Standing Seam vs Exposed Fastener Metal Roofing

A metal roof is a set of long steel panels laid from eave to ridge. The two systems differ in one decision: where the fasteners go.

Standing seam. Each panel has raised legs along both long edges. Clips are screwed to the roof deck, the panel legs hook over the clips, and the next panel's leg locks over the first, either by snapping together or by being folded with a seaming tool. The fasteners sit under the seam, an inch or more above the flat of the panel where water runs. Nothing penetrates the surface that sheds water.

Exposed fastener (also called through-fastened, screw-down or R-panel). The panels overlap at their edges and are screwed straight through the face into the deck or framing below, row after row across the roof. Each screw carries a washer, usually EPDM rubber, that compresses against the panel to seal the hole.¹

Everything else in this comparison follows from that difference: how the roof handles heat, what ages first, what maintenance it needs, and what it costs.

Steel grows when it heats and shrinks when it cools, by about 6.0 to 6.9 millionths of an inch, per inch of length, per degree Fahrenheit.² That sounds like nothing until you multiply it out. A 30-foot panel is 360 inches long. For a 100°F change in panel temperature:

360 in × 0.0000060 to 0.0000069 per °F × 100°F ≈ 0.22 to 0.25 inch.

A dark metal panel in direct sun gets much hotter than the air, and it cools fast after sunset, so a swing of that size is ordinary. It happens every day the sun shines, for the life of the roof.

A standing seam system is built around that movement. Its panels are usually pinned at one fixed point, often near the ridge or eave, and held everywhere else by clips the panel can slide past. The panel grows and shrinks in place without tearing anything.

An exposed-fastener panel is pinned at every screw. The panel still wants to move, so the force lands on each screw hole: the hole can ovalize, the washer gets worked back and forth, and the fastener can loosen in its substrate as the roof cycles.¹ The Metal Construction Association also lists restricted expansion and contraction as one cause of oil canning.³ The full physics is in thermal cycling science.

On an exposed-fastener roof, the waterproofing at each screw is a rubber washer. A fastener industry executive writing in Metal Construction News put it plainly: most exposed-fastener metal roofs rely on EPDM or similar elastomeric washers "to form the primary seal," and a leak path begins "when the sealing material hardens, cracks, shrinks, or loses compression."¹

The same article describes the two installation errors that shorten washer life. An overdriven screw crushes the washer and can damage the seal before the crew leaves. An underdriven screw leaves the washer barely compressed and loose enough that movement enlarges the hole over time. Lower-quality washers also degrade faster under sunlight and temperature cycling.¹

None of that makes exposed-fastener metal a bad roof. It makes it a roof with a maintenance schedule. Plan on having the fasteners checked periodically, and on re-sealing or replacing the ones that have backed out or whose washers have cracked, for as long as you own it. A standing seam roof has no equivalent field of washers to maintain; its weak points are the same as any roof's, the flashings at walls, valleys and penetrations, covered in flashing failure modes.

The Metal Construction Association defines oil canning as "visible waviness in the flat areas of metal roofing and metal wall panels." Its technical bulletin is clear on the stakes: "Oil canning is generally an aesthetic issue. Structural integrity is typically not affected."³

The bulletin lists the causes: stresses from coil production and forming, expansion that perimeter flashings restrict, overdriven fasteners, an uneven substrate, and joints that don't let stress relieve. It notes the waviness becomes more pronounced as the flat width of the panel increases.³

That is why oil canning is mostly a standing seam conversation. A standing seam panel has a wide, smooth pan between seams. An exposed-fastener panel has closely spaced ribs that break up the flat area, so waviness has less room to show. The MCA's mitigation list includes stiffening ribs in the profile, thicker metal ("the smaller the gauge number"), a backer rod under the pan, and low-gloss or embossed finishes that are less reflective.³ The bulletin also notes that no manufacturer or installer can assure total prevention, so if a perfectly flat look matters to you, discuss profile and gauge before ordering.

Steel roofing thickness is given in gauge, and a smaller number is thicker steel. A metal coil supplier lists 24-gauge at a minimum of 0.023 inch and 26-gauge at a minimum of 0.018 inch, and describes 24-gauge as the usual standard for standing seam and 26-gauge as the usual standard for exposed-fastener roofing.⁴ Thicker steel is stiffer, dents less easily, and oil-cans less.

Be careful with impact ratings on metal. The same supplier points out that a panel can carry a Class 4 impact rating while the test "DOES NOT measure denting likelihood," and recommends 24-gauge for hail-prone regions.⁴ A UL 2218 Class 4 metal panel is one that resisted cracking and penetration in the lab, not one that won't dent.

Whether a dent matters is a separate question. In a 2025 IIBEC study from a Fort Worth roof consulting firm, simulated hail dents in Galvalume-coated steel showed no cracking or pitting of the coating in salt-spray testing, and a hail-dented Fort Worth roof showed no corrosion at the dents 27 years after the storm. The authors concluded such dents generally don't meet the definition of functional damage unless they open a path for water, such as a split panel or a disengaged seam.⁵ Your insurance policy may treat that differently. Whether cosmetic marks are covered depends on your policy. Many Texas policies now exclude cosmetic roof damage by endorsement. Check yours.

Texas insurers can credit impact-resistant roof coverings, including formed metal panels, and each company sets its own discount.⁶ The standing seam panels Atrium installs are 24-gauge and Class 4 impact rated. For how hail damage gets assessed, see hail damage.

• Standing seam fits a home you plan to keep: long service life, no field of washers to maintain, and the cleaner look. It is Atrium's main metal system, covered in detail on San Antonio metal roofing.
• Exposed fastener fits barns, shops, carports, patio covers and outbuildings, where the lower purchase price matters more and a maintenance schedule is acceptable. On a house it can work too, if you go in knowing the fasteners will need attention over the years.
• Converting an existing exposed-fastener roof to standing seam removes the recurring fastener work. It is priced as a replacement.

Atrium installs exposed-fastener metal when a customer requests it. If you are deciding between metal and shingles in the first place, the broader comparison is on roofing materials.

Central Texas works on both of a washer's enemies at once: strong sun and large daily temperature swings. Long summers keep panels moving and keep UV on every exposed washer, the same sun and temperature cycling that wears out lower-quality seals fastest. A standing seam roof keeps its fasteners out of the sun entirely.

Hail is the other local factor. Spring storms across San Antonio, Boerne and New Braunfels regularly bring hail, and thicker panels dent less. Before a metal roof goes on, ask your agent how your policy treats cosmetic dents on metal, since that answer affects what a hail claim on that roof would cover.

At Atrium's published rates, standing seam metal runs $800–$1,300 per roofing square installed, or $23,200 – $37,800 on a 2,400 sq ft home footprint at medium pitch. Exposed-fastener metal is installed on request; its ballpark range is on our metal roofing page, and the final price is quoted for the specific building. See San Antonio metal roofing for those ranges. The calculator on the roof cost guide uses the same per-square rates.

On an exposed-fastener roof, a handful of backed-out screws or cracked washers is routine maintenance: re-seat or replace those fasteners and move on. Widespread leaking at fastener lines, rust at many laps, or repeated repairs point toward replacement. Atrium's rule of thumb is that repair wins when it costs under 20 percent of a replacement. Small jobs are scoped on roof repairs.