Jettying

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A double jettied timber-framed building. The ends of the multiple cantilevered joists supporting the upper floors can easily be seen. DoubleJettiedBuilding.jpg
A double jettied timber-framed building. The ends of the multiple cantilevered joists supporting the upper floors can easily be seen.

Jettying (jetty, jutty, from Old French getee, jette) [1] 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. [2] [3] In the U.S., the most common surviving colonial version of this is the garrison house. [4] Most jetties are external, but some early medieval houses were built with internal jetties. [5]

Contents

Structure

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. Hildesheim-Markt-Knochenhaueramtshaus.Detail.01.JPG
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 ] 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 are unclear but some reasons put forward for their purpose are: [6]

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 ]

Structurally, jetties are of several types:

Vertical elements

Paul Revere House Boston, Massachusetts, US, built 1680. This is framed on a few cantilevered beams. Paul Revere House Boston MA.jpg
Paul Revere House Boston, Massachusetts, US, built 1680. This is framed on a few cantilevered beams.
An example of a hewn jetty in Glattfelden, Switzerland Glattfelden - Klingelehaus (Gottfried-Keller-Zentrum), Gottfried-Keller-Strasse 8 2011-09-15 13-49-20 ShiftN.jpg
An example of a hewn jetty in Glattfelden, Switzerland

The vertical elements of jetties can be summarized as:

Horizontal elements

Jetties in French are called an encorbellement and may be decoratively carved. Prieure de Saint-Arnoult, France Dragon-encorbellement-Prieure de Saint-Arnoult-21-09-2007.jpg
Jetties in French are called an encorbellement and may be decoratively carved. Prieuré de Saint-Arnoult, France

The horizontal elements of jetties are:

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. [10]

Mediterranean area

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

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

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

See also

Related Research Articles

<span class="mw-page-title-main">Timber framing</span> Traditional building technique

Timber framing 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 pegs. If the structural frame of load-bearing timber is left exposed on the exterior of the building it may be referred to as half-timbered, and in many cases the infill between timbers will be used for decorative effect. The country most known for this kind of architecture is Germany, where timber-framed houses are spread all over the country.

<span class="mw-page-title-main">Joist</span> Horizontal framing structure

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 subfloor sheathing, allowing it to function as a horizontal diaphragm. Joists are often doubled or tripled, placed side by side, where conditions warrant, such as where wall partitions require support.

<span class="mw-page-title-main">Hammerbeam roof</span> Type of English Gothic roof

A hammerbeam roof is a decorative, open timber roof truss typical of English Gothic architecture and has been called "...the most spectacular endeavour of the English Medieval carpenter". They are traditionally timber framed, using short beams projecting from the wall on which the rafters land, essentially a tie beam which has the middle cut out. These short beams are called hammer-beams and give this truss its name. A hammerbeam roof can have a single, double or false hammerbeam truss.

<span class="mw-page-title-main">Rafter</span> Supporting structural member in roof construction

A rafter is one of a series of sloped structural members such as steel beams that extend from the ridge or hip to the wall plate, downslope perimeter or eave, and that are designed to support the roof shingles, roof deck, roof covering and its associated loads. A pair of rafters is called a couple. In home construction, rafters are normally made of wood. Exposed rafters are a feature of some traditional roof styles.

<span class="mw-page-title-main">Framing (construction)</span> Construction technique

Framing, in construction, is the fitting together of pieces to give a structure support and shape. Framing materials are usually wood, engineered wood, or structural steel. The alternative to framed construction is generally called mass wall construction, where horizontal layers of stacked materials such as log building, masonry, rammed earth, adobe, etc. are used without framing.

A tie, strap, tie rod, eyebar, guy-wire, suspension cables, or wire ropes, are examples of linear structural components designed to resist tension. It is the opposite of a strut or column, which is designed to resist compression. Ties may be made of any tension resisting material.

<span class="mw-page-title-main">Wall plate</span> A horizontal, structural, load-bearing member in wooden building framing

A plate or wall plate is a horizontal, structural, load-bearing member in wooden building framing.

This page is a glossary of architecture.

<span class="mw-page-title-main">Domestic roof construction</span>

Domestic roof construction is the framing and roof covering which is found on most detached houses in cold and temperate climates. Such roofs are built with mostly timber, take a number of different shapes, and are covered with a variety of materials.

