Roofing
Metal roof types compared: standing seam, exposed fastener, and shingles
How to choose a metal roof: the fastening split that decides everything, standing seam vs exposed-fastener panels, metal shingles and stone-coated steel, the metals and coatings, the slope and deck limits, and the cost-and-life trade.
Direct answer
Metal roofs split into two families by how the panel is fastened. Concealed-fastener standing seam locks above the water line and floats on clips, lasting 40 to 60 years. Exposed-fastener panels screw through the face, cost less, and leak first at the washers. The panel manufacturer governs slope, gauge, and warranty.
Key takeaways
- Metal roofs split into two families by fastening: concealed-fastener standing seam (nothing pierces the weather surface) and exposed-fastener panels screwed through the face.
- Standing seam lasts 40 to 60 years because clips let panels float; exposed-fastener panels run 20 to 30 years before the gasketed washer holes wallow out and leak.
- Standing seam mechanically double-locked seams go lowest, toward 1/2/12 to 2/12; snap-lock, exposed-fastener, and metal shingles want about 3/12 and up.
- Gauge: 29 for budget/ag panels, 26 common residential exposed-fastener, 24 standard for standing seam and high wind, 22 for heavy commercial; lower number is thicker.
- PVDF (Kynar) holds color with 30 to 40 year paint warranties (AAMA 2605); SMP fades sooner at 20 to 25 years; the manufacturer governs slope, gauge, and warranty.
Metal roof types, and the split that decides everything
A metal roof is sorted first by one thing: how the panel is fastened to the building. The metal, the gauge, the coating, and the look all hang off that one decision, because the fastening method sets how long the roof lasts and what it costs. Two families cover almost all of it. Concealed-fastener systems, which standing seam leads, hide the fasteners under the panel so nothing pierces the weather surface. Exposed-fastener systems, the through-fastened panels, screw straight through the panel face into the structure.
The split matters more than the metal does. A cheap exposed-fastener panel and a premium standing seam panel can be the same 24 gauge Galvalume steel with the same paint, and one outlasts the other by twenty years on the fastening alone.
The third group, metal shingles and tiles and stone-coated steel, is a steep-slope look that mimics asphalt, slate, or wood shake, and it fastens its own way. This guide sorts the families, the principle behind the split, and how to pick between them. The how-to for building a standing seam roof is in the standing seam metal roof installation guide, and renewing an aging one in place is in the metal roof restoration and coating guide.
What is the difference between standing seam and exposed fastener?
The difference is whether a fastener pierces the panel face. Standing seam is a concealed-fastener system: the panels ride on hidden clips or a fastened flange, the screws pass through those into the deck or purlin, and the raised seam between panels locks up above where water runs. Nothing on the weather surface is a hole. Exposed-fastener, also called through-fastened or screw-down, is the opposite. Every panel is screwed straight through its face into the structure, with a rubber or neoprene washer under each head doing the sealing.
That washer is the whole story. An exposed-fastener roof has hundreds to thousands of gasketed holes in its field, and a standing seam roof has none. The trade-off is cost and speed against life. Exposed-fastener goes down fast and cheap. Standing seam costs more in panel and labor and lasts far longer.
The seam types, the clips, and the install sequence for standing seam are worked end to end in the standing seam metal roof installation guide. Why the screws leak, and how to fix them on an aging roof, is in the metal roof restoration and coating guide.
Why does standing seam outlast screw-down?
Metal expands and contracts a lot with temperature, and what the panel does with that movement is the root reason one type lasts and the other wears out. A steel panel roughly 30 ft long grows and shrinks about 1/4 in across a 90 degree F swing, and a dark panel in the sun runs well above air temperature, so the real travel is bigger than the weather report suggests. Aluminum moves close to twice as much as steel. That movement happens every day, hot afternoon to cold night, for the life of the roof.
Standing seam lets the panel float. The clips hold it down but let the seam slide, so the panel grows and shrinks freely while the fasteners stay put and dry. A through-fastened panel is pinned by every screw. The panel still wants to move, so it works each screw in its hole. Over years the holes wallow out oversized, the washers harden and crack, and the screws back out. Now there are open holes in the field of the roof, which is exactly where you cannot afford them.
