[HINOKIYA Report VOL.2] Verification of Summer Electricity Bill Reduction Effect of Insulation Grade 6 in 3 Regions: Regions 3, 4, and 6
Hinokiya Group has released "HINOKIYA Report VOL.2," which verifies the impact of detached house insulation performance on summer electricity bills. The study compared homes with insulation grades 5 and 6 in three locations across regions 3, 4, and 6. The electricity bill reduction effect was confirmed only in Region 6, with only a slight difference in other regions.
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- 📰 Published: May 12, 2026 at 01:00
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Hinokiya Group Co., Ltd. (Headquarters: Chiyoda-ku, Tokyo; Representative Director, President and CEO: Akira Kondo; hereinafter, Hinokiya Group) announced today that it has conducted a similar experiment (hereinafter, "this experiment") and verification for the summer period, following the publication of "HINOKIYA Report VOL.1" in June 2025, which presented the results of an experiment on the impact of differences in residential insulation performance on winter electricity consumption, in response to the growing awareness among customers considering detached houses regarding housing performance and electricity bills.
Hinokiya Group Hinokiya Home Experimental House Exterior (Nasushiobara City, Tochigi Prefecture)
"Aquafoam" on-site spray foam insulation construction image
This experiment was conducted under the supervision of Associate Professor Masayuki Mae of the Graduate School of Engineering, The University of Tokyo, for three months from July 2025 to September 2025, at three locations with different thermal climate zones (*1) (Regions 3, 4, and 6). At each location, two detached houses (total of six houses) with the same floor area but different insulation performances (insulation performance grades 5 and 6) were used. All houses were two-story, approximately 30 tsubo (approx. 99 sqm) in total floor area, using "Aquafoam" on-site spray foam insulation, and the "Z-Air Conditioning" whole-house air conditioning system was operated all day to maintain a room temperature of 26°C in each living space. The outdoor temperature and room temperature in each room, as well as the electricity consumption of the air conditioners, were measured at various observation points inside and outside, and the differences between the two houses at each location were compared. In addition, monthly electricity bills were calculated from the electricity consumption to verify the cost-effectiveness.
Furthermore, in Region 6, where the average daily outdoor temperature during the period exceeded the set room temperature, an additional detached house with insulation performance grade 6 specifications, using a different insulation material (glass wool) with different airtightness, was added, making a total of three houses. The electricity consumption and electricity bills were calculated and compared.
The location where the electricity consumption (electricity bill) reduction effect due to insulation grade in summer was confirmed in this experiment was only one of the three target locations (Region 6: Yashio City, Saitama Prefecture). In the other two locations (Region 3: Saku City, Nagano Prefecture, and Region 4: Nasushiobara City, Tochigi Prefecture) and in the comparison between glass wool grade 6 and Aquafoam grade 5 in Region 6, the monthly electricity bill difference remained at approximately 200 to 500 yen, which was very small. For detailed results of this experiment and verification of the electricity consumption (electricity bill) reduction effect over six months (December to February, July to September), including the winter results published in "VOL.1," please refer to the main report (separate attachment).
Hinokiya Group will utilize the verification results of this experiment for product and service development, and will continue to promote high-airtightness and high-insulation home building with added value, supporting customers' comfortable living environments.
*1 Refer to the thermal climate zone classification established by the Ministry of Land, Infrastructure, Transport and Tourism https://www.mlit.go.jp/common/001500182.pdf
[About "HINOKIYA Report"]
Hinokiya Group conducts various demonstration experiments related to building insulation and airtightness using housing exhibition halls and experimental houses nationwide, and continuously investigates the electricity consumption and electricity bills of its self-developed whole-house air conditioning system "Z-Air Conditioning" over a long period. The results of these experiments, analyses, and investigations are published irregularly as "HINOKIYA Report."
・HINOKIYA Report VOL.1 (Issued June 2025)
"Regarding the electricity consumption measurement experiment due to differences in insulation performance in winter 2025"
・HINOKIYA Report VOL.2 (Issued May 2026)
"Regarding the electricity consumption measurement experiment due to differences in insulation performance in summer 2025"
[About Masayuki Mae]
Associate Professor, Department of Architecture, Graduate School of Engineering, The University of Tokyo
Born in 1975. After completing his doctoral course in Architecture at the Graduate School of Engineering, The University of Tokyo in 2003, he worked at the Building Research Institute as a Japan Society for the Promotion of Science Research Fellow. From April 2004, he became a researcher at the National Institute for Land and Infrastructure Management, and from October 2004, a visiting associate professor at the Tokyo Electric Power Company Endowed Chair, The University of Tokyo. He has been in his current position since April 2008. Doctor of Engineering. His specialty is architectural environmental engineering, and his research theme is overall energy consumption in housing.
