NCCER Roofing cheat sheet

Roof slope is expressed as rise over run (vertical rise per 12 in. of horizontal run); a 4-in-12 slope rises 4 in. per foot. Slope below 3:12 generally requires low-slope or membrane systems rather than standard shingles.

Underlayment overlap depends on slope: on slopes of 4:12 and steeper, laps are typically 2 in.; on slopes from 2:12 to 4:12, laps increase to about 19 in. horizontal (double coverage) to shed water.

Asphalt shingle exposure is set by shingle type and manufacturer: common 3-tab shingles use about 5 in. exposure (12 in. shingles with 7 in. headlap), giving roughly 80 shingles per 100 sq ft. Always follow the bundle label.

Roofing quantities use the square: 1 square = 100 sq ft of roof area. Order 10-15 percent extra for hips, ridges, valleys, and waste; hip roofs waste more than gable roofs.

Fastener rules for asphalt shingles: use corrosion-resistant nails long enough to penetrate 3/4 in. into wood decking or through the deck; place nails above the exposure line and keep them out of the sealant strip area.

Ice and water membrane is required at eaves in cold climates: install from the eave edge up at least 24 in. inside the exterior wall line, and in valleys where code or manufacturer requires it.

Flashing basics: step flashing is woven shingle-by-shingle at sidewalls; counterflashing laps over it; valley flashing is installed under shingles on each side, with the steeper roof plane shedding over the flatter one.

Ventilation rule of thumb: provide roughly 1 sq ft of net free vent area per 150 sq ft of attic floor area when balanced 50/50 between intake (soffit) and exhaust (ridge/static); 1:300 may apply with a vapor barrier and balanced vents.

Safety: fall protection is required at 6 ft or more in general construction; use guardrails, personal fall-arrest systems, or safety nets. Roof brackets and staging must be secured to structural members, not just sheathing.

Decking: minimum 15/32 in. or 7/16 in. OSB/plywood is common for shingles; panels are laid with the long dimension across supports and gapped about 1/8 in. at edges to allow expansion.

Low-slope membranes: built-up roofing (BUR) uses alternating plies of felt and bitumen; modified bitumen is torch- or adhesive-applied; single-ply includes EPDM (rubber), TPO, and PVC, seamed by adhesive, heat weld, or tape.

Metal roofing: panels are attached with concealed clips or exposed fasteners with neoprene washers; fasteners are driven in the flat, not the rib, and panels expand/contract, so screw holes are oversized along the length.

Tile and slate: fasten to battens or directly to deck per system; weight matters (concrete tile can exceed 9-10 lb/sq ft), so verify structural design and use double underlayment on lower slopes.

Valley types: open valleys use metal flashing with shingles cut back; closed valleys (woven or cut) hide the flashing. Closed valleys are not permitted below certain slopes; check manufacturer instructions.

Drip edge: install along eaves under the underlayment and along rakes over the underlayment, lapping joints in the direction of water flow (typically 2 in. minimum).

Inspection points before cover: verify deck fastening, straightness, underlayment laps, flashing at penetrations, and that all penetrations (vents, chimneys, skylights) are flashed and sealed before shingles go on.