What Is Metal Roofing?

What metal roofing is

A metal roof is a roof whose top, weather-facing layer is metal. That layer is called the roof covering.

Under it sit the same parts any roof has: the deck (the plywood or boards on the rafters) and the underlayment (a sheet that acts as a second line of defense against water).

The code requires underlayment under metal panels and metal shingles, just as it does under other coverings ¹.

People often say "tin roof," but modern home roofs are almost never tin. Most are steel with a zinc or zinc-aluminum coating and a paint finish. Aluminum, copper and zinc are the other common metals.

Each one behaves a little differently in salt air, in hail and as it ages, which is why the metal matters as much as the panel shape.

Metal roofing also comes in many looks. The Metal Roofing Alliance lists vertical panels, metal shingles, and panels made to look like slate, tile or shake ³. So a metal roof does not have to look like a barn.

How a metal roof keeps water out

Metal itself does not leak. Water gets in at the places where pieces meet or where something goes through the metal. So every metal roof system is really a plan for its joints and fasteners.

On a lapped panel, one panel overlaps the next, and screws pass through both into the deck or into wood strips called purlins. Water runs over the laps.

If the roof is fairly flat, water can sit at those laps, so the code asks for sealant in the laps on lower slopes ¹.

On a standing seam panel, the edges of two panels rise up and lock together in a seam that stands above the water.

Hidden clips hold the panel to the deck, so no screw goes through the part of the panel that carries water.

Metal also grows and shrinks with heat and cold. A long panel can change length during the day. Standing seam clips are made to let the panel slide a little.

Exposed screws, by contrast, hold the panel tight in one spot, so the screw hole works back and forth over the years. That movement is one reason the washers under those screws wear out.

Types of metal roofing: exposed-fastener vs standing seam vs shingles

Most home metal roofs fall into one of three types. The slope rules come from the 2021 International Residential Code ¹.

Corrugated metal is the wavy kind of exposed-fastener panel. Ribbed panels with flat areas between the ribs are a newer shape of the same family.

Sources: [1]

The metals compared: steel, aluminum, copper and zinc

The panel shape and the metal are two separate choices. This table describes how each metal is known to behave. It gives no lifespans, because those depend on the coating, the climate and the maker.

Mixing metals needs care. The Metal Construction Association warns that some metals do not perform well in contact with certain other metals, and that the wrong fastener can cause the same kind of corrosion ⁵.

Roofing screws on exposed-fastener panels

Roofing screws are the fasteners on exposed-fastener metal roofs. Each one has a rubber or rubber-like washer under its head. When the screw is driven to the right depth, the washer squeezes against the panel and seals the hole.

Two things go wrong. If the screw is driven too tight, the washer is crushed and splits. If it is too loose or crooked, the washer never seals.

Over time, sun and heat also dry out the washer, and the panel moving back and forth can loosen the screw. A leak around a screw is one of the most common metal roof repairs.

The code says fasteners must match the metal: galvanized fasteners for steel, copper, brass or stainless for copper, and stainless steel is allowed with any of them ¹.

Using the wrong metal can lead to the corrosion the Metal Construction Association warns about ⁵. Ask your roofer what screw they plan to use and whether it is the one the panel maker calls for.

Worked example: which types does the code allow on three roofs?

Three illustrative roofs, matched to the 2021 IRC slope limits ¹. Learn how slope is written on our roof pitch page.

Slopes are rise in inches for each 12 inches of level run. A roof flatter than ¼ inch per foot cannot take any of these metal coverings under the code; it needs a low-slope membrane instead. The panel maker's own minimum can be higher than the code's, and the higher number wins.

Where metal roofing is used

Metal shows up on almost every kind of building. On homes, it covers whole roofs, porch roofs, and small accent areas like bay windows.

Standing seam is a common pick for low-slope sections, because the code lets it go down to ¼ inch per foot ¹.

Exposed-fastener panels are common on barns, sheds, garages and many rural homes.

Metal is also used where other materials struggle. Aluminum is chosen near the ocean because it does not rust.

Steel and copper are common where wildfire is a concern, because metal sheets on a noncombustible deck are a Class A fire covering under the code ².

And in snowy places, a smooth metal surface lets snow slide off, which is helpful but also means you may need snow guards over doors and walkways.

