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What Are the Types of Joinery for Timber Homes?

The joinery in your frame not only connects and secures the timbers, 
but also plays a role in transferring the loads and stresses of your house from one frame to another. All of the many types of joints are designed
for specific functions. Some of the most common are described here.



Birdsmouth

A complex cut made at the tail end, or bottom, of a rafter that allows the timber to extend over and past the wall top plate, providing 
a greater bearing and attachment surface.

Butt

One of the least complicated joints, in which mating pieces are square-cut and simply butted against one another. Because this joint has little inherent strength and depends on gravity or fasteners to remain in place, it is typically limited to intersections that are not subject to movement or strong opposing forces, such as where timber posts rest atop horizontal beams.   

See also Timber Framing 101: What is a Timber Frame House?

Dovetail

A commonly used joint that includes 
a fan-shaped tusk or tenon that drops into and interlocks in a similarly shaped pocket cut. The wedge-like shape of this extremely strong joint prevents the interlocked timbers from shifting or separating from one another.      

Lap

A joint in which the ends of two timbers are cut at matching angles and simply overlaid, or “overlapped,” then fastened to each other. Because the wood grain direction of the mating pieces is parallel, these joints are easily concealed and often invisible. Lap joints are typically used to extend, or lengthen, timbers in long horizontal runs.

Mortise & Tenon

A frequently used joint in 
timber framing, it includes a male end (tenon) 
cut onto the end of one timber that fits into a square-cut matching female receptacle (mortise). Like many timber frame joints, it is often locked 
in place by the addition of hardwood dowels, or pegs, called trunnels (“tree nails”). 

Pocket Cut

Similar to a mortise, this joint receptacle typically is “open” in two dimensions; cut 
into the side or top face of a timber, it is designed to receive an identically shaped tenon or tusk formed at the end of a mating timber.  

Step-Lapped Rafter Seat

An improved type of birdsmouth and overlapping joint, it typically includes complimentary cuts in the rafter and 
plate to resist downward and outward thrust, as well as side-to-side movement.    

See also What’s a Timber Frame?

Shoulder

A ledge cut into the face of a joint; this added facet increases a beam’s load-carrying capacity by transferring downward force directly 
to the post while the joint’s tenon resists the 
lateral load, or tension.

Tongue & Fork

A specialized joint often used to connect the upper ends of rafters that meet to form a peak, or gable. One timber end is cut in an open U-shaped configuration (the fork), and a single tongue formed on the intersecting timber closely fits into the space between the fork ends.