Roof Trusses

A lay-on gable frame is typically connected from the top during truss placement, but after sheathing is installed, this connection is no longer visible for the building inspector to verify. This creates a need for an alternate connection that is visible from below. The goal of this Research Report is to analyze a simple, cost-effective, toe nail connection between the lay-on gable frames and supporting truss system that is visible after sheathing is installed.

  • Today’s complex truss designs can present significant installation challenges to framers if there isn’t good communication between the framer and the manufacturer.
  • From storage and lifting pick points to critical bearing conditions, safe handling and installation practices need to be effectively communicated to installers.
  • During the design phase, manufacturers can help ensure smooth installation by considering the framing challenges a complex design may create and facilitate cross communication between parties.
  • When analyzing a girder truss, the Truss Designer needs to keep in mind the assumptions the truss analysis program makes regarding reaction capacities.
  • It is the Building Designer’s responsibility to verify the capacity of the bearing surface, but the Truss Designer must ensure that the truss-to-bearing connection has a chance of being made without crushing.
  • The article provides a series of concepts to use if a truss needs to be designed without knowing the bearing surface type and its feasibility of providing adequate support for the trusses.
  • Field splices provide a means of connecting two truss sections together creatively at the jobsite, to allow manufacturing, shipping and installation greater flexibility in serving customer needs.
  • A field-spliced truss should be designed as one component so that the proper load transfers at the splice.
  • Correct installation is important to avoid increased deflection of the field-spliced truss and potential long-term serviceability problems.
  • The contractor should examine the trusses when they are delivered and determine if there is any damage that would impair the structural integrity of the trusses.
  • BCSI recommends that trusses stored outside for more than a week be stacked on blocking and have a cover that provides adequate ventilation.
  • The contractor is responsible for the construction means, methods, techniques, sequences, procedures, programs, and safety in connection with the receipt, storage, handling, installation, restraining, and bracing of the trusses. 

 

The March 2012 issue of SBC highlighted the benefits of assembling wood roof trusses on the ground. Here, we see an example using cold-formed steel trusses for a Winco Foods Store in Mesa, AZ. Westco Steel Systems designed the store’s roof so the contractor could build each section on the ground and hoist it into place as a fabricated section.

How do you build a house?

  • The Building Designer providing accurate wall or beam/header information in the Construction Documents is essential in order for the Truss Designer to arrive at the correct bearing width.
  • There are two key bearing related considerations—bearing capacity of the truss and bearing capacity of what the truss is sitting on; often, the bearing capacity of this material is an unknown and an assumption must be made.
  • The options for dealing with insufficient bearing need to be considered and specifically dealt with on a case-by-case basis.