The Qing government’s building regulations: twenty-seven standard building types with every member specified, measured in doukou (the width of the slot in the great bearing block) for buildings with bracket sets, and in column diameters for those without.
Like the Yingzao fashi six centuries earlier, the Qing regulations of 1734 were written to control the cost of state building. They describe standard types (halls, gate-houses, pavilions, corridors, granaries) and give for each the dimensions of every member as a multiple of a module. For bracketed buildings the module is the doukou, the width of the mortise in the lu dou block, available in eleven grades; for plain buildings it is the diameter of the eave column.
Compared with the Song system the Qing one is simpler and more rigid. Bracket sets had become small and closely spaced, more ornament than structure; the roof section is drawn not by depressing purlins from a straight line but by giving each rafter span a fixed slope (half-pitch at the eaves rising to nine-tenths at the ridge), which produces the steeper, more sharply curved roofs of the Forbidden City. Rank is expressed through roof type, the number of bays, the colour of tiles and the number of beasts on the ridges.
The book, part by part
I Standard building types
Twenty-seven types, each described member by member.
II The module (doukou) and bracket sets
Eleven grades of doukou; bracket sets spaced at eleven doukou between centres.
III Roof raising (jǔjià)
Each rafter span rises by a set fraction of its run: 5 tenths at the eaves, then 6½ or 7, then 9 near the ridge.
Rules: Qing jǔjià: five-tenths at the eaves, nine at the ridge
IV Rank and ornament
Practice of the Ming and Qing courts: the hierarchy of roof types and ridge ornaments.
Rules: The roof declares the rank