The haiden's core is just 3 x 1 bays, but it is surrounded on three sides by a 1-bay wide mokoshi (pent roof), bringing the building's external dimensions to 4 x 4 bays.
Mugenan is a modern Shoin-zukuri style house which inherits the traditional elements of a samurai residence.
Shoin-zukuri, a new architectural style influenced by Zen Buddhism, developed during that time from the shinden-zukuri of the earlier Heian period's palaces and the subsequent residential style favored by the warrior class during the Kamakura period.
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Other representative examples of early shoin style, also called shuden, include two guest halls at Mii-dera.