Benefits of metal roofing

• Long service life. The Metal Roofing Alliance puts metal roofs at 30 to 50+ years, against 12 to 20 years for asphalt roofs ³. That is the trade group's figure, not a warranty.
• Fire resistance. Metal sheets and shingles on a noncombustible deck are a Class A covering, the highest class ².
• Low-slope option. Standing seam can go on roofs as flat as ¼ inch per foot, where shingles cannot go ¹.
• Cool roof finishes. The Department of Energy lists metal products among cool roof options for both low-slope and steep roofs ⁶.
• Recycled content. The Metal Roofing Alliance says metal roofs contain at least 25% recycled material, depending on the metal ³.
• Less tear-off waste. Metal can often go over an existing roof where the code and the maker allow it, which avoids a dumpster of old shingles ³.

Limitations of metal roofing

• Higher first cost than asphalt shingles on most homes. The Metal Roofing Alliance compares its price to tile or cedar shake, not to asphalt ³.
• Oil canning. Flat areas of a panel can show waves, especially in low sun. The Metal Construction Association says no maker or installer can promise to prevent it fully ⁴.
• Denting. Softer metals like aluminum and copper can dent in large hail.
• Screw upkeep. Exposed-fastener roofs have many washers that age and need checking.
• Fewer skilled installers. Standing seam, copper and zinc need crews who do that work often.
• Snow slides. Snow can slide off in one sheet; snow guards may be needed over doors, decks and lower roofs.

What drives the cost of a metal roof

We do not quote prices here. These are the things that move a metal roof quote up or down. To see numbers for your roof, use the metal vs asphalt calculator.

• Panel type. Standing seam takes more labor and trim than exposed-fastener panels.
• Metal. Copper and zinc sit well above coated steel and aluminum.
• Thickness. Thicker metal (a lower gauge number on steel) costs more and dents less.
• Paint finish. Higher-grade finishes hold their color longer and cost more.
• Roof shape. Valleys, dormers, skylights and chimneys each need custom trim and flashing.
• Roof size. Measured in roofing squares of 100 square feet each.
• Tear-off or recover. Removing the old roof adds labor and disposal; going over it adds battens or other prep.
• Underlayment. Some metal systems call for a high-temperature underlayment under the panels.

How a metal roof is installed

This is what you should see happen. It is not a do-it-yourself guide. Roof work is a fall risk, and a licensed roofer should do it.

1. The crew checks the slope against the code and the panel maker's minimum for the panel chosen ¹.
2. The old roof is torn off, or prepared for a recover if the code and the maker allow it.
3. The deck is checked and repaired. Metal panels can go on solid or spaced sheathing, but metal shingles need a solid or closely fitted deck ¹.
4. Underlayment goes down, plus an ice barrier at the eaves where the local code requires one.
5. Eave trim goes on first, doing the same job a drip edge does on shingles.
6. Panels go on with clips or screws, using fasteners that match the metal ¹.
7. Valley, wall, chimney and vent flashings go in, then the ridge cap and rake trim.

The layer diagram shows what the crew builds in the steps above: each layer is a backup for the one on top of it.

Caring for a metal roof

• Have a roofer look at the roof after big storms and every few years, from a ladder or with a drone.
• On exposed-fastener roofs, ask for a screw check: cracked, dried or crushed washers and backed-out screws.
• Keep valleys and gutters clear of leaves, which hold water against the metal.
• Keep tree branches off the roof; rubbing wears through the paint.
• Touch up deep scratches on steel with the maker's touch-up paint so rust does not start.
• Do not let a satellite or solar installer screw through panels without a sealed, approved mount.
• Do not walk the roof yourself; metal is slick, and the wrong step can dent panels.

Warning signs and problems to watch

• Water stains on the ceiling under rows of screws, a sign of failed washers
• Rust at cut panel edges, around screws, or where copper water drips onto steel or aluminum
• Panels lifted at the edges after high wind
• Loose or missing ridge cap and trim
• Gaps in flashing around chimneys, skylights and vent pipes
• Steel panels touching treated lumber, which the Metal Construction Association flags as a corrosion risk ⁵

Each sign points to a possible cause, not a diagnosis. Only an inspection confirms what is wrong.

What the building code says about metal roofs

These rules come from the 2021 International Residential Code, read as adopted in Maryland. Most states adopt the IRC, sometimes with changes, so your building department's edition is the one that applies.

