Mark:
3 places to look. 1. UBC Table 7-B fire ratings of partitions, IBC Table 720.1. 2. Gypsum Association (GA) www.gypsum.org. Fire ratings for wood stud partitions. A similar condition is GA file No WP3330 using wood fiberboard under drywall. 3. U.L. publishes fire rated design assemblies.
Respectfully,
Bob Freeman, Architect, Structural Designer
Integrated Design Services, Inc.
(949) 387-8500