Metal Roof Myths: Noise, Lightning, Rust, Heat and Cell Signal

Most of what people worry about with metal roofs comes from barns and sheds, not houses. A metal roof installed over a solid deck with underlayment and an insulated attic is about as quiet as any other roof, it does not attract lightning, and modern coatings keep steel from rusting for decades. Here is the truth behind each common metal roof myth, from noise and lightning to rust, heat and cell signal.

Myth: metal roofs are loud in the rain

The sound you are picturing comes from a pole barn, where thin panels are screwed to purlins with open air underneath and the whole roof acts like a drum. Houses are built differently. The panels rest on a solid deck of plywood or boards, there is an underlayment between the two, and under the deck sit rafters, an attic, a thick layer of insulation and a drywall ceiling. Each layer absorbs sound, and by the time rain noise reaches the living room it is no louder than it was with shingles. Many homeowners say they notice it less.

What actually controls roof noise

Three things: a solid deck, an underlayment and attic insulation. If you have a vaulted ceiling with no attic, ask the installer about a thicker underlayment or a sound-deadening layer, and expect rain to sound about as it does on any roof over a cathedral ceiling. Metal roofs installed over an old shingle roof are quieter still, since the shingles add mass. The style of panel matters very little. For what belongs under the metal, see our underlayment and ventilation guide.

Myth: metal roofs attract lightning

Lightning looks for the shortest path from the cloud to the ground, which means the tallest object in the area or whatever offers the most direct route: a tree, a chimney, a utility pole, a hilltop. It does not shop for materials. A metal roof on a house is no more likely to be struck than a shingle roof on the same house, because the roof’s height and surroundings decide the odds, not its surface.

If lightning does strike, metal is the better surface to be hit. Metal does not burn, so there is no fuel at the point of contact, and because the whole roof is conductive the energy spreads across a large area instead of concentrating on one spot the way it does on wood or shingles. Fire from a lightning strike is less likely with a metal roof, not more.

If you want lightning protection anyway

Homes on exposed hilltops, in open country or in regions with heavy thunderstorm activity sometimes add a lightning protection system of air terminals, conductors and ground rods. These systems are installed to the NFPA 780 standard and UL 96A by specialty contractors, and they work with any roof type. A metal roof does not need to be grounded to be safe, and a roofer who sells you a grounding kit as a requirement is selling you something you do not need. More on fire and roofs in our metal roofs and fire guide.

Myth: metal roofs rust

Bare steel rusts. Roofing steel is not bare. It is coated at the mill with either zinc, called galvanized, or with Galvalume, an alloy of about 55 percent aluminum and 45 percent zinc that protects steel exceptionally well, and then it is painted with an SMP or PVDF paint system on top. Quality painted steel roofs are commonly expected to last 40 to 70 years, and the paint finish itself typically carries a 25 to 40 year warranty against chalk and fade. Aluminum, copper, zinc and stainless steel do not rust at all.

Where rust actually shows up

• Cut edges and deep scratches, where the coating is broken; good installers hem exposed edges and use touch-up paint sparingly on scratches.
• Dissimilar metals in contact. Copper flashing, copper pipes or copper gutters draining onto steel or aluminum cause galvanic corrosion. Keep them apart.
• Treated lumber. Modern pressure-treated wood is corrosive to steel and aluminum, so panels and trim should not sit directly on it without a barrier.
• Wrong fasteners. Screws should be coated or stainless to match the panel metal; a plain steel screw in an aluminum roof rusts and stains.
• Salt air. Paint warranties on steel usually exclude the first stretch of shoreline. Aluminum is the usual answer there.
• Debris. Wet leaves and needles held in a valley for years can stain and eventually eat through a finish. Keep the roof clear.

Myth: metal roofs make the house hot

A metal roof heats up fast in the sun, which is probably where this one started. It also cools down fast once the sun is off it, because thin metal holds almost no heat, and painted metal reflects more sunlight than dark asphalt shingles to begin with. Light colors and dark colors made with infrared-reflective pigments keep the attic cooler than a shingle roof, not warmer. Attic temperature still depends mostly on insulation and ventilation, as our energy savings and cool roof guide explains.

Myth: metal roofs dent if you look at them

Hail can dent metal, and a thin 29 gauge agricultural panel dents more easily than a 24 gauge residential panel. But many metal roofing products carry the highest UL 2218 Class 4 impact rating, which means the panel stays watertight even when struck by a two-inch steel ball, and ribbed, textured and stone-coated profiles hide small dents well. As for foot traffic, trained installers walk on metal roofs every day by stepping in the flat of the panel near supports. You should not be up there regardless of what the roof is made of, so leave inspections to a roofer with a ladder or a drone.

Myth: metal roofs block cell signal and Wi-Fi

Wi-Fi is unaffected, because the router is inside the house with your devices. Cell signal is a fair question. A large sheet of metal overhead can weaken a signal that reaches the house mainly from above, and if your coverage is already marginal you might notice it. So can foil-faced insulation, low-e window coatings and the wire mesh behind stucco, which is why plenty of homes with shingle roofs have the same problem. Most homeowners notice no difference. If you are worried, turn on Wi-Fi calling on your phone or budget for a signal booster, both of which fix the problem completely.

Myth: metal roofs are too heavy for my house

It is the reverse. Metal roofing is among the lightest roof coverings made, lighter per square foot than asphalt shingles and a small fraction of the weight of concrete tile or slate. No structural reinforcement is needed on an ordinary house, and the low weight is one reason many codes allow metal over one existing layer of shingles. Even stone-coated steel, the heaviest common metal style, is far lighter than the clay or concrete tile it imitates.

Myth: a metal roof cannot be repaired or matched

Metal roofs can be repaired. Individual standing seam panels can be removed and replaced by a metal roofer, metal shingles are designed to be swapped one at a time, and trim and flashing are refabricated as needed. The honest caveat is color: a paint finish that has weathered for fifteen years will not perfectly match a panel fresh from the coil, though PVDF finishes drift very little and the difference fades as the new panel weathers. Keep a few spare panels or shingles from the original job and the problem mostly goes away.

Myth: a metal roof needs no care at all

Low maintenance is not no maintenance. Sealants at penetrations age, exposed screws on screw-down panels loosen as their washers harden, debris collects in valleys, and gutters still need cleaning. A look from the ground each season and a professional inspection every few years keep a metal roof on track for its full life. Our metal roof maintenance guide lays out a simple schedule.

Talk to someone who installs them

The fastest way to put a myth to rest is to stand under a metal roof in the rain. Ask any installer you interview for the addresses of a few finished roofs you can see from the street, and ask the owners how they find it. Our directory lists metal roofing companies by state, style and metal.