That is the leak mechanism, and it is covered in depth, with the fixes, in the metal roof restoration and coating guide. The float versus pin difference is why a standing seam roof commonly runs 40 to 60 years and a screw-down roof runs 20 to 30 before it needs re-screwing or recovering.
Standing seam: concealed clips and the seam types
Standing seam is a family sorted by its seam. The two you choose between are snap-lock and mechanically seamed. Snap-lock panels have edges rolled so the next panel snaps down over the last by hand, with no seaming machine, faster to install, and they suit moderate slopes. Mechanically seamed panels are set with the seam open, then a powered seamer folds it closed. A single lock folds the seam about 90 degrees. A double lock folds it again to roughly 180 degrees, wrapping the seam tight on itself for low slope and hard weather.
A separate split is how the panel attaches. True standing seam rides on concealed clips that let it float. Nail-strip, or fastener-flange, panels fasten a flange directly and the next panel hides it, which is cheaper but pins the panel and limits its length. The structural-versus-architectural divide, covered below, is a third axis.
Seam height runs from about 1 in on architectural panels to 1.5 in or more on structural and mechanically seamed profiles. Taller seams carry water better and span farther. The profile, the clip, and the seam are a matched set from one manufacturer, and you do not put one line's clip under another's panel. The full seam-by-seam detail and the install sequence are in the standing seam metal roof installation guide.
Exposed-fastener panels: R-panel, PBR, corrugated, 5V, and ag-panel
Exposed-fastener panels are the through-fastened, screw-down side of metal roofing, and they go by their profiles. R-panel, and its roof-rated cousin PBR (the purlin-bearing-rib version with a leg that supports the lap over framing), is the most common, a boxy rib about 1.25 in tall on 12 in centers, the workhorse of commercial and agricultural metal. Corrugated is the old wavy profile, the classic round rib. 5V crimp is the residential and light-commercial panel named for the V-shaped crimps at its edges and center. Ag-panel, or multi-rib, is the cheapest and most common on barns and pole buildings.
What they share is the fastening: screws with gasketed washers driven through the rib into purlins or a deck. Cheaper material, faster install, and a profile you can buy at any supply house. The weak point is the same across all of them, the fastener and its washer sitting in the field of the roof.
These panels live on agricultural, utility, and budget commercial buildings, where a 20 to 30 year life and an eventual re-screw is an acceptable trade. When that roof ages and leaks at the screws, restoring it in place rather than tearing it off is worked in the metal roof restoration and coating guide.
Metal shingles, tiles, shakes, and stone-coated steel
Metal shingles are the steep-slope, architectural side of metal roofing, stamped and finished to look like asphalt shingle, slate, clay tile, or wood shake while carrying the strength and life of steel. They install in interlocking pieces or short panels rather than long vertical runs, with concealed nailing flanges that hide the fasteners, so like standing seam they keep screws off the weather surface. They suit an owner who wants metal performance with a traditional roof look instead of the modern vertical line of standing seam.
Stone-coated steel is the common version: a steel panel surfaced with acrylic-bonded stone granules that give it the texture and color of tile or shake and a matte, non-metallic finish. It hides oil canning that a smooth panel would show, takes high wind and hail and the top fire rating, and costs less than standing seam while still beating asphalt on life. The granular surface reflects a little less and runs a touch warmer than a bare metal panel, which matters in hot climates.
These are steep-slope products. They want the same solid deck and underlayment an architectural panel does, and they are not a low-slope answer.
What metal and gauge should a metal roof be?
The metal is usually steel, and the steel needs a metallic coating under the paint to keep it from rusting. Galvalume, an aluminum-zinc alloy coating that is roughly 55 percent aluminum, outlasts plain galvanized zinc in most exposures and is the common choice, with AZ55 the roofing-grade coating weight. Aluminum panels are the other option, lighter and immune to red rust, which is why they win on the coast and in corrosive air where steel struggles. Aluminum costs more, dents easier, and moves more with heat.
