Bracing purlin braces or any other roof braces ridge braces hip rafter bracing along with valley bracing must not be supported off the ceiling joists.
Stronback roof bracing.
Bracing prevents trusses from bending twisting or otherwise deforming.
Underneath 2x6 strongbacks laid on edge should run continuously through the webs of all the.
On bottom chord bearing trusses the ends are tied together with 2x4 ledgers that also serve as a nailing base for the perimeter of the plywood deck see illustration below.
As with the supporting beam or joist found in the home the strongback in the ship design often helps to provide additional support to the skeleton or frame of the vessel by running along the length of the ship and bracing the frames that make up the overall body of the ship.
Strongback bridging is an excellent and inexpensive way to improve the overall rigidity of the floor system and eliminate vibration.
In homes with conventional ridges the rafters support the weight of the roof and transmit the roof load down through the walls to the foundation and finally to the soil.
Larger joist framing materials for instance 2x10 or 2x12 s can be doubled or tripled up with plywood in between and glued to create a flush.
If not then you may want to consider tying the brace off with a diagonal brace much like lateral bracing is tied off with diagonal bracing to provide triangulation of the system.
Bracing must be installed off of walls or beams.
It serves to make the floor more comfortable for those living and working in a structure.
For more information on bracing parallel chord trusses see sbca s bcsi b7 summary sheet.
Strongbacks can be altered to allow hvac installations as long as three 3 consecutive joists are attached.
The strongback is also often used in the construction of different types of boats and ships.