Sources: [1] [2]

Metal roofing vs other roof coverings

Asphalt and tile slopes are from the same chapter of the 2021 IRC; fire classes from R902.1 ^{1 2}. Compare costs over time on the roofing materials guide.

Common misconceptions

Myth Metal roofs are loud in the rain.

Reality The Metal Roofing Alliance says there is little difference between metal and other materials for rain or hail noise, once the roof has a deck, underlayment and an insulated attic under it ³.

Myth Metal roofs attract lightning.

Reality We found no code rule treating metal roofs as a lightning risk. The trade groups say metal is no more likely to be struck; the code does not address it.

Myth All metal roofs rust.

Reality Aluminum, copper and zinc do not rust the way bare steel does, and coated steel resists rust until the coating is broken.

Myth A tin roof and a metal roof are the same thing.

Reality Modern home metal roofs are coated steel, aluminum, copper or zinc, not tin.

Myth Standing seam and corrugated are just two styles.

Reality They are different systems: one hides its fasteners under seams, the other screws through the face. The code gives them different slope limits ¹.

Local codes and climate

The rules on this page come from the 2021 International Residential Code. States, counties and cities adopt the code on their own schedule and can amend it. Your building department decides which edition applies, whether a permit is needed, and whether a metal roof can go over your existing one.

Climate matters too. In wildfire areas, local rules may require a Class A roof assembly, which metal on a noncombustible deck meets ².

In cold areas, the eaves may need an ice barrier and snow guards may be wise.

Near the coast, ask about aluminum and about wind ratings, because the code ties underlayment type to wind design areas ¹.

In hot areas, the Department of Energy notes that cool roofs save the most in hot and warm climates, while in winter a cool roof can raise heating needs a little ⁶.

Is metal roofing right for you?

• Metal is worth a close look if you plan to stay in the home a long time, live in a wildfire or heavy-snow area, or have a low-slope section shingles cannot cover.
• Pick standing seam if you want fewer holes and less upkeep; pick exposed-fastener panels if first cost matters most and you will keep up with screw checks.
• Pick the metal for your site: aluminum near salt water, coated steel for most homes, copper or zinc for looks and long life.
• Ask every roofer for the panel type, metal, thickness, finish, screw or clip type, and underlayment in writing.
• Run your numbers in the metal roof payback calculator before you decide.

Keep going

• Roof material selectorCompare metal with other roof coverings for your home
• Roof replacementWhat a full reroof involves
• Roof pitch calculatorCheck your slope against the metal limits
• Roof repairFixing leaks at screws, seams and flashing

Related terms

Standing Seam Metal Roof

A standing seam metal roof is a metal roof made of long panels whose edges rise up and join in raised seams, with hidden clips under the seams holding the panels to the roof deck, so no screw passes through the flat part that carries water.

Roof Pitch

Roof pitch is the steepness of a roof, written as the inches it rises for every 12 inches it runs horizontally, so a 6/12 roof climbs 6 inches per foot.

Roof Underlayment

Roof underlayment is a sheet laid over the whole roof deck before the shingles or other roof covering go on.

Roof Flashing

Roof flashing is thin, water-shedding material, usually bent metal, installed at the joints of a roof where shingles alone cannot keep water out: along walls, around chimneys and pipes, in valleys and at the roof edges.

Roofing Square

A roofing square is a unit of area equal to 100 square feet of roof surface, a 10-by-10-foot patch, and it is the unit in which shingles are sold and most roofing quotes are priced.

Ice and Water Shield

Ice and water shield is a self-adhering, rubberized asphalt membrane laid directly on the roof deck under the roof covering, where it seals around nails and blocks water that ice dams or wind-driven rain push back under the shingles.

Drip Edge

Drip edge is a strip of bent metal flashing installed along a roof's eaves and rake edges that carries water off the edge of the roof and away from the fascia and the deck beneath.

Asphalt Shingles

Asphalt shingles are roofing pieces made from a fiberglass mat coated with asphalt and topped with mineral granules, laid in overlapping rows so water runs off the roof.

Also referenced from: Roof Pitch, Low-Slope Roof, Impact-Resistant Shingles, Standing Seam Metal Roof, Slate Roofing, Clay Tile Roofing, Composite Roofing, Solar Shingles, Roof Wind Uplift, Roof Life Expectancy