What a truss is
A truss is a framework whose members are arranged in triangles. A triangle cannot change shape once the lengths of its sides are fixed, so the overall form holds without heavy demands on the joints. Loads are resolved into pulling or pushing forces in the individual members, and slender pieces can carry large loads.
Trusses are therefore used to span wide openings without intermediate supports: in the roof frames of buildings and in the girders of bridges. In Japan the truss was introduced from the West from the Meiji era, and a roof frame built of trusses is called Yōgoya, distinguished from the traditional Wagoya.
Roof trusses come in types defined by their layout, such as the king post truss with a single central post and the queen post truss with two. They may be of timber or of iron and steel.
Reading the records and the building
Records name it as the roof-frame type, noting a timber truss roof or trusses used in the roof frame. Storehouses and workshops often keep a traditional exterior, gabled and pantiled, with trusses hidden inside. The record for the steaming shed of the Marumoto brewery notes a truss roof frame with an otherwise traditional design, and the connecting passage of the same brewery carries trusses on posts or beams to form an open loading area. The stone storehouse of Aizanso has an iron truss beam at the centre of its roof frame carrying the ridge beam.
Trusses allow a wide interior free of posts, one reason they were adopted in buildings that needed large floors for brewing, storing rice or other work.
On site, look into the roof space or up at an open ceiling. A forest of short posts standing on level beams indicates wagoya; inclined and horizontal members joined in triangles indicate a truss.
References
- 旧長島家住宅米蔵｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00014739
- 丸本酒造釜場｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/heritage/detail/101/00003699
- 丸本酒造取合廊下｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/heritage/detail/101/00003701
- 愛山荘石蔵｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00011682
Last verified: 2026.09.26