the concept of energy conservation of houses has been developed and began to be applied widely since the first oil crisis. now we can say definitely that insulating a house is the most effective way of saving energy, and the renewable energy sources are useful only when the demand for space heating and hot water is minimized by insulating. if a house is well insulated, it will need a much smaller, simpler and cheaper heating system. so it will be less efficient to put a solar collector and wind generator on a poorly insulated house. architects and engineers should have a certain level of practical knowledge of insulation for house to persuade customers using insulating materials and structure. moreover, it is very essential to amend the existing building codes in order to facilitate this basic necessity. for instance, the building regulations of denmark requires a u-value of 0.4 w/m exp 2 degc for heavy weight external wall. if the cavity wall has outer and inner leaf of just normal brick with internal finish of 20 mm cement mortar, which is a typical wall construction for houses in korea, the thickness of insulation materials to the cavity can be calculated in order to fullfil the u-value of 0.4 w/m exp 2 degc in addition to the cavity of the external heavy wall: expanded polyurethane 58 mm, urea formaldehyde foam 67 mm, expanded polystyrene 78 mm, mineral wool 94 mm. the economic feasibi. (era citation 07:050727)