A hammer beam is a short horizontal beam that projects inward from the wall or post and carries the lower part of a roof truss. Unlike an ordinary tie beam, the hammer beam does not run from wall to wall but spans only a small distance. This keeps the space beneath the ridge open.
How it works
The hammer beam is the defining element of the hammer-beam roof:
- The hammer beam projects a short way inward from the wall
- At its end stands a vertical post (the hammer post) that carries the roof further upward
- Beneath the hammer beam there is often a curved brace that carries the force back to the wall
- Through this system the outward thrust of the roof is absorbed without needing a continuous tie beam
Applications
The hammer-beam roof, and thus the hammer beam, was used mainly where a large, open span with a handsome exposed roof structure was wanted:
- Medieval churches and chapels
- Great halls and banqueting halls
- Historic town halls and guildhalls
- Restoration of monumental timber roofs
The advantage is that a wide space can be spanned without an intrusive horizontal beam at eye level. The disadvantage is that the structure is complex and places heavy demands on the joints and timber. During restoration, the joints between hammer beam, brace, and hammer post are the most vulnerable.
Related terms
- Truss
- Tie beam
- Brace
- Roof structure
- Timber frame
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