What consists of a 1/2 hour wall?

[Coder]

I am looking at the fire resistance rating reduction exception in the 2009 IRC for the separation wall/walls in sprinkled duplexes. 1/2 hour wall? I am assuming 1/2" sheetrock on the two surfaces would do the trick. 1 layer of 1/2" sheetrock = 15 minutes. Anyone know more? Thanks in advance.

 

[fatboy]

A quick google search, I found an article with this, you can see the informations at; http://www.awci.org/cd/pdfs/8309_f.pdf

Based on below, you would not make 1/2 hour unless you used 1/2 Type X or C. Just with some quick research.

Regular gypsum board, after wateris driven off by heat from a fire,reduces in volume, develops largecracks in the board, and eventuallyfails. A 5/8 inch regular gypsum wallboardpanel exposed to 1850°F., willfail in 10 to 15 minutes. By extrapolation,a 1/2-inch board would probably

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fail in 10 to 12 minutes.

 

[mark handler]

45 Minutes Fire-Rated Construction

1/2" Sheetrock Firecode C Core gypsum panels

2 x 4 wood stud 16" o.c.

UL Des U317

 

[cda]

Also in the Ibc gives rating on different materials , forgot what section

 

[mtlogcabin]

A wood stud at 16" OC gives you 20 minutes. 1/2" gypsum wallboard gives you 15 minutes = 35 minute rating

Table 721.6.2(1) and 721.6.2(2)

d. The membrane on the unexposed side shall not be included in determining the fire resistance of the assembly. When dissimilar membranes are used on a wall assembly, the calculation shall be made from the least fire-resistant (weaker) side.