Take the section of the standard timber, the cai, as the module of the building: it is 15 fen high and 10 fen wide, and every member is dimensioned in fen.
1 cai = 15 fen (height) × 10 fen (width)
The ang: reach further without climbing
Where the eaves must project far, replace the outer arms by slanting levers (ang) that run down and out beyond the bracket set and rise inward to be held down under an interior purlin.
A horizontal arm raises the eave purlin 21 fen for every 30 fen it projects. The ang, a long timber pivoting on the bracket set like a see-saw, carries the outer block forward while dropping it, so the eaves can project far without lifting them so high that they shade the whole façade. Its tail, rising inside the building, is weighted by the roof above; its tip, cut to a sharp beak, is the most recognisable feature of Tang and Song bracketing.
In the generator each ang tier adds its full 30 fen of reach but only about 10 fen of height.
Related rules
Between two stacked arms leave a spacer of 6 fen, the zhi; a cai plus a zhi, 21 fen, is a “full timber” (zucai) and the vertical step of each tier of a bracket set.
zucai = 15 + 6 = 21 fen
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
Set the heads of the outer columns inward: on the front and back by 1 fen for every chi of height (1/100), on the ends by 8 li per chi (8/1000); the corner columns lean both ways.
lean = 1/100 of height (front) · 8/1000 (flanks)
Build the sanctuary of unpainted cypress on posts set directly in the ground, with a raised floor and veranda, a straight thatched gable roof entered on the long side, crossed finials (chigi) and ridge billets (katsuogi), and a free-standing post at each gable carrying the ridge.
Cite this page Chris Paton, “The ang: reach further without climbing”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/ang-lever. Text, drawings and models licensed under CC BY-NC 4.0.