Rules · Domes · Roofs · Ornament
Lift each dome on a tall drum and give it a bulbous outer shell that swells beyond the drum and draws up to a point under the cross; build the shell as a light timber frame sheathed in metal over the structural vault below.
onion Ø ≈ 1.2–1.3 × drum Ø; height ≈ 2 × its base radius
Unlike the Byzantine dome, which is the ceiling seen from below, the Russian onion is chiefly an exterior form. Inside, the drum is usually covered by a low masonry vault; the onion above it is a separate roof of timber covered in copper, tin or gilded sheets. Its steep profile sheds snow, and its silhouette makes the church visible from a great distance.
Where the form came from is debated: Byzantine helmet domes grown taller, Islamic bulbous domes seen through trade with the East, or the carpentry of timber churches. By the seventeenth century it was universal, and Russian towns are identified from afar by their clusters of gilded and painted domes.
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
Divide a square naos into nine bays: dome the central one on a drum over four columns, barrel-vault the four arms of the cross, and cover the four corner bays lower; add three apses to the east and a narthex to the west.
arms = central bay width; corners lower; dome on pendentives over four columns
Crown the four corner bays of a cross-in-square with smaller domes on drums around the great central dome, making a five-domed quincunx.
Divide each wall into bays with pilaster strips and end each bay in a semicircular gable, the zakomara, that follows the curve of the barrel vault behind it; shape the roof to the gables.
usually 3 zakomary per façade, one per bay
Mount from the walls to the drum in stepped tiers of decorative gables with pointed ogee heads, the kokoshniki, each tier set back and narrower than the one below, so that the body of the church rises into its domes in a pyramid of arches.
Instead of a dome, crown the church with a tall octagonal pyramid of masonry (the shatyor, or tent) set on an octagon over the square body, with kokoshniki at the transitions and a small cupola at the top.
Ascension, Kolomenskoye (1532): ≈ 62 m high; cube → octagon → tent → cupola
Cite this page Chris Paton, “The onion dome on a tall drum”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/onion-dome-drum. Text, drawings and models licensed under CC BY-NC 4.0.