IBC 2006/2009/2012
2-Story, 2B (could be any Type I or II)

Section 603 clearly identifies where combustible material is allowed in Type I & II construction. My question pertains to "blocking" and when does a certain of amount of "blocking" become sufficient to justify fire-retardant material.

Often we use 3/4" plywood on the back side of a parapet framed with metal studs to allow attachment of flashing/roofing. The plywood serves both as the wall cladding and blocking. The parapet could range in height from 2' to say 8'-10'. At some point it seems suitable to use fire-retardant since this becomes more of a wall then just blocking. On taller walls (above 4') we have used non-fire-retardant plywood on the lower 18" and then gypsum board above.

Just curious of what others are seeing/doing. I have not had a jurisdiction say one way or another. My gut tells me there is so little fuel (since only cladding might be combustible) in the "big" picture that is probably does not matter, but also technically might not comply with code language.

Original Post
Is not "blocking" different then sheathing? Each with a different purpose?

Blocking is intended to be solid between two similar solid materials while sheathing spans or bridges across supporting material.

Blocking is intended to stop or limit the spread of smoke and fire, is it not?
ADAguy: There is blocking and then there is fireblocking.

Blocking is wood or other material used within a wall for attachment of other items, such as cabinets, handrails, grab bars, etc.

Fireblocking is a solid material used to prevent the spread of fire within a concealed space.

For interior partitions, I would use FRTW. For parapets and exterior walls, you'll need to comply with Section 1406 (2012 IBC).

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