The Japanese Association for Conservation of Architectural Monuments

Heritage buildings in Japan

Japan has a rich and varied architectural heritage. Currently, over 4800 buildings are designated as Important Cultural Properties at the national level. Among them, around 280 buildings of exceptional cultural significance are designated as National Treasures. Furthermore, there are over 10,000 buildings designated as cultural properties by local administrations and a similar number of buildings listed as registered buildings.

In addition, 16 cultural sites are currently inscribed in the World Heritage List as places of outstanding universal value for all humanity.Wood is the main traditional building material in Japan and around 90% of heritage buildings are wooden buildings. Both monumental and vernacular architecture was historically built in wood. Wooden heritage buildings include Buddhist temples and Shinto shrines, castles, residences and farmhouses. The oldest standing wooden buildings in the world, built in the late 7th century, can be found at the Buddhist temple of Horyu-ji in Nara, Japan.

Brick, steel, concrete and modern construction techniques were introduced in Japan from the late 19th century together with Western style architecture; these techniques were used to build government buildings, palaces, and public buildings. Furthermore, factories, railway stations, bridges and other infrastructure and facilities were built using these new materials. These structures are a testimony of the rapid Industrialization of the country from the late 19th century to the early 20th century. This process is considered to be the first successful transfer of Western industrialization technology to a non-Western country, and therefore a significant moment in world history.The main task of the conservation architects at JACAM is to design, implement, and manage repair projects for these heritage buildings in order to safeguard them and hand them down to future generations.

Architectural conservation in Japan

Historically, buildings in Japan have been traditionally maintained and repaired throughout centuries. In addition, modern heritage conservation concepts were introduced during the late 19th century, and the first law for the conservation of architectural heritage, the Law for the conservation of Ancient Shrines and Temples, was enacted in 1897. During over 100 years of modern architectural conservation, the Japanese approach has developed into a highly specialized and methodical practice.

The aim of architectural conservation is to safeguard the cultural significance of the building, its authenticity and integrity. The original material, the structural system, and the building techniques are some of the aspects that convey the cultural significance.
In order to achieve this goal, the Japanese architectural conservation method employs thorough surveys and analysis of the building to devise the best possible conservation strategy. Surveys include a careful recording of the current condition, including measurements, causes and extent of damage, previous repair works, and analysis of the traces and marks left in the building throughout its construction history. A structural analysis to evaluate the seismic performance of the building is also carried out in order to determine the need for reinforcement.

On the basis of these surveys and analysis, the general conservation strategy is decided and the repair project is designed by the conservation architects. The conservation strategy includes planning how the building will be used after the repair work, and the conservation and management plan.
The traditional building techniques that were employed for each part of the building and during each construction period are also researched. During conservation work, these techniques are employed to repair the damaged elements of the construction. At the same time, compatible modern techniques and materials are also selectively employed when necessary.

All the steps of the conservation work, techniques, materials and treatments employed, and the results of the different surveys conducted are thoroughly recorded and documented. This documentation is published in the form of a Conservation and Repair Work Report, which also includes measured drawings and pictures of the building before and after the repair. Over 2000 such reports have been published to date, and are kept and made available to the public in main libraries, universities, and cultural heritage research institutions.

The repair methodology of Japanese wooden buildings

In the Japanese climate, with large rainfalls, mild temperatures, and high humidity, the rate of decay of wood due to insects and fungi can be very fast. Wooden buildings have to be continuously maintained and repaired in order to preserve them for the future.
Depending on the extent of damage and decay in a wooden building, conservation work can range from minor repairs and maintenance, to major repairs.
Minor repairs and maintenance include repairing decayed elements such as pillar bases or wattle-and-daub panels, and reroofing.
Major repairs are carried out when the extent of damage is generalized, the main structural frame members have decayed, and joints have become loose, leading to leaning and subsidence of the whole structure. The repair is carried out by carefully dismantling the timber frame, repairing the decayed elements, and reassembling the structure, realigning the frame and correcting the deformations.

The repair process of a wooden building through dismantling and reassembly

When a major repair including dismantling and reassembly of a timber structure is considered necessary,
the repair work is carried out according to the following steps:

Inspection, preliminary surveys, and basic repair project.

The condition of the building before the repair is surveyed and recorded. The cause, type and extent of damage to each part of the building are assessed and its cultural significance is evaluated in order to decide the best conservation strategy. A structural analysis of the building is carried out. On the basis of this information, a basic repair project is designed. Measured drawings and photographs of the building before the repair are taken.

Dismantling.

After numbering every member to register its original position, the frame is carefully dismantled, limiting the damage to the original elements. During the dismantling process, the building is thoroughly surveyed, analyzing and recording traces in every member, including marks that are usually hidden and become exposed during the dismantling process. The damage level, wood species and grading, surface finishing, and building techniques employed in each timber member is identified and recorded. On the basis of this new information, the final detailed repair project is designed.

Repair of individual members.

As much as possible of the existing wooden members is reused. When a wooden member is decayed, traditional carpentry techniques are used to substitute the decayed part by new wood, employing woodwork joints to splice the new and the existing part. Replacement timber employed is of the same species as the original, with the same grading and physical characteristics, and it is worked using the same techniques and tools. New timber is discreetly marked with the date of the repair so it can be identified later. As a principle, traditional building and repair techniques are employed. The use of present-day materials and technologies is kept to the minimum.

Reassembly.

The structure is reassembled employing the original repaired members. The frame is realigned and deformations corrected. If structural reinforcement is necessary, reinforcements are introduced without damaging the existing members, and if technically possible, in a reversible manner.

Recording and documentation.

General and detail drawings of the building before and after the repair are prepared. Photographs of the completed work are taken. A detailed, step-by-step description of the works that have been carried out and the results of the different surveys is published as a Conservation and Repair Work Report.

Conservation Approach