South Korea must submit its targets for greenhouse gas reduction by 2030 to comply with the Paris Agreement. While South Korea’s government has announced a roadmap for achieving greenhouse gas reduction targets by 2030, issues are present regarding the methodology used to set reduction targets, select the reduction method, and estimate the potential emissions reduction in the building sector. Accordingly, the present study identified the limitations based on an analysis of the roadmap and suggested an improvement plan for each limitation. To improve the roadmap, the methodology used to set emissions targets was changed from business-as-usual (BAU) to the absolute emissions method, the Intergovernmental Panel on Climate Change (IPCC) guidelines were applied to estimate greenhouse gas emissions, and methodology for determining emissions targets by year was proposed. The reduction method has been proposed abstractly, and five methods have been suggested: Energy consumption by building age and establishment of gross floor area for cooling/heating, supply status for each type of lighting, estimation of reduction amount through supply of LED lighting, reduction amount estimation by analyzing current supply status data for home appliances and office equipment, proposal of methodology for improvement of duplicate estimation for building energy maintenance systems (BEMS), and estimation of reduction potential by applying efficiency improvement in power generating equipment.