Will metal roofing rust?

Metal roofing can rust over time, but proper maintenance and treatment can minimize rusting. Metal roofs are often galvanized or coated in aluminum or zinc, which forms a protective barrier against corrosion. When this coating is intact, oxygen and moisture cannot reach the metal underneath, and rusting is prevented.

However, the coating can become scratched, dented, or imperfect over time, exposing the bare metal. At these spots, rusting can develop. Regular inspections, touch-ups of any damage, and occasional cleaning/lubricating of the metal panels help sustain the rust-proofing. Periodic re-coating of the entire roof may also be needed for best results.

While some rusting is inevitable with metal roofs, especially in humid or coastal areas, proper care and maintenance techniques can maximize the time between re-coating or replacement. When rusting does occur, minor surface rust can often be simply painted over, while more extensive rust may require sanding and re-coating the affected areas. With the right approach, metal roofing can provide durable, long-lasting protection against the elements while minimizing undesirable rust.
How can you tell your metal roof is rusting?
If you suspect your roof is rusting, here are a few things to look out for:

Visual Inspection Carefully check your roof for any visible rust spots, stains, or flaking metal. Rusting will often appear as reddish-orange spots or patches on the metal surface. Peel or flake off any loose rust before it spreads further. Serious rusting will require sanding, priming, and painting for prevention.

Water Staining Excessive water buildup on the roof or running down walls, especially after rains, can indicate rust forming at weaknesses or seams in the metal surface. Rust discoloring the surface of puddles is a clear sign to inspect the underlying metal thoroughly. Rust holes or perforations can lead to leakage and water damage.

Paint Peeling If your roof has a coat of paint or another protective coating, peeling or blistering paint around seams or edges may indicate rust forming underneath. Gently pry up peeling paint to check for visible rust. Bare rust requires priming and matching paint for appearance.

Pooling & Leaks If water is pooling on certain areas of the roof or if leaks develop inside the structure, it likely means rust has formed holes or perforations in the metal surface, allowing water to penetrate. Leaks from rust can cause interior water damage and require roof patching or metal repair/replacement.

Noisy Rustling Sounds As rust expands, metal flakes break off, and rust particles crumble, it can produce small creaking, grinding, or rustling noises that get louder over time. Sounds of metal-on-metal movement require immediate roof inspection and potential roof stabilization. Loose or unstable metal sheets are unsafe.
What are some common causes of rust on metal roofs?
Typically, most metal roofs can last decades. However, there are situations that can reduce their lifespan by causing the to rust. They include: 
Exposure to MoistureMetal roofs can rust when exposed to constant moisture due to factors like high humidity, leaky seams or joints, or inadequate ventilation. The moisture condenses on the metal and accelerates oxidation and rusting. Installing gutters and downspouts, sealing seams or holes, and improving attic ventilation can help prevent excess moisture buildup.

Salt AirMetal roofs located near coastal areas or heavily salted roadways can rust quickly due to airborne salt particles. The salt promotes the oxidation of iron and steel. Wash metal roofs periodically in coastal areas and consider coatings like galvanization for added protection.

Acid RainThe acids in pollution and acid rain damage the protective layer of paint or other coatings on metal roofs and cause rusting. Acidic precipitation can alter the pH of the metal surface and speed up corrosion. There are protective coatings available for metal roofs in high-acid areas.

Metal ImbalanceIf a metal roof contains different alloys or metals, galvanic corrosion can occur where they meet. The metals form an electrolyte; one metal corrodes while the other is protected. Using compatible metal types, insulators, or coatings can prevent this rust.
Lack of Proper Coatings
Uncoated or unpainted metal roofs will rust more quickly due to a lack of environmental protection. Paints, galvanization, patinas, and other anti-weathering coatings help shield metal roofs from rusting agents like moisture, oxygen, and salt. Applying or reapplying roof coatings will help stop and prevent rust on metal roofs.
What are some common maintenance practices for metal roofs?
Metal roofs require routine inspection and maintenance to maximize their longevity. Here are some of the best practices for metal roof care:

InspectionsConducting periodic visual inspections of the roof, especially after severe weather, is critical. Check for leaks, damaged or loose panels, rusted spots, or other issues. Early detection of problems prevents further water damage or structural issues.

Sealing and PaintingUnpainted metal roofs like galvanized steel will develop a natural patina over time. But painting or sealing the surface helps prevent excess oxidation and rust. Metal roof coatings provide a durable, waterproof barrier. For perforated or copper roofs, sealants can be applied to the underside.

Tightening FastenersMetal roof panels and flashing joints are fastened with screws or special metal roofing clips and bolts. As the roof ages, these fasteners can loosen slightly. Use an impact driver to tighten all screws and bolts every few years. Loose screws affect the panel's integrity and weather resistance.

CleaningWashing metal roofs with detergent and water and then rinsing thoroughly removes built-up dirt and grime. For steel roofs, a pressure washer can be used at moderate pressure (1200-2000 PSI). Avoid abrasive cleaners, which can damage the metal surface. Harsh detergents can strip the natural protective oil coatings from copper and zinc roofs.

Snow RemovalPromptly remove excess snow from metal roofs to prevent leaks at joints and seams. Use a roof rake for slope roofs and a paddle for flat roofs to prevent water damage during spring thawns. Excess weight from snow can also cause panels to buckle or loosen from fasteners.

Insect/Pest RemovalInsect nests or pest droppings must be fully removed from metal roofs as they promote corrosion and reduce water resistance. Use professional pest control services to treat the underside and adjacent attics or crawlspaces. Clogged gutters increase moisture problems, so inspect and clean gutters at least once a year.

Metal roofs are popular for many homes and businesses due to their durability, longevity, and weather resistance. Proper maintenance and routine inspections allow a metal roof to last many years without deterioration or rusting. Common maintenance practices for metal roofs include inspecting for damage, sealing, and painting, tightening fasteners, cleaning, snow removal, and insect/pest removal. By following these practices, homeowners can extend the life of their metal roof and ensure its maximum protection and performance.