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Reference · Metal Roofing Terms
191 metal roofing terms defined in plain English, from oil canning and standing seam to UL 2218, Galvalume, and kick-out flashing. Written and maintained by The Metal Roofers, a metal-only roofing company working in Middle Tennessee since 2003, with more than 1,000 metal roofs installed and more than 10,000 metal roof repairs behind the definitions.
✦ Reviewed by The Metal Roofers Technical Team
The roof types themselves: how each system is built, what it looks like, and where each one belongs.
Also called: 5-V crimp; five-vee panel
5V crimp is a traditional exposed fastener panel with five small V-shaped ribs across its width, two at each edge forming the sidelap and one in the center.
It is the classic Southern farmhouse and cabin roof, still specified when the goal is a period-correct look on a simple gable. Like all exposed fastener panels, its fasteners are the maintenance item.
Also called: box rib; batten roof
A batten seam roof runs a raised cap over the joint between panels rather than folding the panel edges together, producing a bold square or trapezoidal rib line.
Historically the batten was a wood strip with metal wrapped over it. Modern versions use a metal cap snapped or seamed over the panel legs, and the look is chosen when a heavier shadow line suits the architecture.
Also called: Classic Panel; ribbed panel
Classic Rib is a 3-foot-wide exposed fastener steel panel with evenly spaced raised ribs, the most common agricultural and budget residential metal roof in Middle Tennessee.
It installs quickly on simple rooflines, barns, shops, and outbuildings. Because the flat area between ribs is wide, lighter gauges can show oil canning, and every screw is a maintenance point.
Also called: wavy panel; corrugated panel
Corrugated metal roofing is panel stock formed in a continuous wave rather than flat pans with ribs, a shape that stiffens thin metal and hides waviness well.
The rounded profile is why corrugated panels rarely show oil canning even in lighter gauges, and why they remain common on barns, sheds, and agricultural buildings across Middle Tennessee.
Also called: through-fastened panel; screw-down roof
An exposed fastener panel is a metal roof whose screws pass straight through the face of the panel into the deck or purlin, with a rubber washer under each screw head making the seal.
It is the lowest-cost metal roof and the fastest to install, and its lifetime maintenance item is fastener backout: screws loosen over years of thermal movement and eventually need re-driving or upsizing. Common profiles include Classic Rib, R-panel, PBR, and 5V crimp.
Also called: first-flush diversion
A first flush diverter captures and discards the first few gallons of runoff from each storm, the dirtiest water, before the rest reaches the storage tank.
Between rains a roof collects dust, pollen, and bird droppings, and the opening wash carries most of it. Diverting that volume is the simplest water quality improvement in any catchment system.
Also called: four-sided interlock
A four-way interlock is a metal shingle design where each panel locks to its neighbors on all four edges, so the roof behaves as a connected grid rather than a field of separate pieces.
That interconnection is what lets a metal shingle resist wind lifting one piece at a time, the progressive failure mode that starts most asphalt shingle blow-offs.
Also called: stamped metal shingle; metal tile
A metal shingle is a stamped or formed metal panel made to look like slate, cedar shake, clay tile, or dimensional asphalt while interlocking on multiple edges and hiding its fasteners.
Metal shingles suit homes where a vertical standing seam line would look wrong: traditional brick, historic streets, and HOA neighborhoods. The four-way interlock is what separates a premium system from a stamped panel that simply nails down.
Also called: metal wall panel; wall cladding
Metal siding is wall cladding formed from the same coated steel or aluminum as roofing, installed in profiles such as board and batten, standing seam wall panel, or corrugated.
It carries the same finish systems and the same immunity to rot, termites, and repainting cycles as a metal roof, and it is often specified on gable ends, dormer cheeks, and accent walls.
Also called: purlin bearing rib panel
A PBR panel is an R-panel with an added purlin bearing leg under the sidelap, a small return that supports the overlapping edge so the sidelap seats evenly and seals more reliably.
The bearing leg is the practical difference between PBR and plain R-panel on a commercial roof, and it is worth asking which one a bid includes.
Also called: PBR panel; industrial rib
R-panel is a wide-rib exposed fastener steel panel used mainly on commercial and industrial buildings, typically installed over purlins rather than solid decking.
PBR is the variant with a purlin bearing leg, an extra lip under the sidelap that supports the panel edge and makes the lap more consistent. Both are steep-slope products and are not appropriate for near-flat roof sections.
Also called: rainwater collection; catchment
Rainwater harvesting is collecting roof runoff for reuse, and a smooth, non-porous, non-toxic standing seam metal roof is the highest-efficiency catchment surface available.
Collection efficiency, first-flush diversion, and storage sizing all follow from the roof surface. Rainwater harvesting is legal in Tennessee with no state-level cap on how much may be collected or stored.
Also called: salvaged panel; barn tin
Reclaimed metal roofing is salvaged panel taken off older buildings and reused for its weathered patina, most often on accent roofs, interiors, and rustic architecture.
Reclaimed panel is bought for appearance rather than performance, and its remaining service life and fastener condition should be assessed before it goes onto anything that has to stay dry.
Also called: cedar-look metal shingle
A shake profile is a metal shingle stamped to imitate hand-split cedar, delivering the grain and shadow of wood without absorbing water or feeding algae and moss.
In Nashville's humidity and tree cover, real cedar cups, splits, and grows biological matter. Shake-profile metal keeps the look and drops the maintenance.
Also called: slate-look metal shingle
A slate profile is a metal shingle stamped to imitate quarried slate, reproducing cleft lines, chipped edges, and uneven thickness without slate's weight or brittleness.
It suits formal and traditional architecture, particularly brick homes, and it goes on structures that were never framed to carry real slate.
Also called: solar-compatible roof
A solar-ready roof is one that can carry a photovoltaic array without new penetrations, which in practice means a standing seam metal roof that solar racking can clamp onto at the seams.
The practical case is timing: a metal roof lasting 50 years and a solar array lasting 25 to 30 should go on in the right order, so the panels never have to come off for a re-roof.
Also called: concealed-fastener metal roofing
Standing seam is a metal roof system whose panels are joined by raised vertical seams that hold the fasteners underneath the metal, so no screw passes through the weather surface.
Because the attachment is hidden, there is no field of exposed rubber washers aging in the sun. Panels are held by clips that let the metal expand and contract, which is why standing seam is the system specified for long service life and for solar mounting.
Also called: granulated steel shingle
Stone-coated steel is a metal shingle finished with a basecoat adhesive and ceramic-coated stone granules rather than paint, giving it the texture and sound damping of asphalt or tile.
It is a distinct category from smooth PVDF-finished stamped steel: different surface, different maintenance behavior, different price, and a granule layer that can shed over time the way asphalt granules do.
Also called: tin roofing; terne
Tin roof is a historical term now used loosely for any exposed fastener metal roof, though true tin roofing meant terne, a steel or iron sheet coated in a tin-lead alloy.
Almost nothing sold as a tin roof today contains tin. The modern equivalents are Galvalume-coated steel panels, and understanding that distinction matters when matching a historic roof.
Also called: hybrid roof; mixed-system roof
A two-system roof uses different roofing systems on different sections of the same building, typically metal panels on the steep slopes and a membrane or seamed metal on the low-slope areas.
It is the correct answer on most homes with a low-pitch porch, addition, or dormer, and forcing one system across every slope is a common way those sections start leaking.
The parts of a standing seam roof and the mechanics of how metal panels lock together and move.
Also called: sheet metal brake; folder
A brake is the sheet metal tool that folds flat coil into trim, flashing, and closures by clamping the metal and bending it along a straight line.
Brake work is what separates a roof detailed for the actual house from a roof assembled out of stock parts. Custom-formed valley metal, counterflashing, and wall pans are all brake work.
Also called: continuous cleat; eave cleat
A cleat is a continuous strip of metal fastened to the deck that a panel or trim piece hooks onto, holding the edge down without a face fastener.
