Accoya tongue-and-groove and Color Grey acetylated-wood siding
This is a listed siding assembly. Listing 8140-2421:0001. This site cites OSFM BML. Match the model and orientation.
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Accoya tongue-and-groove and Color Grey siding are both listed in California, but only inside one exact wall assembly.
CAL FIRE's Office of the State Fire Marshal carries two live listings for this acetylated-wood siding: 8140-2421:0001 for the tongue-and-groove boards and 8140-2421:0002 for the Color Grey boards, both current as of late August 2026, filed under the same product category. What each listing covers is not the boards by themselves; it is a complete wall assembly built around them.
That assembly is specific: 5/8-inch DensGlass Gold sheathing behind the siding, sealed gaps at the sheathing joints, a one-inch air cavity, and 2-by-4 framing and bracing spelled out in the listing itself. Swap the sheathing, skip the cavity, or fasten it a different way, and the boards are no longer what the state listed. The live BML records do not name a test protocol behind either number, and none should be assumed.
For anyone specifying this siding on a wildfire-area project, the listing is the assembly, not the plank. Model, thickness, framing, sheathing, cavity depth, orientation, and fastening all need to match the current listing and installation documents exactly, and nothing in Accoya's own literature should be read as filling in the missing protocol.