What's Causing the Black Streaks on My Roof? 

This problem didn't exist when shingle companies used Ceramic granules. So to save money they went to limestone dyed granules. Screwed everyone.

I noticed many years ago that there was never any staining on our farm's outbuilding roofs below any copper or galvanized flashings or roof vents. I think there would be a market for some sort of copper or galvanized zinc cap shingle of that would do the same thing. Something more permanent than the product shown in the video at :59.

No one here has mentioned leaching. This refers to the tar becoming so hot in the summer that it leaches out on the shingles. This is caused by inadequate venting of the attic space or more commonly on cathedral ceilings not having an airspace between the insulation and roof sheathing. Not bacteria growth

Also tree fungus. They show up and are far more obvious on white shingles (which are rare) and zonolite roofs.

I paid premium price for 40 year shingles that bragged of 3M algae resistant chemistry. At 8 years, lots of algae. I also read that while zinc strips look better along the caps, they only work properly when installed a few rows down, so that more rain will wash over them to release the metal. But that is unsightly, so most installers do it wrong.

Erie home has permanent roofing systems that has copper coated ceramic granules that are painted with a Titanium dioxide paint. They won’t grow algae or fade due to the UV rays. Guaranteed for 30 years. Their metal roofing systems also incorporate the same technology and are Guaranteed for 50 years. They are also rated as the number #1 residential reroofing company in America! Permanent Roofing Systems are the best solution!!!

I choose to not look at the black streaks, problem solved. 😊.

Can't you just sprinkle zinc powder on your roof, it's way cheaper?

Whatever you use as a cleaning agent must be properly mixed before application.

Yes, I just had a new roof installed on my house. I had a roofing company explain this process. My new roof won't do this

Check for PFAS in materials.

Probably the same thing staining Stucco Finish. Lol.

Roof decay .... cheap shingles

Limestone is a cheap filler material used all too much these days.