Timber framing


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.
The method comes from working directly from logs and trees rather than pre-cut dimensional lumber. Artisans or framers would gradually assemble a building by hewing logs or trees with broadaxes, adzes, and draw knives and by using woodworking tools, such as hand-powered braces and augers.
Since this building method has been used for thousands of years in many parts of the world, particularly across Europe and Asia, many styles of historic framing have developed. These styles are often categorized by the type of foundation, walls, how and where the beams intersect, the use of curved timbers, and the roof framing details.

Types of timber frames

Box frame

A simple timber frame made of straight vertical and horizontal pieces with a common rafter roof without purlins. The term box frame is not well defined and has been used for any kind of framing. The distinction presented here is that the roof load is carried by the exterior walls. Purlins are also found even in plain timber frames.

Cruck

A cruck is a pair of crooked or curved timbers which form a bent or crossframe ; the individual timbers are each called a blade. More than 4,000 cruck frame buildings have been recorded in the UK. Several types of cruck frames are used; more information follows in English style below and at the main article Cruck.
  • True cruck or full cruck: blades, straight or curved, extend from ground or foundation to the ridge acting as the principal rafters. A full cruck does not need a tie beam.
  • Base cruck: tops of the blades are truncated by the first transverse member such as by a tie beam.
  • Raised cruck: blades land on masonry wall, and extend to the ridge.
  • Middle cruck: blades land on masonry wall, and are truncated by a collar.
  • Upper cruck: blades land on a tie beam, similar to knee rafters.
  • Jointed cruck: blades are made from pieces joined near eaves in a number of ways. See also: hammerbeam roof
  • End cruck is not a style, but on the gable end of a building.

    Aisled frames

Aisled frames have one or more rows of interior posts. These interior posts typically carry more structural load than the posts in the exterior walls. This is the same concept of the aisle in church buildings, sometimes called a hall church, where the center aisle is technically called a nave. However, a nave is often called an aisle, and three-aisled barns are common in the U.S., the Netherlands, and Germany. Aisled buildings are wider than the simpler box-framed or cruck-framed buildings, and typically have purlins supporting the rafters. In northern Germany, this construction is known as variations of a Ständerhaus.

Half-timbering

Half-timbering refers to a structure with a frame of load-bearing timber, creating spaces between the timbers called panels, which are then filled-in with some kind of nonstructural material known as infill. The frame is often left exposed on the exterior of the building.

Infill materials

Gallery of infill types:
The earliest known type of infill, called opus craticum by the Romans, was a wattle and daub type construction. Opus craticum is now confusingly applied to a Roman stone/mortar infill as well. Similar methods to wattle and daub were also used and known by various names, such as clam staff and daub, cat-and-clay, or torchis, to name only three.
Wattle and daub was the most common infill in ancient times. The sticks were not always technically wattlework, but also individual sticks installed vertically, horizontally, or at an angle into holes or grooves in the framing. The coating of daub has many recipes, but generally was a mixture of clay and chalk with a binder such as grass or straw and water or urine. When the manufacturing of bricks increased, brick infill replaced the less durable infills and became more common. Stone laid in mortar as an infill was used in areas where stone rubble and mortar were available.
Other infills include bousillage, fired brick, unfired brick such as adobe or mudbrick, stones sometimes called pierrotage, planks as in the German ständerbohlenbau, timbers as in ständerblockbau, or rarely cob without any wooden support. The wall surfaces on the interior were often "ceiled" with wainscoting and plastered for warmth and appearance.
Brick infill sometimes called nogging became the standard infill after the manufacturing of bricks made them more available and less expensive. Half-timbered walls may be covered by siding materials including plaster, weatherboarding, tiles, or slate shingles.
The infill may be covered by other materials, including weatherboarding or tiles, or left exposed. When left exposed, both the framing and infill were sometimes done in a decorative manner. Germany is famous for its decorative half-timbering and the figures sometimes have names and meanings. The decorative manner of half-timbering is promoted in Germany by the German Timber-Frame Road, several planned routes people can drive to see notable examples of Fachwerk buildings.
Gallery of some named figures and decorations:
The collection of elements in half timbering are sometimes given specific names:

History of the term

According to Craven, the term:
was used informally to mean timber-framed construction in the Middle Ages. For economy, cylindrical logs were cut in half, so one log could be used for two posts. The shaved side was traditionally on the exterior and everyone knew it to be half the timber.

