# Is a 2x8 considered a joist for a fire rated floor / ceiling assembly?



## Mech (Jul 31, 2013)

2009 IBC

From Table 720.1(3), Minimum protection for Floor and Roof Systems, the floor construction of Item 21-1.1 is "_Wood joists, wood I-joists, floor trusses and flat or pitched roof trusses spaced a maximum 24″ o.c. with __1__/__2__″  wood structural panels with exterior glue applied at right angles to  top of joist or top chord of trusses with 8d nails. The wood structural  panel thickness shall not be less than nominal __1__/__2__″ nor less than required by Chapter 23._"

What is a wood joist?  My floor is framed with 2x8s.  Is a 2x8 considered a wood joist for this assembly?

Thanks.

ps - I am looking for a 1 hour rated floor/ceiling assembly using 2x8 @ 16", gypsum board ceiling, and a 3/4" T&G subfloor that permits fiberglass insulation.  I do not know what the floor finish will be.  I looked in the IBC, UL, and GA 600; no assemblies using 2x8, only 2x10.


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## mtlogcabin (Jul 31, 2013)

Frequently Asked Questions

*For one-hour fire-rated wood joist assemblies, how do I compensate using a 2x8 rather than a 2x10?*

 One-hour rated floor/ceiling assemblies that are derived by ASTM E119 testing are typically constructed with 2x10 or 2x12 joists. Joists of lesser depths, such as 2x8, are generally not permitted to be substituted unless the assembly is retested. However, with approval of the building official, the empirical methods in IBC 721.6 and AF&PA's _DCA 4_ can be used to estimate fire endurance times for 2x8 floor/ceiling assemblies without testing.

Download it here: http://www.awc.org/publications/DCA/DCA1/DCA1.pdf.

FAQ Files

Table 721.6.2(2) will give you 10 minutes for a wood floor joist space 16" OC

Table 721.6.2(1) will give you 40 minutes for 5/8" Type X gypsum board

I would use 2 layers for the additional time because most GA assemblies require the extra layer when using insulation. The insulation allows more heat build up


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## RJJ (Aug 1, 2013)

MT: An great answer to a question that is always coming up in one fashion or another.


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