Metal roofing has moved from barns to the mainstream on the strength of one number, a service life double or triple asphalt’s, and the buying decision inside the category is mostly one fork: hidden-fastener standing seam versus exposed-fastener panels. Metal roofing types differ more in that detail than in the metal itself, and the folklore (noise, lightning) mostly dissolves on inspection. This reference covers the systems, the metals, and the ownership realities.
The fork: standing seam versus exposed fastener
Standing seam is the premium architecture: vertical panels joined at raised interlocking ribs, fastened to the deck with hidden clips that let each panel float through thermal expansion. No fastener penetrates the weather surface, which retires the category’s classic failure at the design level, and the clip float handles the daily growth and shrink that metal insists on. Costs run highest in the category; lifespans run 40 to 60 years with the finish, not the seam, setting the aesthetic clock.
Exposed-fastener (screw-down) panels, the corrugated and rib profiles of agricultural heritage, fasten through the panel face with thousands of gasketed screws. The economics are compelling and the maintenance contract is explicit: thermal cycling works the screws and ages their neoprene washers, so a screw-down roof owes inspection and a re-fastening round (oversized screws or full replacement of backing-out originals) by years 10 to 15, and its leaks, when they come, come at fasteners and lapped ends. Installed and maintained honestly, 25 to 40 years; installed over open purlins without underlayment discipline, the shorter end.
Both systems share the metal family’s constants: noncombustible ratings that some insurers reward, snow-shedding behavior that demands snow guards over doorways and gutter systems in snow country (metal delivers its snow and rain in a hurry, one input to gutter sizing), and wind performance that architectural shingles envy.
The metals
Galvanized and Galvalume steel dominate: strong, economical, and living or dying by their coating, with Galvalume’s aluminum-zinc alloy outlasting plain galvanizing and cut edges plus coastal salt being the corrosion frontiers. Aluminum rustproofs the coastal problem at a price premium and a softer surface. Copper and zinc are the century metals, self-healing patinas and price tags to match, appearing on landmark work and details, with copper adding the runoff quirk of staining and its galvanic rules about touching other metals, aluminum gutters included, a real detailing point wherever metals mix. Finishes rank alongside metals: PVDF (Kynar-class) paint systems hold color and chalk resistance for decades and are the spec worth asking for by name, while economy polyester finishes fade on the sunny slopes first, per the same solar arithmetic that ages shingles.
The myths, retired
Noise: over solid decking and underlayment, the installed system measures within a few decibels of asphalt; the rain-on-a-drum memory belongs to open-framed barns. Lightning: strikes choose height and path, not material, and a metal roof neither attracts them nor burns when they arrive, points the insurance industry has long since priced. Walkability and hail: metal walks fine with placement care (ribs and purlin lines) and takes hail cosmetically, denting where shingles bruise, with the hail assessment logic of function-versus-appearance applying doubly, and some policies writing cosmetic-damage exclusions for metal specifically, fine print worth reading before the storm.
Ownership notes
Flashing remains the leak frontier as everywhere, penetrations, sidewalls, and chimneys executed in the system’s own trims and boots, with pipe-boot collars aging on the same UV clock as any roof’s. Re-roofing over existing shingles is common and legitimate with proper underlayment and furring decisions, weight being metal’s easy advantage. And condensation under panels, the unvented-assembly gotcha, is an underlayment-and-attic-ventilation design point rather than a metal defect, one the quoting contractor should answer fluently as a screening question.
The bottom line
Standing seam for the buy-once roof, screw-down for the budget with a fastener maintenance contract attached, Galvalume steel as the default metal, PVDF as the finish worth naming, and snow guards plus sized gutters wherever winter is serious. The folklore is retired; the remaining questions are detailing and the installer’s fluency in them.