hottatebashira　掘立柱

KEY WORD :　architecture / general terms

Also written 掘立て柱, 掘建て柱. Earthfast posts. Posts *hashira 柱 whose feet, nemoto 根元, are embedded directly into the earth. Hottatebashira were ubiquitous in Japanese timber framed structures in the Joumon, Yayoi and Kofun periods and continued to be used even after the introduction of foundation stones. In the 6-8c, hottatebashira were widely used even in the Nara capital Heijoukyou 平城京, not only for dwellings of the lower classes, but also for the imperial residential compound of the palace dairi 内裏, the mansions of the aristocracy, and for most of the structures such as offices and storehouses in administrative compounds. The central post *shinbashira 心柱 of a pagoda *tou 塔 was also a hottatebashira. The use of foundation stones at ground level spread gradually during the succeeding centuries, first to the residences of the upper classes and then into vernacular houses *minka 民家, but hottatebashira were still used in farmhouses until as late as the mid-18c. By the end of the Edo period, their use was mainly confined to temporary huts and ancillary structures. The principle advantage of hottatebashira was that they gave a timber frame great structural stability. Their main weakness was their tendency to rot at the point where the post entered the ground, thus limiting the lifespan of the building. Details of construction varied according to period and the status of the building: In the Joumon period, a circular hole larger than the diameter of the post was excavated to a depth exceeding its diameter, the post inserted, and the hole backfilled and tamped. In soft ground, the end of the post was sometimes cut to a sharp point, and then pushed down into the earth at the bottom of a 'v' section pit. With the advent of iron digging tools in the Yayoi-Kofun periods, excavation became easier and the holes larger, square in plan, and rectangular in section. Hottatebashira reached a peak of sophistication in the Asuka-Nara periods, in the major building complexes of the capital, and in provincial administrative centers. The bottom of the pit was sometimes lined with a bed of small pebbles *kuri-ishi 栗石, to make a solid level base. A flat piece of wood *soban 礎盤 or stone ishi-no-soban 石の礎盤 or *soseki　礎石, larger than the diameter of the post was often used to spread the load of the post and prevent excessive settlement. Another technique employed to spread the load was the use of timber cotters, makuragi 枕木, let into carefully cut channels in the base of the post. Accurate positioning of posts became increasingly important in section as well as in plan, and this was reflected in the use of timber wedges *kusabi 楔, set upon the soban to adjust the height of posts. To slow down the onset of rotting where the post entered the ground, it was often encased in clay, nendomaki 粘土巻き, either just at the interface, or sometimes right down to the base. The most elaborate protective detailing was reserved for the central pillars of pagodas which were first surrounded by laths *soegi 添木, bound in position with rope, and then cased in clay from ground level to the base of the post. The use of hottatebashira continued into the medieval period, but its decline was related to the development of more sophisticated frame construction which provided stability and rendered the hottatebashira unnecessary.

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