Rules · Doors & windows · Ornament
Break the architrave of a door or window with blocks of plain stone laid across it, alternately larger and smaller, and set a keystone in the middle of the head.
Gibbs did not invent the motif, which comes from Italian Mannerist practice, but his books spread it so widely that it carries his name. It gives a plain opening weight and shadow at little cost, and suits a door or a lower storey.
Gibbs used it himself on the side windows of St Martin-in-the-Fields (1722–26).
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
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.
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.
Make the architrave round a door or window as wide as a sixth part of the opening’s breadth, and dress the openings of the principal floor more richly than those of the storeys above and below, with a frieze and cornice, and on the grandest a pediment.
architrave = ⅙ × width of the light
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.
Over a window in a brick front, turn a flat arch of soft red bricks rubbed and cut (gauged) to radiate from a centre below, laid with the finest joints, and give it a keystone of stone where the front is dressed in stone.
Cite this page Chris Paton, “The Gibbs surround”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/gibbs-surround. Text, drawings and models licensed under CC BY-NC 4.0.