Timber Roof Purlins

Purlins are non pressure treated 1 x 4 x 12 lumber that is installed on to the roof in a specific layout pattern and screw pattern.

Timber roof purlins.

Purlins are a series of horizontal timbers laid across or connected to as depicted above the principal rafters and support the roof covering typically 2 6 tongue and groove boards conventional or structural insulated panels sips and roofing. The rafters are the beams of wood angled upward from the ground. Do all roofing projects require purlins. This is a very traditional concept in heavy timber roof framing.

The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to. Purlins are installed horizontally under metal roofs. They meet at the top of the gable at a ridge beam which has extra bracing to attach it to the rafters. They give added support to the roof and also provide a nailing surface for the end panels and drip edge.

They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. In lightweight timber roof construction under purlins were used to support rafters over longer spans than the rafters alone could span. Under purlins were typically propped off internal walls. The purlins are the large beams perpendicular to the rafters.

From this shot it appears that there are three purlins on either side of the roof. Purlin is a well known material in the field of architecture structural building or structural engineering.