Here is a description of Japan Offspring Fund’s new eco-building in Saitama prefecture, north of Tokyo.


Japan Offspring Fund wanted to move from central Tokyo to Saitama prefecture for a number of reasons, including the high risk of a large earthquake. We had concluded that a Tokai Earthquake could lead to a cloud of radiation spreading to Tokyo if the old nuclear reactors in Hamaoka, southwest of the capital, were damaged. Previously, we had thought that it would be possible to escape from Tokyo by train. But when earthquakes occur, all trains stop in the region that is affected. Thus, it was becoming painfully obvious that the bridges across Arakawa River would be so congested that escape from central Tokyo would become virtually impossible.

Mr. Junichi Kowaka, the director of Japan Offspring Fund embarked on an ambitious project with the vision that the three most important concepts of the new building should be health, durability, and a low impact on the environment. The three-story wooden house would last 300 years. Wanting to build an earthquake-proof office building that was also a genuine eco-building led us to conclude that we would have to move out of Tokyo.


Starting From the Foundation

Construction of a 3 floor building with reinforced concrete requires a strong foundation. In particular, as we had determined that the walls would have to be thick enough to provide proper insulation, our office would have to be supported by piling. The question was how deep they would have to go. Detailed data about the condition of the ground cannot usually be obtained until after the land has been purchased, while general data is available at the Environmental Assessment Center, a Fukuoka-based company that specializes in collecting and providing such data.

We started drilling to perform an investigation of the ground on July 25, 2006. The investigation is done by hanging a heavy steal rod on a special tripod, and ramming it down into the ground at different depths. The effect is then carefully measured and the type of soil is observed. In the Kanto plain region, the ground is generally soft clay, and not suitable for tall buildings. The experts reported that our land was indeed basically wet sand. To get the go-ahead for our plans for a reinforced concrete building we would need a very strong foundation as deep as 9 meters to support our special 3 floor building design. As this was too expensive, we would have to reconsider our original plans and choose to erect a wooden building instead.

Considering the different constraints of Japan Offspring Fund’s budget for the construction, several ideas were discussed, especially how to conserve energy.

“Suggestions such as a green roof with plants or rooftop gardening were rejected,” notes Junichi Kowaka. “There was little evidence that this would actually contribute to energy conservation in our case. This type of roof could make more sense in central Tokyo, where there are few parks and not much vegetation, as a way of dealing with urban heat island issues. But at our location in Saitama there is no real need for this, and the only benefit would be that the office would look charming. Instead, we are growing a gourd plant called hechima (Luffa cylindrical), that grows very high as a vine in the summer, enjoying the shade the leaves provide for the walls.”


Simple Design

By September 2006, we had our new basic design ready. Japan Offspring Fund’s eco-office in Saitama would be a rectangular building, 3 floors high, made entirely out of domestic cedar wood. The simple rectangular shape is actually the best choice from the earthquake-proof perspective. A simple wooden box with pillars inside is the traditional shape for all Japanese houses.

“We call this the Yamaga-style as it was suggested by our architect, Mr. Yamaga Yasuhiro,” says Junichi Kowaka. “We found a number of advantages with this rectangular shape. For example, the simple roof helps avoid the danger of leakage in the case of heavy rain or typhoons. Without rounded walls, construction can be done more efficiently which saves money. Also, an uneven building can cause variation in the pressure on the ground, which can lead to sinking or collapse in the case of an earthquake.”

Sanctifying the Ground

On January 29, 2007 we held a traditional ceremony to “sanctify the ground.” We poured nihonshu (Japanese rice wine) at the center of the construction site, and at each of the four corners, as an offering to the kami of the land, asking for protection. The traditional ceremony is called tokoshizume no matsuri and we ended it by a bow of thanksgiving.


Many adjustments had been made since starting. For example, we wanted a deep cellar for storage below the building. We had planned its height to be 2.15 meters, but learnt that special landslide protection rules would have made that too expensive, and settled for a height of just below 2 meters. Making a smaller cellar also meant we could reduce the amount of soil we had to dispose of by 70%, which we felt was in line with our general concept of making a genuine eco-building.

To avoid landslides during the digging and making of the foundation, special panels must be lowered into the ground. Because we had carefully selected the best earthquake-proof techniques and materials, the work then progressed more slowly than at usual construction sites. A case in point: we used anchor bolts made of stainless steel for extra durability, rather than galvanized iron that is generally used. We also chose reinforcing rods that are 5 cm thicker than usual to avoid corrosion from air pollution.

As workers poured the concrete for the foundation, we felt happy that construction of our new eco-office was now underway. There are tests to make sure that the density of the concrete is correct. The standard is 18 cm as a technical value, but we had decided to raise that to 12 cm for better strength. When we performed the test, our concrete was 11.5 cm, which is hard as stone. The thickness of the foundation’s walls is 20 cm, and we carefully protected the wet concrete against cold by covering it at night, waiting for it to dry. By March 12, when we removed the forms, we were pleased that the concrete surface was dense and smooth, a sign that all the work so far had been done prudently.

