In some instances either 6 8 or 10 c purlins doubled back to back can be used to as rafters as a substitute to structural steel beams.
Light weight roof structure.
Read more about the specifications of this lightweight solution here.
The typical roof structure now consists of steel i beam rafters placed approximately 10 feet this varies depending on purlin size and other variables apart with either 4 6 8 or 10 lightweight steel purlins installed horizontally across the rafters.
In recent decades an expanding range of construction methods and building products particularly wooden truss roofing systems and wood i joists that together are often termed lightweight construction have been widely embraced by residential builders for their ability to deliver economy and functionality.
This modern system designed for light weight bearing construction has been tested over several decades and provides the same durability to a traditional 100 year slate roof.