An evolutionary study of traditional timber framed building in Japan focusing on the principle of framing systems of the roof construction

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This study aims to comprehend the development of roof frame of timber framed building in Japan before modern period focusing on the principle of framing systems.As the beginning, criticizing the current classification from the standpoint of the building elements, and referring to the types of foreign examples, we took a general view of typology of the roof frame including those which was not apply domestic examples. And we reconsidered the roof frame adopted by various building type. Based on the above, this study limited the discussion to farmhouses which show the widest diversity in the type of roof frames in the medieval and premodern period.First, examining closely the framing members, supporting types were extracted from major three supporting systems : ridge and post frame, purlins and posts frame, and sasu frame (similar to the principal rafter). Applying the types of roof frame to 663 houses, distinct aspects of localities were revealed exhaustively and across the nation.Secondly, analyzing the relation between the roof span and the type of frame, there is the tendency that the longer roof span needs more supporting members, however in the case of sasu frame, it's not due to the roof span whether the center post is erected or not.Finally, comparing the transitional forms between post frame (including ridge and post frame and purlins and posts frame) and sasu frame, the following results were obtained. Those which located in the east Japan tended to transform from purlins and posts frame to sasu frame without the process of the original form of ridge and post frame which means the post directly support the ridge piece ; while those which located in the west Japan tended to transform gradually influenced by both ridge and post frame and sasu frame.