Blondel’s stair rule
François Blondel (1675): twice the riser plus the going should equal the length of a natural pace, 24 pouces (≈ 65 cm).
The rules it illustrates
Two risers and a going make a pace. Proportion every step so that twice its height plus its depth equals the length of a natural pace on the level: two feet, or 24 pouces.
The imperial stair. Make the stair of a palace a processional space: one broad flight rising to a landing, then turning back in two flights either side to arrive at the principal floor beneath a single great vault.
An odd number of steps. Give the flight of steps before a temple an odd number, so that one who starts with the right foot will also set the right foot first on the top.
Where to put the staircase. Place the staircase by three tests: its relation to the principal rooms it serves; keeping the main axial communications free of obstruction; and light, for itself and, as a well of light, for the corridors and vestibules around it.
Palladio on stairs. Place the stair where it does not spoil the rooms and yet is easily found; light it well; and make the steps no higher than half a foot and the treads at least a foot deep.
The winding stair. Where space is short, wind the stair round a newel or an open well; measure the going on the walking line, about halfway along the tread, where it should be as generous as on a straight flight.
Where it appears in the book
In the styles Baroque, Rococo.
In the chapters Stairs.