Timber framing

Encyclopedia : T : TI : TIM : Timber framing

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Timber framing is the modern term for the traditional half-timbered construction in which timber provides a visible skeletal frame that supports the whole building. The terms are in fact interchangeable.

The structure

The main structure

By tradition, the timbers, with their riven side facing out, were mortised and pegged together, often receiving triangulated bracing to reinforce other members of the structure.
The spaces between the timber frames were then infilled with wattle-and-daub, brick or rubble, with plastered faces on the exterior and interior which were often “ceiled” with wainscoting for insulation and warmth. This method of infilling the spaces created the half-timbered style, with the timbers of the frame being visible both inside and outside the building.

Jetties

Where the houseowner could afford it the more expensive technique of jettying was incorporated in the construction of the house. Home owners were taxed on the first floor square footage.

A jetty is an upper floor that depends on a cantilever system in which a horizontal beam, the jetty bressummer, on which the wall above rests, projects forward beyond the floor below.

The vertical timbers

The vertical timbers include:

• posts (main supports at corners and other major uprights),
• studs (subsidiary upright limbs in framed walls).

The horizontal timbers

The horizontal timbers include:

• sill-beams (also called ground-sills or sole-pieces, at the bottom of a wall into which posts and studs are fitted using tenons),
• noggin-pieces (the horizontal timbers forming the tops and bottoms of the frames of infill-panels),
• wall-plates (at the top of timber-framed walls that support the trusses and joists of the roof).

It is when jettying is included, however, that by far the greatest number of horizontal elements are present:

• the jetty bressummer (or breastsummer), the main sill on which the projecting wall above rests and which stretches across the whole width of the jetty wall. The bressummer is itself cantilevered forward beyond the wall below.
• the dragon-beam which runs diagonally from one corner to another, and supports the corner posts above and is supported 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. The jetty plates themselves are supported by the corner posts of the recessed floor below.

The sloping timbers

The sloping timbers include:

• trusses (the slanting timbers forming the triangular framework at gables and roof),
• braces (slanting beams giving extra support between horizontal or vertical members of the timber frame),
• herringbone bracing (a decorative and supporting style of frame, usually at 45 ° to the upright and horizontal directions of the frame).

Distinctive features of modern timber frame structures

It is in the United States and Canada, however, that the art of timber frame construction has been revived since the 1970s, and is now experiencing a thriving renaissance of the ancient skills. This is largely due to such practitioners as Jack Sobon and Ted Benson who studied old plans and techniques and revived the technique that had been long neglected.

Timber framed structures differ from conventional wood framed buildings in several ways. Timber framing uses fewer, larger wooden members, commonly using timbers with dimensions in the range of 15 to 30 cm (6" to 12") as opposed to common wood framing which uses many more timbers with their dimensions usually in the 5 to 25 cm (2" to 10") range. The methods of fastening the frame members also differ, in conventional framing the members are joined using nails or other mechanical fasteners while timber framing uses mortice and tenon or more complex joints which are usually fastened using only wooden pegs.

Recently it has become common to surround the timber structure entirely in manufactured panels, such as Sips (Structural Insulating Panels). This method of enclosure means that the timbers can only be seen from inside the building, but has the benefits of being less complex to build and offering more efficient heat insulation. Structural Insulated Panels are a sandwich construction of two rigid composite materials usually wood based like OSB or plywood with a foamed insulating material in between either by gluing billets as in EPS (Expanded Polystyrene) or foamed and formed in place with Urethane. The advantage of this for timber framing in the modern world is less of a dependency on bracing and auxiliary members like minor joists and rafters as the panels can span a considerable distance and greatly increase the stiffness of the timber frame itself.

Alternative ways include the use of straw bale construction. The straw bales are stacked for the walls with various finishes applied to the interior and exterior such as stucco and plaster. This appeals to the traditionalist and the environmentalist as this is using "found" materials to build.

History and traditions

The techniques used in timber framing date back thousands of years, and have been used in many parts of the world during various periods such as ancient Japan, Europe and medieval England.

Half-timbered construction in the Northern European vernacular building style is characteristic of medieval and early modern England, Germany and parts of France, in localities where timber was in good supply and building stone and the skills to work it were in short supply. In half-timbered construction timbers that were riven in half provided the complete skeletal framing of the building.

Some Roman carpentry preserved in anoxic layers of clay at Romano-British villa sites demonstrate that sophisticated Roman carpentry had all the necessary techniques for this construction. The earliest surviving (French) half-timbered buildings date from the 12th century.

The English tradition

Molded plaster ornamentation ("pargetting") further enriched some English Tudor houses. Half-timbering is characteristic of English vernacular architecture in East Anglia, Worcestershire, Herefordshire and Cheshire, where one of the most elaborate surviving English examples of half-timbered construction is Little Moreton Hall. In the Midlands, the oldest timber house in Sheffield, the "Bishops' House" c1500, shows traditional "half-timbered" construction.

In the Weald of Kent and Sussex, the half-timbered structure of the Wealden house, consisted of an open hall with bays on either side and often jettied upper floors.

Half-timbered construction went with colonists to North America in the early 17th century but was soon left behind in New England and the mid-Atlantic colonies for clapboard facings (another tradition of East Anglia).

