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Timber framing Timber framing is the method of creating framed structures of heavy timber jointed together with pegged mortise and tenon joints. To deal with the variable sizes and shapes of hewn and sawn timbers, the two main historical layout methods used were: scribe carpentry and square rule carpentry. Scribing was used throughout Europe, especially from the 12th century to the 19th century, and was brought to North America where it was common into the early 19th century. In a scribe frame, each timber will only fit in one place, so each timber has to be numbered. Square rule carpentry was developed in New England in the 18th century and features housed joints in main timbers to allow for interchangeable braces and girts. Today, regularized timber can mean that timber framing is treated as joinery, especially when timber is cut by large CNC machines. To finish the walls, the spaces between the timbers were often infilled with wattle and daub, brick, or rubble. Plastered faces on the exterior and interior 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. Timbers Historically, the timbers would have been hewn square using a felling axe and then finish surfaced with a broad axe. If required, smaller timbers were ripsawn from the hewn baulks using pitsaws or frame saws. Today it is more common for timbers to be bandsawn, and the timbers may sometimes be machine planed on all four sides.The vertical timbers include posts main supports at corners and other major uprights, Wall studs subsidiary upright limbs in framed walls, for example, close studding. 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. Modern features Porch of a modern timber-framed house Here is a look at the interior of a modern hand hewn post and beam home.In the United States and Canada, 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 Steve Chappell, Jack Sobon, and Tedd Benson, who studied old plans and techniques and revived the technique that had been long neglected. Once a hand crafted skill passed down, timber-frame construction has now been modernized with the help of CNC machines. These machines have helped the industry grow to where it is today, allowing for more affordable frames and shorter lead times for projects. Timber-framed structures differ from conventional wood framed buildings in several ways. Timber framing uses fewer, larger wooden members, commonly timbers in the range of 6" to 12", while common wood framing uses many more timbers with dimensions usually in the 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, whereas timber framing uses mortice and tenon or more complex joints that are usually fastened using only wooden pegs. Modern complex structures and timber trusses often incorporate steel joinery such as gusset plates. The steel is used for both structural and architectural purposes. It has become common to surround the timber structure entirely in manufactured panels, such as SIPs (Structural Insulated 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 polyurethane. 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. |
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Timber Frame & Post and Beam definitions. AIR DRIED - stacking wood prior to installation to allow air movement to evaporate moisture for a prescribed period of time BRACE a structural component, on a slope, used to secure other parts of the structure. May be permanent or temporary. BAY The space between two timber frame bents. BEAM a principal horizontal structural member, used to carry vertical loads. BEAM POCKET a notch in a wall prepared to receive the ends of a beam. BENT The structural network of timbers, in a wall or truss, making up one cross sectional part of a timber frame. BLIND MORTISE a mortise that does not extend completely through the piece. COLLAR PURLIN horizontal, longitudinal beams that support collar ties. COLLAR TIE a horizontal log or timber between 2 adjacent rafters that prevent sagging and spreading of the roof structure. CROSS-GRAIN deviation of grain direction from the longitudinal axis of a piece of wood or from the stem axis in a tree. DRAW BORING (DRAW-PINNING) offsetting holes in a mortise and tenon joint, into which a tapered pin is driven. DRYING (AIR DRIED, KILN DRIED, SEASONED) the condition or process defining the moisture content of wood; in lumber grading, having a moisture content of no more than 19%. EQUALIBRIUM MOISTURE CONTENT (EMC) the moisture content eventually attained in wood exposed to a given level of relative humidity and temperature. FLITCH PLATE (KNIFEPLATE) a metal plate cut into the center of a log or timber connections, bolted to the components, in order to provide additional shear and tension strength. FLY RAFTER the end rafter on a roof overhang, typically on a gable end, that is supported by the ridge, trimmer, and lookout rafters. GIRDER a horizontal beam carrying floor joists. GIRT a horizontal timber connecting 2 posts. Traditionally used for attaching vertical sheathing. GREEN (LOGS) freshly cut and unseasoned wood; having moisture content in excess of 19%. GUSSET the connectors used on truss work that provide strength to the joints. May be plywood, metal, boards, or other materials of equal strength. GUY WIRE an anchored cable acting as a brace. HANDCRAFTED LOG SYSTEMS the craft of producing a structure from logs. HEADER horizontal member that spans over the top of an opening. HOUSED MORTISE a recessed mortise where bearing is provided for the entire tenoned member KEYWAY refers to the groove cut in the end grain at the side of a door or window opening. A wood or metal spline (key) is inserted to stabilize the wall sections around the opening. KILN-DRY WOOD wood dried to constant weight in an oven maintained at temperatures of 101 to 105 degrees Celsius. KING POST as part of a truss, the vertical post that extends from a horizontal member (chord, joist, girt, etc.) to the peak; connected with the principal rafters. KNEE BRACE a diagonal brace, typically at a 45-degree angle between a post and a beam. KNEEWALL a short wall section; typically above the 2nd floor ending with a roof plate. KNOT a portion of a branch overgrown by the expanding girth of the bole or a larger branch; that area of the trees stem that a branch grows out of; on smooth and planed surfaces appears as a hard round or oval shaped section. LAP a place or part where one log crosses over another. LATHE in log building a lathe type machine may be used for rough peeling of the bark or in the case of machine-cut logs to shape the log to its finished form. MOISTURE CONTENT the weight of water in the cell walls and cavities of wood, expressed as a percentage of oven-dry weight. MORTISE a square or rectangular notch, slot, or hole cut into a structure component that will accept a corresponding tenon. MORTISE AND TENON a joint which a projection (tenon) on one end of a piece is inserted into a notch, slot or hole (mortise) on another piece. OUTRIGGER BEAM a beam beyond or outside of the exterior wall that becomes the roof plate. Typically the supports are the overhang or projection of gable and corresponding cross walls. PEG a 1 or larger, wooden dowel, typically made of Oak. PURLIN Horizontal roof beams, typically located between the plate and the ridge. Used to provide mid-span support for the rafters. SCARF the cuts made on the sides of a log, at the location of a notch, as the receiving portion of a Saddle Notch. SCARF JOINT a joint made when notching and lapping two timbers. SEASONED (SEASONING) -- the act of drying wood to the etent that the moisture content has reached equilibrium with the outdoor atmospheric humidity. SPLINE a piece placed in slot cuts, grooves, dados, etc. to strengthen joints between two components. Made of wood or metal. In Log Building splines are typically used in openings tostabilize wall sections. THROUGH-BOLTS a threaded metal rod, extending the fullheight of a wall, fastened at each end with nuts and washers. Used to provide rigidity, and the ability to tighten a wall section as settling occurs. Compression springs may also be used to adjust for settling. TIMBER FRAME the methods of joining large timbers into a braced structural frame. At times referred to as Post and Beam construction. |