Rules · Modules · Proportion
Fix the bay (the distance between column centres) and derive every other member from it by fixed ratios: the column from the bay, the brackets and beams from the column, the rafters and their spacing from the brackets, the eaves from the rafters.
Kiwari (“dividing the wood”) is the Japanese counterpart of the Chinese cai–fen system (Everything is measured in cai and fen) and of the classical module. The Heinouchi manual gives, for each type of gate, hall, shrine and pagoda, a chain of proportions starting from one dimension; a master who remembered the chain could lay out a correct building of any size. Different families kept different ratios, and the manuals were guarded as secrets of the lineage.
Rafter spacing was especially important. Japanese builders often made the bay an exact multiple of the rafter interval (shitenwari) so that rafters fell symmetrically over every column, a discipline visible in the regular rhythm of rafter ends under the eaves.
Build the bracket set (puzuo) of blocks (dou) and arms (gong) crossing at right angles, each tier projecting no more than 30 fen beyond the one below; a set of n projecting tiers is called an (n + 3)-puzuo, from four to eight.
projection per tier ≤ 30 fen · rise per tier = 21 fen · puzuo = tiers + 3
Project the eaves from the centre of the eave purlin by 3½ chi for rafters of 3 cun diameter and 4 to 4½ chi for rafters of 5 cun; beyond them add flying rafters projecting six-tenths as far again.
eave projection ≈ 3½–4½ chi · flying rafters = 0.6 × eave projection
Set out the posts of a house on a square grid of one ken (six shaku, about 1.82 m) and size rooms, doors, screens and mats to fit the grid.
1 ken = 6 shaku ≈ 1.82 m · 1 tsubo = 1 ken² ≈ 3.3 m² = 2 mats
In the Kyoto system (kyō-ma) fix the mat (6.3 × 3.15 shaku, about 1.91 × 0.955 m) and set the posts outside it; in the Edo system (edo-ma) fix the post grid at 6 shaku and cut the mats to fit between the posts, making them smaller.
kyō-ma ≈ 191 × 95.5 cm · chūkyō-ma ≈ 182 × 91 cm · edo-ma ≈ 176 × 88 cm
Make each storey of a pagoda narrower than the one below and derive all from the bay of the first storey; in the oldest Japanese pagodas the top storey is about half as wide as the first.
top storey ≈ ½ first storey (Hōryū-ji)
Divide the capital into blocks (machi) forty jō square; gather sixteen blocks into a ward (bō) and the wards into rows (jō); separate the blocks by lanes of four jō and the wards by avenues of eight to twelve, and make Suzaku-ōji, the central avenue, twenty-eight.
machi = 40 jō (c. 120 m) · kōji 4 jō · ōji 8–12 jō · Nijō 17 jō · Suzaku-ōji 28 jō (c. 84 m) · city 1,508 × 1,753 jō
Cite this page Chris Paton, “Kiwari: size every member from the bay”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/kiwari. Text, drawings and models licensed under CC BY-NC 4.0.