Gauge is the steel thickness, and a smaller gauge number is thicker metal. The rough map: 29 gauge on the lightest budget and agricultural panels, 26 gauge as a common residential exposed-fastener thickness, 24 gauge as the standard for standing seam and high-wind work, and 22 gauge for heavy commercial wide-span panels. Aluminum is sold by decimal inch instead, with .032 in common for panels. Thicker metal oil-cans less, spans farther, and dents less, and it costs more.
Match the metal and gauge to the exposure and the wind, and confirm the panel's coating weight and warranty against the manufacturer, because the substrate corrosion warranty and the paint warranty are two separate things.
Coatings and finish life: PVDF versus SMP
The paint on a metal roof is a performance choice, not just a color, and two systems split the market. PVDF, the fluoropolymer resin sold as Kynar 500 or Hylar 5000, holds its color and resists chalk and fade for decades and meets the high-end AAMA 2605 performance class. It carries the long paint warranties, commonly in the 30 to 40 year range, and it is the finish to spec on a roof you mean to keep. SMP, silicone-modified polyester, costs less and fades and chalks sooner, with paint warranties more often in the 20 to 25 year range. SMP earns its place on agricultural and budget panels where some color drift is acceptable.
Bare Galvalume, with no paint at all, is a third option that weathers to a dull gray and is sometimes specified for its low cost and long substrate life, though it lacks the reflectance and the color choices of a painted finish.
Spec the finish, not just the color, because two panels in the same shade can carry very different lives. A factory paint finish is not the same thing as a field-applied restoration coating. Renewing a weathered finish with a coating is its own system, worked in the metal roof restoration and coating guide.
Structural or architectural: does the panel need a solid deck?
Whether the panel needs a solid deck under it is the structural-versus-architectural divide, and it decides what you build beneath the metal. Structural panels are engineered to span open framing, purlins or battens, with no continuous deck, carrying snow and wind loads across the gap themselves. They have taller seams, commonly 1.5 in to 3 in, and can go to lower slopes. Architectural panels are water-shedding, not structural. They carry no span load and must sit on a solid deck with underlayment, and they want a steeper slope, generally 3/12 and up.
The rough line is the seam height and the rib. A taller, stiffer profile tends to be structural and a low-seam profile tends to be architectural, but the manufacturer's load tables set the actual purlin spacing, not a rule of thumb. Hybrid profiles exist that fall between the two and can go over either a deck or purlins.
The deck or framing under the panel is its own decision, the sheathing type, the underlayment, the ventilation, and it is worth getting right by the roof deck and underlayment topic. For metal the point is matching the panel to what is under it. An architectural panel over open purlins has no deck to shed onto, and a structural panel does not need the solid deck you paid for.
What is the minimum slope for each metal roof type?
The minimum slope depends on the panel and its seam, and it splits along whether the roof is watertight or water-shedding. A hydrostatic roof is built to hold back standing water, the way a folded, sealed seam does. A hydrokinetic roof only sheds water moving down a slope and leaks if water sits or backs up. Standing seam, especially a mechanically double-locked seam with in-seam sealant, is the hydrostatic case and goes the lowest, down toward 1/2/12 to 2/12 on the right profile. Snap-lock standing seam is water-shedding and generally wants 3/12 or more. Exposed-fastener panels and metal shingles are water-shedding too and want a steeper minimum, commonly 3/12 and up, because their joints are not sealed against standing water.
Go below a panel's minimum and you have built a slow leak, and the warranty is gone. This is one of the most manufacturer-specific numbers in the trade, published by profile and seam, and it does not carry between brands.
The slope detail and the low-slope sealant rules for standing seam are in the standing seam metal roof installation guide. When the slope is genuinely low, a single-ply membrane is often the better roof than forcing metal below where its seam wants to live.
The clip, the fixed point, and wind uplift
On a concealed-clip roof two things happen at the clip: the panel is held against the wind, and it is left free to move. A fixed clip locks the panel to the structure at one place, the fixed point. A floating, two-piece sliding clip holds the panel down but lets the seam slide as it grows and shrinks. The roof is anchored once and floats everywhere else. Put a fixed clip where a floating one belongs, or pin the panel at both ends, and it buckles when it heats up. Exposed-fastener and nail-strip panels skip the clip and pin the panel everywhere, which is simple and holds well against uplift but gives the metal nowhere to move.
