Metal Roofing Calculator

Why Metal Roofing? Metal roofing lasts 40–70 years versus 20–30 for asphalt shingles. It reflects heat (reduces cooling costs), withstands wind up to 140 mph, and is fire resistant. Common in commercial and agricultural buildings, and increasingly popular for residential use. Standing seam is the premium option; corrugated and R-panel are common for barns and commercial.

Panel Types and Coverage Standing seam: hidden fasteners, 12"–18" wide panels, “flat” look between seams. Premium option. Corrugated metal: exposed fasteners, traditional wavy profile, 26" total width with 24" coverage. R-panel, also called PBR (Purlin Bearing Rib): exposed fasteners, rib profile, about 38" total width with 36" coverage. Coverage width is never the same as panel width. Panels overlap at the ribs, so effective coverage always comes in below the nominal sheet width. Order by coverage, not by sheet size.

Roof Pitch and Slope Factor Roof pitch is expressed as X:12 (rise over run). A 4:12 pitch rises 4 inches for every 12 inches of run. Slope factor = √(1 + (rise/12)²) A 4:12 pitch has slope factor 1.054, about 5.4% more material than a flat surface. Always measure the plan (horizontal) area and apply the slope factor, not the actual surface.

Calculating Roof Area Gable roof: plan area = (length × width). Total roof area = plan area × slope factor × 2 sides. Hip roof: the footprint is the ridge length plus one rafter run at each end, by two rafter runs wide. Set “4 sides” and the calculator works that out for you. Measure to the edge of the eave, not to the wall. A typical overhang adds 12"–24" per side to the plan dimensions, and the panels themselves should then project another 1"–2" past the fascia for drip.

Waste and Overage Standard waste: 10% for simple roofs, 15–20% for complex roofs with many hips/valleys/penetrations. Always order at least 10% extra. Metal panels cannot always be matched later, and a color run that has moved on is a problem you cannot patch. Panel lengths: typically 8, 10, 12, 16, or 20 feet. Longer panels = fewer seams = less leakage risk.

Fasteners Standing seam: 1 clip per panel per purlin. Clips hidden under seam. Exposed fastener panels: screws at each rib, every 12"–24". Count roughly 80–120 screws per square (100 sq ft). Use self-drilling hex-head screws with an EPDM (Ethylene Propylene Diene Monomer) washer to seal each penetration.