Three Causes Of Corrosion On A Metal Roof And How To Address Them
Corrosion occurs when iron or iron alloys react with water and oxygen to form rust. Over time, rust leaves holes in metal, leading to leaks and structural damage. If you have a metal roof, you should actively inspect it for rust and repair damaged sections to protect the structure from leaks. Below are the causes of corrosion, plus tips on how to address them.
Seawater and Salty Sea Air
Salty water is an electrolyte solution that speeds up metal corrosion. If you live in coastal areas, your roof is constantly exposed to salt spray and salty sea air. Over time, the metal will react with the water and corrode. If your metal roofing has rust, you can take the following measures:
- Apply rust-inhibitor coatings on the roof to protect it against surface rust.
- Apply spray polyurethane foam to the roofing to create a protective barrier against saltwater.
Your roofer can use mechanical or power tools to remove surface rust on the metal before applying the protective coatings. If you have a large roof repair budget, consider re-roofing with aluminum or zinc, as these metals perform better in coastal environments.
Incompatible Metals
Incompatible or dissimilar metals are metals with different chemical properties. When dissimilar metals touch, an electrochemical reaction occurs, causing one metal to corrode. This is known as galvanic corrosion, and it can affect your metal roof. For example, carbon steel and copper are incompatible metals and shouldn't be used together. Other examples of incompatible metals are:
- Stainless steel and aluminum
- Zinc and copper
- Stainless steel and zinc
- Copper and aluminum
Galvanic corrosion will occur where the two dissimilar metals come into contact. Thus, replace your roof fittings and accessories with ones compatible with your metal roofing. For example, you can use stainless steel and copper together. Other compatible metals are:
- Aluminum and zinc
- Stainless steel and copper
- Copper and lead
Check the areas where your gutters, skylights, solar panels, and HVAC equipment come into contact with the structure. If there is rust, the metals used aren't compatible with your roofing. As you repair the corroded roof panels, replace the incompatible metals to curb galvanic corrosion.
Lack of Underside Coatings
Underside coatings protect metal roofing from moisture and corrosion. If your roof underside isn't coated, the moisture that gets trapped between the underlay and the roof panels can cause the metal to corrode. Underside corrosion can spread undetected for years and weaken your roofing structure from the inside out. Therefore, replace the affected panels and apply protective coatings on the underside to prevent future corrosion.
When detected early, surface rust on the roof can be treated without replacing the affected panels. Contact your roofer for a detailed inspection and professional metal roofing repair.