November 21, 2003
Flame spread varies with wood species, and OSB has a lot of glue exposed. I think it would have to be separately tested (ASTM E84) to establish a flame spread rating.
OSB can be substituted for plywood in fire-resistance rated assemblies (tested to ASTM E119).
August 13, 2007
Thanks for the answer maniac.
Alot to absorb, but after my 1st read it appears both APA & UL consider OSB & plywood to be equal (as long as the panels meets the generic reqmts)?
March 7, 2001
OSB and plywood in UL fire-rated assemblies
Many fire-rated assemblies specified and built today were originally tested and approved with
plywood as the floor covering. Because APA often supplied panels for tests, some specifications
still list APA-rated panels as the approved sheathing in these assemblies. In 2000, engineers at
Underwriters Laboratories (UL) of Northbrook, Illinois, determined that OSB of an equivalent
thickness could be substituted for plywood in these designs. Going one step further, UL revised
its UL fire-rated assembles to no longer limit use of structural panels to those of a single
certification agency. The revision, sponsored by TECO, was necessary because original language
appeared to exclude the use of plywood and OSB panels unless certified by APA. While never
intending to restrict panel use to a single agency, UL recognized this language as exclusionary and modified the assembly designs to include the use of all panels meeting PS 1 and PS 2 standards.
The new, revised language is included in the 2000 edition of the UL Fire Resistance Directory. A
subsection 13 has been added to the General section at the beginning of Volume I and includes
"Wood Structural Panel is a structural panel product composed primarily of wood and meeting
the requirements of the U.S. Department of Commerce Voluntary Standard PS 1, Construction
and Industrial Plywood or the U.S. Department of Commerce Voluntary Product Standard PS 2, Performance Standard for Wood-Based Structural-Use Panels. Wood structural panels include all -veneer plywood, composite panels containing a combination of veneer and wood-based material, and mat-formed panels such as oriented strand board and waferboard. The panels are to bear the label of a code-recognized certification organization with a specific reference to the PS 1
or PS 2 standard. The panels shall also be marked Exposure 1 or Exterior. Some individual designs may limit the type of panel that can be used.
As an alternate, wood structural panels evaluated in accordance with APA ? The Engineered Wood Association Standard PRP-108, Performance Standards and Policies for Structural-Use Panels, or PFS Research Foundation Standard PRP-133, Performance Standards and Policies for Wood -Based Structural-Use Panels, and meeting the description for the panel type in the individual designs, may be used."
In addition, all references to trade names have been removed from the individual design assembly
descriptions and replaced with more generic terminology.
"19/32-in. thick wood structural panels, min. grade "C-D" or "Sheathing." Face grain of plywood
or strength axis of panels...."
"23/32-in. thick wood structural panels, min. grade "Underlayment" or "Single-Floor." Face
Architects and engineers specify fire-rated wall, floor and roof assemblies extensively in
structures where one- and two-hour fire protection is required. The UL Fire Resistance Directory is available from Underwriters Laboratories by calling (847) 272-8800. The complete UL Fire Resistance Directory is also available on the Internet at UL?s website (http://www.ul.com).
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