Uplift is what keeps the roof on the building in a storm, and it is rated by test, not guessed. Wind loads a roof hardest at the corners, then the perimeter, then the field, so clip or fastener spacing tightens at the corners and edges. Set one spacing across the whole roof and you under-build the corners, which is exactly where roofs peel.
The ratings come through ASTM E1592 on the panel and UL 580, UL 90, and FM approvals on the assembly, matched to the design wind pressure the building code sets through ASCE 7. Install to the tested spacing or you do not have the rating on the submittal. The full clip, fixed-point, and uplift detail is in the standing seam metal roof installation guide.
What is oil canning?
Oil canning is the visible waviness in the flat of a metal panel, the gentle ripple you see between the seams when the light catches it. It is stress in the metal showing up as a surface wave, and the honest word for it is cosmetic. It does not leak, it does not weaken the panel, and no reputable manufacturer warrants a panel against it. That last part starts arguments on a job, so set the owner's expectation before the panels go up.
It shows most on wide, flat, smooth panels, because a big flat field of metal has nothing to stiffen it. The causes stack: stress left in the coil at the mill, roll forming, rough handling, and fastening the panel so it cannot move. Striations, the fine parallel lines rolled into the pan, break up the surface so the eye does not read the waves, and tension-leveled coil and narrower panels start flatter.
Smooth standing seam and flat panels show it most. Stone-coated steel and ribbed exposed-fastener panels hide it, because the granules and the ribs break up the surface. The full causes-and-cures detail is in the standing seam metal roof installation guide. Nobody cures oil canning. You pick a profile and finish that hide it.
Dissimilar metals and galvanic corrosion
Mixing the wrong metals on a roof corrodes one of them, and on a roof there is always water present to drive it. Galvanic corrosion happens when two different metals touch with moisture between them, and the more active metal eats away while the nobler one sits fine. Copper is the worst offender against steel, Galvalume, aluminum, and zinc, and it does not even need direct contact. Water running off a copper flashing, pipe, or roof onto a Galvalume panel below carries enough copper to corrode the panel where it lands. So you do not drain copper onto a steel or aluminum roof.
The same caution covers fasteners and accessories. Use clips, screws, and trim compatible with the panel metal, not a bare steel fastener in an aluminum panel or the reverse. Keep the panels off pressure-treated lumber, fresh concrete runoff, and bare iron, all of which attack the coating.
This is a selection issue as much as an install one, because the metal you pick has to live with the flashings, gutters, and neighboring materials already on the building. Where you cannot separate incompatible metals, isolate them with a gasket or a barrier so the circuit cannot form. The detail and the field cases are in the standing seam metal roof installation guide.
Trims and details: ridge, eave, rake, and valley
The field of any metal panel is the easy part. The roof is won or lost at the terminations, and metal has its own set. At the eave the panel hooks an eave cleat or a hemmed edge that holds it down while letting it slide. At the ridge and hip the panels stop short and a ridge cap covers the gap, with foam or metal closures under it to keep weather and pests out. At the rake the panel meets a gable trim over a cleat. Valleys carry the most water, so they get a wide valley metal under the panels with the panel ends held back to leave an open channel.
The principle running through all of it is hold the metal against the wind, keep water out, and still let the panel move. On an exposed-fastener roof the trims are simpler and screwed down like the panels. On standing seam they have to hold the edge without pinning a panel that needs to float.
Penetrations, the pipes, curbs, and skylights, are flashed above the seam and lapped on the upslope side, never fastened through the pan. Those flashing principles are common to every roof and worth knowing by the roof penetration and flashing topic. The metal-specific versions are in the standing seam metal roof installation guide.
