For occupants' convenience, the government announced that balcony remodeling would be legal from this year. But when the balcony is remodeled, problems would take place such as noise, dew condensation, increase in heating energy, and so on. Building energy consumption takes up to 24% of total energy consumption. Now, construction companies design apartment considering balcony remodeling. So they must consider that insulation performance should be improved and window area ratio should be controled with the balcony remodeling in advance of construction. As alternatives for these problems of thermal performance, we suggested that additional insulations within walls and thermal-improved windows like Low-e glazing and Argon glazing , decrease of window area ratio might be effective, and we simulated the effect of the alternatives. we expected that building energy consumption would be kept up if insulation performance of wall and window is improved at expanded area and window area ratio is decreased.