For a typical office building in Hong Kong, air-conditioning is the largest component of energy use consuming nearly half (48%) of the total energy consumption. With increasing concerns of the greenhouse gas emission arising from electricity consumption and the rising energy cost, the demand for better thermal insulation in the building envelope has drastically increased. The thermal insulation of building envelope can be improved by constructing the exterior wall with foamed concrete that has lower thermal conductivity than normal concrete. Foamed concrete is a lightweight material containing entrapped homogeneous pores in the matrix. By optimizing the mix compositions, foamed concrete with excellent heat insulation, satisfactory strength and high dimensional stability can be achieved. Furthermore, a thin layer of light weight pseudo-ductile Fiber Reinforced Cementitious Composite (FRCC) can be used to wrap around the foamed concrete to increase the ductility and strength of the entire pre-cast wall.