A design model for solid timber frame members in floor and wall assemblies exposed to ISO 834 standard fire exposure is developed. The assemblies considered consist of solid timber members - joists or studs - linings of gypsum plasterboard or gypsum plasterboard backed with wood-based panels, and cavity insulation made of rock or glass fibre. Ceiling linings may be fixed to resilient channels perpendicular to the direciton of the joists.