JAPAN

Report #: 86

Report Date:

Country: JAPAN

Housing Type:

Housing Sub-Type:

Author(s): Norio Maki, Satoshi Tanaka

Last Updated:

Regions Where Found: Buildings of this construction type can be found in all parts of Japan. Wood structures comprise a major structural type throughout Japan. Only in the Okinawa prefecture in the southern part of Japan does the non-wood structure housing stock exceed the wood structure housing stock. This type of housing construction is commonly found in both rural and urban areas. In 1993 the percentage of non-wooden structure housing in urban areas (40.8%) was larger than that in rural areas.

Summary: Japan has a long tradition related to wood construction. The main building of the Horyuji-temple, which was constructed in the late 7th century, is the oldest existing wooden structure in the world. Most Japanese housing is of wood construction. In 1993, 68.1% of the 45.8 million units of housing stock consisted of wooden structures. However, in newly constructed housing, the percentage of wooden structures is decreasing. In 1995 the percentage of wooden structures in newly constructed housing was 45.5%. The Hanshin Awaji Earthquake Disaster in 1995 damaged many wooden structures, especially housing which was constructed according to the pre-1980 building code. Despite the severe damage at the time of the Hanshin Earthquake Disaster and governmental encouragement of seismic upgrading, retrofitting of these houses is not common.

Length of time practiced: More than 200 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Single dwelling

Typical number of stories: 1-3

Terrain-Flat: Typically

Terrain-Sloped: Typically

Comments:

In 1998 single-family housing was still the major architectural type in Japan (57.5%), and 93% of single-family houses were wood

Plan Shape: Other

Additional comments on plan shape: It is different throughout the country, depending on the location of the housing. Single-family housing in urban and suburban areas is typically just one building, and farmers' houses in rural areas consist of 2-3 buildings, including the main house, storage, etc. There are also apartment houses of wood in urban areas.

Typical plan length (meters):

Typical plan width (meters):

Typical story height (meters): 2.8

Type of Structural System: Wooden Structure: Load-bearing Timber Frame: Post and beam frame (no special connections)

Additional comments on structural system: Gravity load-bearing structure consists of a system of posts and beams. Wooden posts, with cross-sectional dimensions ranging from 105 to 150 mm, carry gravity loads. The roof structure is made out of wood and it is covered by roof tile or slate. The roof load is transferred to the wood frame. The roof-supporting system in Japan is different from that of western countries and it is based only on vertical and horizontal members. There are no diagonal members, common for similar construction in western countries.

Japanese wooden housing is built using “post-and-beam” construction. Lateral load resistance is provided by wooden shear walls with interior diagonal brace members or alternatively, with plywood or manufactured wood panels (“particle board”) nailed to the vertical wooden members. The building code regulates the number and dimensions of shear walls. Metal joints and plates are used to stiffen the wood frame in recent wooden housing. However, the traditional Japanese house did not have a diagonal brace. A thin lumber running through posts, called Nageshi, and a thick wood post, provide lateral resistance. The traditional Japanese carpenter was reluctant to use a diagonal brace because it could cause a diagonal crack in a mud-plastered wall.

Gravity load-bearing & lateral load-resisting systems: There are several structural systems that are used in Japanese wood housing. While post and beam construction is most common, some buildings of this type are of balloon frame construction.

Typical wall densities in direction 1: >20%

Typical wall densities in direction 2: >20%

Additional comments on typical wall densities: The typical structural wall density is none. There is a wide variation in wall density.

Wall Openings:

Is it typical for buildings of this type to have common walls with adjacent buildings?: No

Modifications of buildings: Modification of utilities in the kitchen and bathroom, or extension of the living space is common. However, seismic retrofitting is not very common.

Type of Foundation: Shallow Foundation: Rubble stone, fieldstone isolated footingShallow Foundation: Reinforced concrete strip footing

Additional comments on foundation: Infrequently, deep foundations are also used.

Type of Floor System: Other floor system

Additional comments on floor system: Timber: Thatched roof supported on wood purlins ; Wood planks or beams that support clay tiles

Type of Roof System: Cast-in-place beamless reinforced concrete roofCast-in-place beam-supported reinforced concrete roofWooden beams or trusses with heavy roof covering

Additional comments on roof system:

Additional comments section 2: There is no specific data on a typical separation distance between buildings. Minimum separation distance is decided mainly by building code regulation for the insulation duration within a room. The Civil Code also regulates a minimum distance of at least 50 cm. Traditional shop houses in Japan, Machiya, do not have a separation distance between buildings When separated from adjacent buildings, the typical distance from a neighboring building is 0.5 meters.

Plan Dimensions: There is a wide variation in dimensions. Typical Number of Stories: Building code regulations limit the height of wooden structures to a maximum of three stories. A special permit is necessary for wooden buildings with four or more stories. Typical Story Height: This story height measurement does not include the height of the basement. Therefore, the story height of first floor includes the typical story height, plus the height of basement and is usually 3.4 meters. Typical Span: Modular coordination is conducted according to Tatami mat size in Japanese housing. The typical module dimension in Japanese housing ranges between 0.9-1 meter. The typical span (distance between the posts) is equal to two modules (i.e. 1.8-2 m). The typical storey height in such buildings is 2.8 meters.

