A metal roofing panel arrives as one long run, custom-cut to the ordered length. Choosing the panel material comes before measuring anything, because the product sets the coverage width, the minimum slope, the gauge and the finish, and every quantity downstream depends on those figures. This guide covers the material decision: profile family, gauge, finish and the accessories that must match the panel.
Which panel family should you buy?
Two families cover most roofs. Exposed-fastener panels take screws through the panel face into the structure, and the rubber-sealed screw heads stay visible. Standing-seam panels hide their fasteners: clips hold the panel while the raised seam snaps or folds over them. Buy exposed-fastener panels for budget jobs and simple roofs, including roofs over open framing. Buy standing seam when you want concealed fasteners on a solid deck.
| Product | Family | Coverage width | Gauges | Minimum slope |
|---|---|---|---|---|
| Metal Sales Classic Rib | Exposed-fastener | 36 in | 29, 26 | 3:12 |
| Metal Sales 1.25 in Corrugated | Exposed-fastener | 24 in | 29, 26 | 3:12 |
| McElroy Medallion-Lok | Snap-lock standing seam | 12, 16, 18 in | 24 | 3:12, solid deck |
| McElroy 238T | Mechanically seamed standing seam | 16, 18, 24 in | 22, 24 | 1/2:12 |
These are product-specific figures from named manufacturers, not industry standards. The supplier's own spec sheet for the exact product controls the order. Coverage width alone runs from 16 to 36 in across these examples, which is why no guide can supply one memorized width for every panel.
What does the gauge number mean?
Gauge names the steel thickness, and the numbers run backward: a lower number means thicker, heavier steel. The Classic Rib section properties show the series directly: 29 gauge weighs 0.62 lb per sq ft, 26 gauge weighs 0.79 lb and 24 gauge weighs 1.03 lb. In the market, 29 gauge is the common residential exposed-fastener panel, 26 gauge is a step up and 24 gauge is the standing-seam standard. Thicker steel spans farther between supports, but span ratings come from the manufacturer's load tables, never from the gauge label alone.
Which finish should the panel carry?
Two paint systems dominate steel panels. PVDF, sold as Kynar 500, is the premium finish and manufacturers publish it for long color and chalk resistance. Siliconized polyester, sold as SMP or WeatherXL, costs less and carries shorter finish expectations; one supplier publishes a 40-year limited finish warranty for it. Both sit on a Galvalume or galvanized coating that carries its own substrate warranty. Read the finish warranty for the exact product before comparing two quotes, because warranty terms differ by product.
What else does the material set include?
Panels alone are not a roof. The complete material set is chosen against the same profile, and every line travels with the panel order:
| Item | What it is |
|---|---|
| Ridge and hip cap | Cover for the peak and the hips, formed to the roof |
| Rake (gable) trim | Covers the sloped edges of the roof |
| Eave trim and drip edge | Installed before the panels along the bottom edge |
| Valley flashing | Installed before the panels where two slopes meet |
| Sidewall and endwall flashing | Where the roof meets a wall |
| Profile closures | Foam or z-shaped closures shaped to the panel profile; they seal the ribs at the eave and ridge |
| Fasteners | Woodgrip screws with EPDM washers for exposed-fastener panels; stitch screws at laps; pancake-head screws for standing seam |
| Underlayment | Synthetic or peel-and-stick layer under the panels |
| Butyl sealant tape | At trim laps, closures and penetrations |
| Pipe boots | Seal plumbing vents through the panels |
Closures are profile-specific: a foam closure shaped for a 3/4 in trapezoidal rib does not fit a standing-seam rib. Fasteners match the system: exposed-fastener panels take screws through the face, standing-seam panels take clips and screws through flanges.
Worked example: how the product choice changes the count
A gable roof has 32 ft eaves and a 15 ft slope at 4:12 pitch.
Option A, Metal Sales Classic Rib, exposed-fastener with 36 in coverage: 32 x 12 = 384 in across the eave; 384 / 36 = 10.67, rounded up to 11 runs per plane. Two planes: 22 runs, each cut to 15 ft. The 4:12 pitch satisfies the 3:12 minimum, and 29 gauge is available.
Option B, McElroy Medallion-Lok, snap-lock standing seam with 16 in coverage: 384 / 16 = 24 runs per plane. Two planes: 48 runs, each cut to 15 ft. The product is published in 24 gauge steel with a Kynar 500 finish and needs a solid deck.
