What a flat roof is
A flat roof, rokuyane in Japanese, is a roof with almost no pitch. The Japanese reading is rokuyane, also rikuyane; roku is the carpenters' word for level. A slight fall is given to drain rainwater, but from outside the roof looks flat.
Flat roofs spread with roof slabs of reinforced concrete. A pitched timber roof sheds water with tiles or boards, whereas a flat roof is covered entirely by a waterproof membrane. The roof can be used for drying laundry or as a viewing terrace, and its edge is usually enclosed by a Parapet. From the Meiji era onward flat roofs were common on Western-style buildings of reinforced concrete or brick and on factories and power stations.
They are distinguished from pitched roofs such as gabled and hipped roofs by the absence of slope. Records use rokuyane for true flat roofs and rokuyane-fū, flat-roof style, for buildings whose pitched roof is hidden behind a parapet so that they look flat from the front.
Reading the records and the building
Records give the roof type alongside the structure. The Yumicho Hongo Church in Bunkyo, Tokyo, a four-storey building of the Nakamura system of reinforced concrete blocks, has a flat roof and a tower at the street corner. The Kamidaki power station in Toyama, a reinforced-concrete building of one storey with a partial second floor, has a roof built in flat-roof form. The bathhouse of the former Matsui family villa in Wakayama sets a reinforced-concrete flat roof slab on brick walls, with a parapet along the top.
As an example of the flat-roof style, the main house of the Okuyama family in Nishiyodogawa, Osaka, raises parapets of varying height so that it appears flat-roofed. Articles should distinguish, using the record's wording, between a roof that is really flat and a front that only looks so.
On site, look at the building from a little way off or from the side to see whether the roof slopes. A railing or tower visible on top usually means a flat roof used as a terrace.
References
- 日本基督教団弓町本郷教会｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00013966
- 上滝発電所｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00002377
- 旧松井家別邸（がんこ六三園）浴室棟｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00009365
- 奥山家住宅主屋｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/heritage/detail/101/00004145
Last verified: 2026.09.26