Cost and service life by type
The cost and the life run together, and they sort the types cleanly. Exposed-fastener panels are the cheapest to buy and the fastest to install, and they give the shortest service life before the fasteners need attention, commonly 20 to 30 years before a re-screw or a restoration coating. Metal shingles and stone-coated steel sit in the middle on cost and run long, often 40 to 50 years, with the architectural look as the draw. Standing seam is the premium, the most expensive in panel and labor and the longest-lived, commonly 40 to 60 years because nothing pierces the weather surface to wear out.
The number to watch is not the install price. It is the cost over the life. A screw-down roof that is cheap to install but needs re-screwing and a coating to reach the age a standing seam roof reaches on its own can cost more across forty years than the standing seam would have. Restoring an aging metal roof in place, rather than replacing it, is the move that changes that math, and it is worked in the metal roof restoration and coating guide.
| Type | Fastening | Typical minimum slope | Service life / cost |
|---|---|---|---|
| Standing seam, mechanical seam | Concealed clips, panel floats | About 1/2/12 to 2/12, per profile | 40 to 60 yr / highest |
| Standing seam, snap-lock | Concealed clips, panel floats | About 3/12 and up | 40 to 60 yr / high |
| Metal shingle / stone-coated steel | Concealed nailing flange | About 3/12 and up, solid deck | 40 to 50 yr / mid |
| Exposed-fastener (R-panel, PBR, 5V, ag) | Screws through face, pinned | About 3/12 and up | 20 to 30 yr / lowest |
How do I choose a metal roof type?
Choosing a metal roof comes down to five things weighed together: slope, what is under the roof, budget, look, and climate. Take slope first, because it can rule out a type outright. A genuinely low slope pushes you to a mechanically seamed standing seam or off metal entirely. A steep slope opens up everything, including shingles. Then the structure. Open purlins with no deck means a structural panel; a solid deck suits architectural standing seam or metal shingles.
Budget and life come next, and they pull against each other. An exposed-fastener panel is the cheapest roof today and the one you re-screw or coat down the road. Standing seam costs the most now and the least over forty years. The look decides between the modern vertical line of standing seam and the traditional shingle, shake, or tile of stone-coated steel. Climate sets the rest. High wind wants a tested standing seam assembly and the right gauge. Coastal salt air wants aluminum or a heavy coating. Snow country wants a slick standing seam with snow guards and a low-slope-capable seam.
No single type wins every job. The honest answer is to let the slope and the structure narrow the field, then let budget, look, and climate pick within it.
Metal over an existing roof
A metal roof can often go over an existing roof rather than after a tear-off, which saves the cost and the disruption of stripping the old one and keeps the building dry during the work. Metal over an old shingle roof usually runs on battens or a recover board that gives a flat plane and the airspace the panel wants. Metal over an old metal roof uses retrofit sub-purlins, hat channels or notched zee members, that nest over the existing ribs and fasten through to the structure below, creating a new level plane to carry a new standing seam or exposed-fastener roof above the old one. The cavity between can hold insulation or stay a ventilated air space.
This is a re-roof and an engineered call, because the existing structure has to carry the added load and the local code has to allow the recover. It is not the same as restoring the existing metal roof in place by coating it. When the old metal is sound enough to keep, restoring it is the cheaper path, worked in the metal roof restoration and coating guide. When it is too far gone to coat but the building cannot take a tear-off, the metal-over-metal recover is the answer.
Commercial and data-center metal roofs
Big commercial and institutional buildings lean on metal for the same reasons a house does, plus span and uptime. The acres of roof over a distribution center, a manufacturing plant, or a data hall are commonly structural standing seam over open purlins, because the panel spans the framing and skips the cost of a solid deck across a huge area. Where the building is insured or institutional, an FM-approved assembly is often required, and that requirement reaches down to the clip spacing and the fasteners.
Over a critical building the tolerance for a leak is different. A leak over a data white space or a packed warehouse aisle is downtime or ruined stock, not a stained ceiling tile, so the seam type runs to a mechanically double-locked seam, the uplift assembly is matched tight to the wind zone, and the QC is closer.
These roofs also get coated or restored in place rather than torn off when they age, because taking the roof off an operating facility is the expensive, disruptive option. That restoration work over a live building is covered in the metal roof restoration and coating guide.
