Fire hazard is a common threat in longhouses in Sarawak. Among things that are crucial in fire prevention is the evacuation route, in which highly dependent on house construction and layout. This study aims to observe the evolution of the Iban longhouse architectural design and materials used to build the longhouse. The qualitative analysis method was applied through 2D photo analysis as well as on-site visual observation and measurement. Construction materials used have been surveyed to determine its combustibility. It has been noted that longhouses have evolved over the years, from traditional to semi-traditional and modern longhouses design. The changes include the layout design and construction materials of the longhouses. Traditional and semi-traditional longhouses are often built using wooden materials that are highly flammable, while modern longhouses are made from concrete materials. The types of construction materials contribute to fire severity. It can be concluded that the longhouse architectural design, along with its construction materials, plays an essential role in the understanding of fire hazard, which will serve as fundamental on the longhouse fire reduction.