This report presents results of three full-scale fire tests conducted on double stud party wall/floor joints. The first two assemblies were tested with various fire stop materials (semi-rigid glass and rock fibre insulation boards, sheet steel, and oriented strand board) placed between the joist headers, to investigate whether these materials will prevent flame spread into the upper storey cavity between studs for 15 minutes. The third assembly was tested, with no fire stop material in the space between the joist headers, to investigate the effect of the width of the vertical air space between insulated double-stud frames on flame spread to the upper storey cavity between studs.