Metal roofs attract considerable myths and half-truths. Some people believe that metal roofs are noisy or attract lightning; fortunately, most of these aren't true at all. However, one thing that many people get right is that metal roofs do rust, and rusted metal roofs wear out faster than others. Here are some of the common forms of rust that may attack your metal roof:
Like the name suggests, underside corrosion affects the underside surfaces of metal roofing products. It is common with roofing products that are better-coated on their top surfaces as compared to their undersides. It can also happen if the roofing metal sheets are installed over something, say asphalt shingles, that scratches their undersides and rids them of their protective surfaces. What happens is that moisture gets trapped between the insulation or underlayment and the underside of the metal sheet, leading to corrosion that eventually weakens the affected area.
Galvanic corrosion occurs when two dissimilar metals, such as aluminum and galvanized steel, come into contact. It occurs because when two dissimilar metals with different electrochemical levels come into contact in the presence of an electrolyte, such as moisture, metal ions move from one metal to another causing corrosion. This problem typically arises when a metal roof is patched up with a different metal from the original one.
Cut Edges Corrosion
Metal roofing sheets are typically covered with protective materials to protect them from rusting. However, cutting metal sheets, which is sometimes necessary during installation, exposes the uncoated metal underneath, which is susceptible to corrosion. This type of corrosion is usually minimal, but it increases with the number of cut edges on the roof. The occurrence of holes or damages on the roof may also expose the actual metals and encourage this type of corrosion.
Salt is a corrosion catalyst so metal roofs exposed to salt water corrode faster than other types of roofs. Saltwater corrosion is common with coastal houses, which is why many manufacturers don't offer paint warranties in coastal regions. Saltwater corrosion is also common with commercial establishments whose business operations involve the use of salt.
Fortunately, there are various treatments that can be used to prevent metal roof rusting. Most metal roofing materials come from the manufacturer already treated, but you can also paint the metal sheets, apply a roof coating, and keep your roof dry and clean to keep rust at bay. Consult a roofing contractor for help if your metal roof is showing signs of rust.
For more information, talk to companies like Absolute Roofing.