Metal Roofing Types: Standing Seam, Exposed Fastener, and Metal Shingles

Residential metal roofs come in three systems that differ in how they attach: standing seam panels held down by clips or fastener flanges hidden under raised seams, exposed-fastener panels screwed through their face, and interlocking metal shingles. Attachment decides how many holes the roof has, how it copes with heat movement and how much upkeep it needs, so choose the system first and the metal second.

The National Roofing Contractors Association’s materials overview lists metal among the main steep-slope coverings, but “metal roof” on a quote can mean any of these three systems. If you are still deciding whether to go metal at all, read metal roof vs. asphalt shingles first; for the full materials comparison, see the roofing materials hub.

Three Metal Roof Systems, Sorted by How They Attach

The table compares the systems on how they are held down and what that means on the roof. Minimum slopes are the 2021 International Residential Code (IRC) figures as printed in the 2021 Seattle Residential Code, Chapter 9; your town may enforce another edition or its own amendments, so confirm the local figure.

Read the table as a set of tradeoffs, not a ranking; the sections below explain where each system fits.

Standing Seam: Concealed Attachment and Raised Seams

A standing seam panel is a long, flat pan with its two edges turned up. Neighboring panels join at those raised edges, and the joint, the seam, stands above the flat of the roof. Water runs down the pans and never has to cross the joint at the low point of the roof surface.

The panels are held down in one of two concealed ways. Clips are screwed to the deck and hook into the seam. Nail-flange (fastener-flange) panels instead have a slotted strip along one edge that is screwed or nailed to the deck, and the next panel’s seam covers it. Either way, no fastener pierces the exposed face of the panel in the field of the roof. That is the system’s main advantage: the weather side of the roof has no screw holes to maintain.

Attachment also decides how the roof handles movement. Metal grows and shrinks as it heats and cools, and a long panel moves more than a short one. Whether a given clip or flange lets the panel slide, and how long a panel it can hold, is set by that system’s installation instructions, not by a general rule, so treat the panel maker’s document as the authority. Ask whether the quoted system uses sliding clips or a fastener flange, what maximum panel length its instructions allow, whether your roof’s runs fall within it, and how the panel is fixed at one point so it does not creep downhill.

Standing seam is the metal system the IRC text allows down to 1/4:12, but that is the code floor: a panel profile can carry a higher minimum slope in its own installation instructions, so on a low slope ask for a profile the manufacturer rates for that slope. It also suits long, simple roof planes. A roof with many hips, valleys and dormers means more cut panels and more trim, which is where workmanship shows. Concerns about rain noise and lightning are addressed in metal roof noise and lightning facts.

Exposed-Fastener Panels: Screws Through the Face

Exposed-fastener panels have a corrugated or ribbed profile, overlap at their edges, and are screwed straight through the face into the deck or framing. Each screw carries a sealing washer that compresses against the panel to keep water out of the hole.

The tradeoff is fewer parts and more holes. The system is simpler to install, with no clips and fewer seam components, but every one of those screws is a penetration that depends on its washer. Each washer is a rubber seal sitting in full sun, so its condition, and the tightness of the screw above it, are the things to watch over the life of the roof. The panel and fastener maker’s installation and maintenance documents set how tight the screws should be driven and when they should be checked or replaced; ask for both with the quote.

That makes upkeep part of the system. Plan on periodic checks of fastener tightness and washer condition, and on replacing fasteners as they age; the inspection routine is covered in metal roof fastener upkeep.

Slope matters more here than with standing seam, because the laps are where water can be pushed in. The IRC text requires 3:12 for lapped, nonsoldered-seam panels without lap sealant, or 1/2:12 when applied lap sealant is used.

Metal Shingles and Shakes

Metal shingles are small formed units, shaped to resemble asphalt shingles, wood shakes, slate or tile, that interlock with their neighbors along their edges. They are fastened through a flange that the next unit covers, so most or all fasteners end up hidden.

Because each unit is small, heat movement is spread across many joints instead of building up along a long panel. The tradeoff is the number of joints, which makes underlayment and the interlock design part of the waterproofing. The IRC text sets a 3:12 minimum slope for metal roof shingles.

