Roofing Materials and Systems
Know the systems, not just the products
Start by being able to classify systems by slope: low-slope (generally under 3:12) uses membrane or built-up systems - modified bitumen, EPDM, TPO, PVC, and BUR - while steep-slope uses asphalt shingles, clay/concrete tile, wood shakes, metal, and synthetic. Questions love to test the minimum slope at which a product may be applied without special detailing, and the underlayment requirement that changes with slope.
Know each material's strengths and failure modes. Asphalt shingles are graded by weight and by ASTM D3462 (fiberglass) or D225; class ratings (Class A/B/C) refer to fire resistance from external exposure, not impact or wind. Impact ratings are separate (UL 2218, Class 1–4). Metal roofing questions turn on fastener type, thermal movement, and coating (Galvalume vs. Kynar 500). Tile questions test weight per square and the need for a structural check. Single-ply membranes differ by seam method (heat-welded TPO/PVC vs. adhesive EPDM) and by attachment (mechanically attached, ballasted, adhered).
Traps: confusing fire class with wind/impact rating; assuming a product rated for one slope is acceptable at a lower slope; mixing up "square" (100 sq ft) with actual material count; and forgetting that some systems require a slope change or cricket before they can be used.
Rule of thumb: always check the manufacturer's published minimum slope and application method before selecting a system - no generic rule overrides the manufacturer's written instructions.