A method of constructing a steel house formed of frame members of thin lightweight section steels and structural surface materials installed thereon and capable of achieving the lowering of occurrence of dew condensation, remarkable deceleration of deterioration rate of the house, remarkable increase in service life, realization of healthy environment, the reduction in the number of heaters, reduction of heating space, and increase in energy efficiency by uniformizing the hot environment inside the house, comprising the steps of, to promote the uniformization of the thermal temperature environment, forming the frame materials having thin lightweight section steels (6) with a high heat conductivity and a specified plate thickness in such a range that the upper and lower limit ratios of the surface area of in-house thin lightweight section steels to a construction area (m<2>/m<2>) are 10 to 20 and that the upper and lower limit areas of the weight of the thin lightweight section steels (6) to the construction area (kg/m<2>) in the range of the upper and lower limit ratios of the surface area of 10 to 20 are 35.0 to 115.0, and constructing the steel house (1) by an outer siding thermal insulation method. |