Stone-coated steel, with granules bonded to the surface, is one type of metal shingle or panel with its own considerations; see stone-coated steel roofing.

Steel, Aluminum, Copper, and Their Coatings

Once the system is chosen, the metal and its coating decide how the roof resists corrosion.

Steel needs a metallic coating to protect it from rust, and it can carry a paint finish over that. Quotes describe the metallic layer as galvanized (zinc) or as an aluminum-zinc alloy coating, which you may see under trade names such as Galvalume. The coating is what keeps the steel from rusting; scratches, cut edges and wear expose the steel underneath, so ask how cut edges are treated. If the quote gives steel thickness as a gauge, a lower gauge number means thicker metal; ask for the gauge and the coating in writing. If you are weighing galvanized against aluminum-zinc coated steel, ask each panel maker which coating its data sheet and warranty specify for your site, especially near salt water. Treat any general claim that one coating outlasts the other as unproven until the maker shows the test.

Aluminum does not rust the way steel does, which is why it comes up for coastal houses; it is quoted with its own thickness and finish.

Copper weathers to a patina instead of being painted, and it is chosen as much for that look as for its function.

Near the coast, salt air moves metal and fastener choice to the top of the list. FEMA’s Coastal Building Materials fact sheet (No. 1.7, December 2010) covers corrosion and decay resistance of materials in coastal construction, and the full discussion is in roofing near the coast.

Runoff is a separate consideration if you collect rainwater or drain to a sensitive stream. Washington State’s Department of Ecology, in Cu L8r, copper and zinc, describes a 2014 study in which roofing such as copper and zinc-aluminum coated panels showed higher levels of metals in their runoff, and explains that copper can harm fish and other aquatic life.

Attachment in High-Wind Areas: What to Ask For

In high-wind regions, how the panels are held down needs its own questions, whichever system you pick. FEMA’s Home Builder’s Guide to Coastal Construction (P-499, 2010 edition) includes Fact Sheet 7.6, Metal Roof Systems in High-Wind Regions, listed in the P-499 fact sheet flyer. FEMA also published a Hurricane Ike Recovery Advisory on metal roof systems in high-wind regions in February 2009, recommending practices for designing and installing them. Both are older federal guidance, so pair them with your current local code.

Translate that guidance into written questions for the roofer:

• Which tested panel assembly is being installed, and what wind rating does that assembly carry for your local design wind speed?
• What clip or fastener spacing does that assembly require, and does the spacing tighten at the edges, corners and ridge?
• What deck thickness and attachment does the assembly assume, and does your existing deck meet it?
• How are the eave, rake and ridge trims fastened?

A panel is only as wind resistant as the assembly it was tested in. If the quote names a panel but not an assembly, ask for the test report or the manufacturer’s installation instructions for your wind zone.

Which Metal System Should You Ask For?

Start with slope. Below 3:12, standing seam is the system the IRC text allows down to 1/4:12, provided the panel’s own instructions also allow your slope, and exposed-fastener panels need applied lap sealant and at least 1/2:12. At 3:12 and steeper, all three systems are open to you.

Then weigh upkeep. If you want the fewest exposed fasteners to maintain, ask for standing seam or metal shingles. If you accept periodic fastener checks in return for a simpler system, exposed-fastener panels fit. If you want a shingle, shake or tile look, ask for metal shingles. Near the coast, settle the metal and coating before anything else.

Whichever you choose, ask every quote to name in writing the system, panel profile, metal, metallic coating and paint finish, gauge or thickness, fastening method, and the tested assembly for your local wind zone. Quotes that all say “metal roof” can then be compared line by line.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• Roofing Materials, National Roofing Contractors Association
• 2021 Seattle Residential Code, Chapter 9: Roof Assemblies, City of Seattle Department of Construction and Inspections
• Coastal Building Materials, FEMA Technical Fact Sheet No. 1.7, FEMA, listed by the U.S. Department of Energy Building America Solution Center
• Cu L8r, copper and zinc, Washington State Department of Ecology
• FEMA P-499 Homebuilder’s Guide to Coastal Construction flyer, Federal Emergency Management Agency
• Metal Roof Systems in High-Wind Regions: Hurricane Ike Recovery Advisory, FEMA, listed by the U.S. Department of Energy Building America Solution Center