The panel stamp shows a roof span rating that permits these panels over supports spaced 24 inches on center provided the unsupported edges are supported, the trusses are set at 24 inches on center, and the long edges between panel rows have no clips, no tongue-and-groove joint and no blocking. What is the correct finding?
- AIt passes, because the underlayment and the shingles laid over the joint will bridge between the rows of panels and support the unsupported panel edges above.
The roof covering is not a structural element and bridges nothing. Two unsupported panels deflect independently at the joint, which telegraphs through the shingles and concentrates stress at the fastener line.
- It fails, because at this support spacing the unsupported panel edges need approved panel clips, tongue-and-groove edges, or blocking beneath the joint.
- CIt fails, because roof sheathing has to be at least three-quarters of an inch thick wherever the trusses are spaced 24 inches on center below it.
Sheathing thickness is set by the panel span rating, and this panel is rated for 24-inch spacing provided the edges are supported. Substituting a thickness rule ignores the condition the rating carries.
- DIt passes, because edge support at unsupported panel joints is a floor sheathing requirement and does not carry over to a roof deck of this kind.
Edge support applies to both roof and floor sheathing, with the roof condition tied to the wider support spacings. Treating it as a floor-only rule leaves a deck that ridges along every long joint.
Why B is correct
Where the panel rating requires edge support at the support spacing being used, the joint between panel rows has to be handled by approved panel clips, tongue-and-groove edges, or solid blocking. None of those are present, so the deck does not meet the rating on its own stamp. Adding clips at the midpoint between trusses is the normal correction and restores the load sharing the rating assumes.
What this question is testing
Whether the candidate reads a panel span rating as a set of conditions rather than a single number, and knows the three accepted means of supporting an unsupported panel edge. It also tests refusing to let the roof covering stand in for structural continuity.
On the job
Missing clips are easy to spot from the ground once the shingles are on, because the roof plane shows a wavy line at every panel row. That is far too late. At the sheathing inspection, walk the deck and look at the long joints, and check the stamp rather than assuming, since thicker panels at closer spacing may not require clips at all. On reroofs where the old deck stays, the same evaluation applies to what is already there.
Memory technique
Every long joint on a deck needs a clip, a tongue, or a block under it.
Exam tip
When a stem quotes a span rating with the words edge support, the answer is clips, tongue-and-groove, or blocking.
Where to look it up
IRC Chapter 8, roof sheathing, and the wood structural panel tables with the footnotes covering edge support and panel orientation.