What a roof frame is
The roof frame, koyagumi in Japanese, is the structure set on top of the posts and walls to carry the roof and pass its weight down into the building. Beams spanning the walls support short posts, purlins and the ridge beam, and rafters laid across these take the roofing. Where a ceiling is fitted the frame is hidden above it; where there is none, it can be seen from the floor.
Japanese builders long used the wagoya, in which vertical posts stand on the beams to hold the purlins and ridge. From the Meiji era the yogoya arrived, carrying the roof on trusses of members arranged in triangles, and it spread through warehouses and factories that needed wide clear spans. Japanese records almost always say which of the two a building has.
Heritage descriptions sometimes single out the roof frame. The Myojogura brewing hall of the Aramasa Sake Brewery in Akita City, built in 1887, spans 7.5 m, and the Agency for Cultural Affairs notes that its ridge is carried on a double tier of beams, a frame found here and there in the region.
What to look for
In storehouses, workshops and village stages without a ceiling, a glance upward from the doorway shows the frame. Vertical posts standing on the beams mean a wagoya; diagonal members forming triangles mean a yogoya. If it is a truss, check for a single central post (king-post truss) or a pair (queen-post truss).
The beams themselves can be worth a look. Wagoya builders often used naturally curved logs. In the south storehouse of the Isamigoma Sake Brewery in Yokote, Akita Prefecture, built in 1886, the Agency points to an upward-arched beam finished with adze marks as a detail found in none of the brewery's other buildings.
In writing, follow the record: name the frame type, or the truss type, where it is given. Where the record is silent, do not guess the frame from the exterior.
References
- Agency for Cultural Affairs, Database of National Cultural Properties: Aramasa Sake Brewery Myojogura
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00009880
- Agency for Cultural Affairs, Database of National Cultural Properties: Isamigoma Sake Brewery Head Office South Storehouse
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00002601
- Agency for Cultural Affairs, Database of National Cultural Properties: Satake Glass Workshop
- https://kunishitei.bunka.go.jp/heritage/detail/101/00002157
Last verified: 2026.10.04