Option C, a 2:12 addition on the same house: neither product above qualifies, since both require at least 3:12. A mechanically seamed system such as McElroy 238T, rated down to 1/2:12, fits that slope.
The profile choice, not the roof size, drives the run count: 22 runs against 48 on the same roof. Order math waits until the product is chosen. When the product is fixed, the measuring guide converts the roof into panel runs, cut lengths and trim records.
Which mistakes change the material choice?
- Ordering panels before reading the spec sheet. Coverage widths run 16 to 36 in across products, and dividing by a memorized width miscounts the order.
- Mixing profiles or manufacturers mid-roof. Profiles are not interchangeable, and closures fit only one profile.
- Ignoring the minimum slope. A 2:12 slope needs a low-slope system, not a 3:12-minimum panel.
- Comparing finishes on price alone. PVDF and siliconized polyester carry different finish expectations, so read the warranty.
- Treating trim and fasteners as afterthoughts. They must match the chosen profile and system, so they belong in the same decision.
Safety and project limits
Standing on a roof exposes workers to serious fall hazards. U.S. residential guidance from OSHA treats roof sheathing and weatherproofing as serious fall-hazard work, and a qualified installer handles roof access. This guide does not replace the panel manufacturer's installation instructions, structural design, drawings, permits, codes or a qualified professional. It does not set allowances, prices, fastener schedules, underlayment choices or code compliance. All figures are examples from named manufacturer products; the supplier's spec sheet for the exact product controls the order.
Sources and source scope
- Metal Sales Manufacturing Corporation, Metal Sales Product Catalog: Classic Rib (36 in coverage, 3/4 in trapezoidal rib on 9 in centers, 29/26 ga, minimum slope 3:12); 1.25 in Corrugated (24 in coverage, 29/26 ga, minimum slope 3:12).
- Metal Sales Manufacturing Corporation, Classic Rib Installation User Manual (effective 6/14), page 7: section properties (29 ga 0.62 psf, 26 ga 0.79 psf, 24 ga 1.03 psf) proving the gauge-weight relationship; fastener types.
- Metal Sales Manufacturing Corporation, Classic Rib panel information (effective 8/19), via archive.org text mirror: panel length minimum 5 ft, maximum 45 ft recommended; 29/26 ga standard, 24 ga optional.
- McElroy Metal, Roof and Wall Systems booklet: Medallion-Lok snap-lock (12/16/18 in widths, 24 ga Galvalume, Kynar 500 PVDF, minimum slope 3:12, solid deck); 138T (12/16/18 in, 1-3/8 in rib); 238T (16/18/24 in, 2-3/8 in rib).
- City of Los Angeles, Research Report RR 26085 (issued 2024-10-01): McElroy 238T panels in 16 or 18 in widths, 24 ga steel; Medallion-Lok 16 in, 24 ga; formed from 22/24 ga steel per ASTM A792.
- Mid Florida Metal Roofing Supply, Multi Rib Panel Installation Guide: panel storage (dry location, off the ground on wood; trapped moisture stains paint and shortens roof life); underlayment overlap guidance.
- McElroy Metal, 8 FAQs for Installing Exposed Fastener Metal Roofs: standing seam generally covers 16-18 in per panel; exposed-fastener panels most often cover 36 in.
- OSHA, Fall Protection in Residential Construction: U.S. residential roofing fall-hazard context.
Source scope: Metal Sales and McElroy sources support the product figures in the tables and example only; they do not recommend one product over another. The City of Los Angeles report confirms product gauges and widths exist in the market; it is not a product recommendation. Mid Florida supports storage and installation-order statements only. OSHA supports U.S. employer safety context. No source sets an allowance, confirms local stock, states a current price or approves a project order. The reader's supplier spec sheet controls the order.
Related reading: how roof area is measured, measuring for panel runs and lengths, the roof area calculator and the Roofing Quantity Planning hub. The calculation methodology explains rounding and source checks, and the corrections route accepts documented issues.
Review note: Saleem Sial owns the research and editorial record. Fixtures, source checks, build validation, link crawl, schema review and rendered QA form the internal publication gate. Waseem Sial, External Reviewer and Engineer, is listed for ongoing external review; no completed review date is claimed.