At the eave, hemming the panel over a cleat is what resists uplift at the most vulnerable edge of the roof while keeping the weather surface unbroken.
Also called: panel clip; seam clip
A clip is the small metal bracket that fastens a standing seam panel to the deck from underneath, holding the panel in place while keeping every screw out of the weather surface.
Clips are the reason standing seam has no exposed fasteners. Their spacing and type are engineered choices, tightened at eaves, rakes, and corners where uplift is highest.
Also called: 180-degree seam; double-folded seam
A double lock seam is a mechanically seamed joint folded twice to about 180 degrees, wrapping the panel edges around each other for the tightest standard standing seam closure.
The double fold is the specification for the lowest slopes a metal panel can handle and for the most wind-exposed roofs, because the seam resists both uplift and water travelling sideways under pressure.
Also called: transverse lap
An end lap is a horizontal joint where one panel overlaps another partway up a slope, used when a run is longer than the available panel length.
End laps are avoided on residential metal roofing by cutting panels to the full run. Where they are unavoidable on long commercial slopes they are lapped, sealed, and fastened to a strict detail.
Also called: static clip
A fixed clip is a one-piece standing seam clip that holds the panel in a set position, used on short panel runs where thermal movement is small enough to ignore.
Choosing between fixed and floating clips is a function of panel length, and it is a decision that should be made on paper before the roof is ordered, not on the roof.
Also called: expansion clip; sliding clip
A floating clip is a two-piece standing seam clip with a tab that slides along a base, letting the panel move as it heats and cools without tearing at the fastener.
On long panel runs, thermal movement is measured in fractions of an inch per panel per day. A floating clip absorbs that travel; a fixed clip on the same run would elongate holes and distort the seam.
Also called: hemmed edge; folded edge
A hem is a folded-back edge on a piece of roofing metal, which stiffens the edge, removes the sharp cut line, and gives water a place to break away instead of wrapping backward.
Hemmed panel ends locking into a cleat at the eave, and hemmed drip edges, are small details that separate durable metal work from fast metal work.
Also called: kicked edge; water break
A kick is a small upward or downward bend formed into flashing so water is redirected rather than allowed to run back along the underside of the metal.
Kicks turn up the back of pan flashings and turn down at drip edges. Water follows surfaces stubbornly, and a correctly placed kick is often the only thing standing between a detail that sheds and one that wicks.
Also called: mechanical lock; field-seamed panel
A mechanically seamed panel is a standing seam whose adjoining edges are folded together by a powered seaming machine that rolls the seam closed to either 90 or 180 degrees.
The folded seam grips harder and controls water better than a snapped seam, which is why it is the system used on low-slope metal sections and on exposed, high-wind roofs. It is also the more labor-intensive of the two.
Also called: run length
Panel length is the eave-to-ridge run of a single metal panel, and it drives both how many seams a roof has and how much thermal movement each panel must absorb.
Panels are cut to the roof's actual run so there are no end laps in the field where water could enter. Longer runs mean fewer joints but more movement per panel, which is why long runs call for floating clips.
Also called: coverage width; module width
Panel width, or coverage width, is how much finished roof one standing seam panel covers, commonly 12, 16, or 18 inches on residential work.
Narrower panels cost more per square because there are more seams and more clips, but they show less oil canning and read as a finer line on the roof. Wider panels are more economical and more prone to visible waviness.
Also called: shadow rib; center bead
A pencil rib is a single narrow bead rolled down the middle of a standing seam pan to stiffen the flat and hide waviness without the fully striated look.
It is the middle option between a smooth pan, which shows the most oil canning, and full striations, which change the panel's character noticeably.
Also called: roll former; panel machine
Roll forming is the process of pulling flat coil through a series of shaped rollers that progressively bend it into a finished roofing panel profile.
Panels can be roll formed at a shop or on site from a portable machine, which is how a crew produces panels cut to the exact eave-to-ridge run of a roof with no end laps.
Also called: rib height
Seam height is how far a standing seam rises above the flat of the panel, usually 1 inch, 1.5 inches, or 1.75 inches on residential and light commercial roofs.
A taller seam holds water further from the joint and carries a stronger shadow line, and it is one of the numbers that should appear on a written standing seam estimate alongside panel width, gauge, and seam type.
Also called: seaming machine; power seamer
A seamer is the powered machine that travels along a standing seam and folds it closed to 90 or 180 degrees, the tool that makes a mechanically seamed roof possible.
Each panel profile has its own matched seamer, which is one reason a mechanically seamed roof is repaired by a contractor who has the machine for that system.
Also called: side lap; panel lap
A sidelap is the joint where one panel overlaps the next along its length, sealed by the seam on a standing seam roof or by an overlapping rib and stitch screws on an exposed fastener roof.
Sidelaps are where wind-driven rain tries hardest to get in on low slopes, which is why butyl tape inside the lap and stitch screws holding it closed both matter.
Also called: 90-degree seam
A single lock seam is a mechanically seamed joint folded once to about 90 degrees, giving a positive mechanical grip with one fold of metal.
It is the lighter of the two seamed options and is common where a mechanical seam is wanted but the slope does not demand a full double fold.
Also called: snap-together standing seam
A snap-lock seam is a standing seam whose panel edges are formed so one snaps over the other by hand or foot pressure, with no seaming machine required.
Snap-lock is fast, clean, and appropriate for steeper slopes where gravity does most of the water control. On low slopes and high-exposure roofs a mechanically seamed panel is the more conservative specification.
Also called: stiffening ribs; minor ribs
Striations are shallow parallel lines rolled into the flat of a metal panel to stiffen it and break up reflections so oil canning is far less visible.
A pencil rib is the single-line version, a raised bead down the center of the pan. Both are cosmetic engineering, and both are worth specifying on wide panels or dark colors.
Also called: expansion and contraction
Thermal movement is the expansion and contraction a metal roof goes through every day as its surface heats and cools, and it is the single behavior a metal roof system must be designed around.
A dark panel in a Nashville July can run far hotter than the air around it and then shed that heat after sundown. Floating clips, slotted holes, and correctly detailed terminations give that movement somewhere to go.
What the panel is actually made of, underneath the color: substrates, metallic coatings, and paint systems.
Also called: aluminum panel
Aluminum roofing is panel stock with no iron in the alloy, so it cannot form red rust, which makes it the specification for coastal salt exposure and other corrosive environments.
Aluminum is roughly half the weight of comparable steel and moves more with temperature, so panel lengths and clip strategy are adjusted accordingly. It is softer than steel and dents more readily.
Also called: Galvalume coating weight; AZ designation
AZ50 and AZ55 are ASTM A792 coating weights for Galvalume, meaning 0.50 and 0.55 ounces of aluminum-zinc alloy per square foot measured across both sides of the sheet.
AZ50 is the usual designation under a painted finish, where the paint carries part of the protection. AZ55 is specified for unpainted or acrylic-coated Galvalume, which has no paint layer to help it.
Also called: coil stock; flat stock
Coil is the flat rolled metal a roof is made from before it is formed, ordered by substrate, gauge, width, and finish and then run through a roll former or a brake.
Matching coil is also what makes a future repair possible: the same substrate, gauge, and color from the same supplier is what lets a replacement panel or flashing blend into an existing roof.
Also called: copper roof; copper accents
Copper is a solid, uncoated roofing metal that needs no paint, weathers from bright penny to brown to a green patina, and is measured in ounces per square foot rather than gauge.
It is most often used on bay windows, dormers, porch roofs, standing seam accents, and historic work. Copper runoff stains adjacent materials and reacts with other metals, so flashings, fasteners, and gutters have to be copper or a compatible alloy.
Also called: ASTM A653 G90; zinc-coated steel
G90 is an ASTM A653 designation for hot-dip galvanized steel carrying 0.90 ounces of zinc per square foot across both sides of the sheet, roughly 0.45 ounces per side.
