taruki kouzou　垂木構造

KEY WORD :　architecture / general terms

Lit. rafter construction. Also referred to as odachi toriigumi おだち鳥居組. One of the two principal types of assembly used in the construction of thatched roofs in traditional vernacular houses *minka 民家. The other is sasu construction; see *sasugumi 叉首組. In taruki kouzou a strut resembling a king post, odachi おだち (*udatsu 卯立) or munazuka 棟束, resting upon a longitudinal timber plate, *jimune 地棟 or *tsukabumi 束踏, was used to support the ridge purlin *munagi 棟木 directly. The strut odachi was stabilized by a rectangular frame, shaped like a Shinto gate *torii 鳥居, comprised of horizontal tie beams *tsunagibari 繋梁 connected to flanking verticals called *toriizuka 鳥居束 'gate posts'. The roof membrane was supported by rafters *taruki 垂木 of straight lengths of stripped but otherwise unwrought timber. The rafters were tied in place with straw twine nawa 縄 and spanned from the ridge purlin to the eaves purlin *nokigeta 軒桁, with intermediate support from secondary purlins *keta 桁 laid upon the rectangular torii frame and upon the ends of the main transverse beams *jouyabari 上屋梁. Diagonal braces *sasu 叉首 were not used and taruki kouzou was therefore a 'rafter only' roof construction system. Tarukikouzou is for the most part associated with hipped-and-gabled *irimoya 入母屋 roofs. There were usually three struts odachi: one at the center of the building's longitudinal section, though this was sometimes omitted in smaller structures, and one supporting each end of the ridge purlin. Beyond the odachi at either end, a flanking vertical supported the hipped end of the roof below the gable. Unlike sasu construction, which was found throughout Japan, tarukikouzou was concentrated around the edges of the Kansai 関西 region in parts of Hyogo Prefecture, the mountains to the north and west of Kyoto, the boundaries with Nara and Mie prefectures, and the southern parts of Nara and Wakayama prefectures. It has been found in some of the oldest surviving vernacular houses, including the oldest of all, the hakogi 箱木 'thousand year house' sennenya 千年屋, approx. 15c. From the latter half of the Edo period, taruki kouzou was increasingly superseded by sasu construction, even in those areas. Therefore it is believed to be a survivor of a traditional assembly system dating back at least to the medieval period in the Kansai region.

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