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• What is a truss?

A truss is the upper most portion of your house. This portion spans the entire width of your house and determines the pitch of your roof. They come in many shapes and sizes but what most have in common is that they use the strength of the triangle to ensure the house, often a a more square structure, remains ridged.

• How is a truss assembled?

A truss can be assembled many different ways, and often it is largely depends on the type of truss.

In modern building, thin members of wood two by fours are placed within thin metal braces and nailed together.

This image demonstrates the utilitarian purpose of this truss. They are spaced about 24 inches apart and more than likely are sitting on a stud frame with each stud 16 inches apart on center. This is known as stud framing or balloon framing and became the standard of building when quickness of production mattered over the quality of the building.

In comparison

The image on the right is of a segment of the hammer beam truss in Westminster hall. It demonstrates how the embellishments were with what appears to be thin keys that slid in between two pieces of carved wood and held them together.

Here however, is how the pieces were actually assembled using wooden pegs and many different pieces that latched together and distributed their forces into the other member. To further dissect this image and to more fully answer how trusses are assembled within the scope of timber framing - in this image there are different types of joints.

• A few different types of joints
  

These are two variations of a mortise and tenon joint. These are the most common joints in timber framing. The shouldered mortise and tenon is different in that the downward force isn't placed solely on the tenon, rather, it is also transferred to the mortise beam. Another variation not pictured is the housed mortise and tenon. The housed mortise and tenon allows for the tenon beam to sit within the mortised beam allowing for the forces to be distributed from all and to all directions.

To the right is how a rafter is joined to the post that will hold it up. As you can see the birds mouth joint allows for the horizontal portion of the force to be transmitted into the plate. The vertical will naturally be placed into the plate and then into the post as well.