Galvanizing protects sacrificially: the zinc corrodes before the steel does, including at scratches and cut edges. G90 is the common designation on stamped metal shingle products, while roofing panels more often use aluminum-zinc Galvalume.
Also called: Zincalume; aluminum-zinc coated steel; ASTM A792
Galvalume is steel hot-dip coated in an alloy of roughly 55 percent aluminum, 43.4 percent zinc, and 1.6 percent silicon, the standard substrate for modern painted metal roofing under ASTM A792.
The aluminum contributes barrier protection and the zinc contributes sacrificial protection at cut edges and scratches, which is why the combination outlasts plain galvanizing. Coating weight is designated AZ50 or AZ55.
Also called: dissimilar metal corrosion
Galvanic corrosion is accelerated corrosion that happens when two dissimilar metals touch in the presence of moisture, with the less noble metal sacrificing itself to the more noble one.
On roofs this is why copper must not drain onto Galvalume or steel, why aluminum should not contact untreated pressure-treated lumber, and why fasteners have to match the panel metal. Galvalume also performs poorly in direct contact with brick, concrete, lead, and iron.
Also called: metal thickness
Gauge is the thickness of roofing steel, and the number runs backward: 24-gauge steel is thicker than 26-gauge, and 26-gauge is thicker than 29-gauge.
Residential standing seam is usually 24 or 26 gauge. Exposed fastener panels are often 26 or 29. Thicker metal dents less, holds its formed shape better, resists oil canning, and grips fasteners more securely over decades of movement.
Also called: copper weight; 16 oz copper
Ounce weight is how copper sheet is specified, stated as the weight in ounces of one square foot of the material, so 16 ounce copper is heavier and thicker than 12 ounce.
Copper is measured this way instead of by gauge. Heavier weights are specified for roofing pans and long runs, lighter weights for small accent and trim work.
Also called: weathered finish
Patina is the stable oxide layer that forms on the surface of copper or zinc and then protects the metal underneath, rather than continuing to corrode it the way rust does on steel.
Copper moves from bright to brown to green over years and decades depending on exposure. Zinc forms a matte gray carbonate layer far faster. Both are functional protection, not just appearance.
Also called: Kynar 500; Hylar 5000; fluoropolymer finish
PVDF is the premium factory paint system for metal roofing, a polyvinylidene fluoride fluoropolymer marketed as Kynar 500 or Hylar 5000, with full-strength versions containing a minimum of 70 percent PVDF resin.
PVDF holds color and gloss far longer than the alternatives under Tennessee sun, which is why it is the finish specified on dark colors, reds, and anything a homeowner expects to still look right in twenty years.
Also called: siliconized modified polyester
SMP is a mid-grade factory paint system for metal roofing, harder and cheaper than PVDF but less resistant to fading and chalking under sustained ultraviolet exposure.
SMP is a reasonable choice on light colors, agricultural buildings, and outbuildings. On a south-facing residential roof in a dark or saturated color, PVDF is the finish that holds up.
Also called: base metal
Substrate is the base metal underneath a roof panel's paint, most often aluminum-zinc coated steel, but also galvanized steel, aluminum, copper, or zinc.
Paint is the cosmetic layer and the first line of UV defense; the substrate and its metallic coating are what actually resist corrosion once the paint is scratched or the cut edge is exposed.
Also called: architectural zinc; VMZinc; NedZink
Architectural zinc is a soft, self-healing roofing metal that forms a protective zinc carbonate patina and can close minor scratches over time as the patina reforms.
Pre-weathered zinc arrives in blue-gray or graphite gray so the roof looks finished on day one rather than weathering unevenly for years. Zinc requires ventilated details on the underside and careful separation from copper and untreated wood.
Every place a roof is interrupted. Panels shed water across open field; these details handle everything else.
Also called: headwall flashing
Apron flashing is the piece that closes the joint where a roof slope runs into the base of a wall head-on, carrying water out onto the roof surface below.
The headwall is a high-pressure spot because all the water above it arrives at once. The apron must run up behind the wall covering and be counterflashed, not simply caulked to the siding.
Also called: sealant tape; mastic tape
Butyl tape is a non-hardening sealant strip laid inside seams, laps, and closures to block capillary water while staying flexible as the metal moves.
Unlike caulk squeezed on top of a joint, butyl works inside the joint under compression and does not dry out and crack. It is the sealant most metal roof details are actually built around.
Also called: flue; stack
A chimney is a masonry or framed stack passing through the roof, flashed with a base flashing on the roof side and counterflashing on the wall side, plus a cricket behind wide chimneys.
Chimney flashing is where sealant-only repairs are most common and least durable. Done properly it is two-part metal work, set into or behind the masonry so the roof and the chimney can move independently.
Also called: woven valley; closed-cut valley
A closed valley covers the valley metal with roofing material, either woven together or cut along one side, an approach used on shingles rather than metal panels.
Metal panels cannot be woven, so a metal roof valley is effectively always open. Recognizing the difference matters when comparing a metal quote against a shingle quote.
Also called: foam closure; profile closure
A closure strip is a foam or metal piece cut to match a panel's profile, filling the gaps under ridge caps, at eaves, and at transitions so wind, water, and pests cannot enter.
Outside closures sit under the ridge cap; inside closures fill the panel's underside at the eave. Missing closures are a common shortcut on fast exposed fastener installations.
Also called: cap flashing
Counterflashing is the upper piece of a two-part wall or chimney detail, let into or surface-mounted on the wall so it laps over the base flashing and covers its top edge.
The two-part design lets the roof move independently of the wall while keeping water out of the joint. A single piece of metal caulked to a chimney is not counterflashing, it is a future leak.
Also called: saddle; chimney cricket
A cricket is a small built-up ridge behind a chimney or curb that splits oncoming water and sends it around both sides instead of letting it pond against the obstruction.
Codes generally require a cricket behind wide chimneys. On metal roofs the cricket is formed and flashed in metal so it becomes part of the drainage plan rather than a patch on top of it.
Also called: roof dormer
A dormer is a framed projection with its own small roof set into a main slope, adding windows and headroom and adding several flashed junctions to the roof.
Every dormer brings sidewalls, a headwall, two valleys, and often a low-slope cheek, so dormers are a leading reason a roof is more expensive and more leak-prone than its square footage suggests.
Also called: leader; conductor
A downspout is the vertical pipe carrying water from the gutter to the ground or to a drainage system, sized and spaced by the roof area draining into it.
Too few downspouts is the most common gutter design error. Water that cannot leave a gutter fast enough backs up over the front edge no matter how large the gutter is.
Also called: eave trim; edge metal
Drip edge is the formed metal at the eave and rake that supports the roofing edge and throws water clear of the fascia instead of letting it curl back onto the wood.
Edge metal is also the first thing wind grabs. Hemmed, correctly fastened edge metal is a wind-uplift detail as much as a water detail.
Also called: roof eave
The eave is the lower horizontal edge of a roof, where water leaves the roof and where uplift pressure during a storm is at its highest.
Eave details on a metal roof carry a lot of load: drip edge, cleat, hemmed panel end, ice-and-water membrane, soffit intake ventilation, and the gutter all converge there.
Also called: fascia board
Fascia is the vertical board or metal running along the roof edge behind the gutter, closing the ends of the rafters and carrying the gutter itself.
Wrapping fascia in coil-stock metal ends the repainting cycle and protects the wood behind it, and it is usually done at the same time as a metal roof or gutter project.
Also called: roof flashing
Flashing is formed metal that closes the joint wherever a roof meets something else, such as a wall, chimney, valley, skylight, or pipe, and it is where most roof leaks actually begin.
Panels shed water across open field; flashing handles every interruption. Flashings designed for shingles do not transfer to a metal roof, which is why a proper conversion fabricates every one of them new.
Also called: gable end
A gable is the triangular wall section formed where two roof slopes meet at a ridge, and a gable roof is the simplest and least expensive shape to cover in metal.
