Or can the existing walls (interior non-bearing wall) be layered with sheet rock. Ref. NFPA 101 para. 22.214.171.124.1
Reference: NFPA 220 para. 126.96.36.199.2 Interior nonbearing walls required to have fire resistance rating of 2 hours or less shall be permitted to be fire-retardant-treated wood enclosed within noncombustible or limited-combustible materials, provided that such walls are not used as shaft enclosures.