With rafters it runs in perpendicular from the walls to the ridge while with purlins it runs to the ridge in parallel.
Roof purlin support.
In architecture or structural engineering or building a purlin or purline is a horizontal structural member in a roof.
The support system for the roof is comprised of ridgepole and rafters or purlins.
A common arrangement is a rafter and purlin system which combines purlins and rafters.
Purlins are supported either by rafters or the walls of the building.
Purlins can be fixed to rafters and all joins and laps should be supported by a rafter.
In architecture structural engineering or building a purlin or historically purline purloyne purling perling is a horizontal beam or bar used for structural support in buildings most commonly in a roof.
Using a combination of rafters and purlins is common.
How to support roof purlins.