Jettying (jetty, jutty, from
Old French
Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intelligib ...
''getee, jette'') is a building technique used in
medieval
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the Post-classical, post-classical period of World history (field), global history. It began with t ...
timber-frame
Timber framing (german: Holzfachwerk) and "post-and-beam" construction are traditional methods of building with heavy timbers, creating structures using squared-off and carefully fitted and joined timbers with joints secured by large wooden ...
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
A garrison (from the French ''garnison'', itself from the verb ''garnir'', "to equip") is any body of troops stationed in a particular location, originally to guard it. The term now often applies to certain facilities that constitute a mil ...
house. Most jetties are external, but some early medieval houses were built with internal jetties.
Structure
![Hildesheim-Markt-Knochenhaueramtshaus](https://upload.wikimedia.org/wikipedia/commons/9/97/Hildesheim-Markt-Knochenhaueramtshaus.Detail.01.JPG)
A jetty is an upper floor that depends on a
cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
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
joist
A joist is a horizontal structural member used in framing to span an open space, often between beams that subsequently transfer loads to vertical members. When incorporated into a floor framing system, joists serve to provide stiffness to the s ...
s which are supported by jetty plates. Jetty joists in their turn were slotted sideways into the diagonal
dragon beam
Dragon beam is a horizontal, diagonal beam in the corner(s) of some traditional timber framed buildings. The term is commonly used in both hip roof framing and jettying. Older publications may use the synonyms dragging beam, dragging piece, dragg ...
s at angle of 45° by means of
mortise and tenon
A mortise and tenon (occasionally mortice and tenon) joint connects two pieces of wood or other material. Woodworkers around the world have used it for thousands of years to join pieces of wood, mainly when the adjoining pieces connect at right ...
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:
* to gain space.
* the structural advantage of the jettied wall counteracting forces in the joists or tying a stone wall together
* to shelter the lower walls of the house from the weather.
* to simplify joinery.
* uses shorter timbers, a benefit due to timber shortages and difficult handling of long timbers especially in city streets.
* as a status symbol or "...symbol of wealth and status."
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:
* framed on multiple joists.
* framed on a few beams.
* framed on
bracket
A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. Typically deployed in symmetric pairs, an individual bracket may be identified as a 'left' or 'r ...
s added to the posts.
* hewn jetty also called a false jetty: Framed on projections of the posts rather than on cantilevered beams (or brackets).
Vertical elements
![Paul Revere House Boston MA](https://upload.wikimedia.org/wikipedia/commons/d/dc/Paul_Revere_House_Boston_MA.jpg)
The vertical elements of jetties can be summarized as:
* the more massive corner posts of the timber frame that support the dragon beam from the floor below and are supported in their turn by the dragon beam for the extended floor above.
* the less substantial
studs of the
close studding
Close studding is a form of timber work used in timber-framed buildings in which vertical timbers ( studs) are set close together, dividing the wall into narrow panels. Rather than being a structural feature, the primary aim of close studding is to ...
along the walls above and below the jetty.
Horizontal elements
![Dragon-encorbellement-Prieuré de Saint-Arnoult-21-09-2007](https://upload.wikimedia.org/wikipedia/commons/3/33/Dragon-encorbellement-Prieur%C3%A9_de_Saint-Arnoult-21-09-2007.jpg)
The horizontal elements of jetties are:
* the jetty breastsummer (or bressummer), the sill on which the projecting wall above rests; the bressummer stretches across the whole width of the jetty wall
*the dragon-beam which runs diagonally from one corner to another, and supports the corner posts above and is supported in turn by the corner posts below
*the jetty beams or joists which conform to the greater dimensions of the floor above but rest at right angles on the jetty-plates that conform to the shorter dimensions of the floor below. The jetty beams are morticed at 45° into the sides of the dragon beams. They are the main constituents of the cantilever system and they determine how far the jetty projects
*the jetty-plates, designed to carry the jetty-beams or joints. The jetty-plate itself is supported by the corner posts of the recessed floor below.
Cantilever
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.
Forebay
The
Pennsylvania barn
A Pennsylvania barn is a type of banked barn built in the US from about 1790 to 1900. The style's most distinguishing feature is the presence of an overshoot or forebay, an area where one or more walls overshoot its foundation. These barns were ban ...
in the U.S. has a distinctive cantilever called a forebay, not a jetty.
[Ensminger, Robert F.. "Origin." The Pennsylvania barn: its origin, evolution, and distribution in North America. 2nd ed. Baltimore: Johns Hopkins University Press, 2003.]
Mediterranean area
The traditional
Turkish house is a
half-timbered
Timber framing (german: Holzfachwerk) and "post-and-beam" construction are traditional methods of building with heavy timbers, creating structures using squared-off and carefully fitted and joined timbers with joints secured by large wooden ...
house with a
cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
ed or supported overhang called a cumba.
In the North African
Maghreb
The Maghreb (; ar, الْمَغْرِب, al-Maghrib, lit=the west), also known as the Arab Maghreb ( ar, المغرب العربي) and Northwest Africa, is the western part of North Africa and the Arab world. The region includes Algeria, ...
, houses in medieval city
kasbahs often featured jetties. Contemporary examples still survive in the
Casbah of Algiers
The Casbah ( ar, قصبة, ''qaṣba'', meaning citadel) is the citadel of Algiers in Algeria and the traditional quarter clustered around it. In 1992, the United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed ' ...
.
The House of
Opus Craticum
''Opus craticum'' or ''craticii'' is an ancient Roman construction technique described by Vitruvius in his books '' De architectura'' as wattlework which is plastered over. It is often employed to construct partition walls and floors. Vitruvius d ...
, built before AD 79 in Roman
Herculaneum
Herculaneum (; Neapolitan and it, Ercolano) was an ancient town, located in the modern-day ''comune'' of Ercolano, Campania, Italy. Herculaneum was buried under volcanic ash and pumice in the eruption of Mount Vesuvius in AD 79.
Like the nea ...
, has a supported cantilever.
See also
*
Cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
– modern buildings still use cantilevered floors, but the term jettying is rarely used. See for example
945 Madison Avenue
945 Madison Avenue, also known as the Breuer Building, is a museum building in the Upper East Side of Manhattan, New York City. The Marcel Breuer-designed structure was built from 1964 to 1966 as the third home for the Whitney Museum of America ...
in New York.
*
Machicolation
A machicolation (french: mâchicoulis) is a floor opening between the supporting corbels of a battlement, through which stones or other material, such as boiling water, hot sand, quicklime or boiling cooking oil, could be dropped on attackers at t ...
*
Overhang (architecture)
In architecture, an overhang is a protruding structure that may provide protection for lower levels. Overhangs on two sides of Pennsylvania Dutch barns protect doors, windows, and other lower-level structures. Overhangs on all four sides of barns ...
*
Corbel
In architecture, a corbel is a structural piece of stone, wood or metal jutting from a wall to carry a superincumbent weight, a type of bracket. A corbel is a solid piece of material in the wall, whereas a console is a piece applied to the s ...
s, brackets that may be under a jetty
References
::
{{Commons category, Jetty (timber framing)
Timber framing
Architectural elements
Medieval architecture
fr:Encorbellement