IBC Design 721.1(2) 15-2.3

1-Hour Fire Rated Exterior or interior walls — 3-5/8" No. 16 gage steel studs at 16" on center or 2" x 4" wood…

IBC Table 721.1(2), Item 15-2.3 (d) (Exterior or interior walls): 3-5/8" No. 16 gage steel studs at 16" on center or 2" x 4" wood studs at 16" on center. Where metal lath is used, attach to the exterior side of studs with minimum 1"-long No. 6 drywall screws at 6" on center. Brick units of clay or shale not less than 2-5/8" thick complying with ASTM C216 installed in accordance with Section 1404.6 with a minimum 1" airspace. Interior side covered with one layer of 5/8"-thick Type X gypsum wallboard attached to studs with 1"-long No. 6 drywall screws at 12" on center. Minimum finished thickness (face-to-face) — 1-hr: 7-7/8". Prescriptive assembly from the adopted building code — thicknesses are code minimums, see table footnotes for conditions.