In the simplest form of traditional Japanese roof framing, shown in the image below, two forked posts known as muna-mochi-bashira (棟持柱, lit. ‘ridge holding post’) hold up a ridgepole (munagi 棟木) at its ends; on this ridgepole are laid common rafters (taruki 垂木) which simply run down to the ground on either side, and the roof, which is the whole of the structure, is thatched.

The simplest *tenchikongen-zukuri* (天地根元造り) construction, without wall posts or beams, where the rafters terminate at ground level.

With the development of raised-floor (taka-yuka 高床) construction, this basic structure gained walls, with rows of forked posts known as keta-uke-bashira (桁受柱) in the planes of the long walls bearing wall plates or wall beams (keta 桁), which supported the lower ends of the rafters. In both cases, this system of framing is known as tenchikongen-zukuri (天地根元造り).

Two examples of *tenchikongen-zukuri* in elevation. Top: without walls; bottom: with forked wall posts supporting wall beams.

A simple agricultural structure with two forked *muna-mochi-bashira* posts holding up a ridgepole and three forked *keta-uke-bashira* posts supporting the wall plates or wall beams.

A more sophisticated development of this basic system, tenchikongen-no-miya-zukuri (天地根元宮造), can be seen today in some Shinto shrines, and may have been used in the earliest shrines, going back 1,500 years or more. It should be pointed out, however, that there is no definitive archaeological evidence that tenchikongen-zukuri construction was employed in the earliest built structures in Japan, whether residential or religious, and that, according to some sources at least, the method itself may date back only as far as speculative Edo-era reconstructions.

Kamosu Shrine (*Kamosu-Jinja* 神魂神社), Matsue City, Shimane Prefecture. The building is an example of *tenchikongen-no-miya-zukuri;* the thick *muna-mochi-bashira* post can be seen in the gable wall, running from the ground to the ridge and supporting the ridgepole (not visible).

At any rate, common to all these systems are the muna-mochi-bashira posts than run from the ground to the ridge. In minka, these posts are usually known as udatsu-bashira (うだつ柱). In typical minka construction, however, crown posts known as shin-zuka (真束, lit. ‘true post/stump’) have replaced the full-length ground-to-ridge udatsu; shin-zuka start from and are supported by the roof beams, and in turn support the ridgepole. In the Kansai region, these crown posts are called odachi, which is a variant of the word udatsu (in many regions of Kansai, ‘u’ is or was pronounced as ‘o’). Regardless of what these posts might be called in the many other dialects of Japanese, here we will call them odachi (おだち), and the method of framing that employs them odachi-gumi (おだち組). Most commonly seen in the mountainous areas of the Kinki region (basically the same as the Kansai region), but also found in older minka in the Kantо̄ and Tо̄hoku regions, the method is surmised to have had its conception in the primitive roof framing systems discussed above. The shin-zuka usually bear on longitudinal roof beams called jimune (地棟) that cross above the transverse roof beams (koya-gumi-bari (小屋組梁). These jimune are known as nakaoki (中置) or yuki (ゆき).