Roof Framing, Sheathing, and Structural Considerations
Think in load paths
A roofing crew rarely designs framing, but the exam expects you to know how a roof carries load to the ground: covering, sheathing, rafters or trusses, ridge and hips, wall framing, foundation. Every connection in that chain matters, and in California seismic hardware (hurricane clips, embedded straps, continuous load-path ties) is the usual weak point in a retrofit.
Rafters, ties, and thrust
Stick-framed rafters push outward at the wall line. Ceiling joists acting as rafter ties in the lower third resist that thrust; collar ties in the upper third resist uplift and ridge separation but do not substitute for rafter ties. Ridge boards are sized to the depth of the rafter cut, not by span alone.
Sheathing and fastening
Panel span rating must match rafter spacing - 7/16-in. OSB rated 24/16 spans 24 in. on center for roof support. Fasten panels with 8d common nails at about 6 in. on center at supported edges and 12 in. in the field; leave a small gap between panels and use edge clips where required. Blocking is required where panel edges are unsupported.
Trusses
Never cut, notch, or field-modify an engineered truss without the truss engineer's written approval. Bracing shown on the truss design drawing is part of the structure, not optional.
Traps
Questions showing a notch cut in a rafter, a removed collar tie, or a hole through the middle third of a rafter are testing whether you know the limits. Watch also for overdriven or short nails, and for roofers substituting roofing nails where common nails are required for sheathing.
Worked example: 2x8 rafters at 24 in. on center call for 7/16-in. sheathing with a 24/16 span rating, nailed 8d at 6/12; where wind uplift governs, ring-shank nails are the upgrade.