Galvalume Metal Roof Coatings, Paint Systems and Gauges
A steel roof is built in layers. The mill coats the sheet with metal, a coil plant may paint it, and the panel is rolled from a chosen thickness. Each layer is a separate line on a bid.
Unpainted Galvalume Sheet
Bare Galvalume is the flat silver roof on farmhouses, shops and plenty of porches. Wheeling-Nippon Steel, one of the mills that rolls it, says the coating pairs aluminum's barrier protection with zinc's galvanic protection, and that its corrosion resistance "far exceeds" plain galvanized sheet. Some mills also sell bare sheet with a clear acrylic coat on top (Wheeling-Nippon's version is Galvalume Plus), which the mill says stops fingerprinting during handling. You get one color: mill silver.
G-90 Galvanized Steel
Galvanized sheet has a zinc-only coating made to ASTM A653, and "G-90" names the coating weight. Table R905.10.3(2) of the 2018 IRC lists G-90 next to AZ50 Galvalume as the minimum corrosion protection for steel roofing, so either one passes code. Two panels in the same paint color can sit on different metal coatings, so the bid should say which one is under the paint.
Kynar 500 (PVDF) and SMP Paint Finishes
Painted Galvalume usually carries one of two resin families:
- SMP (silicone-modified polyester). McElroy Metal calls it the middle grade and the most widely used, with about 30% silicone in the resin. It's a hard paint that resists scratches, but the same panel maker warns it can micro-fracture while the panel is being formed, leaving bare metal exposed.
- PVDF, sold as Kynar 500. To use that name, at least 70% of the resin has to be Kynar PVDF. It's softer and bends without cracking, and McElroy rates it best against fading and chalking. Arkema, which makes the resin, lists mildew resistance among its properties.
McElroy also says Kynar adds a little to the material price while the labor stays the same. For a dark or bright color you want looking the same in fifteen summers, PVDF is the one to ask about.
Gauge Choices: 29, 26 or 24
Gauge numbers run backward. IBHS notes that a 26-gauge panel is thicker than a 28. HomeGuide says most residential metal roofing is 24 or 26 gauge, and its national material prices run about $1 to $3 a square foot for 29-gauge against $3 to $7 for 24-gauge. HomeGuide also notes that thicker metal is more durable but costs more and is harder to install. Ask for the gauge in writing, not just "residential grade".
Light, Reflective Roof Colors
Per EPA figures, a reflective roof trims the hottest-hour cooling load of an air-conditioned home by roughly 11 to 27 percent. Don't go looking for an ENERGY STAR label, though. EPA ended the roof-product specification on June 1, 2022, so no roof carries it now. The Cool Roof Rating Council's Rated Roof Products Directory lists solar reflectance, thermal emittance and SRI by product and color, and that's where to compare a light gray against a charcoal.
Why Jackson homeowners call Jackson Metal Roofing Pros
- One independent metal roofer gets your request, not a call list
- A free measure, deck check and written estimate
- Ask for panel system, gauge and paint finish in writing
- The roofing permit is part of the scope: ask who pulls it
- No charge to the property owner for the referral
Galvalume Metal Roof Cost: Paint, Gauge and Panel Style
HomeGuide's national figures put Galvalume material at $1.00 to $4.50 per square foot. Installed, a Galvalume standing seam roof averages $800 to $1,300 per square (100 square feet), and a Galvalume corrugated roof $500 to $1,000 per square. Nobody publishes a Jackson-only figure. The overall metal roof range is on the metal roof installation page.
Inside those bands, four things move the number:
Panel style
Screw-down corrugated and R-panel sits at the low end. Clip-fastened standing seam sits at the high end.Finish
McElroy places SMP at a mid-level price and Kynar a little above it.Gauge
The gap between 29-gauge and 24-gauge material shown above applies to every square on the roof.Trim
Painted ridge, rake and eave trim has to match the panel finish, and a roof with many hips and valleys needs more of it.
Galvalume Metal Roof Care Around Brick, Mortar and Copper
The Metal Construction Association's bulletin on dissimilar metals points to a few hazards that matter on a brick house:
Wet mortar and concrete
Galvalume and other aluminum-bearing coatings have "a severe sensitivity to strong alkalis". Wet mortar, concrete, brick and stucco can leave a black or white stain that turns to red rust. If a chimney is being repointed, ask for the masonry to be finished before the panels go on, or for the roof to be covered while it's done.Copper runoff
Water draining off copper pipe, a copper roof or HVAC lines onto Galvalume stains and corrodes it. The chemicals in treated lumber often carry copper salts too, so the bulletin says treated wood shouldn't be used on metal roofs.Pencil marks
Graphite is "extremely corrosive" to aluminum, so ask the installer to mark cuts with something other than a carpenter's pencil.AC condensate
Condensate is a stronger electrolyte than rain. Pipe it to a drain, not onto the roof.
Galvalume Metal Roof Paperwork to Request
Before you sign, ask for these lines on paper:
Metal coating
AZ50 or AZ55 Galvalume to ASTM A792, or G-90 galvanized to ASTM A653.Paint resin
PVDF (Kynar 500) or SMP, and who made the coil finish.Finish warranty
The paint or panel maker's own published chalk and fade terms. That warranty comes from the manufacturer, not from the roofer or this site.Gauge and panel profile
Both by number and name.Color data
The CRRC listing for the exact color you picked. With roughly 85 days a year reaching 90°F at the Jackson airport station, a few points of reflectance are worth checking.
Pitch decides which panel can go on at all. See low slope metal roof.