Ask an Expert: Do Metal Roofs Rust?

Metal roofs have been used in the construction industry for many years. Both homeowners and commercial building owners choose this technology because of its durability, low price and surprisingly good appearance, especially right after installation. However, our customers have many concerns about the durability of metal roofs and whether they are too susceptible to corrosion.

While rusting is a natural process to which virtually all steel products succumb, and roofs are no exception in this regard, everyone tries to avoid corrosion. As a sheet metal roofing manufacturer, we use special coatings for this purpose, such as Galvalume and Kynar 500, with which we coat various grades of steel. In addition to this, the choice of material is also important – although different chemical processes occur on the surface of virtually every metal. So let’s examine how different types of roofing corrode.

What Causes Metal to Rust?

Rusting is the corrosion process of iron and iron alloy products. Whether your roof or gutters are made of high-carbon steel, cast iron or pure iron, it will be susceptible to corrosion to some degree. However, the speed and severity of these chemical reactions is closely related to the type of material used.

Three key elements must be present for rust to form: iron, oxygen and water. When metal surfaces come into contact with water – whether from rain, humidity or condensation – oxygen molecules in the air react with the metal. Over time, this reaction compromises the structural integrity of the material, causing discoloration, weakening and eventual deterioration. The corrosion of steel sheet serving as a roof is so dangerous that at some point, leaks can appear.

Steel does not rust in the same way in all conditions – exposure to salt, acid rain, industrial pollutants and some chemicals accelerates the corrosion of steel. As a general rule of thumb, roofs located on the shores of Lake Michigan, the Atlantic Ocean or by a large river will corrode more – moisture in the air and possible salt drastically increase the risk of steel oxidation, even if it is protected. The same is true for homes located in extremely snowy areas. Salt used for de-icing roads also settles on surrounding buildings, accelerating the corrosion reaction.

The content of this paragraph refers primarily to steel – it is steel that rusts, covering itself with a characteristic brown tarnish. Other metals also corrode (aluminum, zinc, copper), but in their case, these processes have less impact on the mechanical properties of the materials. In the case of copper, the main effect of corrosion is the formation of patina, which has a characteristic green-blue color. Steel does not cover itself with patina, which is why we use Kynar 500 to protect it.

You can learn more about copper corrosion reading an article Why is Copper the Ultimate Roofing Material?

Do All Metal Roofs Rust?

As we have already mentioned, not every metal roof is equally susceptible to corrosion. In addition to environmental factors such as humidity, the presence of salt in the air and even air temperature, the choice of material is also key. For this reason, some products are made of stainless steel, but this group of alloys is practically not used in roofing applications. Instead, many metal roofs are manufactured from the previously listed aluminum and copper.

Steel Roofing: Prone to Rust Without Protection

Steel is an iron-based metal, which means it can rust when exposed to moisture and oxygen. To counteract this, as a sheet metal roofing manufacturer we coat our products with protective layers. This can be zinc, a mixture of zinc and aluminum (Galvalume®), virtually unheard of lead or Kynar 500.

The application of protective coatings does not ensure that a steel roof will never rust – it is impossible. However, if the protective layer remains intact and is not damaged during installation, for example, a properly protected roof can last up to 70 years.

Aluminum Roofing: Naturally Rust-Resistant

Unlike steel, aluminum does not contain iron, so it does not rust. Instead, it forms a thin, protective layer of aluminum oxide when exposed to the elements, which prevents further corrosion. Instead, it forms a thin, protective layer of aluminum oxide after exposure to the elements, preventing further corrosion in the classic sense. This makes aluminum an excellent choice for coastal areas, where exposure to salt water accelerates the formation of rust on other metals.

However, it is worth being aware that aluminum used in industry usually has some chemical additives that are thought to affect the mechanical performance of the alloys. Unfortunately, as practice shows, they can be highly susceptible to corrosion – in this respect, 7xxx alloys are the worst. Pure aluminum is free from this problem, but is not necessarily suitable for roofing.

Copper Roofing: Patinas Instead of Rust

Copper, of course, also contains no iron, so it is not prone to rusting. The surface of this metal is covered with a patina of a characteristic green-blue color. Copper thus has self-conservative properties – a protective, corroded layer on the surface protects the interior of the metal sheet from further oxidation.

Which Metal is Most Vulnerable to Rust?

