Effectiveness of the use of noncombustible ceiling for the improvement of fire safety in a compartment with wooden wall is studied by full scale burn tests. It has been clarified that the use of noncombustible ceiling lead to notable delay of fire spread along lining surface, and that the criteria and the extent for lateral fire spread along wall surface, the possible cause for flashover can be evaluated by the estimation of heat flux to the wall surface from the smoke layer. For a given smoke layer temperature, the heat flux can be estimated using the total heat transfer coefficient, a=0.04kW/m^2K.