Hammer beam truss

What is a hammer beam truss?

A hammer beam truss is a timber framing system used to construct large span roofs. The key elements are the vertical posts that extend up from the walls, the projecting hammer beams that cantilever inward from the posts, and the central arched or angled ridge piece supported by the hammer beam ends.

Joinery

The connection is the joint between the wall posts and hammer beams. This is typically constructed as a four-way mortise and tenon joint. The post has two horizontal through-tenons projecting out opposite sides near its top end. The hammer beams have corresponding mortises that these tenons insert deeply into.

The joint is locked together by driving wooden pegs through the mortise holes and into the tenons from both sides. Careful layout ensures the four members - two posts and two hammer beams - meet with tight fitting joints when assembled into the four-way connection. Want to see more truss styles? see the 5 most common truss styles.