From subarctic to subtropical, Japan’s varied climates present a challenge for energy-saving housing design. Adding the projected effects of climate change, with temperatures estimated to rise from 1.5 to 3.5°C by the close of the century, there currently is not a standard, one-size-fits-all solution. Therefore, climate-based building design solutions that consider regional differences, thermal comfort, and net-zero carbon goals are urgently needed.
In search for efficient designs, a research group led by Associate Professor Jihui Yuan from Osaka Metropolitan University’s Graduate School of Human Life and Ecology conducted energy simulations for 10 cities across all climate regions in Japan, comparing current and future scenarios using a 120.08 m² two-story three-dimensional residential model. Using weather data and a Genetic Algorithm, they then optimized window-to-wall ratio (WWR) and the thermal resistance performance of the roof, exterior walls, and windows.
As a result, it was found that in cold regions like Sapporo, Hokkaido, strengthening home insulation can reduce the energy used for heating by approximately 15,000 kWh per year. In moderate regions like Tokyo, setting WWR to 0.29 saved approximately 6,800 kWh of energy annually. Meanwhile, in subtropical Naha, Okinawa, setting the WWR to 0.45 can improve ventilation and reduce air conditioning energy consumption by approximately 3,600 kWh. Additionally, it was found that using high-performance windows can reduce the cooling load during the hottest times in south-facing rooms by 23 to 27%.
“This research provides optimal housing design guidelines tailored to each region, contributing to the promotion of net-zero energy housing, the regional optimization of energy efficiency standards, and local governments' climate adaptation policies. Going forward, we plan to work toward “building-city integrated optimization” that combines renewable energy adoption, variable factors in resident behavior, and city-scale environmental measures,” stated Professor Yuan.
The findings were published in Energy Nexus .
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Energy Nexus
Computational simulation/modeling
Not applicable
Optimization of energy-efficient residential building design in Japan: A climate-responsive approach under current and future scenarios
20-Nov-2025
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.