A style used from c. 1860, in which tile-hanging, tall chimneys, half-timbering and other details of the gabled vernacular architecture of south-east England are picturesquely combined.
Open pediment
A pediment with the centre of the base omitted.
Open string
A sloping member of a staircase covering the ends of the treads and risers and cut into their shape; hence an open-string staircase. Compare closed string.
Opus sectile
Decorative mosaic-like facing.
Opus signinum
Composition flooring of Roman origin.
Oratory
A private chapel in a church or house. Also a church of the Oratorians (Roman Catholic).
Order
One of a series of recessed arches and jambs forming a splayed medieval opening, e.g. a doorway or arcade arch. Also, an upright structural member used in series, especially in classical architecture: see Orders.
Orders
The differently formalized versions of the basic post-and-lintel (column and entablature) system in classical architecture. The main orders are Doric, Ionic, and Corinthian. They are Greek in origin but occur in Roman versions. Tuscan is a simple variant of Roman Doric. The Composite capital combines Ionic volutes with Corinthian foliage. Though each order has its own conventions of design and proportion, there are many minor variations. Superimposed orders: orders on successive levels, customarily in the upward sequence of Tuscan, Doric, Ionic, Corinthian, Composite.
Organ loft
In a church, a gallery in which the organ is placed.
Oriel
A bay window which rests on corbels or brackets and starts above ground level.