Roofing Materials, Components, and Systems
Steep-slope coverings
Asphalt shingles dominate Illinois residential work. Three-tab shingles have a single layer and a uniform tab pattern; laminated (architectural) shingles bond two or more layers for thickness and random shadow lines. Regardless of style, three ratings travel separately and exam questions deliberately mix them: fire rating (Class A, B, or C under ASTM E108), impact resistance (UL 2218, Class 1 through 4, with Class 4 the toughest against hail), and wind rating (typically 60–130 mph under ASTM D3161 or D7158). Algae-resistant shingles use copper-bearing granules. Other steep-slope options include SBS and APP modified bitumen, metal panels, clay and concrete tile, synthetic slate, and cedar.
Low-slope membranes
Below about 2:12 the choices are built-up roofing (BUR, multiple plies of felt or ply sheet in hot or cold adhesive), modified bitumen, EPDM (thermoset rubber, seamed with adhesive or splice tape), TPO and PVC (thermoplastics, seamed by hot-air welding), and sprayed polyurethane foam. A frequent trap is treating EPDM and TPO as interchangeable; their seam methods, cleaners, and repair materials are not.
Components and the assembly
A roof is a system: structural deck, vapor control, insulation (polyiso, EPS, XPS), cover board, underlayment (#15 or #30 felt, synthetic, or a self-adhered ice barrier), flashing (drip edge, step, apron, counter, valley), and ventilation (ridge outlet paired with soffit intake, box vents, powered vents). Fasteners must be compatible and corrosion-resistant - electro-galvanized, hot-dip galvanized, or stainless - because corrosion failures are a common inspection finding.
Rule of thumb
Classify by slope and by seam chemistry before naming a product: slope decides which systems are legal, and seam chemistry decides whether the crew needs an adhesive, a torch, or a welder.