls shall be fire-resistance-rated in accordance with Tables 601 and 602 and this section. The required fire-resistance rating of exterior walls with a fire separation distance of greater than 10 feet (3048 mm) shall be rated for exposure to fire from the inside. The required fire-resistance rating of exterior walls with a fire separation distance of less than or equal to 10 feet (3048 mm) shall be rated for exposure to fire from both sides. 

Given _IBC Section 705.5_, we need to know what the FSD is to determine if it must be rated from the exterior. If FSD is greater than 10-ft, an exterior rating is not required.

So... if FSD is greater than 10-ft, use configuration #1 (below)



If FSD is less than 10-ft, use configuration #3 (below)


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## RLGA (Sep 1, 2020)

The assembly is actually UL *U*349, and it does provide three options for a 2-hour exterior wall assembly. 

The first option is only for an interior exposure, which means your exterior wall is required to be 2-hour rated and it must be located more than 10 feet from the lot line to use that assembly. 

The second option provides a 2-hour rating for an interior exposure and a 1-hour rating for an exterior exposure. This would be necessary where you are required to have a 2-hour exterior wall and it is located more than 10-feet from the lot line, but some other requirement of the code requires 1-hour protection, such as a wall for an egress court that is less than 10-feet wide. 

The third option is for an exterior wall that is required to have a 2-hour rating and is located 10 feet or less to the lot line.


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## LDC28 (Sep 1, 2020)

RLGA said:


> The assembly is actually UL *U*349, and it does provide three options for a 2-hour exterior wall assembly.
> 
> The first option is only for an interior exposure, which means your exterior wall is required to be 2-hour rated and it must be located more than 10 feet from the lot line to use that assembly.
> 
> ...




Ron and Ty, Thank you very much for providing some clarity on this! Yes, I am referring to UL-U349 and it would be used on a property line (0' FSD) so therefore the third option would work in this scenario.


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## LDC28 (Sep 1, 2020)

RLGA said:


> The assembly is actually UL *U*349, and it does provide three options for a 2-hour exterior wall assembly.
> 
> The first option is only for an interior exposure, which means your exterior wall is required to be 2-hour rated and it must be located more than 10 feet from the lot line to use that assembly.
> 
> ...



Follow up question- It appears as though UL U349 only allows 2 hour fire protection from both sides when brick is used, curious about an alternate that does not require brick in order achieve 2 hour rating from both sides. Only some of the UL assemblies mention the side from which the fire rating is provided...


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## RLGA (Sep 1, 2020)

Look at Gypsum Association's GA-600, GA File No. WP 8420. It provides a 2-hour assembly (both sides) and uses stucco for the exterior finish.


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## LDC28 (Sep 1, 2020)

RLGA said:


> Look at Gypsum Association's GA-600, GA File No. WP 8420. It provides a 2-hour assembly (both sides) and uses stucco for the exterior finish.



*Context:*
Table 601: Requires 2 hours rating @ IIIB exterior walls
Table 602: Requires min 1 hour rating for Group R or B
Section 705.5 requires specifies that if the FSD is >10', then both interior and exterior need to be rated for exposure.

*Question: *
In an instance of a Type IIIB exterior wall that has FSD of less than 10'-0", wouldn't the exterior exposure be based on table 602 (requiring 1 hour rating), and therefore allowing option 2 of UL-U349 (2 hour rating from interior face and 1 hour from exterior face). UL-U349 is is a "2 hour rated assembly" and this also meets the requirement of Table 601. 

Does the code actually specify the requirement rating of the exterior facing of the assembly? It does not appear to do so within 705.5 and therefore I wonder if option 2 of UL-U349 would pass? 

The reason behind the question is that I need more options for exterior cladding and it appears to be very limited outside of this assembly.


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## RLGA (Sep 1, 2020)

LDC28 said:


> *Context:*
> Table 601: Requires 2 hours rating @ IIIB exterior walls
> Table 602: Requires min 1 hour rating for Group R or B
> Section 705.5 requires specifies that if the FSD is >10', then both interior and exterior need to be rated for exposure.
> ...


Correction to your context above, if FSD is *<*10' then it requires protection for interior and exterior exposure.

To answer your question, no. The exterior exposure rating when less than 10 feet must be equal to or greater than the interior exposure rating. Footnote 'a' of Table 602 states that loadbearing walls are required to comply with Table 601. If the exterior wall is not load-bearing, then the 1-hour fire rating per Table 602 may be used.


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