a triangular prism-shaped house

since April 19, 2013

A survey of Sanrakutei (三楽亭), a triangular prism-shaped house, in Northern Culture Museum, Niigata, Japan

reported by Akiyoshi Kitaoka and Seiichi Tsuinashi, supported by a JSPS kaken-hi grant and R-GIRO

This room appears to be a normal, rectangular room, but the shape is actually parallelogram.

(Visitors usually cannot enter the inside of this house)

Copyright Seiichi Tsuinashi 2012 (August 6) --- photo taken on August 6, 2012

Each corner angle is 60 degrees.

Each tatami is of a parallelogram shape, in which the acute angle is 60 degrees and the obtuse angle is 120 degrees. (photo taken through a fisheye lens)


The portrait shows ITO Bunkichi the 6th Master of Ito's Family, who built this house in 1891. The right man having a camera is Dr. Seiichi Tsuinashi.


The outside appearance

The corner angle appears to be a right angle, but it is actually 60 degrees.

Photos taken through fisheye lens tend to make the corner angle appear to be an acute angle as it is.

The triangular prism-shaped telephone box


Natsuo Tsunoda (1985). Tale of triangular prism-shaped houses. Niigata: Northern Culture Museum.

According to this book, there used to be at least three triangular prism-shaped house in Japan.

It takes about 20 minutes from the center of Niigata city.

Appendix <May 8, 2013>

Professor Kokichi Sugihara made a model of Sanrakutei.

The corner of 60 degrees appears to form the right angle!

PDF of the development view (provided by Kokichi Sugihara)

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