Building Design for 300 Years

Our eco-office is designed to last 300 years. The external galvalume may have to be replaced, but the wooden construction should last at least 300 years. Compared to ordinary Japanese buildings, designed to last only 60 years, this is remarkable. Also, our simple, rational design helps make the building more earthquake-proof.


By April, 2007, the wooden pillars and beams for the walls had been erected to a height of 3 floors. We used domestic timber and avoided chemical treatment of the wood as Japanese cypress is suitable to the local climate. Moreover, we also wanted to support Japan’s lumber industry and help workers maintain and develop domestic know-how. This in turn helps to protect and manage Japan’s forests. All our wood comes from Shimonita in southwestern Gunma prefecture, just north of Saitama.

Good quality wood is superior in many ways to cheaper materials that need to be chemically impregnated to become water-proof. On a rainy day, our crew could quickly start working again after a spring shower, while other materials need to be covered with vinyl to not be damaged by the rain.

As a special feature, we selected specially made stainless steel balancers to create a 2 cm gap between the concrete foundation and the cypress beams. This gap is helpful for ventilation allowing humidity to escape easily, and making sure the wood does not rot. “A house where the wind can pass through” is a important concept that we adopted from the architect, Mr. Akinori Sagane.


We also used a unique method to connect the vertical pillars to the cross-bars that supports the structure. In the event of a strong earthquake or typhoon, these junctions are under intense pressure and may cause the wood to splinter, crack, or break. Normal buildings get away with this, but we selected a special innovative type of support junction that combines several techniques to handle the stress.

Inspired by the world’s largest wooden structure, the Todai-ji Buddhist temple in Nara, originally from the 8th century, which was rebuilt in 1709, we wanted to avoid iron bolts and parts that will rust, and selected support junctions made with stainless steel. Our building has been fitted with parts that are up to 3 times stronger than ordinary Z-shaped junctions. Junichi Kowaka also points out how using weak junctions contribute to the short lifespan of Japanese houses, and has issued a call for the construction industry to start taking this more seriously.


Using Wool as Insulation

Japan Offspring Fund has campaigned for a safe housing environment and warned against using harmful chemical materials as insulation. The “sick house” syndrome is a major issue in modern buildings around the world. A large number of people are now having allergies and eczema, as well as other health problems.

For our eco-building, we selected 100% Australian wool as the insulation material in the walls and under the floor. This is safe not only for the people inside the building but also for the workers who handle it during production and construction. Rock fiber or glass wool insulation can be carcinogenetic, and requires workers to use protective face masks so the tiny fibers do not enter the lungs.

Natural wool is a very good moisture absorber that helps the building handle the changing seasons. Other positive characteristics are the sound-proofing effect. Using wool insulation, echoes inside the building are not a problem, and outside noise does not disturb us!

The Walls

“I love wooden houses,” says Junichi Kowaka. “But it is important that wooden parts are not exposed outside. In Japan, it rains a lot and it is very humid. If wood is exposed, it is easy to be rotten. The building would not last 300 years. So I decided to cover with a special metal material called galvalume.”

Indeed, from outside, the office does not look like a wooden house, since it is all covered with galvalume: a simple, light grey, inorganic material. However, if you open the door, it is completely different. Our office building is a warm, organic, comfortable house made by wood and paper. Synthetic chemicals are not used in this building.

“Galvalume is iron plate coated with aluminum, zinc and silicon,” explains Junichi Kowaka. “Aluminum is durable, and zinc can prevent corrosion. Galvalume is three times more durable than normal galvanized iron simply coated with zinc, which is often used for cheap roofs called tin roof. The galvalume walls may need repair work every 40-50 years, but the actual walls do not need to be replaced. The new galvalume wall can be put directly on the old galvalume wall. In this way, we can reduce the garbage waste, and save money for repair.”

Galvalume has other good characters: it is heat resistant, easy to work with, small scratches can be easily fixed, and it reflects sunshine well thus preventing too high temperatures in summer.

Inside the building, all walls are wood or covered with a plaster made from shells and other natural calcium-rich substances. We found that each year, some 600,000 tons of shells are thrown away, and using them as construction material instead seems like a very eco-friendly idea. We used no chemical adhesives and no formaldehyde in the construction of our eco-office. The only adhesives we used were a natural type made from rice.

The walls of Japan Offspring Fund’s new office have the following merits:

(1) Safety for workers

(2) Using natural materials

(3) Absorption and discharge of humidity

(4) Reduction of condensation

(5) Durability

(6) Comfort

(7) Resource reuse

Welcome to schedule a visit to our new eco-building!