A suspended roof truss is a roof structure in which the horizontal tie beam does not rest on a wall below but is ‘hung’ from the truss at the ridge. This distributes the load of the beam across the entire roof frame, allowing large spans without supporting intermediate walls.
How it works
The suspended truss is usually triangular in design. The beam is linked to the upper part of the truss by a king post (hanging post):
- King post (hanging post) — hangs from the ridge and carries the middle of the tie beam
- Rafters/struts — the sloping members that carry the load to the wall plates
- Tension and compression — the king post is in tension and the rafters in compression; together they reduce the outward thrust on the walls
Application
- Attics and halls without an intermediate wall — where a clear, obstacle-free space is wanted
- Shallow-pitched roofs with larger spans
- Larger spans — a single king post is enough for small spans; wider roofs (10 metres or more) use a double suspended truss (queen post)
Points to watch
- The joints between the tie beam, king post and rafters are often reinforced with steel brackets
- A suspended (hanging) truss differs from a strutted truss, in which the tie beam is supported by struts from below
Related terms
- Roof structure
- Rafter
- Tie beam
- King post
- Purlin
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