[Hinokiya Group Company Profile]
■Company Name: Hinokiya Group Co., Ltd. https://www.hinokiya-group.jp/
■Headquarters: Marunouchi Trust Tower Main Building, 1-8-3 Marunouchi, Chiyoda-ku, Tokyo 100-0005
■Established: October 1988
■Representative: Akira Kondo, Representative Director, President and CEO
■Business Activities: Housing business, insulation material business, real estate investment business, renovation business
■Main Housing Brands: Hinokiya Home, Papamaru House, Resco House
Hinokiya Group Hinokiya Home Experimental House Exterior (Nasushiobara City, Tochigi Prefecture)
"Aquafoam" on-site spray foam insulation construction image
This experiment was conducted under the supervision of Associate Professor Masayuki Mae of the Graduate School of Engineering, The University of Tokyo, for three months from July 2025 to September 2025, at three locations with different thermal climate zones (*1) (Regions 3, 4, and 6). At each location, two detached houses (total of six houses) with the same floor area but different insulation performances (insulation performance grades 5 and 6) were used. All houses were two-story, approximately 30 tsubo (approx. 99 sqm) in total floor area, using "Aquafoam" on-site spray foam insulation, and the "Z-Air Conditioning" whole-house air conditioning system was operated all day to maintain a room temperature of 26°C in each living space. The outdoor temperature and room temperature in each room, as well as the electricity consumption of the air conditioners, were measured at various observation points inside and outside, and the differences between the two houses at each location were compared. In addition, monthly electricity bills were calculated from the electricity consumption to verify the cost-effectiveness.
Furthermore, in Region 6, where the average daily outdoor temperature during the period exceeded the set room temperature, an additional detached house with insulation performance grade 6 specifications, using a different insulation material (glass wool) with different airtightness, was added, making a total of three houses. The electricity consumption and electricity bills were calculated and compared.
The location where the electricity consumption (electricity bill) reduction effect due to insulation grade in summer was confirmed in this experiment was only one of the three target locations (Region 6: Yashio City, Saitama Prefecture). In the other two locations (Region 3: Saku City, Nagano Prefecture, and Region 4: Nasushiobara City, Tochigi Prefecture) and in the comparison between glass wool grade 6 and Aquafoam grade 5 in Region 6, the monthly electricity bill difference remained at approximately 200 to 500 yen, which was very small. For detailed results of this experiment and verification of the electricity consumption (electricity bill) reduction effect over six months (December to February, July to September), including the winter results published in "VOL.1," please refer to the main report (separate attachment).
Hinokiya Group will utilize the verification results of this experiment for product and service development, and will continue to promote high-airtightness and high-insulation home building with added value, supporting customers' comfortable living environments.
*1 Refer to the thermal climate zone classification established by the Ministry of Land, Infrastructure, Transport and Tourism https://www.mlit.go.jp/common/001500182.pdf
[About "HINOKIYA Report"]
Hinokiya Group conducts various demonstration experiments related to building insulation and airtightness using housing exhibition halls and experimental houses nationwide, and continuously investigates the electricity consumption and electricity bills of its self-developed whole-house air conditioning system "Z-Air Conditioning" over a long period. The results of these experiments, analyses, and investigations are published irregularly as "HINOKIYA Report."
・HINOKIYA Report VOL.1 (Issued June 2025)
"Regarding the electricity consumption measurement experiment due to differences in insulation performance in winter 2025"
・HINOKIYA Report VOL.2 (Issued May 2026)
"Regarding the electricity consumption measurement experiment due to differences in insulation performance in summer 2025"
[About Masayuki Mae]
Associate Professor, Department of Architecture, Graduate School of Engineering, The University of Tokyo
Born in 1975. After completing his doctoral course in Architecture at the Graduate School of Engineering, The University of Tokyo in 2003, he worked at the Building Research Institute as a Japan Society for the Promotion of Science Research Fellow. From April 2004, he became a researcher at the National Institute for Land and Infrastructure Management, and from October 2004, a visiting associate professor at the Tokyo Electric Power Company Endowed Chair, The University of Tokyo. He has been in his current position since April 2008. Doctor of Engineering. His specialty is architectural environmental engineering, and his research theme is overall energy consumption in housing.
[Hinokiya Group Company Profile]
■Company Name: Hinokiya Group Co., Ltd. https://www.hinokiya-group.jp/
■Headquarters: Marunouchi Trust Tower Main Building, 1-8-3 Marunouchi, Chiyoda-ku, Tokyo 100-0005
■Established: October 1988
■Representative: Akira Kondo, Representative Director, President and CEO
■Business Activities: Housing business, insulation material business, real estate investment business, renovation business
■Main Housing Brands: Hinokiya Home, Papamaru House, Resco House