The Present and Future of Net Zero Energy Houses in Japan

In April 2014, the Japanese Cabinet approved an energy policy that will make it a goal for all newly-constructed public buildings to be zero-energy by 2020, and all newly-built houses to be zero-energy by 2030.

These ambitious goals come in the wake of the 2011 Fukushima disaster and subsequent shutdown of all of the country’s reactors for inspection in September 2013. Nuclear power used to provide 33% of Japan’s electricity and expensive fossil fuels have had to make up the difference. If you have lived in Japan in the last few years, you have likely seen first-hand evidence of this in increased electricity bills.

According to the Ministry of Land, Infrastructure, Transport, and Tourism, final energy consumption in Japan’s residential and commercial sectors account for over 30% of total energy consumption in Japan. The consumer sector, which includes buildings and residences, has increased its power consumption by 140% over the last 30 years.

Given these issues, Japan has no choice but to increase energy efficiency in its building standards and to work towards a low-carbon society.

What is a Zero Energy House?

A Zero Energy House (ZEH) is a house that consumes less energy than it produces on a net annual basis by creating renewable energy, usually through photovoltaic cells installed on the roof. As Wikipedia explains, ZEHs “do at times consume non-renewable energy and produce greenhouse gases, but at other times reduce energy consumption and greenhouse gas production elsewhere by the same amount.”

Is it possible to build a ZEH?

In a study by Professor Ryozo Ooka of the Institute of Industrial Science at the University of Tokyo, he found that zero-energy houses are theoretically possible to build in Japan. As detailed in the chart below, a typical 138sqm (about 1,485 sq feet) detached house consumes on average 425 Megajoules of energy per square meter per year.

With improved energy-efficiency measures, energy usage could theoretically be decreased by 58%. A 5kW photovoltaic solar panel installed on the roof could produce the remaining needed energy, resulting in a net zero-energy house.

Realizing a net zero energy house will require both reducing energy use and producing renewable energy on-site. Source: Professor Ryozo Ooka, Institute of Industrial Science at the University of Tokyo

Realizing a net zero energy house will require both reducing energy use and producing renewable energy on-site. Source: Professor Ryozo Ooka, Institute of Industrial Science at the University of Tokyo

The conventional thinking about a zero-energy house is that to achieve its energy efficiency goals, a ZEH has to have thick walls (to aid insulation and reduce the heat load), small windows (to prevent energy loss), and a simple design, but as Professor Ooka points out, a ZEH does not necessarily have to be unattractive.

MUJI House

One of the forerunners in the zero-energy house movement is MUJI House, a division of Ryohin Keikaku Co. Ltd., or MUJI, the popular Japanese retailer of minimalist household and consumer goods.

Muji House

MUJI Wood House, Hamamatsu, Tokyo. Source: MUJI House.

MUJI Wood House interior. Source: MUJI House.

MUJI Wood House interior. Source: MUJI House.

In 2004, MUJI House started sales of the “Muji Ryohin House” (“No brand, Good Quality House”), designed to be a “long-lasting, ever-changing,” energy-efficient house.

This July, the company announced (press release is in Japanese) that it had made substantial upgrades to its building standards, focusing on the insulating performance of the windows and walls. (As pointed out in this study by Isamu Ohta of Misawa Homes Institute of Research and Development, one of the key ways to reduce the energy efficiency of houses to improve thermal performance.)

MUJI House now offers aluminum-resin composite shades, argon gas-filled, triple-pane, low e-glass, and double-skin insulated walls in the building specs for its MUJI Wood House series.

Argon Gas-Filled, Triple-Pane, Low e-Glass

The argon gas-filled, triple-pane, low e-glass materials being used by MUJI House are not unique to Japan, but it is worth summarizing how they work because more and more, they will become the standards in energy efficient construction.

Triple-Pane Glass

The “e” in e-glass stands for “emissivity,” which is the ability of a material to radiate energy. Low e-glass improves insulation by reducing the energy that is re-radiated when heat or sunlight hits a window. In triple-pane windows, the two outer panes are glazed with low-e coating. The air spaces are usually filled with argon gas, which is colorless, odorless, and denser than the atmosphere, which means it insulates much better than air.

MUJI House says that by using this technology, its Wood House series boasts an energy efficiency rating more than double the 2013 standard for low-energy construction in the Tokyo metropolitan region.

The Wood House series can be ordered in various dimensions, but for “5 by 4.5” model (105.98 square meters of living space) sells for 17,590,000yen (about $140,950).

MUJI Wood House floorplan. The 5x4.5 model (105.98 square meters of living space) sells for 17,590,000yen (about $140,950). Source: MUJI House.

MUJI Wood House floorplan. The 5×4.5 model (105.98 square meters of living space) sells for 17,590,000yen (about $140,950). Source: MUJI House.

Daiwa House Net Zero Energy Neighborhood and HEMS

As reported Global Energy Affairs, Japan opened its first net zero energy neighborhood in July 2013. Dubbed SMaxECO ORIGINAL, the 17,000 square meter enclave is located south of Osaka. It was built by Daiwa House Group as part of a government-led initiative to promote sustainable living.

Houses in the development are equipped with solar panels and lithium ion batteries, which store electricity generated in the daytime.

The company’s Home Energy Management System (HEMS) allows residents to control their air conditioning and energy use through an iPad app. The HEMS also enables users to monitor and visualize their energy consumption and savings. Daiwa House claims that these technologies will help reduce carbon emissions by 70% compared to the average Japanese household.

Sekisui House’s Green First ZERO Initiative

Sekisui House, one of Japan’s largest home builders, is also a leader in building zero-energy houses. The company’s Green First Zero initiative aims for energy self-sufficiency without sacrificing comfort. Green First Zero homes are designed to offset energy use, with the ultimate goal of achieving zero energy consumption.

The company’s designs focus reducing household energy use to half of conventional levels through heat insulation and high-efficiency equipment and by using photovoltaic panels to generate the remaining half.

Sekisui House’s entry in the zero-energy house market. Source: Sekisui House.

Sekisui House’s entry in the zero-energy house market. Source: Sekisui House.


Photovoltaic panels are a well-known technology for generating renewable energy on-site in residential housing. Less-well known outside of Japan are ene-farms (short for energy farms).


The Ene-Farm generates electricity by extracting hydrogen from natural gas and mixing it with oxygen. Source: Tokyo Gas.

According to Trends in Japan, in 2008, Japan became the first country in the world to begin commercial sales of these refrigerator-sized hydrogen-based generators. To generate electricity, natural gas is pumped from a local utility, from which the ene-farm extracts hydrogen and mixes it with oxygen from the surrounding air. The electricity generated can be used throughout the house after being converted to home AC current. The unit also includes a heat-recovery device, which recovers the heat that is generated as a by-product. The recovered heat is then used to heat water (to as much as 60 degrees C) to be used in the bathroom and kitchen.

According to the gas utilities which sell these units, a single ene-farm system can supply 40% to 60% of the electricity consumed by an average household. Bloomberg reports that about 100,000 houses throughout Japan are currently using ene-farms, but because a single unit costs about $16,700, sales have not taken off as much as the government has hoped, despite subsidies that cover about 18% of the cost.

Key Factors for the Future of Zero Energy Houses

Japan seems to be leading the way in utilizing numerous technologies (only some of which we’ve covered) for realizing a low-carbon society.

The key factors for achieving this goal, as pointed by Isamu Ohta of Misawa Homes, at least on a technological level are: the continuous improvement of thermal performance, increasing solar energy use, and introducing environmentally adaptive building materials.

Political and financial considerations as well as cultural customs, however, will also play some role.