Algae staining

This roof had the worst discoloration from algae staining I have seen. It was only on the north side and the steeper slopes.

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I have seen bird droppings on the peak of the roof cause similar problems. Usually below an Antenna or chimney they can perch on.

Got this narrative off NACHI sometime ago. I believe from rray, but not sure.

“One or more sections of the shingles appear stained. An algae known as Gloeocapsa Magma is the most likely culprit and this algae affects nearly 80 percent of the homes across the United States. The algae causes black streaking and discoloration on asphalt/fiberglass shingles. The black staining you see on many roofs is caused by the life cycle of algae and fungus spores that land on houses via wind or wildlife. While this algae can grow just about anywhere, it prefers humid environments. A preferred food source of this algae is limestone which is used as “filler material” by most shingle manufactures. Higher quality shingles are manufactured with preventative measures such as copper or zinc containing granules. Several methods exist to prevent and clean infected areas. Installing zinc or copper strips near the roof ridge can prevent further algae growth. Application of bleach (non-chlorine) can aid in removing the stains, as well as many available commercial cleaning products. Some products may harm vegetation beneath roof eaves or near downspout extensions. While many remedies can be performed by the home owner, we recommend the use of qualified professionals due to the extreme danger and risk of injury or death associated to roof repairs and cleaning.”


This would be great to use to properly inform the client.

Thje species is correct but not the spread… Very few homes in the arid states are affected.

David, that is strange. I have been running across similar staining on several home slately. All on steeper roofs like that, where you would think you would get good run off.

I have never seen staining in a pattern like this. It is usually more sporadic. It was the same on the other side of the roof. Only on the North slopes.

Extremely common here in the Deep South. The darkening also contributes to the heat retained in the attics.

David, was this on the North side of the home?

Yes, and only on the steeper side slopes. The upper north roof had heavy areas of moss.

There seems to be an increase of those stained roofs around here lately, David.
Riding around the other day and one was replaceing the shingles due to the ugly stains.

I guess they haven’t heard of the products out there where you can clean it and zinc strips to prevent it further.
Here is a link that might help some.