The French tradition

Elaborately half-timbered housefronts of the 15th century are still remaining in Bourges, Troyes, Rouen, Thiers...

The German tradition

In North Germany, Celle is famed for its 16th century half-timbered housefronts. In the later 16th century, timbers are often elaborately carved and spaces infilled with smaller timbering not only for reasons decorative but also structural.

The Deutsche Fachwerkstraße, the “Route that links Germany’s Medieval Timber-framed Houses”, runs from Lower Saxony in the north of the country, via Hesse and southern Thuringia to Bavaria is an area renowned for its highly picturesque half-timbered buildings.

The Canadian tradition

Called colombage pierroté in Quebec as well other areas of Canada, half-timbered construction infilled with stone and rubble survived into the 19th century and was consciously revived at the end of the century. In Western Canada it was used on buildings in the Red River Settlement; the Men's House at Lower Fort Garry is a good example of colombage pierroté.

Revival styles in later centuries

When half-timbering regained popularity in Britain after 1860 in the various revival styles, such as the "Queen Anne style" houses by Richard Norman Shaw and others, it was often used to evoke a "Tudor" atmosphere (see Tudorbethan), though in Tudor times half-timbering had begun to look rustic and was increasingly limited to villages houses (illustration, above left). In 1912, Allen W. Jackson published The Half-Timber House: Its Origin, Design, Modern Plan, and Construction, and rambling half-timbered beach houses appeared on dunefront properties in Rhode Island or under palm-lined drives of Beverly Hills. During the 1920s increasingly minimal gestures towards some half-timbering in commercial speculative house-building saw the fashion peter out.

It should be noted, however, that in the revival styles, such as Tudorbethan, the "half-timbered" appearance is superimposed on the brickwork or any other material as an outside decorative façade rather than consisting of the main timber frame that supported the whole structure as in original half-timbered building.

The benefits of timber framing

The use of timber framing in buildings offers various aesthetic and structural benefits, as the timber frame lends itself to open plan designs and allows for complete enclosure in effective insulation for energy efficiency.

The timber frame structure goes up quickly in its modern incarnation. While some modern shops still cut the timbers with hand tools and hand guided power tools, modern computerized numeric control (CNC) machinery has been readily adapted to the task. This eliminates much of the repetitive labor from the process, but still often requires hand-finishing; most notably, the complexity of hip/valley joinery as of yet cannot be duplicated by CNC machinery beyond simple cuts. Additionally, due to the rigid timber requirements of CNC machinery, odd sized, tree trunk, hand hewn, and recycled timbers are usually hand cut even in the machine dominated shops.

One aid in speeding up assembly on site is prefitting the frame, usually in bent or wall sections that are laid out on the shop floor. This can assure a correct fit and with predrilling for the pegs it speeds the site process. This pre-fitting in the shop is independent of a machine or hand cut system. Valley and Hip timbers usually are not prefit but careful layout and checking can catch most errors.

Quite literally in 2-3 days an average size timber frame home can be erected and within a week to 2 weeks after that the shell of the house is ready for "drying in", which is to say ready for windows, mechanical, and roofing. The shell in this case would be with SIP or Structural Insulated Panels.

The timber frame can give the home owner the ability to make a creative statement through the use of design and specialty touches like carvings of favorite quotes and incorporating timbers from heirloom structures, like a barn from a family homestead.

Disadvantages

Because the structure is made from wood, it inherits any disadvantages wood may exhibit as an engineering material. Some possible disadvantages of wood as opposed to some other building materials include:

• Noise from footsteps in adjacent rooms both above, below and on the same floor in such buildings can be quite audible.

• The possibility of infestation by insects such as termites, cockroaches or wasps, or by other pest animals such as mice and rats.

• Various types of rot in both wet and dry conditions, the latter of which is specifically called dry rot.

• Other fungi that are non-destructive to the wood, but are harmful to humans such as black mold.

• Wood burns more readily than some other materials, making timber frame buildings somewhat more susceptible to fire damage, although this idea is not universally accepted: Since the cross-sectional dimensions of many structural members exceed 15 cm × 15 cm (6" × 6"), timber frame structures benefit from the unique properties of large timbers, which char on the outside forming an insulated layer that protects the rest of the beam from burning. [link][link]

• Many older timber frame buildings, especially those built before the 1950's, are more vulnerable to damage during an earthquake. Many design improvements were made in the latter half of the 20th century that improve the earthquake resistance of this type of structure.

See also

• Norman architecture
• Weatherboarding
• Light-frame construction
• * Platform framing
• * Balloon framing
• Carpenter

External links

• [Buffalo (New York) as an architectural museum]: Half-timber in a variety of North American revival styles
• [The German half-timber route:] where to find half-timbered village and town houses in Germany (map)
• [Website of The Timber Framers Guild]
• [Website of The Carpenters Fellowship]
• [A German tourist route showcasing many historical timber framed buildings]
• [TRADA: Timber Research And Development Association]
• [History & Construction of Medieval Timber-framed Houses in England & Wales] A comprehensive outline with many pictures and links
• [Timber Engineering Reference] Links, Conferences, Standards, Dictionary,...

 

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