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floor constructed with wood I joists

Per the "Structural Board Association" (representing the OSB industry manufacturers) the SDI for OSB is an average of 137. Woods typically used as the top & bottom chords have SDI range from about 60 to 130 depending on species. Microllam is used on some I joists with an SDI of about 80 depending on manufacturer.
 
R302.9.2 allows any material with an SDI less than 450.

I can't think of any material that could not be used.
 
Prior to, or without, the 2012 requirements of R501.3; open BCIs would have met the SDI requirements for a ceiling covering.
 
BCIs could still be used in open roof construction without additional protection on the ceiling.

We will protect the fire fighters on the floors but not on the roof.
 
When my homeplace burned from the basement no sheetrock on 2x12s After fire was out they were sagging a couple inches close to failure.
 
Exposed untreated I-joists are a problem that is compounded by the heating system and electric panel both being located down there with them. Throw in a few cubic yards of combustible storage, a few half empty paint cans, etc.

Some will argue that the increased number of concealed spaces is worse when you add gyp board.

Some will decry the nanny state.

Some will pay the extra $$$ for the intumescent finish.

Some won't because they're toxic.

Some will keep on using dimensional lumber.

Pretty much everybody will come here and kvetch one way or another.

For my part, I think it's a good provision.
 
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