As for the structure, Hoan-den needed to be built from ferro-concrete, have walls 25 cm or thicker, and a complete safe-typed and dual-structured door with either a single swing door or double-leaf doors.
構造は鉄筋コンクリート造、壁厚25cm以上、片開または両開の完全な金庫式二重扉を設けることとされた。