What to document
Choosing a metal roof type is a decision someone will question later, when the roof is being warrantied, re-roofed, or sold, so the selection is worth a record. The file is what tells the next person why this panel, this metal, this slope, and what the roof is rated to.
Capture the panel type and profile, the fastening method, the metal and gauge, the coating and its warranty, the seam type for standing seam, the panel's minimum slope against the actual roof slope, the substrate it sits on, and the tested uplift rating the assembly was installed to. If the choice was driven by a constraint, a low slope, a coastal exposure, an open-framing structure, write down the constraint, because it explains the call. A tool like FieldOS is built to hold this kind of by-area record, the spec, the photos, and the ratings tied to a place, so the file is the one the warranty inspection runs against.
| Field to record | Why it matters |
|---|---|
| Panel type and profile | Sets the slope limit, the clips, and the life |
| Fastening method | Concealed vs through-fastened drives the leak path |
| Metal, gauge, and coating | Drives corrosion life, oil canning, and warranty |
| Seam type (standing seam) | Snap vs mechanical sets the low-slope and weather limit |
| Panel minimum slope vs roof slope | Below the minimum the warranty is void |
| Substrate: deck or open framing | Confirms the structural vs architectural match |
| Tested uplift rating (UL/FM/E1592) | Ties the roof to the wind design |
Common mistakes
- Putting an exposed-fastener or snap-lock panel below its minimum slope, where the unsealed joints take on water.
- Pinning a panel that needs to float, so it oil-cans, wallows its fastener holes, and leaks.
- Mixing dissimilar metals, draining copper onto Galvalume or aluminum, or using incompatible fasteners.
- Using a fixed clip where a floating clip belongs, or setting the fixed point in the wrong place.
- Putting an architectural panel or metal shingle over open framing with no solid deck.
- Speccing the cheaper SMP paint or bare metal on a roof meant to hold its color and warranty for decades.
- Buying on install price alone and ignoring the re-screw and recoat an exposed-fastener roof needs to reach the same age.
- Carrying a slope minimum, a gauge, or a warranty term from one manufacturer onto another's panel.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The panel manufacturer governs more of a metal roof than any published standard. The slope minimums, the gauges and coatings, the clip type and spacing, the seam and sealant, and the warranties all come from the specific product line, and they do not transfer between brands. Read the manufacturer's data and details for the exact panel first, because that document is what the warranty inspection runs against.
Around that, a few bodies set the framework. The Metal Construction Association, the MCA, publishes guidance on metal roof systems, oil canning, clips, and thermal movement. SMACNA, the Sheet Metal and Air Conditioning Contractors' National Association, sets the architectural sheet metal standards behind the flashings and trims, and MBCI and similar manufacturers publish the panel profiles and load tables. The NRCA covers roofing practice generally. For finishes, the ASTM material specifications and the AAMA 2605 and 2604 performance classes define the paints, and Galvalume coating weights like AZ55 are set by ASTM. For uplift, ASTM E1592, UL 580, UL 90, and FM Global approvals rate the assembly against the design wind pressure the building code sets through ASCE 7.
Cite the standard that controls the point, and let the project specification and the manufacturer's instructions override a rule of thumb when they are stricter. Verify the adopted code edition and any local amendments, and never carry a slope minimum, a gauge, or a warranty term from one manufacturer onto another's panel. Never invent a section number. Cite a standard by name and topic and confirm the designation against the current edition.
Units, terms, and references
Metal roofing carries its own vocabulary, and the same part or number reads differently across a data sheet, a spec, and a drawing.
Gauge describes steel thickness, where a higher number is thinner metal, while aluminum is sold by decimal inch like .032 in. Slope is written as rise over run, a 3/12 meaning 3 in of rise per 12 in of run, and sometimes as a percent or in degrees. Coating weight on Galvalume is given as AZ followed by a number, AZ55 a common roofing grade. Paint performance is graded by AAMA class, 2605 the high-end PVDF tier. Panel coverage is the finished width each panel covers. Service life is in years, and the warranty splits into a paint warranty and a separate substrate corrosion warranty.
