An arch pushes outward on its supports as well as down. For the same load and span the horizontal push grows as the rise falls: halve the rise and you roughly double the thrust.
H ≈ w·s² ⁄ 8f (uniform load w per metre, span s, rise f)
Rules · Doors & windows · Arches · Façades
The Serliana
Combine a central arched opening with two narrower flat-headed openings on either side, the arch springing from the entablature of the side openings.
side lights ≈ ½ central span; arch springs from the lintel of the sides
Named after Serlio, who published it, the motif is also called the Palladian or Venetian window. Palladio used it in a double-storey loggia round the Basilica in Vicenza, where the flexible side openings absorb the irregular spacing of the medieval hall inside.
Related rules
To find how thick the pier of an arch must be, divide the intrados into three equal parts; draw a line from the springing through the first division, and produce it beyond the springing by its own length. A vertical through the end of that line marks the outer face of the pier.
pier ≈ ¼ span (semicircle) · ≈ 0.23 span (equilateral) · less for a lancet
In a row of arches the thrusts of neighbouring arches cancel over each intermediate pier, which may therefore be slender; at the ends of the row nothing balances them, so the outermost piers must be made wider or buttressed.
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.
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
Take the plan, the orders and the details from the builders’ pattern books, simplified for timber and for the carpenter: a symmetrical front, a central hall and stair with rooms either side, a doorway under a pediment or fanlight, and mouldings drawn to be made with the plane.
Cite this page Chris Paton, “The Serliana”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/serliana. Text, drawings and models licensed under CC BY-NC 4.0.