text.skipToContent text.skipToNavigation

URS: Methods for Specifying

Specification of Uplift Restraint Systems

In the previous section of this guide, we shared wind uplift rod run component model numbers and capacities along with the design requirements published by ICC-ES in Acceptance Criteria 391. While some of these design considerations are for the rod run components, others are for the wall-framing elements that transfer load to the rod runs. Simpson Strong-Tie used these requirements to earn the only system evaluation report (ICC-ES ESR-1161) in the industry. However, AC391 also allows for reports that consider only rod run components and not the wall-framing elements. This allows the Designer of Record to specify a rod run based on the allowable load deflection values for the rod run itself, and determine for themselves an appropriate spacing of the rod runs to ensure the wall-framing elements satisfy load and deflection limits for their structure. To assist Designers in the specification, we offer guidance below for two methods of specifying our Strong-Rod URS.

Designer Selects System and Specifies on Building Plans

Once Designers knows their wood framing species, net uplift at roof-bearing walls, length of rod run, then they can specify the following information on the plans:

  • Hurricane ties to transfer uplift from roof truss/rafter to top plates
  • Method (possibly hurricane ties) of restraining top-plate rotation
  • URS model which includes:
    1. Rod diameter, shrinkage compensation device, length and spacing
    2. Specification format:
      URS {3, 4, 5, 6} – {RTUD, ATUD} x {length in ft.-in.} @ {on-center spacing in inches}
      (Example: URS4-RTUD x 30'-8" @ 36")
  • URS rod run termination details (anchorage at foundation or at a raised floor)

To assist in this specification, reference p. 67. Table 1 provides the allowable tension load (PA) of each URS rod run based on model number (rod diameter and take-up device). Table 2 provides the equations to calculate the deflection of each URS model based on demand tension load, length and wood species. For simplicity, Tables 3 and 4 provide tabulated deflection values for various combinations of tension load and length.

Handling Deferred Submittals

Designers may choose to provide performance specification as part of their construction documents and require the contractor to submit deferred design calculations and shop drawings. To do so, the following performance criteria should be on the plans.

  • URS rod run allowable demand tension load
  • URS rod run on-center spacing
  • URS rod run deflection limits
  • URS rod run shrinkage compensation amount required
  • URS rod run termination details (anchorage at foundation or at a floor)
  • Hurricane ties to transfer uplift from roof truss/rafter to top plates
  • Method (possibly hurricane ties) of restraining top plate rotation
  • Any additional requirements as determined by the Designer of Record