What a sawtooth roof is
A sawtooth roof repeats single-pitch slopes like the teeth of a saw. One face is a shallow slope and the other nearly vertical, and the vertical face is glazed.
Factories use it. Facing those windows north keeps direct sun out and gives even light through the day, spreading steady illumination across a wide floor.
The former Shinmachi spinning mill in Gunma Prefecture, whose buildings include work of 1877, is recorded as an Important Cultural Property described as the first state-run silk spinning mill in Japan, established by the Home Ministry, directed by a named official and built by Japanese carpenters under German instruction. It operated until 1909, with extensions and new buildings added throughout. The entry notes that the main range with its Kirizuma-zukuri roof belongs to the state period and combines Western and native technique in its unusual trusses, while the sawtooth-roofed extensions and the brick engine house and stores show how a Meiji spinning mill developed.
The contrast between the gabled original and the sawtooth extensions is the point. As the works grew, the demand for light grew with it and the roof form changed.
Among modern factory buildings
The same record judges the mill to be of high historical value as a rare timber factory surviving almost complete and showing the building technique of the early Meiji period, and of high academic value as the only surviving silk spinning mill of that era, evidence of how the industry developed.
A Wagoya does not suit this roof. Carrying repeated single slopes calls for triangulated framing, so it is usually combined with Western trusses such as the King post truss.
It differs in purpose from a monitor roof. A monitor sits on the ridge to vent smoke or admit light and appears on Machiya and storehouses; this form makes the roof surface itself repeat, and it is confined to large works.
On site, look at the building from the side. A roof line repeating in triangular waves with windows on one side only is this form, and checking which way the glazing faces reveals the intention behind it.
References
- Agency for Cultural Affairs: National Treasures and Important Cultural Properties (structures)
- https://www.bunka.go.jp/seisaku/bunkazai/shokai/yukei_kenzobutsu/kokuho_bunkazai.html
- National Cultural Properties Database: former Shinmachi spinning mill, its sawtooth-roofed extensions showing how the works developed
- https://kunishitei.bunka.go.jp/bsys/maindetails/102/00004791
- National Cultural Properties Database: former Shinmachi spinning mill, a rare timber factory surviving almost complete from the early Meiji period
- https://kunishitei.bunka.go.jp/bsys/maindetails/102/00004794
- National Cultural Properties Database: Sakai brewery Showa storehouse, small hoods on iron brackets over its high windows
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00003099
Last verified: 2026.09.11