purlin

One of several horizontal timbers supporting the rafters of a roof.

In carpentry, a piece of timber laid horizontally upon the principal rafters of a roof to support the common rafters on which the covering is laid. Also called side timber or side waver. See cut under roof.

In root construction, a horizontal member supported on the principals and supporting the common rafters.

A longitudinal structural member bridging two or more rafters of a roof.