The term half-timbering is not as old as the German name Fachwerk or the French name colombage, but it is the standard English name for this style. One of the first people to publish the term "half-timbered" was Mary Martha Sherwood, who employed it in her book, The Lady of the Manor, published in several volumes from 1823 to 1829. She uses the term picturesquely: "...passing through a gate in a quickset hedge, we arrived at the porch of an old half-timbered cottage, where an aged man and woman received us." By 1842, half-timbered had found its way into The Encyclopedia of Architecture by Joseph Gwilt. This juxtaposition of exposed timbered beams and infilled spaces created the distinctive "half-timbered", or occasionally termed, "Tudor" style, or "black-and-white".

Oldest examples

The most ancient known half-timbered building is called the House of opus craticum. It was buried by the eruption of Mount Vesuvius in 79 AD in Herculaneum, Italy. Opus craticum was mentioned by Vitruvius in his books on architecture as a timber frame with wattlework infill. However, the same term is used to describe timber frames with an infill of stone rubble laid in mortar the Romans called opus incertum.

Alternative meanings

A less common meaning of the term "half-timbered" is found in the fourth edition of John Henry Parker's Classic Dictionary of Architecture which distinguishes full-timbered houses from half-timbered, with half-timber houses having a ground floor in stone or logs such as the Kluge House which was a log cabin with a timber-framed second floor.

Structure

Traditional timber framing is the method of creating framed structures of heavy timber jointed together with various joints, commonly and originally with lap jointing, and then later pegged mortise and tenon joints. Diagonal bracing is used to prevent "racking", or movement of structural vertical beams or posts.
Originally, German master carpenters would peg the joints with allowance of about, enough room for the wood to move as it 'seasoned', then cut the pegs, and drive the beam home fully into its socket.
To cope with variable sizes and shapes of hewn and sawn timbers, two main carpentry methods were employed: scribe carpentry and square rule carpentry.
Scribing or coping was used throughout Europe, especially from the 12th century to the 19th century, and subsequently imported to North America, where it was common into the early 19th century. In a scribe frame, timber sockets are fashioned or "tailor-made" to fit their corresponding timbers; thus, each timber piece must be numbered.
Square-rule carpentry was developed in New England in the 18th century. It used housed joints in main timbers to allow for interchangeable braces and girts. Today, standardized timber sizing means that timber framing can be incorporated into mass-production methods as per the joinery industry, especially where timber is cut by precision computer numerical control machinery.

Jetties

A jetty is an upper floor which sometimes historically used a structural horizontal beam, supported on cantilevers, called a bressummer or 'jetty bressummer'; to bear the weight of the new wall, projecting outward from the preceding floor or storey.
In the city of York in the North of England the famous street known as The Shambles exemplifies this, where jettied houses seem to almost touch above the street.

Timbers

Historically, the timbers would have been hewn square using a felling axe and then surface-finished with a broadaxe. If required, smaller timbers were ripsawn from the hewn baulks using pitsaws or frame saws. Today, timbers are more commonly bandsawn, and the timbers may sometimes be machine-planed on all four sides.
The vertical timbers include:
The horizontal timbers include:
  • sill-beams,
  • noggin-pieces,
  • wall-plates.
When jettying, horizontal elements can include:
  • The jetty bressummer, where the main sill on which the projecting wall above rests, stretches across the whole width of the jetty wall. The bressummer is itself cantilevered forward, beyond the wall below it.
  • The dragon-beam which runs diagonally from one corner to another, and supports the corner posts above and supported by the corner posts below
  • The jetty beams or joists conform to floor dimensions above, but are at right angles to the jetty-plates that conform to the shorter dimensions of "roof" of the floor below. Jetty beams are mortised at 45° into the sides of the dragon beams. They are the main constituents of the cantilever system, and determine how far the jetty projects.
  • The jetty-plates are designed to carry the jetty beams. The jetty plates themselves are supported by the corner posts of the recessed floor below.
The sloping timbers include:
  • Trusses
  • Braces
  • Herringbone bracing