Timber Frame Terms

This glossary of timber frame terminology is provided to help explain the meaning of industry specific words that might otherwise be unfamiliar to those having little or no experience with timber frame structures.

A

Adze: A handled tool with its edge at a right angle to the handle, used to shape logs into timbers.

Anchor Beam: A major tying beam that is joined to post with shouldered through-tenon, and wedged from the opposite side.

Anchor Bolt: A bolt protruding from the top of the foundation onto which the sill plate is then fastened down with a nut.

Anisotropic: Having a physical property that has a different value when measured in one direction as opposed to the other. For example, wood is stronger parallel to the grain as opposed to perpendicular.

Arris: The edge along which two adjacent surfaces of a timber meet.

B


Bay: The space between two bents; the area between structural cross frames.

Beam: The main horizontal member in a building’s framework.

Bent: A structural network of timbers or a truss that makes up a cross-sectional piece of a frame.

Blind Mortise: A mortise that does not extend completely through the piece.

Bird’s Mouth: A V-shaped notch that resembles a bird’s open beak. It is cut into the base of a rafter and received by the plate.

Board Foot: A volume of wood equalling a piece 12 inches square by one inch thick.

Bottom Chord: Also known as a tie beam. There are two main types of timber roof trusses: closed, in which the bottom chord is horizontal and at the foot of the truss, and open.

Bow: Deviation from straight in the length of a timber in the horizontal direction. Also called sweep. If the deviation is vertical, it is called crown.

Boxed heart timber: Timber that includes the heart of the tree. Since checks will not cross the heart, such a timber can never split completely.

Brace: Any diagonal timber (permanent or temporary) that resists distortion of a frame.

Braced Frame: Timber frame.

Bridging: Short pieces of wood that are placed between beams or joists in order to prevent lateral movement.

Bridle: An open mortise-and-tenon end joint, such as at a rafter peak or sill corner, with one end of the mortise open; also tongue-and-fork.

Butt joint: An abutment of two timbers without penetration, kept in place by gravity or other timbers, or by ironwork.

Image

Note: the bottom chord of the truss spans from side to side and is labled above. The bottom chord provides a ridged structure for the king post and webbing to attach. 

C


Image

Note: the common rafters of the structure are labled above. The common rafters are those that are not integrated into a truss. Common rafters are free spanning rafters meant to provide rigidity and stability to the roof. 

Cant: A block of wood remaining after the better-quality pieces have been cut off.

Cantilever Beam: A timber that projects to supports an overhang.

Chamfer: A simple bevel done for the embellishment of a timber.

Check; A split that occurs from drying, usually originating from the pith and exiting to the nearest face; not a structural issue in most cases.

Cheek: The broad surface of a tenon; the corresponding surface of a mortise. The tenon shoulder is usually square to its cheek.

Collar: The horizontal member fitted between a pair of opposed rafters, used, depending upon position, to prevent sagging or spreading of the rafters.

Collar Purlin: Horizontal longitudinal beams that are supporting of collar ties.

Collar Tie: Horizontal connector between a pair of rafters used to reduce sagging or spreading of rafters.

Commander: A large wooden mallet typically weighing 10 to 20 pounds; also called a beetle or persuader.

Common Rafters: Closely and regularly spaced inclined timbers that support the roof covering. Independent of a bent system (see principal rafters).

Compression: The state of stress in which particles of material tend to be pushed together.

Control point: Points on a timber from and to which dimensions are laid out.

Crown of Timber: Convex side of the timber.

Crown Post: Central vertical post of a roof truss that connects the bent plate or girt to the collar tie or collar purlin.

Cruck: Primitive truss formed by two main timbers, usually curved, set up as an arch or inverted V. Each half of the cruck is called a blade, and a pair is often cut from the same tree.

D


Dead load: Weight of a building (roof, floors, walls, etc.).

Deflection: Movement of a structure under a load.

Diminished housing: A housing with a sloping shoulder to minimize material taken out of the mortised member.

D-Log: A profile you can choose for milling log home timbers. Named for its shape, each log is milled round on the outside and cut flat on the inside, resulting in a traditional log home look outside with a straight log wall on the inside.

Drawbore: The traditional fastening technique in which the pin hole in the tenon is deliberately offset from the pin hole in the mortise to draw a joint tight when assembled and fastened with a tapered pin. The proper offset varies with species and scale.