- Standing seam
- A concealed-fastener panel with a raised, interlocking seam above the water line; the panel floats on clips
- Exposed / through-fastener panel
- A panel screwed through its face with a gasketed washer at each hole, the common leak point
- Stone-coated steel
- A steel panel surfaced with bonded stone granules to mimic tile, shake, or shingle
- Structural vs architectural
- Structural panels span open framing; architectural panels need a solid deck and a steeper slope
- Galvalume
- An aluminum-zinc alloy coating on steel, roughly 55 percent aluminum, for corrosion resistance
- PVDF / Kynar vs SMP
- PVDF is the premium fluoropolymer paint; SMP is the cheaper, faster-fading polyester finish
- Snap-lock vs mechanical seam
- Snap seams press together by hand; mechanical seams are folded closed by a powered seamer
- Hydrostatic vs hydrokinetic
- Hydrostatic seams hold back standing water; hydrokinetic roofs only shed water on a slope
FAQ
What is the difference between standing seam and exposed fastener?
Standing seam hides its fasteners under concealed clips, so nothing pierces the weather surface, and the panel floats with temperature. Exposed-fastener panels are screwed through their face with a gasketed washer at every hole. Those washers and holes wear out and leak, which is why standing seam lasts far longer and costs more.
What is standing seam?
Standing seam is a metal roof system whose seams stand up above the flat of the panel and lock together over hidden clips, so no fasteners pierce the panel face. The clips let the panels float as they expand and contract with heat. It is the longest-lived metal roof type, commonly 40 to 60 years.
Which metal roof lasts longest?
Standing seam lasts longest, commonly 40 to 60 years, because nothing screws through the weather surface to wear out. Metal shingles and stone-coated steel run 40 to 50 years. Exposed-fastener panels are shortest at 20 to 30 years before a re-screw or coating. The finish, PVDF over Galvalume, drives much of the life.
What is oil canning?
Oil canning is the visible waviness in the flat of a metal panel, stress in the metal showing as a ripple. It is cosmetic, not a leak, and no manufacturer warrants against it. Smooth standing seam shows it most; striations, narrower panels, and ribbed or stone-coated panels hide it. Nothing cures it.
How much more does a standing seam roof cost than exposed fastener?
Standing seam costs more than an exposed-fastener panel in both material and labor, often roughly double, because the panels, clips, and seaming take more work. Exposed-fastener is the cheapest metal roof to install. Over forty years the gap narrows or reverses, because the screw-down roof needs re-screwing or a coating to last as long.
What is stone-coated steel roofing?
Stone-coated steel is a steel roof panel surfaced with acrylic-bonded stone granules that give it the look and texture of tile, shake, or shingle. It hides oil canning, takes high wind and hail and the top fire rating, and costs less than standing seam while outlasting asphalt. It is a steep-slope product needing a solid deck.
What is the minimum slope for a metal roof?
It depends on the panel. A mechanically seamed standing seam roof goes lowest, toward 1/2/12 to 2/12, because its folded seam holds back standing water. Snap-lock standing seam, exposed-fastener panels, and metal shingles want about 3/12 and up. The exact minimum is manufacturer-specific and does not carry between brands; below it the warranty is void.
Do I need a solid deck under a metal roof?
Not always. Structural panels span open purlins or battens and need no continuous deck, carrying snow and wind loads themselves. Architectural standing seam and metal shingles are water-shedding, not structural, so they require a solid deck with underlayment and a steeper slope. Match the panel to the structure, and confirm load tables with the manufacturer.
Is aluminum or steel better for a metal roof?
Steel, coated with Galvalume, is the common and lower-cost choice and holds up well inland. Aluminum costs more and dents easier but never red-rusts, which makes it the better pick on the coast and in corrosive, salt-laden air. Aluminum also moves more with heat. Match the metal to the exposure, not the price alone.
What do I do if my screw-down metal roof is leaking?
A screw-down roof usually leaks at the fasteners, where the washers age out and the holes wallow as the panel moves. If the metal is still sound, you can restore it in place: tighten or upsize the screws, seal the seams, treat the rust, and coat it. If it is rusted through, replace it.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.