A roof beam (Dutch: kapbalk) is an attic-floor beam: the beam that carries the attic floor and forms part of the roof structure at the top of a building. The Dutch term is also used for sawn timber with a square or nearly square cross-section (English: baulk). In construction, the first meaning — the load-bearing beam in the roof — is the most common.
The roof beam as an attic-floor beam
The roof beam lies horizontally within the roof structure and carries the floor of the attic or loft. The beams lie at regular spacing side by side (centre-to-centre), with the floor boarding or floor panels on top. Together with the other parts of the roof — such as trusses, purlins, and rafters — the roof beam forms the framework that carries the roof and the attic floor.
The Dutch name goes back to the Late Latin cappa (head covering), related to classical Latin caput (head): the roof sits like a ‘cap’ on top of the building.
Application
- Carrying the attic floor — the roof beam distributes the load of the floor, people, and storage to the load-bearing walls or trusses
- Part of the roof structure — the beam works together with trusses and purlins to form a stable whole
- Sometimes as a tie beam — in certain roof shapes a horizontal beam holds the roof planes together and prevents the walls from being pushed outward
Point to note
The size (cross-section) and the spacing of the roof beams depend on the span and the load. For a safe structure a calculation by a structural engineer is needed, especially for large spans or heavier loads.
Related terms
- Attic beam
- Roof structure
- Joist layer
- Truss
- Purlin
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