Nusantara is the future capital of Indonesia, located on the east coast of Borneo in East Kalimantan province. As of July 2022, Nusantara construction began, with the first phase of clearing land and installing roads. As a matter of fact, Indonesia's main problem is its high energy consumption. Over one-third of the country's energy consumption is consumed by buildings. Therefore, energy-saving strategies will be essential to making the cities more sustainable, especially in Nusantara. Since Nusantara was planned to be a model sustainable city that could serve as an example for other Indonesian cities. An analysis of tropical-climate residential building design is presented in this paper. A strategy for energy-efficient buildings is outlined based on literature analysis and results from a case study in tropical cities. An energy simulation analysis shows that middle-rise residential houses adapted from Lamin houses will likely consume less electricity (8%) than typical apartment buildings. The simple adaptation of a traditional local building, Lamin house, to a modern mid-rise residential building suggested an open plan with a long and narrow floor plan, overhang over the window, and cross ventilation through window openings.