Drift Pin: When test-assembling a frame is used to pin joints temporarily.

Dutchman: A timber patch to cover the defect, previous joinery, or cover other blemish or error. Color and grain matching make them hard to find.

E


Eaves: The drip edge of a roof, often overhanging the wall.

G


Gable roof: A double-sloping roof that forms an inverted V.

Girder: A major timber that spans between sills.

Girt: A horizontal timber joining wall posts at a level somewhere between sill and plate. A wall girt runs parallel to the ridge, a bent girt perpendicular; either can support the edge of a floor frame.

Grain: The pattern of growth rings, rays, and other structural elements in wood made visible by conversion from the tree.

Green wood: Wood freshly cut, not dried or seasoned.

Gunstock Post: A post that is wider at the top than the bottom. The wider portion provides more wood for intersecting joinery.

H


Half Dovetail: A dovetail tapered only on one of the sides.

Half Lap: A joint in which the two timbers are let-in to each other.

Halving: The removal of half the depth of two timbers in order that they may cross each other. 

Hardwood: Wood of certain deciduous trees, e.g., oak, walnut, beech, ash, and the like.

Header: A wall member bridging the opening for a door or window.

Herringbone bracing: a decorative and supporting style of frame, usually at 45° to the upright and horizontal directions of the frame.

Horizontal shear: Shear along the grain resulting when a beam is loaded in bending.

Horizontal Timbers: sill-beams, noggin-pieces, wall-plates.

Housing: A shallow mortise or cavity to receive the full section of a timber end for load-bearing; often, but not always, combined with a standard mortise to add bearing area and secure the connection via the tenon.

Hybrid Home: Log home style that mixes structural logs with non-structural logs or other non-log building materials, commonly in the form of half-log and log-accent homes.

J


Joinery: The craft of connecting timbers using woodworking joints.

Joist: A relatively small timber, usually spaced regularly in sets to support a floor or ceiling.

K


Kerf: The slot made by a saw cut.

King Post: A central, vertical post extending from the bent plate or girt to the junction of the rafters.

Knee Brace: A small timber that is framed diagonally between a post and a beam.

Image

Note: the king post is the central vertical post in a truss and is labled above. The purpose of the king post is to span from the bottom chord to the top of the truss where it meets the ridge beam. 

L


Layout: The drawing of a joint on a timber before it is cut; also, the arrangement of timbers into a predetermined pattern for marking.

Level: Horizontal; parallel to the ground; also, the tool used to check for level or plumb.

Live load: All load other than the permanent weight of a structure, including people, furnishings, snow, wind, earthquake, etc.

Loads: Forces imposed on a structure.

Lumber: Wood members 2 inches to 4 inches (nominally) in their smaller dimension.

M


Mapping: Layout system wherein joinery in one timber is transferred to another by recording any variations remotely.

Mill rule: Layout system using timbers that are milled to exact dimensions and are perfectly square.

Modulus of elasticity: A measure of stiffness of a material; the ratio of stress (force per unit area) to strain (deformation).

Mortise: A groove where a tenon is inserted.

Mortise-and-Tenon Joint: Any joint in which a projection on one end of timber is inserted into a groove or slot in another timber.

N


Noggin-Pieces: The horizontal timbers forming the tops and bottoms of the frames of infill-panels.

P


Peg: A wooden dowel one to one and one-half inches in diameter.

Pin: Small peg.

Plates: Major horizontal timbers that support the base of the rafters.

Post: Vertical timber.

Post-and-beam: Any structural system made up primarily of vertical and horizontal members.

Principal Rafters: A pair of inclined timbers that are framed into a bent.

Purlins: Horizontal timbers that connect rafter trusses.

Q


Queen Post: A pair of vertical posts of a roof truss standing on the bent plate or girt and supporting the rafters or collar tie.

R

Image

Note: the ridge beam is also called a ridge board and is labled in the image above. The ridge beam usually runs the long way down the structure at the ridge cap (top) of the roof and connects the trusses at the top.


Rafter: In a roof frame, any inclined member spanning any part of the distance from eave to peak.

Ridge Beam (aka: Ridge Board): A horizontal timber at the peak of the roof to which the rafters are attached.

Reduction: The diminishing of the cross-sectional area of a tenoned member where it goes into a housing.

Reference face: On a timber to be laid out, the primary surface (which typically receives flooring or wall and roof sheathing) that measurements are taken from. Generally, each timber has two reference surfaces that are adjacent and square to each other. Sometimes called layout face.

