Editing Jettying

{{short description|Medieval building technique}}
{{about|the building technique|the marine structures|jetty}}
{{redirects|Oversailing|oversailing by tower cranes|Crane (machine)#Tower}}

[[Image:DoubleJettiedBuilding.jpg|thumb|right|A double jettied [[timber framing|timber-framed]] building. The ends of the multiple [[cantilever]]ed joists supporting the upper floors can easily be seen.]]

'''Jettying''' (jetty, jutty, from [[Old French]] ''getee, jette'')<ref>Oxford English Dictionary, 2nd ed. 1989. Jetty</ref> is a building technique used in [[medieval]] [[timber framing|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''.<ref>[https://www.geograph.org.uk/photo/943487 Illustration of a jettied house]</ref><ref>{{cite web|url=http://www.today.plus.com/houses/page4.html |title=Developments: Jettying |archive-url=https://web.archive.org/web/20210922180449/http://www.today.plus.com/houses/page4.html |archive-date=September 22, 2021}}</ref> In the U.S., the most common surviving [[American colonial architecture|colonial version]] of this is the [[Garrison (architecture)|garrison]] house.<ref>Noble, Allen George, and M. Margaret Geib. Wood, brick, and stone: the North American settlement landscape. Amherst: University of Massachusetts Press, 1984. 22.</ref> Most jetties are external, but some early medieval houses were built with internal jetties.<ref>Alcock, N. A., Michael Laithwaite. "Medieval Houses in Devon and Their Modernization". ''Medieval Archaeology'' vol. 17 (1973), 100–125.
http://archaeologydataservice.ac.uk/catalogue/adsdata/arch-769-1/dissemination/pdf/vol17/17_100_125.pdf accessed 01/08/2013</ref>

== Structure ==
[[File:Hildesheim-Markt-Knochenhaueramtshaus.Detail.01.JPG|thumb|The under-side of jetties in Germany are sometimes decorated and called a windbrett (wind board). This is an example of a jetty supported on brackets.]]
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'').{{dubious|This is just one way of hadling a jetty, and one not used by one -half, that is, of the illustrations.|date=December 2015}} The [[bressummer]] (or breastsummer) itself rests on the ends of a row of jetty beams or [[joist]]s which are supported by jetty plates. Jetty joists in their turn were slotted sideways into the diagonal [[dragon beam]]s 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 are unclear but some reasons put forward for their purpose are:<ref>Harris, Richard. Discovering timber-framed buildings. 2d ed. Aylesbury: Shire Publications, 1979. 55–57.</ref>
* 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 "symbol of wealth and status."<ref>Harris, Richard. Discovering timber-framed buildings. 2d ed. Aylesbury: Shire Publications, 1979. 56.</ref><ref>Garvan, Anthony N. B., Architecture and Town Planning in Colonial Connecticut (New Haven: Yale University Press, 1957. 92.</ref>

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.{{citation needed|date=November 2017}}

Structurally, jetties are of several types:
* framed on multiple joists.
* framed on a few beams.
* framed on [[bracket (architecture)|bracket]]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).<ref>Davies, Nikolas, and Erkki Jokiniemi. Dictionary of architecture and building construction. Amsterdam: Elsevier/Architectural Press, 2008. 144. false jetty.</ref>

===Vertical elements===
[[File:Paul Revere House Boston MA.jpg|thumb|[[Paul Revere House]] Boston, Massachusetts, US, built 1680. This is framed on a few cantilevered beams.]]
[[File:Glattfelden - Klingelehaus (Gottfried-Keller-Zentrum), Gottfried-Keller-Strasse 8 2011-09-15 13-49-20 ShiftN.jpg|thumb|An example of a hewn jetty in Glattfelden, Switzerland]]
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 [[Wall stud|studs]] of the [[close studding]] along the walls above and below the jetty.

===Horizontal elements===
[[File:Dragon-encorbellement-Prieuré de Saint-Arnoult-21-09-2007.jpg|thumb|Jetties in French are called ''encorbellements'' and may be decoratively carved; Prieuré de Saint-Arnoult, France]]
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==
{{Main|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]] in the U.S. has a distinctive cantilever called a forebay, not a jetty.<ref>Ensminger, Robert F.. "Origin." The Pennsylvania barn: its origin, evolution, and distribution in North America. 2nd ed. Baltimore: Johns Hopkins University Press, 2003.</ref>

==Mediterranean area==
The traditional [[culture of Turkey|Turkish]] house is a [[Timber framing#Half-timbering|half-timbered]] house with a [[cantilever]]ed or supported overhang called a cumba.

In the North African [[Maghreb]], houses in medieval city [[kasbah|kasbahs]] often featured jetties. Contemporary examples still survive in the [[Casbah of Algiers]].

The House of [[Opus craticum|Opus Craticum]], built before AD 79 in Roman [[Herculaneum]], has a supported cantilever.

==See also==
* [[Cantilever]] – modern buildings still use cantilevered floors, but the term jettying is rarely used. See for example  [[945 Madison Avenue]] in New York.
* [[Machicolation]]
* [[Overhang (architecture)]]
* [[Corbel]]s, brackets that may be under a jetty

== References ==
{{Reflist}}
:: {{Cite book
  |last=Alcock | first=N.W. 
  | last2=Barley | first2=M.w. 
  | last3=Dixon | first3=P.W. 
  |last4=Meeson | first4=R.A. 
  | year=1996 
  | title=Recording Timber-Framed Buildings
  | publisher=Council for British Archaeology, Practical Handbook in Archaeology
  | isbn=1-872414-72-9 
}}

{{Commons category|Jetty (timber framing)}}

[[Category:Timber framing]]
[[Category:Architectural elements]]
[[Category:Medieval architecture]]

[[fr:Encorbellement]]