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.
The mansard: a storey in the roof
Break the slope of the roof on all four sides: a steep lower slope, nearly a wall, which holds a storey of rooms lit by dormers, and a shallow upper slope, often invisible from the street.
lower slope ≈ 60–75° · upper slope ≈ 15–30°
The broken roof (comble brisé) appears in France in the sixteenth century, at Pierre Lescot’s Louvre, but takes its name from François Mansart (1598–1666), who used it with great elegance; his great-nephew Jules Hardouin-Mansart spread it through the building works of Louis XIV. Blondel discussed its proportions and construction in his course for architects. Its advantage is economic: it turns the attic into rooms nearly as good as those below. In Haussmann’s Paris of the 1850s–70s, where rules limited the height of the façade to the cornice, the mansard allowed one or two more storeys above it, and it spread with the Second Empire style across the world.
The gambrel is its two-sided cousin: a gable roof with a break in each slope, familiar from Dutch and American barns.
Related rules
Seek in every building only fitness (solidity, healthiness, convenience) and economy (symmetry, regularity, simplicity); a building that has these will please, and ornament added for its own sake is waste.
Build every type (temple, museum, college, hospital, barracks) from the same small set of elements, combined about axes parallel, perpendicular or concentric to one another.
Arrange the principal spaces as a sequence along the main axis (steps, portico, vestibule, great hall, and beyond) so that the visitor’s progress through the building is itself the composition.
Understand every building as a combination of four elements (the hearth, the roof on its supports, the enclosure and the mound), each descended from a craft: ceramics, carpentry, weaving and masonry.
Divide the whole front of the cornice into nine parts; give one of them to the height of the tympanum, measured at its centre.
tympanum height = cornice width ⁄ 9 (≈ 12½°)
Cite this page Chris Paton, “The mansard: a storey in the roof”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/mansard-broken-roof. Text, drawings and models licensed under CC BY-NC 4.0.