Introduction
Panel profile, gauge, and coating are the three material decisions that shape everything else — the panel math, the installed cost, the lifespan, and the look of the finished roof. Get them right for the building and the budget, and the estimate practically writes itself. Get them wrong, and no amount of careful measuring fixes a profile unsuited to the roof’s pitch or a gauge too light for the look you want.
The Metal Roof Calculator takes your quantities from any profile you choose — this guide helps you choose. Below: the four main profiles compared, gauge and thickness explained, coatings decoded, and underlayment and trim covered.
Panel Profiles Compared
| Profile | Typical coverage width | Fastening | Min. roof slope | Cost tier | Best for |
|---|---|---|---|---|---|
| Standing seam | 12–18 in (305–457 mm); 16 in common | Concealed clips | 3/12 (some systems 1/12 with sealant) | $$$ | Homes, premium look, low slopes, long life |
| Corrugated | ≈26 in (660 mm) | Exposed screws | 3/12 | $ | Sheds, barns, agricultural, budget re-roofs |
| R-panel / PBR | 36 in (914 mm) | Exposed screws | 1/12 (with sealant) | $$ | Commercial, agricultural, low-slope utility roofs |
| Metal shingles / tiles | Sold by the square | Exposed screws / interlock | 3/12 | $$$$ | Slate/tile look at lower weight, HOA neighborhoods |
Standing seam
Raised seams (typically 1–2 in / 25–50 mm tall) lock panels together over concealed clips — no fasteners pierce the panel surface. That’s why it lasts 40–70 years with minimal maintenance: no exposed screw washers to age and no penetrations to leak. The trade-off is cost and skill — installed costs run well above exposed-fastener profiles (see the cost guide) — and long panels demand experienced handling. Minimum slope is typically 3/12, though some mechanically seamed systems go lower with sealant in the seams.
Corrugated
The classic wavy profile, fastened with exposed screws through the panel into the deck or purlins. Inexpensive, fast to install, and honest about what it is — but every screw is a potential leak point as EPDM washers age, so plan on a screw-maintenance pass every 10–15 years (the pro tips guide covers what that involves). Best on outbuildings and budget-conscious re-roofs where the economics favor it.
R-panel / PBR
A trapezoidal-rib commercial profile covering a full 36 in per panel — the fastest coverage per panel in the industry. PBR is the variant with a purlin-bearing leg designed to lap over purlins on open-framing construction. The wide coverage means fewer panels and fewer seams, which is why the panel-count math in the formula guide looks so different for it: a 40 ft eave needs just 14 R-panels per slope (480 ÷ 36 = 13.33 → 14) versus 30 standing seam panels.
Metal shingles and tiles
Stamped or formed pieces that mimic slate, wood shake, or clay tile at a fraction of the weight — often light enough to go over existing roofs where tile couldn’t. Sold by the square like shingles, installed piece by piece, and priced at the top of the range. The estimating math shifts from panel counts to squares plus a cutting-waste factor.
Gauge and Thickness
Gauge is the thickness standard for sheet metal, and it runs backwards: a lower number means thicker steel. Thickness affects stiffness (resistance to oil canning), dent resistance (hail, foot traffic), and span capability.
| Gauge | Approx. thickness | Typical use |
|---|---|---|
| 29 ga | 0.0142 in (0.36 mm) | Economy corrugated; sheds, agricultural |
| 26 ga | 0.0187 in (0.48 mm) | Residential standard for exposed-fastener profiles; common standing seam |
| 24 ga | 0.0239 in (0.61 mm) | Premium standing seam; best oil-canning resistance, hail and foot-traffic durability |
For a primary residence, 26-gauge is the sensible minimum and 24-gauge the premium choice — the upcharge buys a visibly flatter roof and better impact resistance. On wide standing seam coverage (18 in and up), the heavier gauge matters more, because wider flats oil-can more readily. Match gauge across all panels and trim on a single roof; a mid-roof gauge change reads as two different roofs.
Coatings: Substrate and Paint
A metal panel is a steel core, a metallic anti-corrosion coating, and a paint system. All three matter, but buyers mostly choose the paint.
Metallic coatings: galvanized vs. galvalume
Galvanized steel carries a pure-zinc coating; galvalume carries a zinc-aluminum alloy coating that generally offers superior corrosion resistance, especially at cut edges. Galvalume is the standard substrate under painted residential roofing. Unpainted galvalume (“mill finish”) is also sold as a economical, bright-silvery option — it weathers to a matte gray.
Paint systems: polyester vs. Kynar (PVDF)
Standard silicone-modified polyester (SMP) paint is the economical finish — good color, adequate fade resistance, typically warranted 30–40 years. Kynar 500 / PVDF is the premium fluoropolymer finish — superior chalk and fade resistance, typically warranted longer, and roughly 10–20% more expensive. In intense sun or on a forever home, the upgrade pays for itself in appearance retention. Either way, get the paint warranty terms in writing from the manufacturer, not just the supplier.
Underlayment
Underlayment is the secondary water barrier beneath the panels — required by most manufacturers and codes, and the roof’s last defense if a panel is ever damaged.
- Synthetic underlayment: the modern standard — light, strong, high-temperature rated versions available. Rolls typically cover 10 squares (1,000 ft²). The default choice under metal.
- High-temperature peel-and-stick: self-adhering membrane rated for the heat metal roofs generate. Used in hot climates, at eaves in snow country (ice-dam protection), and in valleys. More expensive per square, worth it where specified.
- Felt (15-lb / 30-lb): the traditional option — cheaper, heavier, lower temperature tolerance, shorter life. Still seen on budget jobs, but synthetic has largely replaced it.
Estimate rolls with Formula 6: total squares ÷ squares per roll, rounded up — and note that metal-roof manufacturers often require high-temp-rated underlayment specifically, so check the panel warranty terms and confirm the choice on the pre-installation checklist.
Trim, Flashing, and Fasteners
A complete trim list for a typical gable roof: ridge cap (linear feet of ridge), eave drip edge (linear feet of eave), rake/gable trim (linear feet of rake), valley flashing (linear feet of valley, plus width), pipe boots (one per penetration, sized to the pipe), foam or profile closures (eave and ridge, matched to the panel profile), and butyl tape/sealant for laps. Order all of it from the same coil lot as the panels.
Fasteners split by system: exposed-fastener screws with EPDM washers, color-matched, correct length and type for the substrate — counted per Formula 5. Standing seam clips — fixed or floating per the engineering; floating clips are the norm where thermal movement matters, which is nearly everywhere panels exceed 15–20 ft.
Related Guides
- Metal Roof Calculator — Complete Guide — the full estimating overview.
- Cost Guide — what each material choice costs installed.
- Pro Tips — ordering and handling by profile.
- Step-by-Step Estimating Guide — from measurements to order list.
- Metal Roof Calculator FAQ — quick material questions answered.
Choose, Then Measure
Profile sets the look and the budget, gauge sets the stiffness and lifespan, coating sets the appearance retention — decide all three before you measure, because the coverage width in your panel math comes from the profile you chose. Then run the numbers through the Metal Roof Calculator and confirm every spec — coverage width, gauge, coating, coil lot — with your supplier in writing before you order.
Open the Metal Roof Calculator
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Product specifications vary by manufacturer — verify coverage widths, gauges, coatings, and warranty terms on the supplier’s spec sheet. Consult a licensed roofer or contractor for material selection and installation decisions, and check local building code requirements before starting work.