Who is involved with the design process?: EngineerArchitectOther

Roles of those involved in the design process: Any licensed architect can design wooden structure housing. For this type of building, the role of the engineer and architect is not large. The building is designed and constructed mainly by a licensed design builder, who is a contractor responsible for both the design and construction of the structure.

Expertise of those involved in the design process: The building standard mandates that buildings of this type must be designed by a licensed architect. The licensing system for architects in Japan is unique in that the license is issued to engineers. There are three licensing levels: Wooden Structure, Second Class, and First Class. To take the examination for a license for Wooden Structure, one must have graduated from a school of architecture or civil engineering; For a 2nd class license, two years experience in the field is required. The 1st class license requires two additional years experience after the 2nd class license is issued.

Who typically builds this construction type?: BuilderOther

Roles of those involved in the building process: The builder lives in this construction type.

Expertise of those involved in building process:

Construction process and phasing: The construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its final constructed size.

Construction issues

Is this construction type address by codes/standards?: Yes

Applicable codes or standards: Japanese Building Standard, The first building standard was established in 1919 and dealt mainly with buildings in urban areas, primarily large-scale wooden structure housing. In 1950, the Japanese Building Standard was issued, which addressed almost all wooden structure housing. The last amendment was issued in 2000. The main objectives of this amendment were 1) performance-based regulation, 2) enforcement of a building inspection system, 3) involvement of the private sector in building inspections.

Process for building code enforcement: Drawing check - interim inspection - final inspection. The requirement for an interim inspection depends on the scale of the housing. Interim inspections were introduced by an amendment of the building standard in 2000.

Are building permits required?: Yes

Is this typically informal construction?: Yes

Is this construction typically authorized as per development control rules?: No

Additional comments on building permits and development control rules:

Typical problems associated with this type of construction:

Who typically maintains buildings of this type?: BuilderOwner(s)

Additional comments on maintenance and building condition:

Unit construction cost: JPY 0.4-1 million/3.3 m2

Labor requirements: Average cost of carpenter/day: JPY 10, 000 - 20,000 without cost

Additional comments section 3:

Damage patterns observed in past earthquakes for this construction type: The magnitude of each earthquake is JMA magnitude. The 1923 Kanto earthquake killed more than 140,000 people, heavily damaged 120,000 buildings and burned 440,000 buildings. Fire following earthquake was the most prevalent cause of damage. There were many earthquakes during the 1930s and 40s, such as the Tottori in 1943, which killed 1,083 people, the East Nankai in 1944, the Nankai in 1996, and the Fukui in 1949, which killed 3,769 people. There was a reduction in the number of earthquake disasters during 1950s-80s. However, the Niigata earthquake in 1964 spotlighted damage by liquefaction and the Miyagiken-oki earthquake in 1978 spotlighted damage by a landslide occurring at a hillside housing complex. The 1995 Hyogo-ken Nanbu earthquake killed 6,435 people. They died mainly from the collapse of wooden housing. In 2001 during the Tottori-ken Seibu earthquake, many wooden housing units were damaged by ground motion and liquefaction.

The main reference publication used in developing the statements used in this table is FEMA 310 Handbook for the Seismic Evaluation of Buildings-A Pre-standard, Federal Emergency Management Agency, Washington, D.C., 1998.

The total width of door and window openings in a wall is: For brick masonry construction in cement mortar : less than ½ of the distance between the adjacent cross walls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; For precast concrete wall structures: less than 3/4 of the length of a perimeter wall.

Additional comments on structural and architectural features for seismic resistance: All structural and architectural features related to seismic resistance, which are indicated above, refer to housing constructed according to the present building code. There are many problems found in housing that was constructed according to the pre-1980 building code.

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: See Structural Features

Earthquake-resilient features in walls: See Structural Features

Seismic deficiency in frames: See Structural Features

Earthquake-resilient features in frame: See Structural Features

Seismic deficiency in roof and floors: See Structural Features

Earthquake resilient features in roof and floors: See Structural Features

Seismic deficiency in foundation: See Structural Features

Earthquake-resilient features in foundation: See Structural Features

For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

Has seismic strengthening described in the above table been performed?: Yes. The new building code requires usage of metal joints and of a diagonal brace.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?: In spite of encouragement by the government through low interest loans, retrofitting work for housing is not very popular. In earthquake recovery activities, people prefer to reconstruct their housing rather than to repair it with seismic upgrades with a view toward its resale value.

Was the construction inspected in the same manner as new construction?: No. Few people get building permission for repair or renovations, though the building code requires getting permission for large-scale repairs or renovations.

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?: The contractor is the main retrofitter. Building repair by a homeowner is not so popular. Recently, some private companies that are not specialized for building construction have begun to promote housing retrofit service.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes?: No data.

Statistics Bureau & Statistics Center, Government of Japan: 1998 Housing and Land Survey, http://www.stat.go.jp/english/data/jyutaku/index.htm

Non-Life Insurance Rating Organization of Japan: System of Earthquake Insurance (In Japanese), http://www.nliro.or.jp/contents/rate/index.htm

Urban Developers' Association of Japan: Gap between price of mid-raised condominium and average annual salary (In Japanese), http://www.udaj.or.jp/kairi2002kami.htm

Uchida, Syouya etc.: Building structure system, Ichigaya syuppansya, 2001.

Housing Bureau, Ministry of Construction, Japanese Government: Japanese Housing rev.2, Gyousei, 1998.