Rules · Doors & windows · Pediments · Façades
Over a long row of windows on the principal floor, set triangular and segmental pediments in turn, so that the row is read in pairs and does not run on monotonously.
The alternation became one of the standard dresses of the palace front from the Farnese onward, and passed by way of Inigo Jones to the English Palladians.
Front a basilican church with two storeys of the order: the lower as wide as nave and chapels, the upper as wide as the nave alone, joined by scrolls and crowned by a pediment.
Il Gesù (reconstructed): lower ≈ 34 m wide, upper ≈ 20 m; scrolls fill the difference
Build up a façade in layers: let the wall advance in stages towards the central bay, double the pilasters or columns as it advances, and break the entablature forward over every support.
Mark the main door by setting a segmental pediment inside a larger triangular one, or by breaking the pediment open to hold a cartouche or statue.
To unify a façade of two or more storeys, run a single order of pilasters or columns through all of them, from the base to the main cornice.
Let the wall of a façade curve in plan (concave, convex, concave) so that the front answers the street, the light and the space within, and the order bends with it.
Lift the dome on a cylindrical or polygonal drum pierced with windows between the ring of the pendentives and the springing of the dome, to light the centre of the church and to make the dome visible from afar.
drum height ≈ ⅓–1 × its radius (Byzantine); much taller in Russian churches
Cite this page Chris Paton, “Pediments that alternate”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/alternating-pediments. Text, drawings and models licensed under CC BY-NC 4.0.