Roofing Foreman cheat sheet

Roof System Installation Knowledge and Performance

• Minimum slope by system: asphalt shingles generally 2:12 (4:12 for some low-slope installations); standing-seam metal 3:12 minimum for mechanically seamed panels; built-up roofing 1:4:12; modified bitumen 1:4:12 minimum; single-ply membrane (EPDM/TPO/PVC) may go to 1:4:12 or dead flat only with a designed drainage path.

• Underlayment rules: asphalt-saturated felt No. 15 is the baseline; No. 30 or synthetic is required in ice-dam regions and under metal. Ice barrier membrane is required along eaves from the eave edge to 24 in inside the exterior wall line (or per local code, often 36 in) in areas with a history of ice damming.

• Fastener schedule: 6 nails per shingle for slopes up to 60 degrees (20 squares or less), 8 nails above 60 degrees and in high-wind zones; fastener must penetrate at least 3/4 in into wood decking or through the deck where the deck is less than 3/4 in thick.

• Decking: minimum 15/32 in (1/2 in nominal) plywood or OSB for shingle roofs, 19/32 in (5/8 in) for some tile and heavy systems; panel gaps of 1/8 in between sheets and 1/8 in at end joints allow expansion; fasteners 6 in on center at panel edges and 12 in in the field.

• Ventilation math: net free ventilating area (NFVA) = 1/150 of the insulated ceiling area; may be reduced to 1/300 when a vapor retarder is installed on the warm side or when 50-80% of vent area is at the ridge and the balance at the soffit. Balance intake and exhaust roughly 50/50.

• Flashing: step flashing is woven or layered with each shingle course at sidewalls; counterflashing is embedded in a reglet at least 1 in deep; valley lining (metal or membrane) extends at least 12 in each side of the valley centerline; chimney flashing uses a cricket for chimneys wider than 30 in.

• Wind performance: shingle wind ratings are per ASTM D7158 (Class D, G, H) and ASTM D3161 (Class A-F); the rating must meet or exceed the design wind speed for the site. Metal panels are rated by uplift pressure per ASTM E1592 or UL 580, not by slope alone.

• Low-slope membrane attachment: fully adhered, mechanically fastened, or ballasted; ballast weight is typically 10-12 lb/sf for pavers and 1,000-1,200 lb per 100 sf for gravel; attachment method must match the wind-uplift calculation from ASCE 7 for the building height and exposure category.

• Tile and slate: require a minimum 3:12 slope for most profiles (some flat tile at 2.5:12 with double underlayment), corrosion-resistant fasteners, and a designed load path - tile dead load ranges from about 6 lb/sf (lightweight concrete) to 10-12 lb/sf (clay) and must be checked against the roof structure.