Simple gables have long uninterrupted panel runs, minimal waste, and few flashings, which is why the same house area can price very differently from a cut-up hip-and-valley roof.
Also called: rain gutter; eavestrough
A gutter is the channel at the eave that collects roof runoff and routes it to downspouts, sized by roof area, slope, and expected rainfall intensity.
Metal roofs shed water faster than shingles, so gutter and downspout sizing that was adequate before a conversion may overflow after it. Undersized gutters are a common complaint following a re-roof.
Also called: round gutter
A half-round gutter is a semicircular trough, the historically correct profile for older architecture and the usual choice in copper.
Half-round drains and self-cleans well because there are no interior corners for debris to catch in, and in copper it is the standard partner to a copper roof or copper accents.
Also called: head wall junction
A headwall is the junction where the top of a roof slope meets a vertical wall, as opposed to a sidewall where the wall runs alongside the slope.
Headwalls collect the full runoff of the slope above and are among the most common leak locations on any roof, metal or otherwise.
Also called: hip line
A hip is the external angle where two roof slopes meet and run downward, the opposite of a valley, capped with formed metal trim.
Hips add cuts, waste, and labor to a metal roof, which is a large part of why a hip roof costs more per square than a simple gable of the same area.
Also called: ogee gutter
K-style is the common gutter profile with a flat back and a decorative ogee front face that resembles crown molding, holding more water than a round gutter of the same nominal size.
It is the default residential profile in Middle Tennessee, typically 5 inch on average homes and 6 inch where roof area or rainfall intensity calls for more capacity.
Also called: diverter flashing
Kick-out flashing is a small angled piece at the bottom of a sidewall that throws water away from the wall and into the gutter instead of letting it run behind the siding.
It is a cheap part that prevents an expensive failure. Missing kick-outs are one of the most common causes of rotted wall sheathing and interior water staining below a roof-to-wall junction.
Also called: exposed valley metal
An open valley leaves the valley metal exposed down the center with the roofing cut back on both sides, the standard approach on metal roofs.
Open valleys drain fast, are easy to inspect, and are easy to clear of leaves and pine needles, which matters on wooded Middle Tennessee lots.
Also called: roof penetration
A penetration is anything passing through the roof plane, including plumbing vents, flues, exhaust fans, skylights, conduit, and mechanical curbs, and each one is a deliberate hole that must be flashed.
Field panel almost never fails on its own. Roofs leak at penetrations, transitions, and terminations, which is why an inspection spends most of its time there.
Also called: pipe flashing; roof jack
A pipe boot is the flexible flashing that seals around a plumbing vent or other round penetration, with a metal or rubber base on the roof and a collar gripping the pipe.
On a metal roof the boot is the part with the shortest life: the rubber cracks from ultraviolet exposure years before the panel needs anything. Replacing boots is among the most common metal roof repairs we perform.
Also called: gable edge; rake trim
The rake is the sloped edge of a roof at a gable end, trimmed with formed metal that closes the panel edge and finishes the line against the wall or fascia.
Rake trim is highly visible from the street, so its shadow line and color are aesthetic choices as well as weather details.
Also called: raggle; saw kerf
A reglet is a groove cut into masonry to receive the top edge of counterflashing, so the metal is set into the wall rather than surface-sealed against it.
A reglet-set counterflashing sealed with the right compound is the durable way to terminate metal against brick or stone, and it is a hallmark of chimney work done to last.
Also called: roof peak
The ridge is the horizontal peak where two roof slopes meet at the top, capped with metal trim and usually the location of the roof's exhaust ventilation.
A ridge cap on a metal roof needs closures under it: foam or metal pieces shaped to the panel profile that block wind-driven rain and pests while still letting the ridge vent breathe.
Also called: caulk; roof sealant
Sealant is a flexible compound used to close small gaps in a roof assembly, correctly applied as a secondary defense inside a properly lapped detail rather than as the detail itself.
Every sealant has a service life shorter than the roof it is on. A detail that depends on caulk to stay watertight is a scheduled failure, which is why good metal work laps, hems, and folds first.
Also called: side wall junction
A sidewall is the junction where a roof slope runs parallel alongside a vertical wall, closed with step flashing on shingles or a continuous formed pan on metal.
Sidewalls are where a kick-out flashing belongs at the bottom end, and where its absence quietly rots wall sheathing for years.
Also called: roof window
A skylight is a glazed opening in the roof, flashed with a manufacturer kit or a custom formed metal pan depending on the roofing system around it.
Metal roofs generally use a custom-formed pan and head detail rather than a shingle-style kit. A skylight older than the roof around it is usually replaced during a re-roof rather than reflashed.
Also called: snow retention; snow bar
A snow guard is a device fixed to a metal roof that holds accumulated snow and ice in place so it melts and sheds gradually instead of releasing all at once.
Metal sheds snow better than any other roofing material, which is exactly the hazard: a released sheet can damage gutters, landscaping, vehicles, and people. Guards go above entries, walkways, driveways, and mechanical equipment.
Also called: stepped flashing
Step flashing is a series of individual L-shaped metal pieces woven up a sloped wall junction, each one lapping the course below so water is handed down the roof piece by piece.
On metal roofs the sidewall detail is usually a continuous formed pan rather than shingle-style steps, but the principle is identical: lap the joint downhill and never rely on sealant alone.
Also called: roof valley
A valley is the internal angle where two roof slopes meet and drain together, carrying more water than any other part of the roof and demanding the most careful metal work.
Metal roofs generally use an open valley with a formed W or V pan, with the panels cut and hemmed back from the centerline so water runs free. Ice-and-water membrane belongs under every valley.
Also called: W-shaped valley metal; center rib valley
A W-valley is valley metal formed with a raised rib down the center, which stops water sheeting off one slope from being driven up under the roofing on the opposite slope.
On steep intersecting slopes and in heavy Tennessee downpours the center rib is what keeps a hard-running valley from crossing over. It is a small forming step with a large effect.
What sits under the panels and how the assembly breathes, which is where roofs quietly succeed or fail.
Also called: balanced ventilation; roof ventilation
Attic ventilation is a balanced system of low intake at the soffit and high exhaust at or near the ridge that moves air through the attic and carries heat and moisture out.
Code sizes it around a ratio of 1 square foot of net free vent area per 150 square feet of attic, with a path to 1:300 when the layout qualifies. Balance matters more than hole count: exhaust without matching intake pulls conditioned air out of the house.
Also called: insulation baffle; rafter vent
A baffle is a channel installed at the eave that keeps insulation from blocking the soffit intake, preserving a clear air path from the soffit up to the ridge.
Blown insulation slumps into eaves over time and quietly strangles intake ventilation. Baffles are cheap, invisible once installed, and a common finding on an attic inspection.
Also called: decking; sheathing; roof deck
The deck is the structural sheathing a roof is built on, usually plywood or OSB on modern homes and board decking on older ones, and it is what fasteners and clips actually bite into.
Metal is unforgiving of a bad deck: waves in the sheathing telegraph through flat panels as visible distortion. Deck condition is only truly known after tear-off, which is why an honest estimate carries a decking allowance priced by the sheet.
Also called: tar paper; asphalt felt; 30 lb felt
Felt is traditional asphalt-saturated paper underlayment, sold by weight such as 15 lb and 30 lb, now largely replaced by synthetics on new metal roofing work.
Felt still appears in specific assemblies, notably 30 lb felt with a rosin slip sheet under copper, where the rosin lets the metal move freely over the layer beneath.
Also called: wall girt
A girt is the horizontal structural member on a wall that siding panels fasten to, the wall counterpart of a roof purlin.
Girts appear in metal building and pole barn construction, and their spacing governs panel selection for wall cladding the same way purlin spacing governs roof panels.
Also called: high-temp membrane
High-temperature underlayment is an underlayment rated to stay stable at the elevated temperatures under a metal roof, where an ordinary membrane's adhesive can soften and migrate.