It should surprise no one that the most corrosion-sensitive metal is unprotected steel. The higher the concentration of iron and the weaker the protective coating, the faster corrosion will progress. A well-maintained steel roof can last many years, up to 70, but it will require more effort than would be required for aluminum or copper roofs.

How Protective Coatings Prevent Rust?

In a sense, there are three ways to protect metal from corrosion:

• You can coat the metal with a coating that will corrode faster than steel – an example would be zinc, which is more reactive than iron. In this way, the structure of the material will be safe until the outer protective layer is completely worn away;
• You can also apply a coating to protect the steel from air, water and salt. The paint, Kynar 500® or lead layer provides a physical barrier that completely blocks corrosive agents until the coating fails;
• A third solution is to use an alloy that is corrosion-resistant due to its properties. Chrome alloyed steel can actually be completely rustproof, even after many years of exposure to salt water.

Kynar 500®: A Superior Rust-Resistant Coating

Kynar 500® is a high-performance PVDF (polyvinylidene fluoride) resin-based coating that provides exceptional durability and corrosion resistance. It is widely used in the metal roofing industry for its resistance to harsh weather conditions, UV radiation and chemical contaminants. From the perspective of protecting metal from rust, Kynar 500 is a more developed version of paint – it works on exactly this principle, sealing off the metal from water and oxygen.

Key benefits of Kynar 500® coatings:

• Prevents rust and corrosion by forming a strong protective layer over the metal;
• Maintains color and appearance by resisting fading, chalking, and oxidation;
• Offers superior weather resistance, including protection from acid rain, salt spray, and extreme temperatures;
• Enhances longevity, often extending the lifespan of a metal roof to 50+ years.

How Does Kynar 500® Compare to Other Protection Methods?

While galvanized steel and Galvalume® coatings offer strong protection, Kynar 500® is considered superior due to its resistance to UV degradation and long-term durability. Unlike basic epoxy coatings or standard paint, Kynar 500® maintains its protective properties for more than 50 years, reducing the need for frequent maintenance.

Is Kynar 500® Worth it for Metal Roofing?

If you’re looking for a rust-resistant, long-lasting roof but don’t want to pay thousands of dollars for a copper roof, Kynar 500® is pretty much the only solution you can choose. It’s an excellent solution that gives you a balance of durability, aesthetics and price, so in many cases, you’re better off choosing Kynar-coated steel or aluminum instead of even the significantly cheaper protective layers, which, however, offer much worse durability.

Learn more about Kynar 500 in this article: Is Kynar Coating Worth it?

Common Myths About Metal Roofs and Rust

Metal roofing is often misunderstood when it comes to rust and corrosion. While it is true that some metals are prone to rust, modern metal roofs—especially those coated with Kynar 500® or other advanced protective finishes—are highly resistant to corrosion. Below, we’ll debunk some of the most common myths surrounding metal roofs and rust.

Myth #1: Metal Roofs Require Frequent Maintenance to Prevent Rust

Fact: High-quality metal roofs are designed to be low-maintenance. With proper coatings like Kynar 500®, Galvalume®, or galvanization, they can withstand harsh weather conditions with minimal upkeep. Routine inspections and occasional cleaning (to remove dirt, debris, and salt buildup in coastal areas) are usually all that’s needed to keep the roof in top shape.

The misconception about maintenance frequency is a remnant of the past. In the old days, when painting was the best way to protect metal roofs, owning one was indeed a hassle. Fortunately, those times ended at least 20 years ago.

Myth #2: Scratches on the Roof Will Lead to Corrosion

Fact: While deep scratches that expose bare steel can potentially lead to rust, most modern metal roofing systems have self-healing properties due to their protective coatings. Minor surface scratches typically do not cause corrosion because coatings like Kynar 500® prevent moisture from reaching the metal. Additionally, small scratches can often be repaired with touch-up paint or protective sealants.

Myth #3: Metal Roofs Rust Faster Near the Ocean

Fact: While salty ocean air does accelerate corrosion in unprotected metals, high-quality aluminum, copper, and Kynar 500®-coated steel roofs are specifically engineered to withstand marine environments. Aluminum roofing, in particular, is naturally rust-resistant, making it an excellent choice for coastal homes. Even steel roofing, when properly coated, can last decades near the ocean without rusting.