What does purlin mean?
A purlin is a horizontal structural member that forms part of a roof's supporting framework. In a traditional timber roof, purlins run parallel to the ridge and support the rafters; in some modern buildings, they support roof joists or decking directly. They are commonly made from timber or structural steel and may be positioned at different heights throughout the roof structure. Although mostly hidden after construction, purlins transfer the weight of the roof covering and any imposed loads to the larger structural framework. The word belongs mainly to architecture, engineering, and building vocabulary rather than general everyday speech. Knowing it can be useful when reading roof plans, construction specifications, building regulations, or descriptions of how a roof is assembled. In many traditional pitched-roof structures, the distinction is simple: rafters extend from the ridge toward the eaves, while purlins run horizontally along the roof.
nounA horizontal structural member that supports a roof. Purlins run along the length of a roof and may support rafters, roof joists, or decking.
- A horizontal beam or similar structural member used to support a roof.
"The new steel purlins were installed before the roof joists were raised."
"Each roof purlin spans across the main rafters and supports the roof covering."
"The engineer specified cold-formed steel for the purlins because it was lighter than timber."
The usual plural form, used when referring to multiple roof-supporting members.
"The warehouse roof is supported by steel purlins spaced regularly across the building."
A purlin runs along a roof, while a rafter usually runs down its slope—together forming the hidden framework that carries the roof.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does purlin come from?
The word was used in English by the 17th century for a member or projection associated with a roof. Its precise pre-English origin is uncertain, although it is commonly associated with Anglo-French roofing terminology.
How purlin is actually used
This is primarily a technical architectural and construction term. Its precise structural role varies with the type of roof and the regional construction tradition.