It is the correct specification under metal in Middle Tennessee, particularly on dark colors and on south and west exposures, and particularly at the eaves and valleys where ice-and-water membrane is used.
Also called: self-adhering membrane; peel and stick
Ice-and-water shield is a self-adhering rubberized membrane that sticks directly to the deck and seals around fasteners driven through it, used at eaves, valleys, and penetrations.
It is the layer that protects the most failure-prone parts of a roof against ice damming and wind-driven water. Under metal it must be the high-temperature version.
Also called: NFA; net free vent area
Net free area is the actual open airflow area of a vent after subtracting its screen and louvers, the number ventilation calculations are based on rather than the vent's overall size.
Two vents of the same physical size can have very different net free areas. Sizing an attic on gross opening size instead of net free area is a common way ventilation ends up short.
Also called: oriented strand board
OSB is an engineered wood sheathing made of compressed wood strands, the most common roof deck material on homes built since the 1980s.
OSB holds fasteners well when dry but loses strength and swells at the edges when it gets wet and stays wet, which is why chronic leaks turn into deck replacement rather than a simple patch.
Also called: CDX plywood
Plywood is a cross-laminated wood sheathing used as roof decking, typically half-inch to three-quarter-inch, that holds screws well and tolerates a wetting event better than OSB.
A copper or premium standing seam roof is generally specified over kiln-dried plywood laid true, because the finished flatness of the deck shows directly in the finished flatness of the metal.
Also called: roof purlin
A purlin is a horizontal structural member spanning between rafters or frames that panels fasten to directly, used on metal buildings, barns, and pole structures instead of solid decking.
Panels over purlins have no continuous substrate behind them, so panel stiffness, gauge, and fastener spacing carry more of the load than they would over plywood.
Also called: ridge ventilation
A ridge vent is a continuous exhaust opening cut along the roof peak and covered by ridge cap, letting hot attic air escape at the highest point.
On metal roofs the ridge vent works with profile closures so the ridge breathes without admitting wind-driven rain, insects, or blowing snow.
Also called: slip sheet; red rosin
Rosin paper is a thin slip sheet laid between underlayment and metal so the panels can slide as they expand and contract without abrading or bonding to the layer beneath.
It appears most often under copper and in traditional sheet metal assemblies, where free movement of the pan is part of the design.
Also called: eave underside
The soffit is the underside of a roof overhang, and on a properly ventilated house it is where intake air enters the attic.
Vented metal soffit panels resist the rot and repainting that plague wood soffits. Whatever the material, the intake area behind it has to be open and baffled or the ventilation is decorative.
Also called: synthetic felt
Synthetic underlayment is a woven polymer sheet that replaces asphalt felt, offering better tear strength, better traction, and far better resistance to wrinkling when it gets wet.
For metal roofing the product also has to be rated for high temperature, because the underside of a metal panel in direct sun runs much hotter than the underside of a shingle roof.
Also called: roof underlayment
Underlayment is the water-resistant layer installed between the roof deck and the metal panels, the secondary barrier that protects the deck during installation and after any future breach.
Metal roofs get hot, so the correct product is a high-temperature synthetic or a high-temperature ice-and-water membrane rated for the panel type. Standard shingle felt is not appropriate under metal.
Also called: vapor retarder
A vapor barrier is a layer that slows water vapor from moving through an assembly, placed on the warm side so moisture does not reach a cold surface and condense.
On metal buildings and agricultural structures a vapor retarder under the panel is standard practice. On ventilated attics, air sealing the ceiling plane usually matters more than adding a membrane.
How metal roofing attaches to the building, and why the screw is the part that decides the life of an exposed fastener roof.
Also called: roofing screw
A fastener is the screw that holds roofing metal or its clips to the structure, chosen by substrate compatibility, length, thread type, and washer material rather than by price.
Wood-grip threads bite into decking; self-drilling points cut into steel purlins. A fastener that is galvanically incompatible with the panel will corrode at every hole, so fastener metal has to match panel metal.
Also called: EPDM washer; sealing washer
A neoprene or EPDM washer is the rubber gasket bonded under a roofing screw head that compresses to seal the hole the screw makes.
That washer is the entire waterproofing of an exposed fastener roof, and it is a rubber part in direct sunlight. Overdriving crushes it, underdriving leaves it loose, and ultraviolet exposure hardens it over decades.
Also called: S-5 clamp; non-penetrating clamp
A seam clamp is a machined bracket that grips a standing seam without penetrating the panel, providing an attachment point for solar racking, snow guards, walkways, or equipment.
Clamping to the seam is why standing seam is the best residential roof for solar: the array attaches with no hole through the panel, the underlayment, or the deck, so the roof warranty stays intact.
Also called: Tek screw; metal-to-metal screw
A self-drilling screw has a drill-point tip that cuts its own hole through steel purlins or girts, used on metal buildings and commercial panel work.
The point length has to match the steel thickness. A point too short work-hardens the hole and strips; too long and the threads engage before the hole is finished.
Also called: lap screw; sidelap screw
A stitch screw is a short fastener that joins two panels to each other at a sidelap rather than fastening them to the structure.
Stitch screws keep the lap tight so wind cannot lift the overlapping edge and drive water under it, and they are frequently left out on rushed exposed fastener installations.
Also called: wood screw; Type A point
A woodgrip screw is a roofing fastener with coarse threads made to hold in wood decking or framing rather than to drill through steel.
Used on residential exposed fastener roofs over plywood, OSB, or board decking. Length matters: the thread has to reach solid wood, not just skim the sheathing.
Also called: zinc-aluminum cap screw
A ZAC fastener is a roofing screw with a zinc-aluminum cap over the head, so the exposed part of the screw corrodes at the same rate as the panel around it instead of rusting first.
On a re-screw job the fastener choice is most of the value. Upgrading to ZAC fasteners with fresh EPDM washers is what turns a re-screw from a short-term fix into a long extension of service life.
The standards and ratings that appear in product literature and insurance paperwork, and what each one actually measures.
Also called: standing seam uplift test
ASTM E1592 is the uniform static air pressure test used to establish the structural performance and load capacity of standing seam metal roof systems, measuring deflection at multiple points as pressure increases.
It is the test data engineers use to size clip spacing and panel selection for a specific building, and it is what separates an engineered standing seam assembly from a panel simply installed to a rule of thumb.
Also called: UL 2218 Class 4; impact-resistant
Class 4 is the highest UL 2218 impact classification, earned when a covering withstands a 2 inch steel ball dropped from 20 feet twice in the same location without cracking, splitting, or opening.
Class 4 is a resistance rating, not a promise that a roof is hail proof, and it says nothing about denting. Many Tennessee insurers recognize Class 4 roofing, so keep the product documentation with your policy paperwork.
Also called: UL 90; Class 90 uplift
Class 90 is the highest standard UL 580 uplift class, and it does not mean the roof is rated for 90 mph wind, a confusion worth clearing up before comparing bids.
It means the assembly held 105 psf of combined differential pressure in a controlled test without failing. Actual wind performance depends on the building, its height, its exposure, and the fastening pattern used on the real roof.
Also called: Class A roof assembly
Class A is the highest roof covering fire classification under UL 790 and ASTM E108, indicating effective resistance to severe external fire exposure.
A metal roof earns Class A as a complete assembly, so the underlayment and deck build-up specified with it are what the rating depends on. Ask for the assembly documentation, not just the panel's rating.
Also called: reflective roof
A cool roof is a roof surface with high solar reflectance and high thermal emittance, meaning it both reflects sunlight and releases the heat it does absorb rather than passing it into the building.
Reflectance and emittance are measured properties, not marketing terms, and are published product by product by the Cool Roof Rating Council. Both initial and three-year aged values are listed, and aged values matter more.
Also called: cosmetic hail damage; denting
Cosmetic damage is surface marking such as dents or scuffs that changes how a roof looks without affecting its ability to shed water, and it is treated differently from functional damage by insurers.
