Fire Resistance Rating | Both Sides? Calculated Fire Resistance IBC 722

[rosegamble]

Hello!

I have a question regarding fire-resistance rating in a wood-framed commercial building. Assemblies in various places (walls and floors) must be 1 hour rated. I have spent some time in IBC 722. I know I can find a UL-approved detail online but I'm interested in understanding how 722 works.

Question (1): Where does the code say a fire-rating must be provided on both sides of a wall? I cannot locate this! For example, a 1-hour interior wall must have rating from both sides, right? Where is this codified? 722.6 says that a 5/8" type x GWB contributes 40 minutes. If I have this on both sides, am I allowed to include the wood studs (contributing 20 minutes) for BOTH sides? So both can share the wood and get to 1 hour.

Question (2): Horizontal Assemblies! I need a 1-hour rated wood floor. Where in the code does it say this rating is only required from the bottom? Not symmetrical like walls? Conceptually, the fire could occur in either floor so it seems odd that you would only need to rate from below, as the UL-approved details seem to be doing.

Thanks so much!

 

[mtlogcabin]

If I have this on both sides, am I allowed to include the wood studs (contributing 20 minutes) for BOTH sides? So both can share the wood and get to 1 hour.

Yes, that is correct

Heat rises so the protection is on the ceiling of a floor/ceiling assembly

 

[RLGA]

See IBC Section 703.2.1.1 for nonsymmetrical wall construction. The rating of an assembly is based on the lowest performance when tested from both sides of the assembly for wall construction.

Regarding the second part of your first question, refer to Section 722.6.2.1. When determining the fire-resistance rating using the calculated method you calculate for exposure from both sides. Each side includes the exposed membrane, any supporting construction (e.g., studs), and insulation. You cannot include the time period for the membrane on the non-exposed side.

Horizontal assemblies are only tested from the bottom exposure since flame and heat rises. Exposure at the ceiling level will be several times more severe than exposure to the floor surface. Should a floor or roof assembly be exposed to a fire below, the structural strength could be comprised more quickly than the exposure on the floor assembly where the fire occurs.

Floor surfaces must comply with the finish classes to minimize the lateral spread of the fire, but the concern of the fire burning downward through the floor assembly is less critical.

 

[Tim Mailloux]

See IBC Section 703.2.1.1 for nonsymmetrical wall construction. The rating of an assembly is based on the lowest performance when tested from both sides of the assembly for wall construction.

Regarding the second part of your first question, refer to Section 722.6.2.1. When determining the fire-resistance rating using the calculated method you calculate for exposure from both sides. Each side includes the exposed membrane, any supporting construction (e.g., studs), and insulation. You cannot include the time period for the membrane on the non-exposed side.

Horizontal assemblies are only tested from the bottom exposure since flame and heat rises. Exposure at the ceiling level will be several times more severe than exposure to the floor surface. Should a floor or roof assembly be exposed to a fire below, the structural strength could be comprised more quickly than the exposure on the floor assembly where the fire occurs.

Floor surfaces must comply with the finish classes to minimize the lateral spread of the fire, but the concern of the fire burning downward through the floor assembly is less critical.

you sure know your stuff! Ever think of writing a book?

 

[rosegamble]

See IBC Section 703.2.1.1 for nonsymmetrical wall construction. The rating of an assembly is based on the lowest performance when tested from both sides of the assembly for wall construction.

Regarding the second part of your first question, refer to Section 722.6.2.1. When determining the fire-resistance rating using the calculated method you calculate for exposure from both sides. Each side includes the exposed membrane, any supporting construction (e.g., studs), and insulation. You cannot include the time period for the membrane on the non-exposed side.

Horizontal assemblies are only tested from the bottom exposure since flame and heat rises. Exposure at the ceiling level will be several times more severe than exposure to the floor surface. Should a floor or roof assembly be exposed to a fire below, the structural strength could be comprised more quickly than the exposure on the floor assembly where the fire occurs.

Floor surfaces must comply with the finish classes to minimize the lateral spread of the fire, but the concern of the fire burning downward through the floor assembly is less critical.

Thanks so much for your time. So it sounds like using the calculated method, you can "double count" the wood studs for example. In other words, they count towards both sides' ratings. But yes, you cannot include both "membranes."

That's what I have heard for horizontal assemblies (bottom ceiling membrane can provide the rating) but struggling to find this in the code. If you know of a reference, I'd be curious to see it!

Thanks again.

 

[RLGA]

That's what I have heard for horizontal assemblies (bottom ceiling membrane can provide the rating) but struggling to find this in the code. If you know of a reference, I'd be curious to see it!

For the calculated method, refer to IBC Section 722.6.2.4.

For tested assemblies, refer to Section 703.2.1, which references ASTM E119 and UL 263. ASTM E119 states the following:

8.6.1 Application—This procedure is applicable to floor and roof assemblies with or without attached, furred, or suspended ceilings and requires the application of the fire exposure to the underside of the test specimen.​

​

UL 263 is essentially ASTM E119, but with UL's specific protocols.

 

[rosegamble]

For the calculated method, refer to IBC Section 722.6.2.4.

For tested assemblies, refer to Section 703.2.1, which references ASTM E119 and UL 263. ASTM E119 states the following:

8.6.1 Application—This procedure is applicable to floor and roof assemblies with or without attached, furred, or suspended ceilings and requires the application of the fire exposure to the underside of the test specimen.​

​

UL 263 is essentially ASTM E119, but with UL's specific protocols.

Got it. Wow, thanks so much!