Standing Seam vs Exposed Fastener Metal Roofing
Standing seam panels use concealed fasteners: panels attach with clips or a pre-punched fastening flange; exposed fastener panels are attached with screws driven through the panel into the deck or purlins (also called through-fastened or screw-down).[1] That changes where each can go: the code allows standing seam from 1/4:12, while lapped panels without sealant need 3:12.[2] One manufacturer that makes both rates exposed fastener installation cost as lower (more economical) and standing seam as higher (more complex installation).[1]
At a glance
| Feature | Standing seam | Exposed fastener | Source |
|---|---|---|---|
| How panels attach | concealed fasteners: panels attach with clips or a pre-punched fastening flange | attached with screws driven through the panel into the deck or purlins (also called through-fastened or screw-down) | [1] |
| Minimum slope in the code | 1/4:12 | Lapped seams: 3:12 for lapped seams without sealant, 1/2:12 with applied lap sealant, 1/4:12 for standing seam | [2] |
| Thermal movement (McElroy) | Panels allow thermal movement through clips or slotted flanges | limited flexibility; fastened through the panel | [1] |
| Installation cost (McElroy) | higher (more complex installation) | lower (more economical) | [1] |
| Materials in the code | Steel galvanized ASTM A653 G90 or aluminum-zinc (Galvalume) ASTM A792 AZ50; aluminum 0.024 inch for roll-formed panels | Same table | [2] |
| Example paint warranty | Depends on the paint system chosen | McElroy commodity panels: 10 years against cracking, flaking or peeling of the polyester paint; void within 1,500 ft of salt water | [3] |
How each one is fastened
McElroy Metal, which makes both types, describes exposed fastener roofing as attached with screws driven through the panel into the deck or purlins (also called through-fastened or screw-down), and standing seam as concealed fasteners: panels attach with clips or a pre-punched fastening flange.[1] On panel movement, it rates exposed fastener as limited flexibility; fastened through the panel, and says standing seam panels allow thermal movement through clips or slotted flanges.[1]
Slope
The residential code sets minimum slopes by seam type: 3:12 for lapped seams without sealant, 1/2:12 with applied lap sealant, 1/4:12 for standing seam.[2] Ask which seam type a panel has: the lapped-seam minimums apply to lapped panels, and the panel maker's own minimum can be higher than the code.
Warranty fine print
Metal warranties are written for the paint and the steel, not for the panel type. McElroy's warranty for its commodity panels with polyester paint covers 10 years against cracking, flaking or peeling of the polyester paint; void within 1,500 ft of salt water.[3] Its Galvalume steel warranty covers 25 years against rupture, structural failure or perforation, and is excluded within 1,500 ft of surf, 800 ft of a large bay, 400 ft of marsh.[4]
Cost
We did not find a neutral, published installed-cost comparison. McElroy, which sells both, rates exposed fastener installation as lower (more economical) and standing seam as higher (more complex installation).[1]
Common questions
Can exposed fastener metal go on a low-slope roof?
Lapped panels need 3:12 without sealant in the residential code; standing seam can go down to 1/4:12.[2]
What is a screw-down metal roof?
Another name for exposed fastener roofing, where panels are attached with screws driven through the panel into the deck or purlins (also called through-fastened or screw-down).[1]
Sources
- McElroy Metal Through-Fastened vs. Standing Seam Metal Roofing: A Comparison (October 28, 2025). Accessed November 3, 2026.
- California Building Standards Commission 2025 California Residential Code, Section R905 Requirements for Roof Coverings (effective January 1, 2026). Accessed November 3, 2026.
- McElroy Metal Commodity Panel Polyester Coating Limited Warranty (MM615) (Rev. 2/16). Accessed November 3, 2026.
- McElroy Metal Galvalume Limited Warranty (MM602) (Rev. 11/12). Accessed November 3, 2026.
We did not install or test these products. Everything on this page comes from the documents listed above. If a source changes, numbers here may be out of date until our next check. Spot an error? Email [email protected].