Where a church has a tall nave and low aisles, give the front a lower storey as wide as the whole church and an upper storey as wide as the nave, and join the two with great scrolls.
Alberti’s marble front for Santa Maria Novella had to complete a Gothic façade already begun, with a nave much taller than its aisles. He placed a classical temple front over the nave and masked the sloping aisle roofs with two scrolls (volutes), and he governed the whole by squares: the façade fits in a square, and the upper storey and the parts of the lower are halves and quarters of it. The device gave every later basilican church a way to reconcile the classical temple front with the cross-section of a nave and aisles, and it became the hallmark of the Counter-Reformation church front (The two-storey church front).
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.
Divide the inside of a dome into coffers that shrink in step with the meridians as they rise, so that their perspective deepens the dome and draws the eye to the light of the lantern.
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.
Cite this page Chris Paton, “Scrolls to join nave and aisles”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/alberti-scroll-facade. Text, drawings and models licensed under CC BY-NC 4.0.