Jettying

Jettying (jetty, jutty, getee (obsolete) from Old French getee, jette) is a building technique used in medieval timber-frame buildings in which an upper floor projects beyond the dimensions of the floor below. This has the advantage of increasing the available space in the building without obstructing the street. Jettied floors are also termed jetties. In the U.S., the most common surviving colonial version of this is the garrison house. Most jetties are external, but some early Medieval houses were built with internal jetties.

A jetty is an upper floor that depends on a cantilever system in which a horizontal beam, the jetty bressummer, supports the wall above and projects forward beyond the floor below (a technique also called oversailing). The bressummer (or breastsummer) itself rests on the ends of a row of jetty beams or joists which are supported by jetty plates. Jetty joists in their turn were slotted sideways into the diagonal dragon beams at angle of 45° by means of mortise and tenon joints.

The overhanging corner posts are often reinforced by curved jetty brackets.

The origins of jettying is unclear but some reasons put forward for their purpose are:

Jetties were popular in the 16th century but banned in Rouen in 1520 relating to air circulation and the plague, and London in 1667 relating to the great fire. They are considered a Gothic style.

Structurally, jetties are of several types:

The vertical elements of jetties can be summarized as:

The horizontal elements of jetties are:

Jettying was used for timber-framed buildings, but was succeeded by cantilever which are used for the same reason as jettying, to maximise space in buildings. This is often utilised on buildings which are on a narrow plot and space is at a premium.

The Pennsylvania barn in the U.S. has a distinctive cantilever called a forebay, not a jetty.

The traditional Turkish house is a half-timbered house with a cantilevered or supported overhang called a cumba.

The House of Opus Craticum built before 79 A. D. in Roman Herculaneum has a supported cantilever.

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