<span class="mw-page-title-main">Bressummer</span> Load-bearing beam in a timber-framed building

A bressummer, breastsummer, summer beam is a load-bearing beam in a timber-framed building. The word summer derived from sumpter or French sommier, "a pack horse", meaning "bearing great burden or weight". "To support a superincumbent wall", "any beast of burden", and in this way is similar to a wall plate.

<span class="mw-page-title-main">Wall stud</span> Component of a buildings wall

A wall stud is a vertical repetitive framing member in a building's wall of smaller cross section than a post. It is a fundamental element in frame building.

<span class="mw-page-title-main">Sill plate</span>

A sill plate or sole plate in construction and architecture is the bottom horizontal member of a wall or building to which vertical members are attached. The word "plate" is typically omitted in America and carpenters speak simply of the "sill". Other names are rat sill, ground plate, ground sill, groundsel, night plate, and midnight sill.

<span class="mw-page-title-main">Overhang (architecture)</span> Architectural Roofing Feature

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 and larger, older farmhouses are common in Swiss architecture. An overhanging eave is the edge of a roof, protruding outwards from the side of the building, generally to provide weather protection.

<span class="mw-page-title-main">Dragon beam</span>

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, dragging tie, dragon piece or dragon tie. Inconsistencies in modern usage are discussed below. In French it is called a coyer or enrayure.

A post is a main vertical or leaning support in a structure similar to a column or pillar, the term post generally refers to a timber but may be metal or stone. A stud in wooden or metal building construction is similar but lighter duty than a post and a strut may be similar to a stud or act as a brace. In the U.K. a strut may be very similar to a post but not carry a beam. In wood construction posts normally land on a sill, but in rare types of buildings the post may continue through to the foundation called an interrupted sill or into the ground called earthfast, post in ground, or posthole construction. A post is also a fundamental element in a fence. The terms "jack" and "cripple" are used with shortened studs and rafters but not posts, except in the specialized vocabulary of shoring.

<span class="mw-page-title-main">American historic carpentry</span>

American historic carpentry is the historic methods with which wooden buildings were built in what is now the United States since European settlement. A number of methods were used to form the wooden walls and the types of structural carpentry are often defined by the wall, floor, and roof construction such as log, timber framed, balloon framed, or stacked plank. Some types of historic houses are called plank houses but plank house has several meanings which are discussed below. Roofs were almost always framed with wood, sometimes with timber roof trusses. Stone and brick buildings also have some wood framing for floors, interior walls and roofs.

<span class="mw-page-title-main">Glas Hirfryn</span> Historic site in Montgomeryshire, Wales

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<span class="mw-page-title-main">Plasau Duon</span> Historic site in Montgomeryshire, Wales

Plasau Duon or Plasauduon is a timber-framed house, formerly in the parish of Carno, but now within the area of the community council of Caersws in the historic county of Montgomeryshire, and now in Powys, Wales. It is located on a site above the left bank of the Afon Carno, on a farm road leading off the lane from the A.470 to Bwlch-y-garreg. It is a fine example of a ‘’Severn Valley’’ house and has a Grade II* listing. It is likely to have been built in the second half of the 16th. century.

<span class="mw-page-title-main">The Royal Hop Pole</span> Historic site in Gloucestershire, England

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References

  1. Oxford English Dictionary, 2nd ed. 1989. Jetty
  2. Illustration of a jettied house
  3. Techniques
  4. Noble, Allen George, and M. Margaret Geib. Wood, brick, and stone: the North American settlement landscape. Amherst: University of Massachusetts Press, 1984. 22.
  5. 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
  6. Harris, Richard. Discovering timber-framed buildings. 2d ed. Aylesbury: Shire Publications, 1979. 55–57.
  7. Garvan, Anthony N. B., Architecture and Town Planning in Colonial Connectucut (New Haven: Yale University Press, 1957. 92.
  8. Harris, Richard. Discovering timber-framed buildings. 2d ed. Aylesbury: Shire Publications, 1979. 56.
  9. Davies, Nikolas, and Erkki Jokiniemi. Dictionary of architecture and building construction. Amsterdam: Elsevier/Architectural Press, 2008. 144. false jetty.
  10. Ensminger, Robert F.. "Origin." The Pennsylvania barn: its origin, evolution, and distribution in North America. 2nd ed. Baltimore: Johns Hopkins University Press, 2003.
Alcock, N.W.; Barley, M.w.; Dixon, P.W.; Meeson, R.A. (1996). Recording Timber-Framed Buildings. Council for British Archaeology, Practical Handbook in Archaeology. ISBN   1-872414-72-9.