5. Justification for inclusion in the World Heritage List a) Reasons for which the property is considered to meet one or more of the World Heritage criteria with, as appropriate, a comparative evaluation of the property in relation to other properties of a similar type

Japan is one of the world's most important examples of a country which has developed an architectural tradition based entirely on wood. Since ancient times, from the emperor's palace, the residences of the aristocracy and the religious architecture of Buddhism and Shintoism to military facilities such as the castles of the warrior period, all architecture was made of wood. Within the framework of development of each architectural type, the design of form and structure, the techniques of joinery, the process of fabrication, and the techniques of coloring and painting have become highly developed and have produced a great variety of architectural styles and expressions during the long history of Japanese architecture. Not only upper-class architectural types but also vernacular houses and accessory buildings for ordinary people have been made mostly of wood, with very few exceptions. Vernacular houses are classified into two basic types: the machiya, or townhouse, and the minka, or the houses found in typical farming villages or fishing villages. The nominated property is a set of farming villages and the groups of historic houses in those villages. In Japanese farming villages, the most typical farmhouse style is a single-story rectangular-plan structure with the entrance on the long side, with exterior walls which have exposed wooden posts and clay infill material; the roof has the form of a hipped gable, and the roofing material is reed thatch. But there are also various other farmhouse types: houses with their entrances located on the gable end; houses with exterior walls covered entirely with clay, or clad with wooden board siding; houses with hip-roof or gable-roof forms; and in some case houses with roofing made of wooden boards. With different combinations of these and other features, in the various parts of Japan, many kinds of farmhouses with special characteristics reflecting their own locality have been created. In the context of this World Heritage nomination, this wide variety of farmhouse styles -- many of which are fully developed as architectural styles in their own right -- is one of the factors which Japan can point to as an example of a vernacular architectural tradition which has universal value. As described above, the forms of Japanese village houses have great diversity -- but if we look at all of these forms and styles as a whole it will be possible to identify a single generalized image of the Japanese farmhouse: in this generalized model the overall size is not unusually large, the height of the ridge is not especially tall, and the slope of the roof is not so steep (the typical slope is less than 45 degrees); the image is of a house form which rests comfortably on the earth, suggesting not confrontation with nature but rather passive harmony with it. In opposition to this image, the nominated Gassho-style houses of the Shirakawa-go / Gokayama areas have a very unique style which has never been seen in any other region of Japan, and these houses have one of the most rational structural systems ever developed in this country. The following points help to illustrate the uniqueness of these Gassho-style houses and to identify the special characteristics of the style: 1. The building size is larger than most other regions' farmhouses. The roof is a tall, steeply-sloped thatched gable roof (with a slope of about 60 degrees), and the overall impression of the exterior image is one of "confrontation" or "confident resistance" against nature. 2. In ordinary Japanese farmhouses the structural space inside the roof is seldom used or is used only for passive functions such as storage of materials, but in the Gassho-style houses the space in the roof structure is typically divided into two, three or four levels which are actively used for such functions as raising silkworms, or used as storage space for mulberry leaves. The steeply-sloped roof structure composed of open-trussed frames provides a large volume of usable interior space for such functions. The introduction of the steep gable roof form made it possible to provide openings in the large gable ends to allow for natural lighting and ventilation of the attic space. This characteristic is very unique in Japanese architecture. 3. The structural weak point associated with the adoption of the repetitive system of truss frames which make up the gable roof structure is the lack of resistance to lateral forces perpendicular to the truss frames; this problem has been solved in the Gassho structure by using diagonal bracing within the sloped plane of the roof, to make the roof itself a rigid plane with strong lateral resistance. This technical invention has not been found in the architecture of any other region of Japan.