The other is just used to support the trusses.
Attic support beams.
In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side.
Once again a 2 by 4 inch piece of lumber is placed between the trusses and parallel to the ceiling joists.
A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof trusses usually occur at regular intervals linked by longitudinal timbers such as purlins the space between each truss is known as a bay.
A great deal depends on the pitch of the roof.
You can t beat sawn lumber for most small window headers but as spans and loads increase stronger materials are a better choice.
The same is true for beams like structural ridge beams and center girders.
This article describes and illustrates the different types of support that prevents roof sagging and wall bulging at buildings including definitions of collar ties rafter ties and structural ridge beams.
Rafters have a tendency to flatten under gravity thrusting outwards on the walls.
Collar ties rafter ties tension beams structural ridge beams.
Sistering is the process of adding a new joist next to each existing joist.
Too often builders gang together 2 inch dimension lumber to support roof and floor loads without considering other options.
If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists.
Some of these can support the roof and prevent ridge sagging and wall spreading.