Abstract: Experimental fire tests platform were built to study the effect of external flame ejected from windows on fire spread of exterior wood-frame walls. Three typical scenarios were studied by considering different construction details and siding materials. Flame spread, carbonization and temperature change with time at different positions were analyzed. Test results showed that the exterior wall with calcium-silicate siding boards and non-cavity had the best performance. For the exterior wall with fiber-cement siding boards and cavity, the fiber-cement boards would deform and break under the flame exposure, leaving the OSB behind the cavity be ignited and the spread of flame and smoke upward along the cavity. For the exterior wall with fire-retardant wooden siding boards and cavity, it experienced ignition, steady burning and vigorous burning stages, and the fire spread upwards and went out of control. For exterior wall with cavities, the metal flush helped to reduce the vertical fire spread upon exterior walls.

Key words: timber composite structure, exterior wall, fire spread, air cavity