Metal Roof Calculator: Panels, Screws and Trim

Each roof plane is figured separately

The calculator figures each plane by itself. Panels don't carry across a ridge or around a valley, so a roof with four planes is four small takeoffs added together.

1. Slope length. If you measured it on the roof, use that number. From the footprint, it's (half the building width + eave overhang) × √(1 + (pitch ÷ 12)²).
2. Panels per plane = eave length in inches ÷ net panel coverage, rounded up. A partial panel still counts as a whole panel on the invoice.
3. Panel length = slope length + panel overhang past the eave, rounded up to the next whole inch.
4. Lin ft = panels × panel length. Squares = lin ft × coverage in feet ÷ 100.
5. Waste goes on last: panels to order = panels × (1 + waste %), rounded up.

The default house shows how it works: 40 by 30 feet, 6/12 pitch, a foot of overhang at the eaves and the rakes, and 16-inch standing seam. The run is 15 + 1 = 16 feet, times 1.118 for the pitch, so the slope is 17.89 feet. The eave is 40 + 2 = 42 feet (504 inches), and 504 ÷ 16 = 31.5, which means 32 panels a side and 64 total.

Each panel is 214.7 inches plus an inch of overhang, rounded to 216, an even 18 feet. Sixty-four of those make 1,152 lin ft, or 15.36 squares of panel against 1,502.6 square feet of actual roof (the half panel and the overhang make up the gap). Add 5% waste and you order 68.

Clips at 24 inches: 216 ÷ 24 = 9, plus one to finish the run, so 10 a panel and 672 with waste. Trim comes to 84 feet of eave (10 sticks, since each 42-foot side takes 5), 71.6 feet of rake (8 sticks) and 42 feet of ridge cap (5). At $10 to $16 a square foot installed, the roof costs about $15,000 to $24,000.

Count panels by net coverage, not sheet width

Count panels by net coverage, never the sheet width, because the side lap takes up the difference. R-panel (PBR) covers 36 inches; the Metal Sales PBR data sheet lists 36-inch coverage with 1¼-inch ribs on 12-inch centers. 5V crimp covers 24 inches (see Metal Roofing Source's 5V page).

Residential standing seam usually runs 12 to 18 inches wide. Narrow panels look tighter and show less oil canning (the wavy look on flat pans), while wide ones go on faster.

Standing seam costs more than screw-down panels

Price depends on the system more than the width. Screw-down panels cost around $6 to $10 a square foot installed and steel standing seam $10 to $16. The metal roofing guide breaks down gauges and paint, and the standing seam guide compares snap-lock with mechanical seam. If you're weighing metal against asphalt, metal vs. shingles runs the cost-per-year math.

Exposed fastener roofs take about 80 screws a square

The calculator defaults to 80 screws a square, which is Fabral's schedule. Midwest Manufacturing calls for 75 (both are quoted in InspectAPedia's fastener spacing notes). Those are field screws only. Trim screws and side-lap stitch screws are extra, and coastal or high-wind jobs tighten the pattern, so buy one more box than the math says.

How far apart are standing seam clips?

Standing seam clip spacing comes straight off the manufacturer's load table for your wind zone, and it varies a lot. Standing seam hides its fasteners under these clips. PAC-CLAD tested its 12 to 18 inch panels on plywood with clips as far apart as 36 inches where the loads allow, while hurricane-zone tables can drop to 12 or even 6. The calculator uses 24 inches as a middle-of-the-road default, so check the table for your panel.

Trim sticks cover 10 feet each

Trim is counted per run in 10'6" sticks lapped six inches, so every stick covers ten feet. A 42-foot eave takes five sticks, not four and a bit.

Exposed panels need foam closures cut to the rib shape, one per panel width: inside closures under the panels at the eave, and outside closures on top at the ridge, on both sides. Standing seam usually hems over an eave cleat and only needs a metal Z-closure at the ridge.

Butyl tape seals those closures and the valley edges. It's cheap (rolls are commonly 45 feet), and skipping it lets wind-driven rain in under the ridge. Under everything, use a high-temp synthetic underlayment. Dark metal in July gets hot enough to soften ordinary products, and the high-temp ones are rated around 240 degrees. Mechanically fastened rolls usually cover 10 squares; self-adhered rolls cover more like 2.

Hips, valleys and flashing need extra material

Hips and valleys are where the takeoff runs short. Every diagonal cut leaves a triangle of panel nobody can use, so raise waste to 10 or 15 percent on a cut-up roof (hips themselves aren't in this takeoff). Chimneys, skylights and dormers need custom-bent flashing that no calculator counts, and the same goes for pipe boots and snow guards.

For shingle and other material prices on the same roof size, the roof cost calculator shows the whole-roof squares and installed range side by side.