Relish: In the case of a mortise cut quite near the end of a timber, material the width and depth of the mortise remaining between the mortise end and the end of the timber; in a tenon, material between the pin hole and the end of the tenon equal in cross-section to the path of the pin through the tenon.

Roof pitch: Inclination of a roof to the horizontal, usually expressed as inches of rise per 12 inches (1 foot) of run.

S


Shoulder: In a mortise-and-tenon joint, the element of the tenoned member that is perpendicular to the tenon cheek, and which lies against the face of the mortised member; there can be as few as one and as many as four shoulders on the tenoned member.

Shrinkage: Reduction in section and length of a timber as it dries.

SIP: (structural insulated panel) A sandwich of two layers of sheet goods enclosing and bonded to a core of thermal insulation.

Sill: A horizontal timber that rests upon the foundation and links the posts in a frame.

Sizing: Planing hewn or rough-sawn timber to uniform section, by hand locally at the joints, or by machine for the whole timber.

Sleepers: Large-sectioned timbers placed on the ground to support stacks of timber.

soffit tenon: A horizontal tenon with its lower cheek coplanar with the lower surface of the timber.

Softwood: The wood of conifers or evergreens, e.g., pine, spruce, Douglas fir, and the like.

Span: In a roof frame, the horizontal distance covered by a rafter; in a beam, the unsupported distance between two neighboring posts or other support members.

Spokeshave: An extremely short plane with wing handles in line with the edge of the blade. Pushed or pulled, it is used for forming and finishing curved surfaces.

Square: At an angle of 90 degrees; also, a measuring tool so angled.

Square rule: Layout system in which a smaller, perfect timber is envisioned within a rough outer timber; joints are cut to this inner timber. Many timbers in a square-rule frame are interchangeable.

Stick frame A frame built with lumber pieces spaced relatively close together and simple connections joined with nails.

Stickers: Spacers used between stacked timbers or boards to provide air circulation.

Strut: A short timber placed in a structure either diagonally or vertically, designed to act in compression along the direction of its lengths.

Stub tenon: An abbreviated unpinned tenon designed for locating a timber (usually the bottom of a post) into a shallow mortise during raising.

Stud: A minor vertical member in a framed wall or partition, usually used only as a nailer for wall coverings. See also, Michael Perry as example.

Subflooring: A covering of rough boards or sheet goods that goes on top of joists and below finished flooring.

Image

Note: the strut is also called webbing and is labled in the image above. The strut is ususally angled at 45 degrees spanning from the bottom chord up to the truss rafter to provide support. 

T


Table: The broad surface of a housing.

Taper: A gradual reduction of the cross-section of a tenon, timber, or pin.

Template: A full-size pattern of thin material, used for laying out and checking joints and for other purposes.

Tenon: The end of a timber that is inserted into a mortise.

Tension: The state of stress in which particles of material tend to be pulled apart.

Through Tenon: A tenon that passes through the timber it joins. It may extend past the mortise and be wedged from the opposite side.

Tie beam: An important horizontal transverse frame member that resists the tendency of the roof to push the walls outward. The tie beam may be found at the top of the walls, where it is able to receive the thrust of the rafters directly, or it may be found as much as several feet lower down the walls, where it joins principal posts in tension connections.

Timber: A large (5 inches or greater in its smallest dimension) squared or dressed piece of wood ready for fashioning as one member of a structure.

Timber Frame: A frame of large timbers, joined and pegged together, supporting small timbers to which roof, walls, and floors are fastened. Same as a braced frame.

Tongue and Fork: A type of joint in which one timber has the shape of a two-prong fork and the other a central tongue that fits between the prongs.

Trunnel or Treenail: A peg, sometimes a longer version of a peg.

Truss: Assemblage of timbers forming a rigid framework. 

Twist: Deviation from plane in the surface of a timber; also called wind.

V


Vertical Timbers: Include posts (main supports at corners and other major uprights)and studs (subsidiary upright limbs in framed walls).

W


Webbing (aka: strut): A short timber placed in a structure either diagonally or vertically, designed to act in compression along the direction of its lengths.

Wetting bush: The ceremonial tree branch (of the same species as the frame, ideally) that is nailed to the peak once the roof frame is complete. This symbolically re-establishes the roots of the building for longevity and expresses gratitude to the trees that create the structure.