Timber Frame Glossary

You’re intrigued with this massive, striking construction method and seriously considering a timber frame home in your future. However, talking intelligently about the subject and using the proper terminology is a little like learning a new language. The words may sound familiar, but you’re not quite clear on what they mean exactly.

Getting a handle on what some of the terminology means and understanding what a potential builder is talking about is important to help you negotiate this new terrain. Once you’re comfortable with the jargon and have a basic understanding of how a timber frame home is constructed, you’ll be in a far better position of deciding whether a timber frame home is right for you.

 Timber Frame Glossary

• • Bay: The area created between two opposing bents and walls in the timber frame structure.

• • Beam: A  horizontal timber used in the structure’s framework.  They are supported at the ends and can be either load bearing, supporting joists or non-load bearing.

• • Bent: A roof truss and the vertical posts that support a structural network of timbers.   They run 90 degrees to the ridge.

• • Cantilever Beam: A timber that projects out from a wall or post and supports an overhang.

• • Chamfer: A decorative cut or round over made in the corners of the post and beams.

• • Checking: Drying or tension placed on a timber that causes the wood fibers to separate.  This is very common in timber frame construction and should be expected.

• • Collar Tie: A  horizontal timber between two rafters that ties the two rafters together that resist spreading in the rafter tails.  These pieces are constantly in tension.

• • Common Purlin Roof System: Includes any frame type that consists of a series of purlins bearing on principal rafters and often spanning from bent to bent at uniform intervals.

• • Common Rafter Roof System: Includes any frame type that consists of roof rafters that span from the eave walls to a ridge beam, principal purlin or opposing rafters

• • Cruck Frame: Cruck frames use largely curved timbers to support the roof directly down to the foot of the posts. The timbers are usually halved from one tree so that the two sides are symmetrical, and are naturally, and irregularly, curved.

• • Draw Boring:  Offsetting of the holes in mortise and tenon joinery that allows the joints to be pulled together when a peg is driven in.

• • Dutchman: A wooded patch to cover defects, previous joinery, or other error when restoring or cutting a timber frame.

• • Embellishment: A decorative detail or feature added to a timber frame truss to add visual interest.

• • Girt: A key horizontal timber or beam used to connect posts or sills.  A girt running in the wall direction is called a wall girt and a girt running in the bent direction is called a bent girt.

• • Green-Wood: Any timber/wood that has not been dried or with a moisture content above 19%.

• • Gunstock Post: A post that is wider at the top that allows extra space for the intersecting joinery that can happen when the post, rafter, and plates all join at the top of the post.

• • Joinery: This word can have two different, but related meanings. It is the craft of connecting timbers with wooden pegs, mortise, and tenons. It can also refer to the fasteners used in connecting the wooden components.

• • Joint: In the simplest form it is where two timbers meet.

• • Joists: Timbers that support a floor system they generally run parallel to each other.

• • King Post: A vertical post that runs from a girt or ties to the ridge. The rafters join with the post to form a king post truss.

• • Knee Brace: A knee brace is a timber that is placed diagonally between a post and a beam that makes the timber frame structure more rigid.

• • Mortise and Tenon: A fastening method for two pieces of wood. One piece of wood has a slot, while the other component has a projecting member that fits in the slot.

• • Peg: A piece of wood shaped into a dowel. The piece is normally 3/4″ to 1″ in diameter. The wood typically used for pegs is oak or locust and can be either round of octagonal.

• • Plate: Horizontal timber that supports and tie together vertical posts. An Eave Plate supports the base of the rafters and sits on top of the wall. A sole plate sits beneath the wall and used to secure the walls to the foundation.

• • Post: A vertical timber.

• • Post and Beam: This is a type of construction that is composed of horizontal and vertical timbers like timber frames. However they utilize exposed steel brackets and plates instead of traditional mortice and tenon joinery.

• • Purlins: These timbers run perpendicular to the rafters that support them connecting the principal rafters of trusses together.

• • Relish: Extra tenon length beyond the pegs in a joint, which resists the loads that are placed upon the beam.

• • Ridge: The ridge is the uppermost point of the triangle created by the rafters of a roof. This may be the joining point of a pair of rafters, a ridge beam or a ridge purlin.

• • Ridge Beam: A beam that supports rafters and other roof timbers at the ridge.

• • Roof Pitch: The angle of incline or slope of a roof. It is determined by the number of inches a roof inclines in the space of one foot. This is also known as inches of rise per foot of run. A 45-degree roof rises 12 inches for each foot of run, so this is called a “12-12 pitch” roof. A roof that rises 9 inches per 12 inches is called a “9-12 pitch” roof.

• • Spline: Usually a hardwood piece of wood that is used in place of tenons to join two or more beams/plates together to a post.

• • Structural Insulated Panels: Or SIP’s are an option for enclosing your timber frame.  They are made by sandwiching a layer of foam to two layers of OSB forming a structural panel.

• • Stub Tenon: Tenon that stops within the timber it joins.

• • Summer Beam: A timber that connects girts or plates generally in a floor system.

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

• • Through Tenon: A tenon that passes through the mortise it joins giving one more relish and decorative flair. It is sometimes wedged on the opposing side.

• • Tie Beam: A tie is a horizontal beam that is placed at a point along the rafters, which creates a smaller triangle. This adds strength to the roof and rigidity to the rafters.

• • Timber Frame: This traditional method of construction uses large size lumber to create a framework that is left exposed. Traditional woodworking methods such as wooden pegs, mortise, and tenon joinery are used instead of nails, screws or other metal fastenings.

• • Trunnel: Another term for pegs and fasteners used in joinery.

• Truss: A framework of timbers based on triangular shapes. In timber framing, they are generally designed to support a roof. Trusses are used for many applications in other forms of construction.

There’s certainly a lot of other words and phrases that you’ll hear as you talk with timber frame professionals and aficionados, but this list will give you a good start in understanding the components and technology that’s used to build a timber frame home.