Plywood on Fire Rated Wall

[Mech]

2018 IBC
Existing Mall Building
Sprinklered
I am assuming the construction type is either 2B or 3B.

Tenant Fitout plans from 1995 identify a 2 hour rated tenant separation wall as 6" metal stud with (2) layers of 5/8" fire rated gyp on each side. That is fine.

The new mercantile tenant's corporate architectural drawings call for plywood over top of the entire existing fire rated wall. I believe the intent is to use it as a substrate to attach shelving, displays, mirrors, etc.

Is this allowed? Must I find a rated assembly that allows plywood? Does the plywood need to be fire rated treated wood?

Can the plywood be left exposed? I assume if plywood is allowed, it can be covered with another sheet of gyp.

 

[RLGA]

Yes, the playwood can be left exposed. Read below...

From GA-600 (if using their assemblies):

"26. ADDITION OF OTHER PANELS - When not specified as a component of a fire-resistance-rated wall or partition system, cementitious backer units, and/or wood structural panels shall be permitted to be added to one or both sides. Such non-gypsum panels shall be permitted to be applied either as a base layer directly to the framing (under the gypsum panels), as a face layer (over the face layer of gypsum panels), or between layers of gypsum panels in multi-layer systems. When such non-gypsum panels are applied under the gypsum or between layers of gypsum panels, the length of the fasteners specified for the attachment of the gypsum panel applied over the non-gypsum panels shall be increased by not less than the thickness of the non-gypsum panels. Fastener spacing for the gypsum panel and the number of layers of gypsum panels shall be specified in the system description."​

​

From UL "Guide Information for Fire-Resistance Ratings" BXUV for UL assemblies:

"6. Wood Structural Panels​

​

"The addition of wood structural panels in fire-rated gypsum board wall assemblies is permitted as described in this section. Wood structural panels that are 4 ft wide, minimum 7/16 in. thick oriented strand board (OSB) or 15/32 in. thick structural sheathing (plywood) complying with DOC PS1 or PS2, or APA Standard PRP-108, manufactured with exterior glue, may be applied horizontally or vertically to the framing members. Vertical joints should be centered on studs, and staggered one stud space from the gypsum board joints. The wood structural panels are permitted to be applied either as (1) a base layer (directly to the wall framing and under the gypsum board), (2) in between gypsum board layers, or (3) over the top of the completed gypsum board layers. When wood structural panels are added to wall assemblies that include furring channels, there should be no more than two layers (either gypsum board or wood structural panel or combination thereof) attached to the furring channel. When wood structural panels are added to the wall assembly, the length of the fastener used for the outermost layer (either gypsum board or wood structural panel) should be sized appropriately to accommodate the additional thickness of the wall panel."​

 

[Paul Sweet]

The plywood might be considered as a finish, and subject to IBC 803.