Many policies now carry a cosmetic damage exclusion or a separate deductible for metal roofs. Functional damage means the roof has cracked, split, punctured, or lost water control, and that is the distinction a claim turns on.
Also called: Cool Roof Rating Council
The CRRC is the independent nonprofit that measures and publishes the solar reflectance and thermal emittance of roofing products, using accredited third-party laboratories rather than manufacturer testing.
CRRC listings publish both initial values and three-year aged values taken after real outdoor weathering, and the directory is public at coolroofs.org.
Also called: design wind load
Design pressure is the wind load a roof assembly must resist at a specific building, calculated from the code wind speed, building height, exposure category, roof shape, and zone of the roof.
For Metro Nashville and Davidson County the adopted residential design criteria list a 115 mph wind design speed. That is an input to the calculation, not a rating any particular roof automatically carries.
Also called: FM ice ball impact test
FM 4473 is an impact test that fires molded ice balls at a roof surface, an alternative to UL 2218 intended to represent hail more realistically than a steel ball.
Both standards appear in product literature. When comparing two products, check which test each was rated under before treating the classes as equivalent.
Also called: FM Global approval
FM Approved means a roofing assembly has been tested and listed by FM Approvals, a certification frequently required by commercial property insurers.
FM listings cover wind uplift, fire, hail, and corrosion in defined assembly configurations, and the approval belongs to the assembly as tested rather than to a single component.
Also called: performance damage
Functional damage is damage that compromises a roof's ability to keep water out, such as punctures, splits, opened seams, displaced panels, or failed flashings.
It is the category insurance policies are written to cover, and it is what a documented inspection sets out to establish, photograph, and describe in terms an adjuster can act on.
Also called: albedo; SR
Solar reflectance is the fraction of sunlight a roof surface reflects rather than absorbs, measured from 0 to 1 under standards such as ASTM C1549.
Higher reflectance means less heat entering the assembly. It falls in the first years as the surface weathers and soils, which is why the aged value is the honest number to compare.
Also called: Solar Reflectance Index
SRI, the Solar Reflectance Index, combines solar reflectance and thermal emittance into a single number calculated under ASTM E1980, where a standard black surface is 0 and a standard white surface is 100.
SRI is the figure most often written into green building requirements and specifications, because it captures both properties in one comparable value.
Also called: emissivity; TE
Thermal emittance is how efficiently a surface radiates absorbed heat back away from itself, measured from 0 to 1 under standards such as ASTM C1371.
Reflectance and emittance work together: bare metal can reflect well but emit poorly, while a coated surface can do both. That pairing is why a coating changes rooftop temperature more than color alone suggests.
Also called: uplift test to failure
UL 1897 is an uplift test for roof covering attachment that is run all the way to failure and reports the maximum uplift pressure the assembly reached.
Where UL 580 answers whether an assembly passes a class, UL 1897 answers how far it actually goes, which is the more useful number when an engineer is matching an assembly to a calculated design pressure.
Also called: impact resistance classification; hail rating
UL 2218 is the steel ball impact standard that classifies roof coverings from Class 1 to Class 4 by dropping steel balls of increasing size from increasing heights, twice in the same spot.
Class 1 uses a 1.25 inch ball from 12 feet, Class 2 a 1.5 inch ball from 15 feet, Class 3 a 1.75 inch ball from 17 feet, and Class 4 a 2 inch ball from 20 feet. Failure means tearing, cracking, splitting, or an opening through the material; cosmetic denting on the surface does not count.
Also called: uplift resistance test; Class 30 60 90
UL 580 is a laboratory uplift test that classifies roof deck assemblies as Class 30, 60, or 90 by applying combined positive and negative pressure to a test deck.
Class 90 corresponds to 48.5 psf of pressure from below combined with 56.5 psf of vacuum from above, a 105 psf combined differential. The test stops at the class limit rather than running to failure, and the class number is not a wind speed.
Also called: fire classification test; Class A fire rating
UL 790 and ASTM E108 are the test methods that classify roof coverings as Class A, B, or C for external fire exposure, with Class A the highest.
Metal itself is noncombustible and will not ignite from embers or radiant heat, but a Class A rating belongs to a tested assembly, not a bare panel. The deck, underlayment, and any layer beneath are part of the classification.
Also called: basic wind speed; 115 mph
Wind design speed is the code wind velocity a structure must be designed for in a given location, listed as 115 mph in the adopted residential design criteria for Metro Nashville and Davidson County.
A design speed is not a guarantee and it is not a product rating. It is the starting number an engineer uses to calculate the actual pressures a roof assembly has to resist at a specific site.
Also called: uplift pressure
Wind uplift is the suction that develops above a roof as air accelerates over it, pulling the roofing upward rather than pushing it down, and it is the force roof attachment is designed against.
Uplift is highest at corners, then edges, then the field of the roof, which is why fastener and clip spacing is tightened at perimeters. Most wind damage starts at an edge and unzips inward.
Flat and near-flat roofing: membranes, coatings, drainage, and the parts of a commercial roof metal does not cover.
Also called: elastomeric acrylic
Acrylic roof coating is a water-based liquid membrane that is inexpensive, easy to apply, and easy to clean up, but vulnerable to standing water because it can re-emulsify.
Acrylics perform reasonably on sloped metal with good drainage in drier climates. In Middle Tennessee's rainfall, humidity, and ponding conditions, silicone is generally the more durable specification.
Also called: coping cap; wall cap
Coping is the metal cap that covers the top of a parapet wall, shedding water to both sides and protecting the wall assembly beneath.
Coping joints move with temperature, so they use splice plates and concealed cleats rather than face fasteners and caulk.
Also called: equipment curb; roof curb
A curb is a raised frame built up from the roof deck to carry rooftop equipment such as an HVAC unit or a skylight, raising the connection above the water plane.
Curbs need proper height, a cricket on the upslope side when wide, and flashing that laps correctly. On commercial roofs, curbs and the technicians who service them are behind a large share of leaks.
Also called: rubber roof; ethylene propylene diene monomer
EPDM is a synthetic rubber single-ply membrane, usually black, joined with tape and adhesive rather than heat welding, and long the dominant flat roof material before TPO.
Its dark surface absorbs summer heat rather than reflecting it, and its seams are adhesive-dependent, which is where aging EPDM roofs typically begin to fail.
Also called: hot air weld; welded seam
A heat weld is a seam made by melting two thermoplastic membrane sheets together with hot air so they fuse into a single material, the standard seaming method for TPO and PVC.
A correctly welded seam is as strong as the sheet itself and is verified by probing it after it cools. Cold welds and skipped probe testing are behind most early single-ply failures.
Also called: low-pitch roof
A low-slope roof is generally one below 3:12, where water drains slowly enough that the roof must be closed against standing and wind-driven water rather than relying on runoff.
Below roughly 3:12 the choices narrow to mechanically seamed standing seam, a single-ply membrane like TPO or PVC, modified bitumen, or a qualified coating restoration. Exposed fastener panels do not belong there.
Also called: DFT; dry film thickness
Mil thickness is the applied depth of a roof coating measured in thousandths of an inch, specified as dry film thickness because the wet coat shrinks as it cures.
Coating warranties are written around a minimum dry film thickness, and verified thickness is what separates a warranted restoration from a thin coat of paint on a roof.
Also called: mod bit; torch-down
Modified bitumen is asphalt roofing reinforced with rubber or plastic modifiers and installed in overlapping plies, applied by torch, hot asphalt, or self-adhering backing.
It is a proven low-slope system still found on many older Nashville commercial buildings, and it is commonly a candidate for coating restoration rather than full replacement when the plies are still sound.
Also called: parapet wall
A parapet is a low wall extending above the roof line around the edge of a flat roof, requiring its own coping cap and flashing where the membrane turns up the wall.
Parapet tops and inside corners are among the most leak-prone locations on a commercial roof, and coping joints are a common place for water to enter and travel unseen.
