Plywood Panels in UL Fire-Resistant Wall Assemblies

Can plywood panels be added to a fire-resistance rated wall assembly to enhance structural stability?

The Guide Information for UL Solution product category BXUV (fire resistance-rated assemblies) is available using Product iQ.  Product iQ is free to use but requires a one-time registration. The Guide information for the Fire-resistance Ratings (BXUV) product category outlines acceptable variations to individual fire-resistance rated assemblies, among other details.

BXUV Guide Info Section II, item 13, and Section VI item 6. Wood Structural Panels detail the acceptable wood structural panels and the fire resistance requirements they must meet. According to Section VI, item 6, of the guide on walls and partitions, the addition of wood structural panels in fire-rated gypsum board wall assemblies is allowed, provided that:

• The panels are 4-feet-wide, minimum 7/16-inch-thick oriented strand board (OSB) or 15/32-inch-thick structural sheathing (plywood) complying with DOC PS1 or PS2, or APA Standard PRP-108, and manufactured with exterior glue.
• The panels can be applied horizontally or vertically to the framing members, as long as vertical joints are centered on studs, and staggered one stud space from the gypsum board joints.
• The wood structural panels can be applied as a base layer (directly to the wall framing and under the gypsum board), between gypsum board layers or over the top of the completed gypsum board layers.
• When wood structural panels are used over gypsum board layers of exterior wall assemblies, the panels should be protected from the exterior environment as specified in the design or as specified in the exterior walls requirements in the guide information.
• 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.