Purlin

Part of speech: noun

Pronunciation: [ˈpɜːɹlɪn]

Definitions

1. A horizontal structural element that reinforces roofs by bearing loads and connecting roofing materials to primary supports
2. A horizontal beam in roof construction that supports roofing materials and transfers weight to vertical structures
3. A structural horizontal member set across roof trusses to help hold the roof covering in place and distribute loads

Etymology: The roof beam called a purlin has an origin that scholars have not settled. Its earliest English appearances date to the 15th century, in the Middle English period, and the Oxford Concise Dictionary suggests it may have come from French, though no French source word has been identified with confidence. Because the word appears in the record only at that late stage, it is hard to trace what it was before it became attached to the timber itself. What is clear is the job the object does. A purlin lies horizontally across the rafters of a roof, running parallel to the eaves and ridge, and it carries the weight of the roof covering and passes it down to the main structural frames. The name describes a structural role rather than a material or shape, which is why the same term applies to a timber beam, a steel section or a stone slab placed in the same position.