Also called: polyvinyl chloride membrane
PVC is a heat-welded single-ply roofing membrane that uses plasticizers to stay flexible and carries stronger chemical resistance than TPO, at a higher cost per square.
PVC is the specification where grease, oils, or chemical exhaust reach the roof, notably over restaurant kitchens.
Also called: roof recover; overlay
A recover is installing a new roof system over an existing one on a commercial building without tearing off, permitted by code only up to a limited number of existing layers.
Recovers are cheaper and faster than a tear-off but they trap whatever moisture is in the existing insulation, so a moisture survey should come before the decision.
Also called: restoration coating; roof restoration
A roof coating is a liquid-applied membrane rolled or sprayed over an existing roof to restore its watertight surface and reflectivity without a tear-off.
Coating works when the substrate is sound and the problem is surface-level wear. It cannot rescue saturated insulation, failed seams throughout, or a deck that has already gone soft.
Also called: interior drain; scupper
A roof drain is the outlet that removes water from a low-slope roof, either an interior drain piped through the building or a scupper through a parapet wall.
Drains need clamping rings, strainers, and a sump so water reaches them, plus an overflow path required by code in case the primary blocks. Blocked drains are a leading cause of ponding and structural overload.
Also called: 100% silicone roof coating; ASTM D6694
Silicone roof coating is a moisture-cured liquid membrane specified under ASTM D6694 that holds up to standing water and ultraviolet exposure better than acrylic, making it the usual choice for humid, rainy climates.
Silicone does not re-emulsify when ponded water sits on it, which is the failure mode that limits acrylics on near-flat roofs. It is also the harder of the two to walk on when wet and requires clean, properly prepared substrate.
Also called: single ply roofing
A single-ply membrane is a flat roof covering installed as one layer of manufactured sheet material, including TPO, PVC, and EPDM, as opposed to built-up multi-ply systems.
Single-ply is attached by mechanical fasteners, adhesive, or ballast, and the attachment method is chosen based on wind design pressure and deck type.
Also called: tapered system; crickets and saddles
Tapered insulation is rigid board cut in a slope pattern and laid over a flat deck to build drainage into a roof that has none, directing water toward drains.
It is the durable answer to chronic ponding on a dead-flat commercial roof, and it is designed as a layout drawing rather than field-improvised.
Also called: thermoplastic polyolefin
TPO is a single-ply thermoplastic roofing membrane made from polypropylene and ethylene-propylene rubber, heat-welded at the seams and the most widely installed flat roof membrane in the United States.
On Nashville commercial buildings TPO usually covers the flat sections while metal covers the steep ones. Its seams are welded rather than taped, which is why weld quality determines the roof's real service life.
The failure modes we are called out for, and the conditions homeowners mistake for leaks.
Also called: capillary draw; wicking
Capillary action is water travelling uphill through a narrow gap between two surfaces, and it is how a metal roof leaks on a low slope even when gravity says it should not.
Tight laps, seams, and unhemmed edges are all capillary paths. Anti-capillary hems, sealant tape in the seam, and taller seams are the standard defenses, and they matter more as slope goes down.
Also called: paint chalk
Chalking is the powdery residue that forms on a painted metal roof as ultraviolet light breaks down the resin at the paint surface and releases loose pigment.
It shows up as a dull, washed-out look and a white film on your hand. Chalking and fading are the two measurements paint warranties are actually written around, and PVDF resists both far longer than SMP.
Also called: attic moisture; sweating roof
Condensation is water forming on the underside of a roof deck or panel when warm moist air meets a surface below its dew point, and it is frequently mistaken for a leak.
Condensation shows up as widespread damp with no single source, often worst on cold clear nights. The fix is ventilation, air sealing, and vapor control, not more sealant on the roof.
Also called: blind valley; low-slope valley
A dead valley is a low or nearly flat area where roof planes meet in a way that gives water nowhere to drain quickly, and it is one of the most reliable leak sources on a house.
Dead valleys are solved with a cricket, a rebuilt slope, a soldered or welded metal pan, or a membrane section, never with sealant and hope.
Also called: condensation point
Dew point is the temperature at which air becomes saturated and releases its moisture as liquid water, the threshold that determines where condensation forms in a roof assembly.
Assemblies are designed so the dew point falls inside insulation or ventilated space rather than on a cold metal surface where water can collect and drip.
Also called: color change; Delta E
Fading is measurable loss of color on a painted metal roof over time, reported in paint warranties as a maximum color change over a stated number of years.
Saturated reds, blues, and dark bronzes fade fastest because their pigments are the most vulnerable to ultraviolet light, which is exactly why those colors should be specified in PVDF rather than SMP.
Also called: screw backout; backing out
Fastener backout is screws working their way loose over years of thermal expansion and contraction, the defining maintenance item of an exposed fastener metal roof.
A backed-out screw stands proud of the panel with its washer no longer compressed, so the hole is open. Left alone the hole enlarges and the fix moves from re-driving to oversized fasteners or panel replacement.
Also called: granule shedding
Granule loss is the shedding of surface granules from asphalt shingles or stone-coated steel, exposing the material beneath to ultraviolet light.
On asphalt it is a primary aging indicator and shows up as grit in gutters. On stone-coated steel the steel beneath is still protected, so the consequence is cosmetic rather than structural.
Also called: hail damage
Hail is frozen precipitation that strikes a roof with enough kinetic energy to dent metal and, at larger sizes, to fracture or puncture roofing materials.
On metal roofs the practical question after a storm is whether the damage is cosmetic or functional, since metal frequently dents while continuing to shed water perfectly. That distinction drives both the repair scope and the insurance claim.
Also called: ice damming
An ice dam is a ridge of ice at the eave formed when snow melts on a warm upper roof and refreezes over the cold overhang, backing water up under the roofing.
Ice dams are less frequent in Middle Tennessee than further north but do occur in ice storms. The defenses are ice-and-water membrane at the eaves, real attic ventilation, and a sealed, insulated ceiling plane.
Also called: stress wrinkling; waviness
Oil canning is visible waviness in the flat area of a metal panel, a cosmetic condition inherent to light-gauge formed metal and not a defect that causes leaks.
It is managed rather than eliminated: heavier gauge, narrower panels, striations or pencil ribs in the pan, a matte or low-gloss finish, a flat deck, and careful handling all reduce how visible it is. Nearly every metal roof manufacturer states plainly that oil canning is not a cause for rejection.
Also called: standing water
Ponding is water that remains on a low-slope roof more than 48 hours after rain stops, a sign of inadequate slope, deflected deck, or blocked drainage.
Ponding accelerates membrane and coating breakdown, adds structural load, and voids many warranties. The fix is usually tapered insulation or drainage correction, not a thicker coating over the puddle.
Also called: re-fastening; screw replacement
A re-screw is replacing every fastener on an exposed fastener roof, typically with upgraded ZAC screws and fresh washers, to restore the seal at each hole.
It is a service-life extension for a panel that is still sound, and it is priced per square rather than per screw. If holes have already elongated, the replacement fasteners are stepped up in diameter.
Also called: deck telegraphing; read-through
Telegraphing is when irregularities in the deck or in an old roof beneath show through the finished metal panels as visible ridges, dips, or lines.
It is the strongest technical argument against installing metal over old shingles: the shingle texture reads straight through the new panel and cannot be corrected afterward.
Also called: heat bridge
Thermal bridging is heat taking a shortcut through a conductive path such as a fastener or framing member, bypassing the insulation around it.
On roofs, bridging shows up as frost or condensation lines that trace the framing, and as visible melt stripes in snow directly above rafters or purlins.
Warranties, insurance, permits, approvals, and the documents that decide what a roof is worth years later.
Also called: claims adjuster; field adjuster
An adjuster is the insurance company representative who inspects the damage, writes the scope of loss, and sets what the carrier will pay.
A contractor meeting the adjuster on the roof is how disagreements about scope get resolved on the spot rather than through weeks of correspondence.
