15 Oct 2021
Roof Discoloration

There’s nothing worse than spending a lot of money and effort on a new roof just to see ugly stains or marks appearing all over it. There are plenty of reasons for roof staining, depending on the roofing materials, location, and roof conditions.

Once you’ve figured out the cause of your green or black roof stains, you can address the underlying issue. The sooner you address the problem, the better, as marks on your roof surface will eventually penetrate the roofing material and structure, which can damage your roof and may require an entire roof replacement.

Roof Age

Every roof has a lifespan, and as the materials start to age, they can begin to discolor. This discoloration is particularly common in asphalt roofing shingles at the end of their lifespan.

An older asphalt roof that’s degrading will start to shed its black pigment, which appears as black streaks on the asphalt shingle roof. These stains can look similar to algal growth since both occur on asphalt shingles. It’s worthwhile to hire a roofing professional to make the final diagnosis. These black streaks are one sign indicating you need to consider replacing your roof.

Roof Algae Growth on Asphalt Shingle Roofs

Algae love asphalt roof shingles, especially cyanobacteria or blue-green algae. These algae thrive on the limestone filler found in asphalt shingles, which is why algae stains are common on even new roofs.

There are two main ways to combat dark streaks caused by algae growth: eliminate roof algae by pressure washing the upper roof or using algae-resistant shingles that stop the growth in the first place.


Metal roofs have become increasingly popular and usually consist of galvanized sheet metal. While sheet metal is rust-resistant, it can still develop rust over time.

Many roofing surfaces also have metal flashing in the form of copper or zinc strips that can discolor when they degrade and oxidize. Water tends to accelerate rust stains, which means that you also need to schedule a roof inspection to check for potential water leaks.

Surface rust is relatively easy to remove with acetic acid or oxalic acid, but corroded metal will need replacement to prevent further roof damage.

Tree Debris

You may find some stains occur only on one part of your roof. If that part is under a tree, you may just be seeing evidence of tree debris, such as leaves, animal droppings, sticks, and rotting organic matter. This debris can cause brown stains that are easy to wash off with a power cleaner. While not harmful like rust stains, metal roofs and other roofing should be kept far away from organic tree debris.

Roof stains can indicate serious problems with your roofing, or they may be a result of age or harmless debris. Only expert roofers can make the distinction and provide you with solutions. Don’t rely on the first result of your “roofing company near me” search. Instead, get in touch with All American Exteriors at (515) 255-4872 today. We have the expertise to get your roof looking good as new!