Standing Seam Systems
Snap-lock seams press together by hand and suit most residential roofs with decent slope. Mechanically seamed panels get crimped with a seaming tool, cost more and hold up better on low slopes and long runs. Both use concealed clips, and on long panels the clips should float so the steel can expand without buckling.
Snap-lockMechanical seamFloating clips
Exposed-Fastener Panels
Screw-down panels like R-panel and corrugated go up fast and cost less, with fasteners driven through the face into purlins. They are common on shops, barns and some homes. The trade-off is that every screw is a potential leak, and the washers will need attention every 10 to 20 years.
R-panelCorrugatedPBR panel
Re-Screwing and Sealant Repair
When washers fail, the fix is backing out old screws and driving oversized fasteners, often a #14 replacing a #12, so they bite fresh wood. The contractor also reseals panel side laps, replaces dried butyl tape at end laps and swaps out flattened foam closure strips under ridge and eave trim. Over-driven screws get replaced, not tightened more.
Oversized screwsButyl tapeClosure strips
Gauge, Coatings and Finishes
Gauge runs backwards: 24 is heavier than 26, and 29 is the lightest common option. Galvalume, coated with aluminum and zinc, generally outlasts plain galvanized in most climates, though not in direct contact with wet concrete or treated lumber. PVDF finishes such as Kynar 500 hold color far longer than SMP paint and cost more.
24 vs 26 gaugeGalvalumePVDF paint
Metal Over Shingles
Going over one layer of shingles with purlins or a synthetic underlayment can skip tear-off. The contractor should still check the decking for soft spots and confirm the local rules. Purlins also create an air gap that helps with heat and condensation.
PurlinsSlip sheetOver-roof
Snow Guards and Oil Canning
Metal sheds snow in sheets, so snow guards or bars above doors, decks and walkways keep it from avalanching onto people or gutters. Oil canning, the wavy look on flat panel areas, is cosmetic. Striations, a heavier gauge and correct clip spacing reduce it.
Snow guardsOil canningPanel striations