Also called: contract change; extra work order
A change order is a written amendment to a roofing contract adding or altering work and its price after the original agreement is signed.
Legitimate change orders come from genuine discoveries such as rotten decking. A pattern of change orders on items that should have been in the original scope is a sign the estimate was incomplete.
Also called: ordinance and law; code compliance item
A code upgrade is work required by current building code that the original roof did not have, such as added ice-and-water membrane, drip edge, or ventilation.
Some policies include ordinance and law coverage for these items and some do not. Metro Nashville adopted the 2024 International Codes for plans and applications submitted after July 16, 2025.
Also called: roof condition assessment; RCA
A condition report is a written commercial roof assessment describing the existing system, its remaining service life, its defects, and the options with budget ranges for each.
Buyers, lenders, and property managers use condition reports for due diligence and capital planning, and a report that ends in one recommendation with no alternatives is a sales document, not an assessment.
Also called: deck repair allowance; per-sheet allowance
A decking allowance is a line on a roofing estimate that prices deck replacement per sheet, covering rotten or damaged sheathing that is only visible once the old roof comes off.
An estimate with no decking allowance is not cheaper, it is incomplete: the same repair becomes a change order at whatever price is quoted mid-project. Ask for the per-sheet number in writing before work starts.
Also called: policy deductible; wind and hail deductible
A deductible is the portion of a covered loss the property owner pays, and many Tennessee policies now apply a separate, larger percentage deductible for wind and hail.
A percentage deductible is calculated on the insured value of the home, not on the claim, so it can be far larger than the flat deductible owners expect. It is worth reading before a storm, not after.
Also called: historic overlay; preservation district
A historic district is an area where exterior changes, including roofing material, profile, and color, require review by a preservation commission before work begins.
Metal is often welcome in historic review because it is historically accurate for many Middle Tennessee building types; the debate is usually about profile and finish sheen rather than the material itself.
Also called: architectural review; ARC submittal
HOA approval is written permission from a homeowners association's architectural committee to install a specific roof color, profile, and material.
Many association rules were written when metal roof meant corrugated barn panel. A submittal with product photographs, a physical sample, the profile specification, and neighborhood precedent is what changes those conversations.
Also called: storm claim; roof claim
A roof insurance claim is a request for coverage after storm damage, which turns on documenting functional damage, matching it to the policy language, and pricing the repair or replacement correctly.
Documentation carries a claim: dated photographs, a written scope, product specifications, and a clear account of what failed and how. Cosmetic exclusions and separate wind and hail deductibles are increasingly common on Tennessee policies.
Also called: material warranty; finish warranty
A manufacturer warranty covers the roofing material and its finish against defined defects such as perforation, chalking, and fading, on terms set by the manufacturer.
Read what is actually covered and for how long. Finish warranties are usually written around specific measurable limits for chalk and color change, and often exclude cosmetic denting entirely.
Also called: roof condition report; roof assessment
A metal roof inspection is a documented assessment of panel, seam, fastener, flashing, penetration, and ventilation condition, delivered as a written report with photographs.
On metal roofs the inspection concentrates where failures actually occur: penetrations, transitions, terminations, fasteners, and sealant, rather than the open field of panel.
Also called: full-value warranty
A non-prorated warranty covers the same value for the whole term rather than declining with the roof's age.
It is the stronger structure and the one worth confirming in writing, along with exactly what triggers coverage and who performs the remedy.
Also called: roofing permit; building permit
A permit is the municipal authorization required for roofing work above a defined scope, pulled before the job and closed out with an inspection afterward.
Metro Nashville defines normal maintenance repairs to include roof repairs that do not exceed 33 percent of the roof area. Larger residential work, commercial roofs, structural changes, and historic overlays follow the permit path.
Also called: declining coverage
A prorated warranty pays out less as the roof ages, reducing the covered amount year by year rather than covering the full cost throughout the term.
A long prorated term can be worth far less in practice than a shorter non-prorated one. The question to ask is what the warranty pays in year fifteen, not what the cover page says.
Also called: recover; metal over shingles
A roof-over is installing new roofing on top of the existing roof without tearing off, sometimes code-legal but generally the weaker choice under metal.
It traps moisture between two roof layers, telegraphs the old texture through the new panels, leaves soft decking undiscovered, and adds weight metal was supposed to remove. Codes also commonly cap a roof at two layers.
Also called: claim scope; estimate of loss
A scope of loss is the itemized list of damaged components and required work that an insurance estimate is built from, line by line.
Most claim disputes are scope disputes rather than price disputes: whether a component is included at all, not what it costs.
Also called: expected lifespan
Service life is how long a roof system can be expected to perform before replacement, measured in decades for metal and in years for asphalt in the Middle Tennessee climate.
Concealed-fastener metal systems are the long end of the range, exposed-fastener panels are shorter and maintenance-dependent, and asphalt in Tennessee heat typically runs a fraction of either.
Also called: pitch; rise over run
Slope is the rise of a roof in inches over 12 inches of horizontal run, written as ratios like 3:12 or 6:12, and it is the first number that decides which roof systems are even allowed.
As slope drops, water spends more time on the roof and works harder at seams, laps, and flashings. Steep roofs shed fast and forgive more; low slopes rely on seam closure, underlayment, and flashing discipline instead of gravity.
Also called: roofing square
A square is the roofing industry's unit of area, equal to 100 square feet of roof surface, and it is how metal roofing is priced and ordered.
A 2,000 square foot roof is 20 squares. Quotes given per square are directly comparable across contractors; quotes given as a lump sum are not, unless the square count is stated.
Also called: steep-pitch roof
A steep-slope roof is one pitched enough that water sheds quickly by gravity, generally 3:12 and above, which is where shingles and exposed fastener metal panels are appropriate.
Most Middle Tennessee houses are steep-slope over the main body with one or two low-slope sections over porches, additions, or dormers, and those low sections usually decide the whole roofing plan.
Also called: claim supplement
A supplement is a request to the insurer to add items or cost to an approved claim after conditions are discovered that the original scope missed.
Deck damage found at tear-off, code-required upgrades, and overlooked flashings are typical supplement items, and they are documented with photographs and code citations.
Also called: strip; removal
Tear-off is removing the existing roof down to the bare deck before installing the new one, which is the only way to inspect and repair the sheathing underneath.
It costs money and dumpster space and it is what a genuinely complete estimate includes. The alternative, a roof-over, buries whatever is wrong with the deck under new metal.
Also called: infrared roof scan; IR survey
Thermal imaging is an infrared survey of a roof that reveals trapped moisture, missing insulation, and heat loss by mapping surface temperature differences invisible to the eye.
Wet insulation holds heat longer than dry insulation, so it glows on an evening scan. It is the diagnostic that answers whether a flat roof can be coated or has to be replaced.
Also called: assignable warranty
A transferable warranty can be passed to the next owner of the home, usually once and often within a stated window after the sale.
It is a real asset at resale because it converts an invisible roof upgrade into documentation a buyer's agent can point at during negotiation.
Also called: roof warranty
A roof warranty is the written promise covering either the material or the installation, and the two are separate documents with separate terms, durations, and exclusions.
A complete roofing file holds both, plus the product data sheets, the impact and fire documentation, the permit close-out, and photographs of the completed work.
Also called: cut waste; overage
Waste factor is the extra material ordered beyond the measured roof area to cover cuts, hips, valleys, and mistakes, expressed as a percentage added to the square count.
A simple gable roof wastes very little. A cut-up roof with multiple hips, valleys, and dormers wastes far more, which is one reason complexity raises the price per square and not just the total.
Also called: labor warranty; installation warranty
A workmanship warranty covers the contractor's installation, as distinct from the manufacturer's warranty on the material itself, and it is the one that answers a leak.
Most roof problems in the first decade are installation problems, not material defects, which is why the workmanship term matters more than the headline number on the panel warranty.
This glossary is maintained by the people who install the roofs, not a marketing department.